ARCHIVED - Chronic Diseases in Canada

Volume 29 · Supplement 1 · 2010

Cancer and the environment: Ten topics in environmental cancer epidemiology in Canada

Shirley A. Huchcroft, Yang Mao and Robert Semenciw, Editors

https://doi.org/10.24095/hpcdp.29.S1.01

Glossary

The chapters in which each item is discussed are given in brackets, using the legend: AP (Air Pollution), DB (Disinfection By-Products), EF (Electromagnetic Fields), ET (Environmental Tobacco Smoke), MM (Metal Mining), OC (Organochlorines), PE (Pesticides), PP (Pulp and Paper), R (Radon), UR (Ultraviolet Radiation). Where no chapters are indicated, the term is considered generic to environmental cancer epidemiology.

Although chemical compounds can have several names, only one is given here for each. Very complex names are not included. Where possible, the CAS (Chemical Abstract Service) registration number is provided in brackets at the end of each entry. This number can be used to search for information on a compound.

The Canadian spelling (“ph”) is used in the glossary whenever there is an option of “ph’ or “f” even though the “f” variant may appear in the text at the discretion of the author and particularly when referring to a product name.

µg/L Micrograms per liter. For aqueous (water) samples 1 µg/L is equal to one part per billion (ppb).

1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE): (C₁₄H₈Cl₄). The stable breakdown product of DDT that is a persistent widespread environmental contaminant, is readily stored in fatty tissues, and has been identified in human tissues such as blood and milk. (72-55-9) (CO, PE)

1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane/dichlorodiphenyltrichloroethane (DDT): (C₁₄H₉Cl₅). An organochlorine implemented largely during WWII as an insecticide to control body lice and insect vectors of malaria and typhus, and subsequently used for agricultural purposes. Its registration for use in Canada was discontinued in 1985. Although DDT is no longer manufactured in North America, trace amounts still enter our environment as a result of leakage from waste sites and long-range transport in the atmosphere. (50-29-3) (CO, PE)

1,2-dibromo-3-chloropropane (DBCP): (C₃H₅Br₂Cl). An organohalide fungicide/fumigant and nematicide. Any that leaches into surface water evaporates within a few days. In air, it takes several months to break down, and it may remain in soil for several years. Exposure is mainly from consuming contaminated water or food. (96-12-8) (PE)

1,3-dichloropropane: (C₃H₆Cl₂). A contaminant of soil fumigants containing 1,3-dichloropropene. It is rarely found in water and is of low toxicity. (142-28-9) (PE)

1,3-dichloropropene: (C₃H₄Cl₂). Used in Canada as a soil fumigant to control fungi and nematodes. A colourless liquid at room temperature, it is soluble in water and evaporates quickly from it and from soil into air, where it is broken down by sunlight. It may leach into and travel in ground water. Trade name is Telone II. (542-75-6) (PE)

1,3,7-trichlorodioxins: By-product contaminants of some pesticides. (PE)

2,3,7,8 congener: (C₈H₅Cl₃O₃). 2,3,7,8-TCDD. The most toxic congener of TCDD. (93-76-5) (PE)

2,3,7,8-TCDD: See 2,3,7,8, congener.

2,3,7,8-tetrachlorodibenzo-p-dioxin: First discovered as a by-product of chlorinated phenol production in the 1950s, TCDD was industrially produced as the by-product of manufacture of 2,4,5-trichlorophenol. It is the most potent carcinogen known to some animals, and is known to bind to some human receptors. (1746-01-6) (PE, OC, PP)

2,4-D acid: Acid form of 2,4-D. (PE)

2,4-D: See 2,4-dichlorophenoxyacetic acid.

2,4-dichlorophenoxyacetic acid (2,4-D): (C₈H₆Cl₂O₃). One of the chlorophenoxyacetic acid herbicides. Its crystals are prismatic, white to pale yellow in colour, and have a phenolic-like odour. A chlorinated phenoxy compound that functions as a systemic herbicide and is used to control many types of annual and perennial broadleaf weeds in fruit, vegetable, turf, and ornamental plantings. It serves a secondary purpose as a plant growth regulator and is applied to crops to induce rooting and blossom set, to control ripening of bananas and citrus fruits, and to prolong fruit life on the tree. As with 2,4,5-T, 2,4-D chemically stimulates plant growth hormones, causing uncontrolled cell proliferation. It contains chlorine, thus posing a risk for dioxin formation, as seen with its use as one of the ingredients of Agent Orange. There are many forms or derivatives (esters, amines, salts) of 2,4-D and these vary in solubility and volatility. (94-75-7) (OC, PE)

2,4,5-T: See 2,4,5-trichlorophenoxyacetic acid.

2,4,5-trichlorophenol (TCP): (C₆H₃Cl₃O). An organochlorine precursor of 2,4,5-T that is structurally similar to phenoxy herbicides and is used as an antiseptic and fungicide/fumigant. A yellow solid, also known as Omal, 2,4,6-T, and Phenochlor, it is broken down in 1 to 9 days by sunlight and by bacteria in soil. (95-95-4) (PE)

2,4,5-trichlorophenoxyacetic acid (2,4,5-T): (C8H5Cl3O3). A chlorophenoxyacetic acid herbicide that was used in Canada in the past as a defoliant to control undesirable brush and woody plants. The crystals can be formulated as soluble or emulsifiable concentrates and are white and pale brown in colour. It should be stated which salt or ester is present: i.e., 2,4,5-T-trolamine; 2,4,5-T-triethylammonium. (93-76-5) (OC, PE)

3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX): A very potent mutagen and genotoxic compound in laboratory animals; it has also been shown to be carcinogenic in rats. MX appears to account for about one third of the mutagenicity of chlorinated drinking water, as determined in in vitro tests.

4-aminobiphenyl: See Para-aminobiphenyl (PAB).

4-chloro-2-methylphenoxy acetic acid (MCPA): (C₉H₉ClO₃). A systemic phenoxy herbicide used to control annual and perennial weeds (including thistle, dock, buttercup and horsetail) in cereals, grasslands, trees and turf. The herbicide works by concentrating in the actively growing regions of a plant where it interferes with protein synthesis, cell division and ultimately the growth of the plant. It should be stated which acid, salt or ester is present. (94-74-6) (PE)

A priori: Based on an hypothesis or theory rather than on experiment or experience. Heuristic.

Acetic acid: (CH3COOH). A colourless pungent liquid that is the chief acid of vinegar; may be a component of vapours emitted from wood pulp. (PP)

Acryl group: (C₃H₃O₂). An unsaturated group that is part of compounds such as acrolein, acrylonitrile, acrylic acid.

Additivity: A mathematical model based on the assumption that the combined effects of several factors is the sum of the effects that would be produced by each of the factors in the absence of others.

Adduct: A complex that forms when a chemical binds to a biological molecule, such as DNA or a protein.

Adenocarcinomas: Tumours in which the cancerous cells are arranged in the form of glands. Cancers of the lung, stomach, pancreas, prostate gland, and ovary are most often adenocarcinomas.

Adjusted odds ratio: An odds ratio that represents the association between two factors after the effects of other confounding effects have been mathematically removed.

Adjustment: A summarizing procedure for a statistical measure in which the effects of differences in composition of the population being compared are minimized. (PE)

Aerated stabilization basin: A water basin with an on-going flow of air bubbles, used to treat waste water. (PP)

Aerosol: A gaseous suspension of fine solid or liquid particles, such as paint, a detergent, or insecticide, packaged under pressure with a gaseous propellant for release as a spray of fine particles.

Aerosolize: Disperse as an aerosol. Radon daughters, which are solid particles, disperse into the atmosphere as an aerosol.

Age-adjusted rates: A mathematical procedure designed to minimize the effects of differences in age composition when comparing rates for different populations. In direct adjustment, the observed age-specific rates in the two populations are applied to a third “standard” population with a known age structure to calculate the expected number of deaths in each of the comparison populations. Indirect adjustment is the mirror image of direct adjustment and is used when the rates in the populations to be compared are either unstable or unknown. In this situation, the expected numbers of deaths in the study populations are calculated by applying the standard population age-specific rates to the study populations.

Agent Orange: A code name for the orange band that was used to mark the drums in which a herbicide, developed for the military, was stored. Primarily for use on broad-leaf foliage, such as the dense jungle found in Southeast Asia, Agent Orange was a 50-50 mix of 2,4-D and 2,4,5-T. The earliest health concerns about Agent Orange were about the product’s contamination with TCDD. (OC)

Ah: See Aryl hydrocarbons.

Ah receptor: A receptor that binds a wide variety of aromatic compounds, including polycyclic hydrocarbons, among which are dioxins (e.g., TCDD), dibenzofurans, and biphenyls (PCBs). Detectable in many tissues and organs, the Ah receptor is responsible for mediating the carcinogenic effects of these agents. (OC)

Alachlor: 2-chloro-2’,6’-diethyl-N-methoxymethylacetanilide (C₁₄H₂₀ClNO₂). An aniline herbicide used to control annual grasses and certain broadleaf weeds in crops such as field corn and soybeans. It is a selective systemic herbicide, absorbed by germinating shoots and by roots. (15972-60-8) (PE)

Aldehydes: Organic chemical compounds belonging to a class of highly reactive substances obtained mainly by the oxidation of primary alcohols. Aldehydes are characterized by the group – CHO and are used industrially in the manufacture of resins, dyes and other organic compounds. (PP, PE)

Aldicarb: 2-methyl-2-(methylthio)propionaldehyde 0-methylcarbamoyloxime (C₇H₁₄N₂O₂S). A broad spectrum, systemic oxime carbamate insecticide and nematicide that is the most toxic of the carbamate insecticides. (116-06-3) (PE)

Aldrin: (C₁₂H₈Cl₆). A cylcodiene insecticide. Aldrin is the name for material containing 95% pure compound. The pure compound has the common name HHDN. Aldrin degrades to dieldrin quickly in the body and the environment. Once used around the world to control soil insects and mosquitoes, in the 1970s its use was restricted to licensed pest control operators for the removal of underground termites. Today it is no longer manufactured or used in Canada. (309-00-2) (PE)

Aliphatic: Saturated or unsaturated hydrocarbon compounds of the open chain formation. (PE)

Alkaline oxide: See Hypochlorite.

Alkyl bromide: An alkyl halide with one or more bromine atoms in its structure. (PE)

Alkyl halide: A chemical compound made up of an alkyl group (C_nH_2n+1) and a halide atom. Halides are compounds containing a halogen atom (chlorine, bromine, fluorine and iodine). (PE)

Alkylation: A chemical reaction in which a hydrogen atom in an organic compound is replaced by an alkyl group (C_nH_2n+1). (PE)

Alpha particle: A positively charged particle ejected spontaneously from the nuclei of some radioactive elements. It is identical to a helium nucleus that has a mass number of 4 and an electrostatic charge of +2. It has low penetrating power and a short range (a few centimeters in air). The most energetic alpha particle will generally fail to penetrate the dead layers of cells covering the skin and can be easily stopped by a sheet of paper. (R, MM)

Ambient: A term used to describe the surrounding environment.

Ames reversion assay: A quantitative measurement of the mutagenicity of a chemical substance by the Ames test. The greater the number of bacterial colonies that grow in the presence of the chemical, the more mutagenic the chemical. (PE)

Ames test: A test for mutagenicity of chemical compounds that uses a special strain of the bacterium, Salmonella typhimurium. The bacteria are incubated in the presence of the suspected mutagen. Growth of bacterial colonies indicates mutagenicity of the chemical. (PE)

Amides: Compounds with the formula RCONH₂. (PE)

Amines: A class of organic compounds having a nitrogen atom attached to a carbon framework by single bonds. (PE)

Aminotriazole: See Amitrole.

Amitrole: 1-H-1,2,4-triazol-3-ylamine (C₂H₄N₄). A triazole herbicide that is applied as a liquid. Trade names include Amerol, Amino Triazole, Amitrol, Amizine, Amizol, Azolan, Azole, Cytrol, Diurol, and Weedazol. (61-82-5) (PE)

Ampere: A unit for measuring the rate of flow of an electric current, defined in terms of the force which a current produces. Approximately one ampere of current is required to produce 100 watts of electric power. (EF)

Amphibole: Any of a group of rock-forming silicate minerals, including hornblende and asbestos. (MM)

Androgen receptor: A member of the subfamily of steroid hormone receptors. The gene for this receptor is localized on the human X chromosome. Androgens enter the cells by passive diffusion and bind to the androgen-binding domain of the receptor, initiating the production of androgen-specific proteins.

Angiosperms: Flowering plants and trees that form seeds inside a protective chamber called the ovary; includes hardwood trees, such as oak and maple. (PP)

Anilides: When aniline is heated with an organic acid, amides called anilides are produced. Commercially they are used as herbicides, such as alachlor, propachlor, pentanochlor and propanil. (PE)

Aniline: (Phenylamine C₆H₇N). A benzene ring with an amine (NH₂) group attached to one of the carbons in the ring. A degradation product of anilides. Pure aniline is a highly poisonous, oily, colourless substance with a pleasant odor. (62-53-3) (PE)

Anion: A negatively charged ion. (AP)

Ankerite: Ca(Mg,Fe+²,Mn)(CO₃)₂. A mineral belonging to the carbonate group, related to dolomite. (MM)

Antibody: A globulin (protein insoluble in water) in the blood or other body fluids which can be incited by the presence of an antigen.

Antibody producing cells: After encountering stimulating antigenic signals, B lymphocytes develop into plasma cells which produce antigenic-specific antibody molecules.

Antigen: A foreign substance that stimulates an immune response.

Antigenic transplanted UV related tumours: UV-induced tumours in the skin of rats or mice are antigenic and are rapidly rejected when transplanted into normal, genetically similar animals. If the tumours are transplanted into animals previously exposed to subcarcinogenic doses of UV-B, they are not rejected and instead grow progressively in the recipients. While the mechanism of suppression of tumour rejection is unknown, such a response might be a critical determinant of cancer risk in human skin. (UR)

Aramite^®: Sulphurous acid, 2-chloroethyl 2-(4-(1,1 dimethylethyl)phenoxy)-1-methyl ester (C₁₅H₂₃ClO₄S). A colourless liquid organochlorine insecticide. (140-57-8) (PE)

Arithmetic mean: Sum of all values in a set of measurements, divided by the number of values in the set.

Aromatic amines: Amines in which one of the organic groups is an aromatic ring. (PE)

Aromatic compounds: A term applied to a large family of compounds structurally similar to benzene; i.e., a closed ring. (OC, PE, PP)

Aromatic hydrocarbons: Aromatic compounds made up of only carbon and hydrogen atoms. (OC, PE)

Aromatic ring: See Aromatic compounds.

Arsenic: (As). A highly poisonous chemical element having three allotropic forms, yellow, black, and grey, of which the brittle, crystalline grey is the most common. Arsenic is widely distributed in nature uncombined or in association with ores of antimony and silver. Extracted from arsenopyrite, arsenic and its compounds are used in insecticides, weed killers and various alloys. (R, PE, MM)

Arsenopyrite: (FeAsS). A primary source of arsenic. Arsenopyrite can be found in veins of lead or silver. (MM)

Aryl: A group derived from an aromatic hydrocarbon by removal of a hydrogen atom from the molecule. (PE)

Aryl hydrocarbons: (Ah). Aromatic hydrocarbons with a hydrocarbon group attached to the ring structure. (OC)

Ascertainment bias: Systematic failure to represent equally all classes of cases or persons supposed to be represented in a sample.

Atrazine: 6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine (C₁₄H₂₀ClNO₂). A chloro triazine herbicide used to control broadleaf and grassy weeds in corn. It acts as a strong inhibitor of photosynthesis and is soluble in water. It is used as a non-selective, granular soil sterilant and can remain in the soil for two years. It has a high potential for ground water contamination. (1912-24-9) (PE)

Autosomal: Referring to the non-sex chromosomes.

Autosomal dominant pattern (of inheritance): The pattern of inheritance in which a trait or disease will be expressed in an organism when only one member of a gene pair (rather than both) on a non-sex chromosome contains the DNA code that carries that trait or disease. In a recessive pattern, both genes of the pair must be affected for the trait/disease to be expressed.

Auxin growth regulators: Chemical compounds that act as synthetic auxins or plant hormones, altering the plant’s metabolism and hence growth characteristics (e.g., chlorophenoxy herbicides). (PE)

Axon: The part of a neuron that carries nerve impulses away from the nerve cell body to other nerve cells or effector organs.

Axonic poisons: Poisons that damage axons. (PE)

Azinphos-methyl: (C₁₀H₁₂N₃O₃PS). A white crystalline solid that is one of the most toxic of the organophosphate insecticides. It has low persistence in soil, the half life being 21 to 68 days under anaerobic conditions. It is unlikely to contaminate ground water and degrades in UV light. Use is being phased out in Canada. (86-50-0) (PE)

Backcasting: A method of estimating what might have happened in the past that relies on existing trends and statistics. (AP)

Basal cell carcinoma: The most common malignant skin tumour in Caucasians, basal cell carcinoma begins to occur in significant numbers in the fourth decade of life and increases with age. The lesions occur in fair-skinned persons and on areas of skin that receive a significant amount of intermittent or continuous sun exposure. Treatment with inorganic arsenical drugs and exposure to ionizing radiation (X- rays, radium) may also contribute fewer than five % of these cases. These cancers rarely metastasize but may be highly invasive locally. (UR)

Bayesian inferences: This method for inference involves working “backward” from effect to cause by estimating the conditional probability of a cause given that certain events have occurred. (AP)

Benomyl: Methyl-1-(butylcarbamoyl)benzimidazol-2-yl carbamate (C₁₄H₁₈N₄O₃). A protective and eradicant benzimidazole fungicide and nematicide effective against a wide range of fungi, such as apple scab and black spot that affect fruits, nuts, vegetables, turf, and field crops. All uses have been discontinued. (17804-35-2) (PE)

Benzene: (C6H6). A thin, colourless, highly flammable liquid that is a coal-tar derivative used in the manufacture of numerous chemical products, including insecticides, detergents and motor fuels; commonly called benzol. (PP)

Benzene ring: Six carbon atoms forming a ring to which are attached six hydrogen atoms. (PP)

Benzimidazole: A compound having a benzene ring fused to an imidazole ring. It is a weak base and remarkably stable. It resists acids and bases and is not easily oxidized. (51-17-2) (PE)

Benzimidazoles: A group of compounds having benzimidazole in their structure, including benomyl, carbendazim, thiabendazole, thiophanate and thiophanate-methyl. They are used as fungicides/fumigants. (PE)

Benzoic acid: Benzenecarboxylic acid, a fungistatic compound widely used as a food preservative. (65-85-0) (PE)

Benzoics: Aryl aliphatic acids that are used as herbicides (e.g., Dicamba). They are applied to soil to prevent germination, or as a post-emergent herbicide. (PE)

Benzo[a]pyrene: A type of polycyclic aromatic hydrocarbon, or PAH, that is probably carcinogenic to human beings. (ET)

Beta rays/particles: A charged particle emitted from a nucleus during radioactive decay, with a mass equal to 1/1837 that of a proton. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron. Large amounts of beta radiation may cause skin burns, and beta emitters are harmful if they enter the body. Beta particles may be stopped by thin sheets of metal or plastic. (R)

Bioconcentrate (bioaccumulate): A chemical present at infinitesimal concentrations in air or water may be increasingly concentrated as it moves up the food chain, until humans eating meat or fish ingest relatively high concentrations. Such chemicals enter the bodies of plants and animals, are not easily expelled, and accumulate over time.

Biodegradable: Can be chemically degraded using natural effectors such as soil bacteria, weather, plants or animals. Bacteria are considered “a biodegradable detergent” because they break down substances in the soil for resorption and uptake in the natural environment.

Biomarkers: A biological indicator (e.g., a genetic locus or a biochemical) useful for measuring the effects of a particular hazardous exposure (e.g., cotinine). Once an exposure has occurred, a continuum of biological events can be detected. These events may serve as indicators of exposure, of susceptibility, or of effect. For example, metabolites of exogenous substances may be detected in the body and indicate exposure. An important metabolite of heptachlor is heptachlor epoxide, which is an oxidation product formed from heptachlor by many plant and animal species.

Biota: Animal and plant life characterizing a given region.

Biotite: Black or dark-coloured mica (a mineral that divides into thin, partly transparent layers, withstands heat, and is used for insulation). (MM)

Biphenyl: An aromatic hydrocarbon, also known as diphenyl, that is composed of two benzene rings. It is used alone or with diphenyl ether, as a heat-transfer fluid. Pure biphenyl is a colourless crystalline solid with a pleasant odour; it is insoluble in water but soluble in ordinary organic solvents. (OC)

Bisdithiocarbamate: A class of fungicide used on potatoes, fruits and vegetables (e.g.,Mancozeb). (PE)
Blind assessment: The person doing the assessment does not know whether the subject is a case or control.

Boron compounds: Compounds containing boron (B), a non-metallic chemical element. (PP)

Brachiopod crustaceans: Small invertebrate, predominantly aquatic animals, having segmented bodies covered with an exoskeleton and two coiled arms called brachia on either side of the mouth, used to draw in food-bearing water; includes lobsters, shrimps, crabs, barnacles, wood lice. (PP)

Bromide: A compound of bromine with a positive radical. (DB)

Bromine: (Br). In its diatomic form, Br₂, bromine is a deep reddish brown liquid at room temperature, but if exposed to air, will emit a pungent brown coloured vapour. Like chlorine, bromine is a halogen. It is found naturally in seawater and saline springs, though at small concentrations. Bromine is used as a fire retardant and pesticide and to make brominated organic compounds. (DB)

Bromodichloromethane: (CHBrCl₂). Methane (a colourless, odourless, flammable gas) that has one bromine and two chlorine atoms in place of the hydrogen atoms. Bromodichloromethane is a product of the reaction between chlorine and naturally-occurring organic matter in water. (DB, PP)

Bromoform: (CHBr₃). A volatile organic compound found in chlorinated water supplies as a consequence of the reaction between chlorine during water treatment and natural organic substances in the presence of bromide ion. One of the four compounds constituting trihalomethanes. (DB)

Bromoxynil: 3,5-dibromo-4-hydroxybenzonitrile (C₇H₃Br₂NO). A nitrile herbicide. Trade names: Brominal, Buctril. It is used on grain, vegetables and grass for post emergent control of broadleaf weeds (1689-84-5). It should be stated which salt or ester is present: Bromoxynil-potassium (2961-68-4) or bromoxynil-octanoate (1689-99-2). (PE)

Bronchiolitis obliterans: Dense, irreversible scarring of the terminal and respiratory bronchioles of the lung. This scarring may partially or totally close off the airway. (PP)

Butylate: S-ethyl-di-isobutylthiocarbamate (C₁₁H₂₃NOS). A thiocarbamate herbicide used on corn. The half-life under crop growing conditions is 1.5-3 weeks. All uses have been discontinued in Canada. Trade name: Sutan (2008-41-5) (PE)

Calcinate: To heat (a substance) to a high temperature but below the melting or fusing point, causing loss of moisture, reduction, or oxidation and the decomposition of carbonates and other compounds. (PP)

Calcining: Heating an inorganic substance to a high temperature, but not high enough to melt or fuse it, in order to bring about evaporation of certain matter in it or cause chemical changes such as oxidation. Limestone is calcined to produce lime. (MM)

Calcite: (CaCO₃). A mineral composed of calcium carbonate. It occurs as limestone, chalk, marble etc. (MM)

Calcium carbonate: (CaCO₃). An inorganic chemical found in nature as calcite (limestone, chalk, marble, etc.) and aragonite (a crystalline carbonate of lime) and in plant ashes, bones etc. (PP)

Captafol/captofol: N-(1,1,2,2-tetrachloroethylthio)cyclohex-4-ene-1,2-dicarboximide (C₁₀H₉Cl₄NO₂S). A broad-spectrum dicarboximide fungicide, also called Captafol and Difolatan, that is effective for the control of almost all fungal diseases of plants, except powdery mildews, and is widely used to control foliage and fruit disease. Captafol is also used in the lumber and timber industry. (2425-06-1) (PE)

Captan: N-(trichloromethylthio)cyclohex-4-ene-1,2-dicarboximide (C₉H₈Cl₃NO₂S). A dicarboximide fungicide powder used to control diseases on many fruit, ornamental, and vegetable crops. It is used in agricultural production as well as by the home gardener. It is also applied to packing and shipping boxes for fruits and vegetables. (133-06-2) (PE)

Carbamates: Derivatives of carbamic acid that inhibit cholinesterase (ChE) and are used as insecticides. Many are designated as N-Methyl carbamates; others have an amide functional group with substituents other than a methyl group. (PE)

Carbamic acid: (H₂NCOOH). A compound that exists only in the form of salts or esters (carbamates), amides (carbamides), and other derivatives. (PE)

Carbaryl: 1-naphthyl methylcarbamate (C₁₂H₁₁NO₂). Also known as Sevin. A wide-spectrum, general use carbamate pesticide that controls insects on citrus, fruit, cotton, forests, lawns, nuts, ornamentals, shade trees, and other crops, as well as on poultry, livestock and pets. It is also used as a molluscicide and an acaricide.(63-25-2) (PE)

Carbathiin: See Carboxin.

Carbofuran: 2,3-dihydro-2,2-dimethyl benzofuran-7-yl methylcarbamate (C₁₂H₁₅NO₃). A carbamate insecticide of lesser toxicity than aldicarb. (1536-66-2) (PE)

Carbon tetrachloride or tetrachloromethane: (CCl4). A colourless oily, incombustible liquid; formerly used as a cleaning agent, but no longer recommended because of its toxicity to the liver and kidney. (PP)

Carboximide: A class of fungicides that includes Carboxin and Folpet. (133-07-3) (PE)

Carboxin: 5,6-dihydro-2-methyl-1,4-oxathi-ine-3-carboxanilide (C₁₂H₁₃NO₂S). A systemic anilide fungicide used as a seed treatment for control of smut, rot, and blight on barley, oats, rice, cotton, vegetables, corn and wheat. One of the leading fungicides in Canada, carboxin is also used to control fairy rings on turf grass. (5234-68-4) (PE)

Carcinogen: An agent capable of initiating development of malignant tumours. May be a chemical, a form of electromagnetic radiation, or an inert solid body.

Case: A person in the population or study group identified as having the particular disease or condition under investigation. Various sources may be used to identify cases (e.g., physicians’ diagnoses, cancer registries and notifications, and abstracts of clinical records).

Case-control study: A study that starts with the identification of persons with the disease or other outcome of interest, and compares them to a suitable control group (comparison or a reference group) of persons without the disease.

Cation: A positively charged ion. (AP)

CDKN2A: A germline mutation at human chromosome 9p21 present in 10–15% of individuals developing two or more independent melanomas. The mutation is also present in many families with two or more affected first degree relatives. At the present time, these germline mutations are thought to be transmitted from one generation to another in an autosomal dominant pattern, with variable penetrance, and individuals with them appear to be at high risk for the disease. (UR)

Cell cycle: An ordered set of events, culminating in cell growth and division into two daughter cells. These events include protein synthesis, DNA replication, DNA repair and mitosis (cell division).

Cell signaling cascade: A chain of events, initiated by an environmental agent, that leads to aberrant cell proliferation and carcinogenesis.

Cellulose: (C₆H₁₀O₅)_n. The main constituent of the cell walls of plants. (PP)

Chalcopyrite: (CuFeS₂). The most common mineral containing copper, found in porphyry copper deposits, skarns, contact metamorphism, hydro-thermal vents and other places. Consists of a sulphide of copper and iron. (MM)

Chinese hamster: An animal whose cells (ovary, lung, bone marrow etc.) are isolated and cultured for use in tests to determine the outcome of hazardous exposures (e.g., pollutants, herbicides). (PE)

Chip chute: A piece of machinery that feeds logs into a heavy, vertically rotating disk where they are shredded into small chips. (PP)

Chloracne: A skin disease that is one of the most sensitive indicators of exposure to dioxins and related chemicals. Clinically it is a persistent acne on the cheeks and behind the ears. (OC, PP, PE)

Chloramination: Treating drinking water by applying chlorine before or after applying ammonia. (DB)

Chloramines: (CH₃C₆H₄SO₂NClNa – 3H₂O). Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia for the purpose of water disinfection. Mono-, di-, and trichloramines may be formed depending on the ratio of chlorine to ammonia, the pH, and the temperature of the water. (DB)

Chlordane: (C₁₀H₆Cl₈). An organochlorine (cyclodiene) insecticide that can cause potentially fatal neurotoxic symptoms, such as muscle spasms and seizures. It is no longer registered as an active ingredient in Canada. (57-74-9) (PE)

Chlordecone: (C₁₀Cl₁₀). A cyclodiene insecticide used on tobacco, ornamental shrubs, bananas and citrus trees and in ant and roach traps. It breaks down slowly in the environment and does not readily dissolve in water. (143-50-0) (PE)

Chlorinated cyclodienes: A group of organochlorines (including dieldrin, mirex, chlordecone – kepone) that are stable in soils and under solar UV radiation and hence are persistent insecticides. Their toxicity increases with the environmental temperature. (OC, PE)

Chlorinated ketones: Ketones in which the hydrogen atom(s) is/are replaced by an equal number of chlorine atoms. Ketones are a group of compounds having a carbonyl group (CO) linked to hydrocarbon groups. (DB)

Chlorinated organic compounds/chemicals/hydrocarbons/synthetics: Compounds having one or more chlorine atoms in place of a hydrogen atom. (PP, OC, PE)

Chlorination: The process of adding chlorine to water, for the purpose of disinfection. (DB)

Chlorine: (Cl). Normally existing in its gaseous diatomic form, Cl₂, chlorine is produced for industry principally by electrolysis of sodium chloride (salt), and is used as a disinfectant and bleaching agent, as well as to disinfect water. Chlorine gas can combine with nearly all other elements, and especially with water, causing it to be highly irritating to the lungs and other mucous membranes at high levels when inhaled. However, under normal conditions of use, the inhalation of mists or vapours from dilute chlorine solutions is not expected to be significant or to result in any health effects in the general population. (PP, DB)

Chlorine dioxide: (ClO₂). A gas generated through the reaction of sodium chlorite and chlorine or by acidification of strong sodium chlorite solution. ClO₂ is a highly effective, environmentally-friendly microbiocide that eliminates planktonic and sessile bacteria, disinfects surfaces, and destroys biofilms. (PP, DB)

Chlorite: A salt of chlorous acid. (MM)

Chloroacetanilide: A benzene ring where one hydrogen atom is replaced by the -NHCOCH₃ group and also having one or more hydrogen atoms replaced by chlorine atoms. (PE)

Chlorodibromomethane: See Dibromochloromethane.

Chloroform/chloroform trichloromethane: (CHCl₃). A volatile organic compound found in water as a consequence of the reaction between chlorine and naturally-occurring substances. One of the four compounds constituting trihalomethanes. (DB, PP)

Chloronitrile: A nitrile having one or more chlorine atoms in its structure. (PE)

Chlorophenols: Organic chemicals in which one or more hydrogen atoms of phenol are replaced by one or more atoms of chlorine. Chlorophenols are formed as a result of the chlorination of humic matter or of natural carbonoxylic acids during the treatment of water. They are well-known chlorination by-products, since they can confer objectionable taste and odour. Chlorophenols are also a class of pesticides with widespread use. There are 19 chlorophenol congeners, many of which are used in Canada in pesticide products or wood preservatives. (PP, PE, DB)

Chlorophenoxyacetic acid herbicides: Chlorophenoxyacetic acid is synthesized from phenol (a benzene ring with a hydroxyl group on the ring) and acetic acid. The chlorinated derivatives include 2,4-D and 2,4,5-T which would have two and three chlorine atoms on the ring respectively. (OC, PE)

Chloropicrin: Trichloronitromethane (CCl₃NO₂). A clear, colourless, oily liquid with a strong, sharp, highly irritating odour used primarily for preplant soil fumigation to control soil borne fungi, diseases and nematodes. It also is used to treat wood poles and timbers for internal decay by fungi and insects. (76-06-2) (PE)

Chlorothalonil: Tetrachloroisophthalonitrile (C₈Cl₃N₂). An aromatic fungicide sprayed on vegetables, trees, small fruits, turf, ornamentals, and other agricultural crops. It also controls fruit rot in cranberry bogs and snow moulds and is used in paints. (1897-45-6) (PE)

Chlorotriazine: (C₃Cl₃N₃). Colourless crystals that react violently with water. Decomposes when heated or burned to produce toxic fumes including hydrogen chloride and nitrogen oxides. (PE)

Chlorovanillins and chlorosyringols: Aromatic or low molecular weight compounds that are by-products of the degradation of lignin using alkaline or chlorine treatment. (PP)

Chloroxanthins: Xanthine (2,6-dihydroxypurine) is found in tea and in animal tissues. Chloroxanthines (having one or more chlorine atoms as substituents) are toxic by-products of some pesticides. Purine is an aromatic heterocyclic compound. (PE)

Chlorpyriphos: O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate (C₉H₁₁Cl₃NO₃PS). An organothiophosphate that acts by interfering with the activities of cholinesterase, an enzyme essential for the proper working of the nervous systems of both humans and insects. Chlorpyrifos is a contact dust, foam or liquid spray used against flying and non-flying insects such as hornets, wasps, ants, cutworms, fungus gnats and spiders. (2921-88-2) (PE)

Cholinesterase: One of many important enzymes needed for the proper functioning of the nervous systems of humans, other vertebrates, and insects. Certain chemical classes of pesticides, such as organophosphates (OPs) and carbamates (CMs) work by interfering with, or ‘inhibiting’ cholinesterase. While the effects of cholinesterase inhibiting products are intended for insect pests, these chemicals can also be poisonous, or toxic, to humans in some situations. (PE)

Chromate: A salt or ester of chromic acid. (PP)

Chromic acid: A solution of potassium dichromate in sulphuric acid. It is a strong oxidant, commonly used as a cleaning agent. (PP)

Chromosome 14q32 (or Band 14q32): A genetic locus on human chromosome 14 (an autosomal chromosome).

Chromosome 18q21: A genetic locus on human chromosome 18 (an autosomal chromosome).

Chromosome breaks: Chromosomes break and rearrange with heterologous and homologous chromosomes during both types of cell divisions (mitosis and meiosis).

CMM: See Cutaneous malignant melanoma.

Co-kriging: A version of kriging that predicts more than one response. (AP)

Co-mutagens: Mutagens that act together or synergistically.

Cobalt: (Co). A silver-white metallic element with a pinkish tint that occurs with and is similar to nickel and iron, used especially in alloys and for making pigments. (MM)

Cohort study: A study in which subsets of a defined population are identified who are, have been, or in the future may be exposed to the agent under investigation. The identified individuals are followed over time for the occurrence of disease.

Conazole: The active part of these compounds is the triazole ring which is a Cytochrome P450 inhibitor. A triazole ring is a five-membered ring of two carbon atoms adjacent to each other, and three nitrogen atoms. (PE)

Confidence interval (CI): A range of values for a variable of interest having a specified probability of including the true value of the variable (e.g., 95%). The end points of the confidence interval are called the confidence limits.

Confounder: A variable/factor, related to both the outcome of interest and the study factor, that can obscure the relationship being studied.

Confounding: A mixing of effects between the exposure, the disease, and a third factor (confounder) that is associated with the exposure and independently affects the risk of developing the disease.

Congeners: A group of chemical substances that share chemical properties and structure. They are derivatives of the same or a similar compound or element belonging to the same family in the periodic table. Unlike isomers, congeners do not necessarily have the same molecular formula. (OC, PE)

Conifer: Trees or shrubs bearing their seeds in cones (e.g., pines, spruces, firs, hemlocks, junipers and cypresses). (PP)

Contact metamorphism: The alteration of a rock due to the introduction of heat (no pressure effects), from an adjacent igneous rock (such as a lava flow). Contact metamorphism does not affect the entire rock, just a relatively thin zone next to the heat source. (MM)

Control: (noun) A person in a comparison group without the factor of interest – exposure in a cohort study, disease in a case-control study. (verb) During analyses, to adjust for or take into account extraneous influences and observations. (adjective) A “control variable” is a variable which has a potential effect on the outcome or disease under study, and which is subject to control by analysis. See Confounder.

Coplanar PCBs: PCBs with atoms arranged in a single plane, resembling dioxins, and with dioxin-like activity via binding with the Ah receptor. (OC)

Correlate: (noun) A variable that changes as another variable changes. (verb) Show the connection or relationship between two variables.

Correlation: The degree to which variables change together; the mutual relation of two or more things.

Correlation coefficient: A measure of association that indicates how closely two variables are linearly related.

Cotinine: ((C₆H₁₂N₂O₂)₂ C₄H₄O₄). A major urinary metabolite of nicotine, used as a biomarker of exposure to tobacco smoke. (ET)

Coumaphos: (C₁₄H₁₆ClO₅PS). An organothiophosphate insecticide of moderate to high toxicity. All uses have been discontinued in Canada. (56-72-4) (PE)

Covariance: A measure of the joint variance of two or more variables.

Covariate: A variable that is possibly predictive of the outcome of the study. A covariate may be of direct interest to the study or may be a confounding variable or effect modifier.

Cox proportional hazards model: A statistical model in survival analysis that relates the time until death (survival time) to a series of measurements thought to influence an individual’s survival.

Credible regions: Sets that contain an uncertain quantity or vector of uncertain quantities with a specific probability. (AP)

Creosote: A complex organic mixture produced from coal that contains more than 300 compounds, including polycyclic aromatic hydrocarbons (PAHs), which account for up to 90% of the total mixture. Creosote is one of the most popular wood preservatives used in Canada. (PE)

Cummingtonite: ((Mg, Fe)₇Si₈O₂₂(OH)₂). A common member of the amphibole mineral group, that contains more magnesium than iron. (MM)

Curie (Ci): The basic unit used to describe the intensity of radioactivity in a sample of material. The curie is equal to 37 billion (3.7x10¹⁰) disintegrations per second, which is approximately the activity of 1 gram of radium. A curie is also a quantity of any radionuclide that decays at a rate of 37 billion disintegrations per second. It is named for Marie and Pierre Curie, who discovered radium in 1898. (MM)

Cutaneous malignant melanoma (CMM): See melanoma. (UR)

Cyanazine: 2-(4-chloro-6-ethylamino-1,3,5-triazin-2-ylamino)-2-methyl propionitrile (C₉H₁₃ClN₆). A triazine herbicide used for pre- and post-emergence weed control for corn, canola and mixed grains. All uses have been discontinued in Canada. (21725-46-2) (PE)

Cyclodines (cyclodienes): Chlorinated hydrocarbon insecticides (such as chlordane, aldrin, dieldrin, heptachlor, endrin and mirex). Cyclodienes have a positive temperature correlation – their toxicity increases with increases in the surrounding temperature. Cyclodienes appear to affect all animals in generally the same way, first with nervous activity followed by tremors, convulsions and prostration. (PE)

CYP1A1 gene: A gene whose enzyme induction and DNA adducts in placental tissue constitute useful biomarkers of early effects induced by environmental exposure to organochlorines. The gene is activated by the binding of organochlorines to the Ah receptor. (OC)

Cytochrome: A respiratory enzyme, chemically related to haemoglobin, capable of alternate reduction and oxidation. (OC)

Cytochrome P450: A cytochrome that has been studied to monitor the bioaccumulation of dioxins and furans. Specifically, cytochrome P450IAI can be used as a measure of Ah receptor activation resultant from environmental exposure. (OC)

Daphnea: Minute freshwater brachiopod crustaceans. (PP)

DBCP: See 1,2-dibromo-3-chloropropane.

DBPs: See Disinfection by-products.

DCM: See Dichloromethane.

DDE: See 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene.

DDT: See 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane.

Deoxyribonucleic acid (DNA): The basic hereditary material in all cells. DNA contains all the information necessary for protein synthesis. (R)

Diallate: S-2,3-dichloroallyl di-isopropyl(thiocarbamate). A thiocarbamate herbicide that inhibits growth of broad-leaf weeds, such as wild oats, in croplands. (2303-16-4) (PE)

Diazinon: O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate (C₁₂H₂₁N₂O₃PS). Also known as dimpylate. An organothiophosphate insecticide used on outdoor lawns and gardens or as a soil drench to control most insects, such as ants, cutworms, gnats and springtails. Diazinon is a colourless oil that is stable in sunlight and unstable in acid and alkali media. It can pollute surface and ground waters. (333-41-5) (PE)

Dibenzofurans: Furans with two benzene groups attached to carbon atoms that normally bind hydrogen. (OC)

Dibromochloromethane: (CHBr₂Cl ). A volatile organic compound found in chlorinated water supplies as a consequence of the reaction between chlorine during water treatment and naturally occurring substances. (DB, PP)

Dicamba: 3,6-dichlororo-o-anisic acid (C₈H₆Cl₂O₃). Also known as Disugran and dianat. A benzoic herbicide used in large quantities for broad leaf weed control on lawns, grain crops, pastures and non-crop areas. It should be stated which salt or ester is present: dicamba-dimethylammonium (2300-66-5), dicamba-potassium (10007-85-0), dicamba-sodium (1982-69-0), or dicamba-methyl (6597-78-0). (PE)

Dichlorodiphenyltrichloroethane (DDT): A synthetic insecticide that was introduced for agricultural purposes in 1945. Although DDT is no longer manufactured in North America, trace amounts still enter our environment as a result of leakage from waste sites and long-range transport in the atmosphere. Registrations of the remaining uses of DDT in Canada were discontinued in 1985. (OC, PE)

Dichloromethane (DCM)/methylene chloride: (CH₂Cl₂). A colourless liquid with a sweet, chloroform-like odour, used as a solvent in a variety of industries and as a fumigant for strawberries and grains. (75-09-2). (PP)

Dichlorvos: 2,2-dichlorovinyl dimethylphosphate (C₄H₇Cl₂O₄P). An organophosphate insecticide used in no-pest strips. (62-73-7) (PE)

Diclofop-methyl: Methyl 2-[4-(2,4-dichlorophenoxy) phenoxy] propanoate (C₁₆H₁₄Cl₂O₄). A diphenylether/chlorphenoxy selective post-emergence herbicide. (51338-27-3) (PE)

Dieldrin: (C₁₂H₈Cl₆O). A cyclodiene insecticide that was a popular pesticide for crops such as corn and cotton. It breaks down very slowly. In the 1970s use was restricted to licensed pest control operators for the removal of underground termites. Dieldrin is no longer registered for use in Canada. (60-57-1) (PE)

Digester fluid: A digester is a vessel in which substances are softened or decomposed, usually for further processing. In chemical pulping, chips and chemicals (sulphates or sulphites) in aqueous solution are cooked together in a pressure vessel (a digester) from which de-lignified pulp is produced for further processing. The cooking mixtures are also called “liquors” (white or black, depending on the process used). (PP)

Dimethoate: O,O-dimethyl-S-methylcarbamoylmethyl phosphorodithioate (C₅H₁₂NO₃PS₂). Also known as phosphamide, dimethoate has many trade names. An organothiophosphate insecticide and nematicide used on field and orchard crops and on ornamentals, as a residual wall spray for house flies in farm buildings, and to control botflies on livestock. It is biodegradable and breaks down quickly in soils. In water it is highly soluble and therefore subject to leaching. (60-51-5) (PE)

Dimethyl sulphide: A reagent used in the wood pulping process to break down the carbon bonds in lignin. (PP)

Dimethylbenz[a]anthracene: A polycyclic aromatic hydrocarbon (PAH) in tobacco smoke. (ET)

Dimethylcarbamoyl chloride: (C₃H₆ClNO). A colourless liquid that decomposes in the presence of water to dimethylamine, carbon dioxide and hydrogen chloride. Three registered pesticides derived from it are Tandex (Karbutilate), dimethilan and Pirimor (primicarb). It is an air pollutant and a chemical intermediate in the production of dyes, pharmaceuticals and pesticides. (79-44-7) (PE)

Dinitroaniline herbicides: Also known as dinitrobenzenamines, these herbicides act by inhibiting the steps in plant cell division responsible for cell wall formation and chromosome separation. The most commonly used dinitroanalines in Canada are trifluralin and ethalfluralin; both are selective, pre-emergence herbicides used to control annual grasses and broadleaf weeds in a variety of crops. (PE)

Dinitrobenzenamines: A group of compounds having two hydrogen atoms of the benzene ring replaced by nitro groups (NO₂) and another hydrogen atom replaced by an amino group. (PE)

Dioxins: See Polychlorinated dibenzo-p-dioxins.

Diphenyl aliphatics: Aliphatic compounds having two phenyl groups as part of their structure. (PE)

Direct standardized comparison: A mathematical method for removing the potential confounding effect of age when comparing rates in two populations with differing age structure. The observed age-specific rates in the two populations are applied to a third “standard” population with a known age structure to calculate the expected number of deaths in each of the comparison populations.

Disinfection by-products (DBPs): A group of chemicals that can form in drinking water when chlorine or another disinfectant reacts with the naturally occurring organic matter. Examples of DBPs are haloacetic acids and trihalomethanes. (DB)

Dithiocarbamates: Typically fungicides with a carbamate structure, where sulphurs replace both oxygens in the amide functional group. They are also used as accelerators in the vulcanization of rubber, as antioxidants in polymer chemistry, and as drugs. The most frequently used dithiocarbamate fungicide in Canada is mancozeb. (PE)

Diuron: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (C₉H₁₀Cl₂N₂O). Also known as dichlorfenidim, trade names include Crisuron, Diater, Di-on, Direx, Karmex and Unidron. A phenylurea herbicide used to control broadleaf and grassy weeds as well as mosses by inhibiting photosynthesis on field and orchard crops and ornamentals. It is moderately to highly persistent in soils and relatively stable in water. (330-54-1) (PE)

DNA: See Deoxyribonucleic acid.

DNA adduct: DNA modified by external chemicals added onto its molecule. (OC)

Dolostone: A sedimentary rock composed of more than ninety percent dolomite (CaMg(CO₃)₂) and less than ten percent calcite (CaCO₃). (MM)

Dose, absorbed: The amount of energy from ionizing radiation deposited in any substance per unit mass. It is expressed numerically in grays (the international system of units).

Dose, effective: A measure of the total potential harm from ionizing radiation over different organs, expressed in Sv (sieverts) or mSv (millisieverts). It is obtained by summing the products of the equivalent dose multiplied by the tissue weighting factor for each organ. Weighting factors account for the different potentials for adverse effects in different tissues.

Dose, equivalent (or biological dose): A measure, expressed in sieverts (Sv), of the potential biological damage to living tissue from various types of ionizing radiation exposure. It is obtained by summing the products of the absorbed dose of each radiation type multiplied by its weighting factor. Weighting factors account for the different potentials for adverse effects of the different types of radiation.

Dose-response relationship: A relationship in which a change in amount, intensity and duration of exposure is associated with a change – either an increase or a decrease – in a specific outcome.

Dysplastic nevus syndrome: A hereditary condition in which affected family members have dysplastic (abnormally developing) nevi (moles) and greatly increased risk of malignant melanoma. (UR)

Ecologic(al) correlation: A correlation in which the units studied are populations rather than individuals. Correlations found in this manner may not hold true for the individual members of the population(s).

Ecologic(al) fallacy: Bias that may occur because an association observed between variables on an aggregate level may not represent the association that exists at an individual level.

Ecologic(al) study: Study in which the units of analysis are populations or groups of people rather than individuals.

Effluent: The liquid waste of sewage and industrial processing. (PP)

Electrical field: A space throughout which an electric force operates. (EF)

Electrical field strength: The force on a stationary positive charge per unit charge at a point in an electric field. Also known as electric field vector, electric field intensity. Electric fields are measured in volts per metre (V/m). (EF)

Electrolytic tanks: Tanks containing an electrolyte (a substance, such as water, that conducts electricity by dissociation into positively and negatively charged ions) and negatively and positively charged electrodes apart from each other. Positive ions in the electrolyte migrate to the negative electrode (cathode), where they combine with one or more electrons; negative ions move to the positive electrode (anode) and transfer one or more electrons to it. Used in the extraction and purification of metals from ores, in electroplating, and to separate compounds (e.g., NaCl (salt) into sodium metal and chlorine gas). (MM)

Electromagnetic field (EMF): Electrical devices and systems produce two different fields— an electric field and a magnetic field. These fields, in combination, are referred to as electromagnetic fields or EMFs. Electromagnetic fields are generated by current-carrying electric wiring, (especially if the conductors are apart, as in the wiring in old homes, or are poorly grounded), radio or TV station transmitters, microwave ovens, power transmission lines and generators, and electrical appliances, especially those with electric motors. (EF)

Electron: An elementary particle with a negative charge and a mass 1/1837 that of the proton. Electrons surround the positively charged nucleus and determine the chemical properties of the atom. (R)

Endocrine disruptors: Chemical substances that mimic the structure and activity of a natural hormone. It is suggested that some chemicals acting as hormonal disrupters may lead to infertility, some cancers, and other hormonally-induced disorders. (PE)

Endrin: (C12H8Cl6O). Also known as nendrin. A cyclodiene insecticide that is a highly toxic chlorinated hydrocarbon; if ingested or absorbed through the skin, it can cause potentially fatal neurotoxicity such as tremors and convulsions. Endrin is no longer registered as an active ingredient in Canada. (72-20-8) (PE)

Epidermal Langerhans’ cells: Langerhans cells can be looked upon as “sentinel” cells of the immune system. They are among the first cells to come into contact with foreign particulate substances encountering the skin. By means of specialized receptors on the cell membrane, the Langerhans cell recognizes invading as opposed to host molecules. By conveying this information to the lymphoid system, the body is able to mount a defensive immunological response to the foreign material. (UR)

Epigenetic events: Events that do not initiate a tumour but, rather, influence the time to the appearance of the tumour.

Erythema: An abnormal redness of the skin due to capillary congestion as in inflammation ( sunburn). (UR)

Ester: A compound resulting from the reaction of an acid with an alcohol, so that the hydrogen of the acid is replaced by the hydrocarbon radical of the alcohol. Animal and vegetable fats and oils are esters. (PE, OC, PP)

Estrogen receptor agonist activity: A chemical compound similar to estrogen (in structure) can bind with estrogen’s natural receptor and compete with estrogen for space on the estrogen receptors.

Estrogen receptor-negative cases: Breast cancer cases with levels of estrogen receptor protein equal to or less than 10 fmol/mg; as measured in breast cancer cells.

Estrogen receptor-positive cases: Breast cancer cases with levels of receptor protein above 10 fmol/mg as measured in the cytoplasm of breast cancer cells.

Ethalfluralin/ethyl fluralin: N-ethyl-α,α,α-trifluoro-N-(2-methylallyl)-2,6-dinitro-p-toluidine (C₁₃H₁₄F₃N₃O₄). A dinitroaniline selective pre-emergence herbicide commonly used in Canada to control annual grasses and broadleaf weeds in a variety of crops. Trade names are Sonalan and Curbit. (55283-68-6) (PE)

Ethoprop: O-ethyl SS-dipropyl phosphorodithioate (C₈H₁₉O₂PS₂). A thiophosphate insecticide and nematicide. Trade names: Mocap, Ethoporphos, Prophos, Rovokil. It acts by inhibiting photosynthesis and is used on sugar cane, potatoes, tobacco, corn, pineapples, beans and cucumbers and for golf course and industrial lawn applications. (13194-48-4) (PE)

Ethyl mercaptan: Mercaptans are thiols. They are analogs of alcohols, having a sulphur atom instead of the oxygen atom in the alcohol. The sulphur atom gives them a strong disagreeable odour, akin to the smell of skunk. Ethyl mercaptan (CH₃CH₂SH) is the analog of ethanol (CH₃CH₂OH). (PP)

Ethylan: 1,1-dicholro-2,2-bis(4-ethylphenyl) ethane (C₁₈H₂₀Cl₂). An organochlorine insecticide. It is also called Perthane and ethyl-DDD. It has been discontinued. Practically insoluble in water. It was used for home mothproofing and for moths and carpet beetles in the dry cleaning and textile industries. It was also used on fruit and vegetable crops. (72-56-0) (PE)

Ethylene dibromide: (C₂H₄Br₂). A soil and post harvest fumigant insecticide. (106-93-4) (PE)

Ethylene oxide (Oxirane): (C₂H₄O). Used as a fumigant. (72-21-8) (PE)

Etiological period: A period of exposure, prior to the onset of disease, during which the disease process was likely initiated.

Excess relative risk model: A mathematical model derived to calculate relative risks of developing the disease based on multiplicative effects (multiple causes). The model implies that the risk is greater than the sum of the risks calculated independently.

Exposure-response relationship: The intensity, duration, and the onset of the response (or manifestation) caused by the exposure. The science of toxicology is based on the principle that there is a relationship between a toxic reaction (the response) and the amount of poison received (the dose). An important assumption in this relationship is that there is almost always a dose below which no response occurs or can be measured. A second assumption is that once a maximum response is reached any further increases in the dose will not result in any increased effect. The toxic effects on an organism are related to the amount of exposure.

Extractives: Products of industries that specialize in obtaining natural substances, such as fossil fuels, from the Earth. Extractive industries include mining, and coal and gas production. (PP)

Familial atypical multiple mole – melanoma syndrome: See Dysplastic nevus syndrome.

Fatty acids: Any of a large group of organic acids made up of molecules containing a carboxyl group (COOH) at the end of a long hydrocarbon chain; the carbon content may vary from C2 to C34. The more common fatty acid residues that occur in higher plants and animals are palmitic, oleic, linoleic and stearic acids. (PP)

Fenitrothion: O,O-dimethyl O-4-nitro-m-tolyl phosphorodithioate (C₉H₁₂NO₅PS). A thiophosphate insecticide and selective acaricide of low ovicidal properties. (122-14-5) (PE)

Fibroblasts: The principal nonmotile cells of connective tissue. Fibroblasts produce an amorphous, gel-like substance that fills the spaces between cells and fibres in connective tissue. (UR)

Fibrotic lung: Formation of fibrosis tissue in the lung. (MM)

Fluorite: (CaF2). A transparent, crystalline mineral that occurs in many colours; calcium fluoride. It is used for fusing metals, making glass etc. (MM)

Fmol (femtomole): One quadrillionth of a mole or 10-¹⁵ mole.

Folpet: N-(trichloromethylthio)phthalimide (C₉H₄Cl₃NO₂S). A carboximide compound and protective foliage fungicide. Its mode of action inhibits normal cell division of a broad spectrum of microorganisms. It is used to control cherry leaf spot, rose mildew, rose black spot, and apple scab. Used on berries, flowers, ornamentals, fruits and vegetables, and for seed- and plant- bed treatment. Also used as a fungicide in paints and plastics, and for treatment of internal and external structural surfaces of buildings. (133-07-3) (PE)

Fonofos: O-ethyl S-phenyl(RS)-ethylphosphonodithioate (C₁₀H₁₅OPS₂). A soil organophosphate insecticide primarily used on corn. It is also used on sugar cane, peanuts, tobacco, turf, and some vegetable crops. Fonofos controls aphids, corn borer, corn rootworm, corn wireworm, cutworms, white grubs, and some maggots. All uses have been discontinued in Canada. (944-22-9) (PE)

Formaldehyde: (CH₂O). An unclassified fungicide and bactericide. (50-00-0) (PE)

Formic acid: (CH₂O₂). A colourless caustic liquid found especially in ants and in many plants and used chiefly in the dyeing industry. (PP)

Free radicals: Reactive molecular fragment with one un-paired electron. (PE)

Fugitive emissions: Toxic emissions released by the pulp and paper and other industries. They include the group of reduced sulphur compounds (collectively called total reduced sulphur or TRS) and the oxides of sulphur and nitrogen. (PP)

Fumigant: Small, volatile, organic molecules that become gases at temperatures above 40°F. They are usually heavier than air and commonly contain one or more of the halogens (Cl, Br, or F). Most are highly penetrating, reaching through large masses of material. They are used to kill insects, insect eggs, nematodes, and certain microorganisms in buildings, warehouses, grain elevators, soils, and greenhouses and in packaged products such as dried fruits, beans, grain, and breakfast cereals. (PE)

Fungicide: An agent that destroys fungi including their spores. (PE)

Furans: See Polychlorinated dibenzofurans (PCDFs).

Furfural: A furan ring having an aldehyde group attached to it. Furan is a five-member ring having four carbons and one oxygen atom in it. (PP)

Galena: (PbS). A grey metallic ore consisting of lead sulphide. It is the most important source of lead. (MM)

Gamma rays/radiation: High-energy, short wavelength, electromagnetic radiation emitted from the nucleus. Gamma radiation frequently accompanies alpha and beta emissions and always accompanies fission. Gamma rays are very penetrating and are best stopped or shielded by dense materials, such as lead or depleted uranium. Gamma rays are similar to X rays. (R)

Garnet: A brittle silicate mineral occurring mainly in red crystals. The transparent, deep-red variety is used as a semiprecious gemstone; other varieties are used as abrasives. (MM)

Generalized estimating equation: A unified and flexible approach to estimating model parameters when it is not desirable and/or possible to make particular distributional assumptions about the observed data. (AP)

Genetic epidemiology: The science that deals with the manifestation, distribution and control of heritable diseases in populations.

Genotoxic effects/genotoxicity: Damage of cellular DNA by a chemical or other agent, resulting in mutations or cancer.

Genotype: An individual’s genetic makeup underlying a specific trait or constellation of traits.

Geological-tectonic setting: A description of the conditions (climate, faulting, etc.) that were in force at the particular place and time that the rocks were formed. (MM)

Geometric mean: A measure of central tendency based on the logarithm of the individual values.

Germline mutation: A change in the genetic material (DNA) of the germ cells (sperm and ovum) with a potential to transmit the change from one generation to the other.

Glioma: A type of brain cancer. (ET)

Gluconic acid: (C₆H₁₂O₇). A crystalline acid obtained by oxidation of glucose and used chiefly in cleaning metals. (PP)

Glutathione depletion: Glutathione is a compound in the body that prevents oxidative stress in most cells and helps to trap free radicals that can damage DNA and RNA. As individuals grow older, glutathione levels drop, and the ability to detoxify free radicals decreases. (MM)

Glyphosate: N-(phosphonomethyl) glycine (C₃H₈NO₅P). A broad-spectrum non-selective systemic herbicide used to control annual and perennial plants. (1071-83-6) It should be stated which salt or ester is present glyphosate-isopropylammonium (38641-94-0), glyphosate-sesquisodium (10393-85-0), or glyphosate-trimesium (81591-81-3). (PE)

Granulomatous lung disease: A granuloma (tumour-like mass or nodule) in the lung. (MM)

Gravimetric sampling: A method of quantitative chemical analysis in which the constituent sought is converted into a substance of known composition that can be separated from the sample and weighed, or a weight difference can be applied without any separation. (MM)

Gray (Gy): The international system (SI) unit of absorbed dose. One gray is equal to an absorbed dose of 1 Joule/kilogram.

Ground water: That portion of the water below the surface of the ground whose pressure is greater than atmospheric pressure. (DB)

Guanine: (C₆H₆N₄O). One of the bases in DNA and RNA. It is a purine, an aromatic heterocyclic compound made up of two fused rings, a six-membered ring of four carbon atoms and one nitrogen atom with an oxygen attached to one of the carbons and an amino (NH₂) group attached to another of the carbon atoms, fused to a five-membered ring that shares two carbon atoms with the six-membered ring. This ring is made up of three carbon atoms and two nitrogen atoms. (73-40-5) (PE)

Gymnosperms: Vascular plants that bear naked seeds not enclosed in any specialised chambers such as ovaries. Softwoods, such as pines and firs, are gymnosperms. (PP)

Gypsum: (CaSO4·2H2O). A mineral used for making plaster of Paris, fertilizer, etc.; hydrated calcium sulphate. Alabaster is one form of gypsum. (MM)

Half-life: The period required for half of the atoms of a particular radioactive isotope to decay and become an isotope of another element. Half-lives can range from less than a millionth of a second to millions of years depending upon the element concerned. After one half-life, the level of radioactivity of a substance is halved, after two half-lives it is reduced to one quarter, after three half-lives to one-eighth and so on. (R)

Halocarbon: Any compound of carbon and one or more halogen (bromine, chlorine, iodine, fluorine) atoms. (PE)

Halogen: Any one of the chemical elements, iodine, bromine, chlorine, fluorine and astatine, that combine directly with metals to form salts. The halogens are the most active elements. (DB)

Halogenated: Containing one or more halogen atoms, i.e., fluorine, chlorine, iodine, bromine or astatine. (DB)

Halogenated acetic acids (HAAs): Acetic acid in which one or more hydrogen atoms are substituted with appropriate numbers of halogen atoms (e.g., chlorine). HAAs are formed along with other disinfection by-products when chlorine or other disinfectants used to control microbial contaminants in drinking water react with naturally occurring organic and inorganic matter in water. The major haloacetic acids are: mono-, di-, and trihaloacetic acids, and mono- and dibromoacetic. (DB)

Halogenated acetonitriles: Various halogenated acetonitriles have been detected in chlorinated drinking water samples, the brominated acetonitriles being formed when bromide is present in the water during chlorination. Dichloroacetonitrile is the most abundant of the acetonitriles. (DB)

Halogenated hydrocarbons: One of a group of halogen derivatives of organic compounds. (DB)

Halogenated volatile organics: See Volatile organic compounds. (VOCs)

Halogenation: The introduction of a halogen atom (flourine, chlorine, bromine, iodine and astatine) into an organic compound (or molecule) by addition or substitution. (DB)

Hazard ratio (relative rate, rate ratio, incidence density ratio, instantaneous relative risk): A useful measure in etiological research that quantifies the strength of the relationship between exposure and risk.

HCB: See Hexachlorobenzene.

HCH: See Hexachlorocyclohexane.

Healthy worker bias: A bias resulting from generalizing findings from studies conducted on occupational groups because working people are relatively more fit and healthy compared to the population in general.

Hemicellulose: (C₆H₁₀O₅ )_n. A type of polysaccharide in plant cell walls whose chemical composition is more complex than sugar and less complex than cellulose. (PP)

Heptachlor: (C₁₀H₅Cl₇). A cylcodiene insecticide first isolated from technical chlordane in 1946. During the 1960s and 1970s, it was used primarily by farmers to kill ants, and soil insects in seed grains and on crops, as well as by exterminators and homeowners to kill termites. Before heptachlor was banned, formulations available included dusts, wettable powders, emulsifiable concentrates, and oil solutions. It acts as a nonsystemic stomach and contact insecticide. (76-44-8) (PE)

Heterocyclic aromatic compounds: Aromatic compounds with an atom other than carbon (e.g., oxygen, nitrogen or sulphur). (OC)

Heterogeneity: The condition or state of being different in kind or nature. The quality of certain genetic disorders that consist of two or more fundamentally distinct entities.

Hexachlorobenzene (HCB): (C₆Cl₆). An aromatic compound used as a selective fungicide for seed protectant treatment (usually for wheat) against common and dwarf bunt. It acts as a fumigant on fungal spores. It is highly persistent. Registration in Canada was discontinued in 1976. Today, trace amounts continue to enter our environment through long-range atmospheric transport, the manufacture and use of industrial chemicals that contain HCB and various industrial and municipal emissions. (OC, PE)

Hexachlorocyclohexane (HCH): (C₆H₆Cl₆). An organochlorine (also known as benzehexachloride – BHC) which has five isomers, alpha, beta, gamma, delta and epsilon. The gamma isomer was isolated and sold as an insecticide under the name lindane. HCH acts in the body similarly to DDT, but much more rapidly. (58-89-9) (OC, PE)

Host factors: Host factors are traits which make an individual at risk (or susceptible) of acquiring a particular disease or health disorder. For instance, the host factors for melanoma are: racial/ethnic origin, pigmentation, skin reaction to sunlight, nevus and freckle density.

HPV: See Human papilloma virus.

Human papilloma virus (HPV): A group of relatively small DNA viruses, many of which are oncogenic or potentially oncogenic.

Human T-lymphocytes: Lymphocytes (white blood cells) originate, in postnatal life, from stem cells in the bone marrow; these stem cells divide continuously, releasing immature lymphocytes into the bloodstream. Some of these travel to the thymus, where they multiply and differentiate (i.e., acquire special properties and functions). The term T lymphocyte (or T cell) stands for thymus-derived lymphocyte (or cell). Once they have left the thymus, T cells join the bloodstream and circulate to and within the rest of the lymphoid organs, where they can multiply further in response to appropriate stimulation. About half of all lymphocytes are T cells.

Hydrocarbons: A class of organic compounds composed entirely of hydrogen and carbon atoms. (DB, OC, PE, PP)

Hydrogen sulphide: (H₂S). An ill-smelling, colourless, flammable, highly toxic gas, used as a reagent in chemical manufacturing. (MM, PP)

Hydrometallurgy: The extraction of metal from ore by using aqueous solutions. It usually involves dissolution of the metal or metal compound by water (sometimes with additional agents such as dilute sulphuric acid), purification of the solution, and recovery of metal from the solution by chemical or electrolytic means. Gold, silver, copper, zinc and many other metals are extracted in this way. (MM)

Hydroxymethylfurfural: Furfural with an hydroxyl methyl (CH₂OH) group attached to the ring. (PP)

Hypochlorite: A salt of hypochlorous acid used during the treatment of pulp to remove lignin and bleach the pulp. The velocity of this reaction is directly proportional to the amount of hypochlorite used, but the risk with a fast reaction with high concentrations of hypochlorite is a subsequent decrease in paper strength. (PP)

Hypochlorous acid: (HOCl). An unstable acid used as a bleach and disinfectant. (PP)

IARC: International Agency for Research on Cancer.

Imide: A compound containing the -CO-NH-CO- group. (PE)

Immunosuppression: The artificial prevention or diminution of the immune response.

In-vivo: Within a living organism: metabolic studies conducted in vivo; in vivo techniques. As opposed to in vitro in which the experiment is conducted in a laboratory environment or in a test tube.

Induction period: See Latency period.

Interaction: The effect of one factor varies according to the level of another factor.

Interpolate: To infer or to estimate the value of a variable within the range sampled.

Interpolation error: Unwarranted high confidence in the interpolated values.

Intrusions/intrusive rock: Rock that was forced into fissures or between strata when molten. (MM)

Inverse exposure/dose-rate effect: For equal total exposure, a high exposure rate and short duration is less harmful than a low exposure rate and long duration. When a more protracted dose is delivered, a higher percentage of the cells have the potential to be affected during a sensitive part of their cell cycle. This results in a higher chance of malignant transformation. (R)

Ionizing radiation: Highly penetrating radiation that results in the formation of ions by displacement of electrons from their path of orbit. Ionizing radiation is capable of breaking chemical bonds, thus causing damage to living tissue through which it passes. (EF, R)

Iron oxides: The main types of iron ore that can be mined profitably for iron. The most common forms are hematite (Fe₂O₃), goethite (α-FeO(OH)), magnetite (Fe₃O₄) and siderite (FeCO₃). (MM)

Isomers: Two or more compounds identical in molecular formula, but having different structural arrangements and exhibiting different properties. (PP, OC, PE)

Isoprene: (C₃H₈). A volatile liquid hydrocarbon used in synthetic rubber and turpentine. (PP)

Isotopes: Any two or more forms of an element having identical or very closely related chemical properties and the same atomic number but different atomic weights or mass numbers. (R)

Isotropy: The condition of having the same or similar values in all directions. For air pollution studies it states that the closer the distance between the two locations, the more similar the concentration levels are. (AP)

Job-exposure matrix: An array of data in rows and columns specially designed to present the duration and intensity of exposure(s) associated with a particular job and to translate job task histories into estimates of exposure to specific agents. It consists of jobs on one axis and specific exposures on the other, with the matrix elements describing the likelihood of an individual’s exposure to a specific substance in a given job either in binary or polytomous categories.

Joule: A unit for measuring energy. One joule is the amount of work done, or energy used, in applying one newton of force to move a body one metre in the direction of the force. (EF)

K-ras gene: K-ras is one member of the Ras family of genes. These genes code for a group of closely-related proteins that are involved in the regulation of normal cell growth and proliferation. K-ras is located on chromosome 12, and is involved in cell cycle control. Mutations in this gene have been associated with several types of cancer, including lung cancer, such that it is considered to be a proto-oncogene. K-ras oncogene activation is known to occur at an early stage in tumorgenesis and maybe an important diagnostic marker. See Biomarkers.

Kaiser Permanente cohort: A cohort of individuals enrolled in the Kaiser Permanente health insurance plan that has been extensively studied by epidemiologists.

Ketones: Any of a class of organic compounds having a carbonyl group (CO) linked to hydrocarbon groups. (PP)

Komatiitic: Like a komatiite or containing komatiite. A komatiite is a series of very old (older than 590 million years) lava flows that were very hot (> 1600 degrees C) when they were extruded onto the Earth’s surface. (MM)

Konimeter: A device for measuring the number of particles in the air, as in a mine or cement plant. (MM)

Kraft (sulphate) pulping process: The principal method of chemical pulping. It involves using sodium hydroxide and sodium sulphate to break down the wood and separate the cellulose fibre from the lignin. (PP)

Kriging: A weighted moving average interpolation (extrapolation) method that minimizes the estimated variance of a predicted point (node) with the weighted average of its neighbors. (AP)

Latency/induction period: Delay between the exposure to a disease-causing agent and the appearance or manifestation of the disease.

Lateritic: Similar to, or containing, a laterite. A laterite is a red soil with large amounts of iron and/or aluminum oxides created by weathering. It forms in forested areas in tropical or temperate climates. (MM)

Leaching: Preferential dissolution of a component using an aqueous solution in order to separate it from other components. (MM)

Lead-210: In the series of unstable products from the radioactive decay of uranium-238, lead-210 results from the decay of radon-222 and is a precursor of the stable isotope lead-206. (R)

LET: See Linear energy transfer.

Lignin: After cellulose, the complex polymer, lignin, is the largest component of wood, accounting for about 25% of wood composition. (PP)

Lime: Calcium oxide (CaO). Manufactured by heating limestone, coral, sea shells, or chalk (made of CaCO₃) to drive off the carbon dioxide (CO₂), leaving CaO. (PP)

Lime kiln: A furnace used to calcinate limestone. (PP)

Lindane: (C₆H₆Cl₆). Gamma HCH. One of the eight isomers of hexachlorocyclohexane (HCH) and the only organochlorine insecticide still licensed for use in Canada. An ingredient in Kwell^® shampoo used to control head lice. (58-89-9) (PE)

Linear energy transfer (LET): The amount of energy deposited by an ejected particle per unit of the track length over which it is deposited. Generally speaking, high LET radiation is more effective at inducing cell damage than low LET radiation. (R)

Linear regression analysis/model: A method of describing the relationship between two or more variables by calculating a best fitting straight line.

Linuron: 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (C₉H₁₀Cl₂N₂O₂). A phenylurea herbicide. Controls broadleaf and grassy weeds by inhibiting photosynthesis. Used on crop and non-crop sites for a variety of vegetable and fruit crops as well as for wheat. It is slightly to moderately soluble in water and is not readily broken down in water. (330-55-2) (PE)

Lipid fractionation: The procedure for separating lipids from other cellular constituents, using organic solvents (e.g., chloroform, methanol), in which they dissolve.

Lipophilic: Tending to combine with or dissolve in lipids. PCBs, for example, dissolve in the lipids of cells.

Lode gold deposits: Veins of gold. (MM)

Logistic regression: Statistical analysis estimating the magnitude of the association between an exposure and a binary outcome after adjusting simultaneously for a number of potential confounding factors.

Long-Evans cinnamon rat: A mutant strain displaying hereditary hepatitis and spontaneous hepatocellular carcinoma, and showing abnormal hepatic copper accumulation, similar to Wilson’s disease in humans.

Macrophage: A large mononuclear cell that ingests degenerated cells, blood tissue, and small exogenous particles; found in large numbers throughout the body, with the greatest accumulation in the spleen, where they remove damaged or aging red blood cells from the circulation.

Mafic-ultramafic: One of three classifications of igneous rocks based on chemical composition (the others are alkaline and calc-alkaline). These rocks are typically dark in colouration, and make up most oceanic crust. They are also found on continents, typically in rift valleys (where continents are pulled apart and new ocean basins form the break), and in flood basalts (a type of lava flow involving a very large volume of lava). (MM)

Magmatic bodies/hosts: See Intrusions.

Magnetic field: The region of magnetic influence or force around a magnet, a magnetic body such as the Earth, or a body carrying an electric current. Also the magnetic forces present in such a region. (EF)

Magnetic flux density: A measure of magnetic field strength per unit area, quantified by units of tesla (T) or gauss. (EF)

Malathion: diethyl (dimethoxythiophosphorylthio)succinate (C₁₀H₁₉O₆S₂). Also known as carbophos, maldison, and mercaptothion. A wide-spectrum aliphatic organophosphate insecticide commonly used in Canada to kill insects on fruits and vegetables, for mosquito control and to kill head and body lice. (121-75-5) (PE)

Mammary tumours: A mass or a tumour located in human breasts or mammary glands.

Mancozeb: Manganese ethylene bis(dithiocarbamate) (polymeric) complex with zinc salt. A dithiocarbamate fungicide that has a very low acute toxicity to mammals. The major routes of exposure to mancozeb are through the skin or from inhalation. Mancozeb sprays and dusts are moderately irritating to the skin and respiratory mucous membranes. (8018-01-7) (PE)

Matched case-control study: A case-control study in which the controls are matched to the cases on factors that could confound the results, should they differ between the two groups. Some commonly matched variables are age, gender, race, and socio-economic status.

Matching: The process of making a study group and a comparison group comparable with respect to variables such as age and sex.

MCPA: See 4-chloro-2-methylphenoxy acetic acid.

Meiotic chromosomal aberrations: Germline mutation resulting from meiosis (cell division whereby each daughter cell receives half the number of chromosomes). These mutations may be transmitted to the progeny.

Melamine formaldehyde: A thermosetting resin made from melamine (a white crystalline compound, C₃H₆N₆) and formaldehyde (a colourless, pungent gaseous aldehyde, CH₂O) used in solution as a disinfectant and preservative. (PP)

Melanoma: A spreading and frequently recurring cancer of specialized skin cells (melanocytes) that produce the protective skin-darkening pigment melanin. Although it represents approximately five % of all cases of skin cancer, melanoma is responsible for nearly three-quarters of all skin cancer deaths.

Meningioma: A common type of benign brain tumour that infiltrates adjacent brain tissue, but does not metastasize. Includes astrocytoma, oligodendroglioma and ependymoma.

Mercaptans: Any substance containing the radical – SH bound to carbon; analagous to alcohols and phenols, but containing sulphur instead of oxygen. (PP)

Mesothelioma: A benign or malignant tumour affecting the lining of the chest or abdomen. Pleural mesothelioma has been associated with exposure to asbestos. (MM, PE)

Meta-analysis: The process of using statistical methods to combine the results of several different studies to produce a weighted summary estimate of risk.

Metabolites: Substances produced by metabolism or metabolic processes. Any substance involved in metabolism (either as a product of metabolism or as necessary for metabolism).

Metallic nickel: A silvery white metal that is moderately hard. It is both malleable and fairly ductile. Metallic nickel is an important industrial metal used in the manufacture of special alloy steels and cast irons. (MM)

Metam sodium: Sodium methyldithiocarbamate (C₂H₅NS₂Na). Also known as metham, methyldithiocarbamic acid, carbam and carbathion. A leading broad spectrum fumigant used in Canada, primarily as a liquid fumigant for pre-planting control of soil-borne fungi. It is also used to control nematodes and weeds affecting a variety of important fruit and vegetable crops. It degrades rapidly to methyl isothiocyanate the primary bio-active agent. (137-42-8) (PE)

Metamorphic rock: Rock derived from either igneous or sedimentary rock that has undergone changes in composition, texture, or internal structure through the action of pressure, heat, moisture, etc. Slate is a metamorphic rock formed from shale. (MM)

Methidathion: (C₆H₁₁N₂O₄PS₃). An organothiophosphate insecticide and acaricide. The compound is used to control a variety of insects and mites in many crops such as fruits, vegetables, tobacco, alfalfa and sunflowers and is also used in greenhouses. All uses have been discontinued in Canada. (950-37-8) (PE)

Methyl isothiocyanate: (CH₃NCS). Also known as MITC, Methyl Mustard, Isothianic Acid Methyl Ester, Vorlex and MIT. A colourless solid, the vapors are heavier than air and it can cause severe burns. It is an unclassified fungicide, herbicide and nematicide. All uses have been discontinued in Canada. (556-61-6) (PE)

Methyl mercuric chloride/methyl mercury chloride: Methyl mercury (II) chloride (chloromethyl mercury) (CH₃ClHg). White crystals used in the manufacture of pharmaceuticals and pesticides. (115-09-3) (PE)

Methylene chloride: See Dichloromethane.

Metolachlor: (α-RS, 1RS)-2-chloro-6’-ethyl-N-(2-methoxy-1-methylethyl) acet-o-toluidide (C₁₅H₂₂NO₂). Trade names are Bicep, CGA-24705, Dual, Pennant, and Pimagram. A chloroacetanilide general use herbicide used in Canada primarily for the control of grasses in corn, beans, soybeans and other crops. It is often used in formulations with other pesticides, often herbicides that control broad leaf weeds. (51218-45-2) (PE)

Mirex: (C₁₀H₁₂). A chlorinated cyclodiene insecticide used especially against ants. It is no longer registered as an active ingredient in Canada. (2385-85-5) (OC) (PE)

Misclassification: The erroneous classification of an individual, a value, or an attribute into a category other than that to which it should be assigned. The probability of misclassification may be the same in all study groups (non-differential misclassification) or may vary between groups (differential misclassification).

Mitotic chromosomal aberrations: Mutations or chromosomal changes (sister chromatid exchange, chromosome breakages) during mitosis (cell division without dividing the number of chromosomes). These mutations are typically not transmitted to the progeny. (PE)

Modelling: The act of representing or describing a phenomenon or set of relationships in mathematical terms to aid understanding; set assumptions about relationships used to study their interactions.

Mole: A unit for measuring amounts of substances that take part in chemical reactions. (OC)

Molecular epidemiology: A branch of epidemiology where the researcher studies specific gene behaviour (or other biological molecules) with the aim of associating cancer-related genetic alterations with specific exposures.

Monomer: A chemical compound consisting of single molecules that can join together to form a polymer. (PP)

Monotonically increases: A sequence is said to increase monotonically if each value is greater than or equal to the previous one, and monotonically decreasing if each value is less than or equal to the previous one.

Moving average: A method of smoothing the curve representing the data. Each observation is replaced by a mean of the observation and the observations on either side of it.

Multiple traversals: Multiple ‘hits’ of individual cell nuclei by alpha particles. (R)

Mutagen: An agent (e.g., radiation) capable of altering the genetic material in living organisms, causing chromosomal damage, point mutations, sister chromatid exchanges, or functional defects in gene replication or cell division.

Mutagenic: Capable of inducing alteration (mutation) in genetic material.

Mutagenicity: The property of an agent (e.g., chemical substance, radiation) to induce mutation.

Mutation: A structural change within genetic material of an organism resulting in the creation of a new character or trait not found in the parental type.

MX: See 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone.

N-acetylation phenotype: The genetically-determined rate at which the liver enzyme N-acetyltransferase detoxifies compounds in the body. (ET)

N-nitroso-di-n-propylamine (NDPA): An unavoidable contaminant in trifluralin-containing products. (621-64-9) (PE)

Nabam: Disodium ethylene bis(dithiocarbamate) (C₄H₆N₂Na₂S₄). A dithiocarbamate fungicide/fumigant. (142-59-6) (PE)

Natural killer (NK) cells: Cells produced by the body’s immune system to destroy or damage a variety of malignant target cells.

NDPA: See N-nitroso-di-n-propylamine.

Nested case-control design study: A case-control study in which cases and controls are drawn from the population in a cohort study.

Neutron: An uncharged elementary particle with a mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen. (R)

Newton: A unit for measuring force. One newton is the force required to give an acceleration of one metre per second to a mass of 1 kg. (EF)

Nickel carbonyl: (Ni(CO)₄). Carbon monoxide reacts with nickel to produce the volatile compound nickel carbonyl. (MM)

Nickel carbonyl process: A process used to separate nickel from other metals and impurities. After iron and copper have been removed by smelting the ore and slow-cooking the nickel matte, the impure nickel is combined with carbon monoxide at 60°C to make the compound tetracarbonylnickel, Ni(CO)₄, which is subsequently decomposed at above 200°C to yield metallic nickel that is 99.8% pure. (MM)

Nickel matte: An impure mixture of sulphides produced during the smelting of nickel sulphide ore. (MM)

Nickel subsulphide: (Ni₃S₂). A major component in the refining of nickel ores. Synonyms: heazlewoodite, nickel sulphide (3:2), and trinickel disulphide. (MM)

Nickel sulphate hexhydrate: (NiSO₄·6H₂O). A water-soluble compound of nickel that is used in nickel plating, as a mordant in dyeing and printing textiles, as a blackening agent for zinc and brass, and in the manufacture of organic nickel salts. (MM)

Nitriles: Compounds containing the cyano (CN) group. (PE)

Nitrogen oxides: Inorganic oxides that contain nitrogen (e.g., nitrogen oxide (NO), nitrous oxide (N₂O), and nitrogen dioxide (NO₂)). (AP)

Nitrophen: 2,4-dichlorophenyl 4-nitrophenylether (C₁₂H₇Cl₂NO₃). Also known as NIP and niclofen. A nitrophenyl ether herbicide. A pre- and post emergent herbicide for grasses and broadleaf weeds. It was used on food and ornamental crops but is no longer sold or manufactured in the US and Canada. (1836-75-5) (PE)

Nitrophenyl: A benzene ring where one of the hydrogen atoms has been replaced by a nitro (NO₂) group. (PE)

Nitrosamines: A group of chemical compounds with the structure R₂N-N=O. (ET)

Nitrosomethylurea (NMU): (C₂H₅N₃O₂). A solid material with a half life of 2-20 days in water. It degrades in ultraviolet and visible light. It is potentially explosive at room temperature and when heated gives off toxic fumes of nitrogen oxides. (684-93-5) (PE)

NK: See Natural killer cells.

NMU: See Nitrosomethylurea.

No-observed-(adverse-)effect level (NOEL)/(NOAEL): A term from toxicology, meaning the highest dose at which no health effects are detected in the animal population. (PP)

NOEL(NOAEL): See No-observed-(adverse-)effect level.

Non-asbestiform amphibole: A mineral of the amphibole group that is not in the form of fibrous needle-like crystals. The general definition of asbestos can include any fibrous mineral from the amphibole and serpentinite mineral groups. (MM)

Non-Hodgkin lymphoma: A group of lymphomas (cancer of the lymphatic system) which differ in important ways from Hodgkin lymphoma (also a type of lymphoma) and are classified according to the microscopic appearance of the cancer cells. The disease is classified as either low grade (slowly growing), intermediate grade or high grade (rapidly growing) and may be treated in a variety of ways depending on the exact diagnosis. Previously called lymphosarcoma.

Non-ionizing radiation: Radiation insufficient to split the chemical bonds of compounds. (EF)

Non-linear regression: A regression problem in which the parameters are nonlinear, which prevents the use of least squares criteria.

Non-parametric model: A statistical model that assumes that the population contributing the sample is not normally distributed regarding the variable under study i.e., the resulting statistical test is distribution free.

Non-selective herbicide: A herbicide that kills any vegetation. (PE)

Nucleotide: One of the compounds into which nucleic acid splits on hydrolysis, consisting of a nitrogenous base, a sugar, and a phosphate group. (PE)

Null hypothesis (H_o): The statistical hypothesis that two or more variables are not related or that two or more populations do not differ from one another. The null hypothesis states that the results observed in a study or an experiment are no different from what might have occurred just by chance.

Octachlorodibenzodioxin: A compound having eight chlorine atoms on the two benzene rings that are attached to either side of the dioxin ring. This compound has no hydrogen atoms in its structure. (PP)

Odds ratio (OR): Main measure of risk derived from case-control studies that quantifies the relationship between an exposure and a health outcome. The ratio of two odds. Mathematically it is represented as ad/bc: a = number of people exposed who have the disease, b = number of people not exposed but have the disease, c = number of people exposed but do not have the disease, and d = number of individuals who have not been exposed and do not have the disease.

Ohm: Unit for measuring the resistance of a conductor to an electric current. A conductor has a resistence of one ohm if it takes one volt of pressure to send a current of one ampere through it. (EF)

Olfactometer: An instrument to test the sense of smell. (PP)

Olfactometry: A procedure to assess the sense of smell. (PP)

Oncogene: A mutated and/or over-expressed version of a normal gene of animal cells (the proto-oncogene) that, in a dominant fashion, can release the cell from normal restraints on growth and thus, alone or in concert with other changes, convert a cell into a tumour cell.

OPs: See Organophosphates.

Optical radiation: Optical radiation (10 nm–1 mm) is radiant energy within the broad region of the electromagnetic spectrum that includes ultraviolet radiation (UR), visible light, and infrared radiation. One nanometre [nm] is one billionth (10-⁹) of a metre, or 10 angstrom units. (UR)

OR: See Odds ratio.

Organic compound: A compound containing carbon. (DB, OC, PP)

Organic materials: Natural substances derived from organisms and containing compounds of carbon (e.g., hydrocarbons, such as crude oils and fossil fuels, or plant decay in soils). (DB)

Organobromides: Organic compounds, also known as brominated hydrocarbons, brominated organics and brominated synthetics, that contain hydrogen and bromine strongly bound to carbon. (PE)

Organochlorines: Organic compounds (also known as chlorinated hydrocarbons, chlorinated organics and chlorinated synthetics) that contain hydrogen and chlorine strongly bound to carbon. Many organochlorines are strongly lipophilic (fat-seeking) and tend to build up in the fatty parts of living creatures where they become more concentrated and toxic. (PP, OC, PE)

Organohalide: Any organic compound having one or more halogen atoms in its structure. See halocarbon. (PE)

Organophosphates (OPs): A class of insecticides (including also one or two herbicides and fungicides) derived from phosphoric esters. With the decision to phase out many of the persistent organochlorines, there was an increase use of organophosphates, despite their much greater acute human toxicity. Organophosphates are generally divided into three groups based on chemical similarities: aliphatics (e.g., malathion, dimethoate and dichlorvos), phenyl derivatives (e.g., parathion, fenitrothion) and heterocyclic derivatives (e.g., azinphos-methyl, chlorpyriphos, phosmet). OPs inhibit certain important enzymes of the nervous system, namely cholinesterase (ChE). This inhibition results in the accumulation of acetylcholine (ACh) at the neuron/neuron and neuron/muscle (neuromuscular) junctions or synapses, causing rapid twitching of voluntary muscles and finally paralysis. (PE, OC)

Organophosphorous: A compound containing phosphorous bound to an organic compound; several organophosphorous compounds are insecticides, as they are highly toxic cholinesterase inhibitors. (PE)

Organothiophosphate: An organic compound having a thiophosphate group in its structure. (PE)

Outlier: A subject or other unit of analysis that has extreme values on a variable. Outliers can distort the interpretation of the data and result in misleading statistics.

Oxidative damage: The action of free radicals on DNA.

Oxidative stress: A harmful condition that occurs when there is an excess of free radicals, a decrease in antioxidant levels or both.

Oxidic nickel: Nickel compounds that contain oxygen (e.g., NiO, (NiCu)O). (MM)

Oxime: Compounds containing the group C-NOH. (PE)

Ozonation: The application of ozone to water, wastewater, or air, generally for the purposes of disinfection or odour control. (DB)

Ozone: (O₃). A form of oxygen, containing three oxygen atoms per molecule. A very powerful oxidant which destroys small organisms in water, including cryptosporidium. Used in water treatment for disinfection or for taste and odour control. Ozone is an key indoor and outdoor air pollutant, and is associated with deleterious human health and environmental effects. (DB)

p53 gene: A gene involved in the control of the cell cycle. p53 is considered to be a tumour suppressor gene, because when the protein function is lost due to a mutation, tumour cells may be more likely to continue to grow and proliferate.

PAB: See Para-aminobiphenyl.

PAHs: See Polycyclic aromatic hydrocarbons.

Para-aminobiphenyl (4-aminobiphenyl/PAB): (C₁₂H₁₁N). A colourless solid with characteristic odour, used as a herbicide and also found in tobacco smoke. (92-67-1) (PE)

Parathion: 0,0-diethyl 0-4-nitrophenyl phosporodithioate (C₁₀H₁₄NO₅PS). Also known as thiophos. An organothiophosphate insecticide. These chemicals act by interfering with the activities of cholinesterase. (56-38-2) (PE)

Parenchymal cells: Cells forming the parenchyma. Parenchyma is the essential or functional elements of an organ, as distinguished from its stroma or framework.

Particulate: Referring to, or produced by, particles (a tiny mass of material.), such as dust, minute germs, etc. (AP, PP)

Particulate matter (PM): Microscopic particles that vary in size and chemical makeup. For monitoring purposes, PM levels are classified as total suspended particulates (TSP), particles with diameters of 10 micrometers (µm) or less (PM₁₀), particles between 10 and 2.5 µm (PM_10-2.5), and particles with diameters of 2.5 µm or less (PM_2.5). Major sources of outdoor PM include industrial and vehicle emissions, road dust, agriculture, construction, wood burning, forest fires, pollen, spores, bacteria and volcanoes. PM can also be formed through atmospheric chemical reactions.

PCBs: See Polychlorinated biphenyls.

PCDFs: See Polychlorinated dibenzofurans.

PCP: See Pentachlorophenol.

Penetrance: The frequency with which a heritable trait is manifested in individuals known to carry the gene that causes it. Clinically, definition of penetrance often depends on the quality of clinical methodologies; for example, magnetic resonance imaging might demonstrate findings not previously recognizable. In the medical context, the gene is usually considered penetrant if diagnostic abnormalities can be demonstrated even if the individual is asymptomatic. In the biological context, the gene can be considered penetrant if it affects the function of the individual.

Pentachlorophenol (PCP): (C₆HCl₅O). A chlorinated hydrocarbon insecticide and fungicide. Pentachlorophenol is phenol with five chlorine atoms in place of the five hydrogen atoms on the ring. It is a solid that is used primarily to protect timber from fungal rot and wood-boring insects. PCP products are very toxic to plants and are used as pre-harvest defoliants and general herbicides. Their use as herbicides is currently restricted to nonagricultural uses along drainage ditches, driveways, and fence rows. PCP, which is found throughout our environment, has been voluntarily withdrawn by manufacturers of wood for domestic use. PCP is classified as a possible human carcinogen, as it can cause cancer in male mice. (87-86-5) (PE, PP)

Pentlandite: ((FeNi)₉S₈). The main mineral that is mined for nickel, typically found in association with other sulphide ores such as chalcopyrite. (MM)

Peroxisome: A liquid-filled sac surrounded by a single membrane. Peroxisomes break down fatty acids and amino acids. These reactions produce hydrogen peroxide, which could harm cells if it were allowed to persist. An enzyme (catalase) breaks down the hydrogen peroxide to water and oxygen, both of which can be used by the cell. Peroxisomes also break down alcohol. The peroxisomes of the liver and kidneys break down nearly half of the alcohol that a person consumes.

Peroxisome proliferation: Increase in the number of peroxisomes as a result of an environmental hazard (e.g., insecticide).

pH: A measure of the acidity or alkalinity of water.

Phagocyte: Any cell that ingests microorganisms, other cells or foreign bodies.

Phenol: (C₆H₅OH). A benzene ring with an hydroxyl group (OH) in place of one of the hydrogen atoms. Phenols/phenolic compounds are caustic, poisonous and crystalline aromatic organic compounds present in coal tar and wood tar that, in dilute solution, are used as a disinfectant. (DB, PE, PP)

Phenotype: In genetics, the visible appearance of an organism, produced by the interaction of its genetic constitution with the environment.

Phenoxy herbicides: A class of herbicides containing the radical (C₆H₅O). (PE)

Phenyl: (C₆H₅). A univalent radical derived from benzene that forms the basis of phenol, and other aromatic compounds. (PP)

Phenyl propane: A form of propane with a phenyl group attached at one of the hydrogen bonding locations. Monomers of phenyl propane make up the lignin macromolecule, which is aromatic. (PP)

Phenylurea: (C₆H₅NHCONH₂). A benzene ring where one hydrogen is replaced by a urea group. (64-10-8) (PE)

Phorate: O,O-diethyl S-ethylthiomethyl phosphorodithioate (C₇H₁₇O₂PS₃). An organothiophosphate insecticide and nematicide. Trade names: Thimet, Rampart, Granutox and Agrimet. Used on corn, potatoes and cotton. Half-life in the soil is 2-173 days. In water it hydrolyzes and one of the products is formaldehyde. (298-02-2) (PE)

Phosmet: 0,0-dimethyl S-phthalimidomethyl phosphorodithioate (C₁₁H₁₂NO₄PS₂). An organothiophosphate insecticide. Also known as phthaliphos and PMP. (732-11-6) (PE)

Phosphates: Esters of phosphoric acid. (OC, PE)

Phosphinic acid: (H₃PO₂). A weak monobasic acid, also called hypophosphorous acid, that is used as a herbicide. (6303-21-5) (PE)

Phosphoric esters: See Phosphates.

Photon: A quantum (or packet) of energy emitted in the form of electromagnetic radiation. Gamma rays and X rays are examples of photons. (R)

Phthalate: The di-ester of phthalic acid. (PE)

Phthalic acid: (C₈H₆O₄). A benzene ring having two COOH groups attached to the carbon ring in place of hydrogen. (PE)

Phthalimides: Imides of phthalic acid. The N-trihalomethyl dithio derivatives are referred to as phthalimides (e.g., folpet and captofol). They are fungicides and are structurally similar to thalidomide. They act as germination inhibitors. (PE)

Pigmentary factors: Host factors, such as fair skin, light eye and hair colour, that put an individual at increased risk of acquiring CMM (Cutaneous Malignant Melanoma). (UR)

Pitchblende: One of the primary mineral ores of uranium, containing three chemical elements – uranium, polonium and radium. (R)

PM₁₀: An airborne particle with a diameter of no more than 10 µm. See Particulate matter. (AP)

Point sources: Situations, places and events which increase the risk of exposures (e.g., concentrations of air pollutants may be higher in a heavily travelled road or an industry producing noxious fumes).

Point-in-time measures: Measurements (usually made under as-is conditions) taken at one time, as opposed to continuous measurements.

Polyaromatic hydrocarbon: Hydrocarbons having more than one aromatic (likely benzene) ring. (Hydrocarbons are a class of organic compounds composed entirely of hydrogen and carbon.) (OC)

Polychlorinated: A chemical compound with more than one chlorine atom. For example, a hydrocarbon with three chlorine atoms attached to either the main carbon chain or a side chain, would be polychlorinated. (PP)

Polychlorinated biphenyls (PCBs): A family of 209 structurally related chemical compounds consisting of two benzene rings and one to ten chlorine atoms. PCBs are stable and non-flammable, appearing as either a clear mobile oil (12%-48% chlorine content) to a white or off-white powder (68% chlorine content). They are hydrophobic (lack affinity to water) and lipophilic. Most are environmentally persistent. PCBs were first produced for industrial purposes in 1929 and were used for several decades in capacitors and transformers, hydraulic fluids, adhesives, plasticizers, heat exchange equipment, inks, lubricants, sealants, caulking compounds and carbonless copy paper. In 1968 an outbreak of PCB poisoning in Japan raised concerns about the toxicity of these substances. Significant quantities remain in certain types of electrical equipment.(OC)

Polychlorinated dibenzofurans (PCDFs): Any of a class of organic compounds of the heterocyclic aromatic series characterized by a ring structure composed of one oxygen atom and four carbon atoms. The simplest member of the furan family is furan itself, a colourless, volatile, and somewhat toxic liquid. Furans are like dioxins, but they have one oxygen atom instead of two. They have a similar range of toxicity as dioxins. (OC, PP, MM)

Polychlorinated dibenzo-p-dioxins: Any in a family of over 200 chlorinated organic chemicals of which 2,3,7,8-tetrachloro-p-dibenzo-dioxin (2,3,7,8-TCDD or TCDD) is the most toxic. TCDD was an impurity in the defoliant AgentOrange and in the pesticide 2,4,5-T. Dioxins are also produced when chlorinated materials, such as some plastics, are burned. (OC, MM, PE, PP)

Polychloroterpene: A terpene is any of a group of hydrocarbons made up of building blocks of isoprene (C₅H₈). A polychlorinated terpene would have more than one chlorine atom in its structure. (PE)

Polycyclic aromatic hydrocarbons (PAHs): A family of complex organic compounds derived by fusion of two or more benzene rings. PAHs are naturally present in fossil fuels and are also formed by the partial combustion of fossil fuels, organic matter and garbage. Canadians are exposed to PAHs primarily through tobacco smoke, wood smoke, contaminated air and food, particularly meat and fish. In Canada, the highest levels of PAHs in soil are found near former gas plants, coking plants and wood-preserving facilities. (AP, ET, MM, PE)

Polycyclic hydrocarbons: Hydrocarbons having two or more rings sharing at least one carbon atom. (OC)

Polymer: Any of a large number of natural or synthetic, organic or inorganic compounds composed of very large molecules that are made up of many light, simple molecules chemically linked together. Cellulose and proteins are naturally-occurring polymers; concrete, plastics and glass are synthetic polymers. (PP)

Polymerization: The chemical process that enables the bonding of two or more single unit or simple compounds (monomers) to form a larger compound (polymer) usually of high molecular weight. (PP)

Polymorphisms: Variant forms of a particular gene that occur simultaneously in a population. (AP)

Polysaccharide: A carbohydrate containing a large number of saccharide units, such as starch and glycogen. (PP)

Pooled analysis: The process of combining epidemiological data from several different studies at the level of the individual to produce a summary estimate of risk.

Population attributable risk: A measure of the proportion of disease in a population that can be attributed to a particular exposure.

Porphyry copper deposit: A low grade ore, less than one percent copper, that can be mined in bulk for copper. A porphyry is an igneous rock containing more than 25% large crystals (phenocrysts) embedded in a ‘ground mass’ of much smaller crystals. The copper is typically present in the form of chalcopyrite (CuFeS₂) within the ground mass. (MM)

Post-emergence herbicides: Herbicides used to destroy or inhibit plant growth after emergence. (PE)

Power boiler: See Recovery furnace.

Power frequency: The frequency at which power is generated and distributed; in most of North America it is 60 HZ (hertz). (EF)

ppb: Parts per billion; a measure of concentration. May represent the concentration of a residue in soil, water or whole animals. For example, one ppb is equivalent to one second in 32 years.

ppm: Parts per million; a measure of concentration. May represent the concentration of a residue in soil, water or whole animals. For example, one ppm is equivalent to one minute in 2 years.

Pre-emergence herbicides: Herbicides used to destroy the plant before emergence. (PE)

Profluralin: N-cyclopropylmethyl-α,α,α,-trifluoro-2,6-dinitro-N-propyl-p-toluidine (C₁₄H₁₆F₃N₃O₄). A dinitroaniline herbicide. Trade name: Tolban 4E. Used on cotton, vegetable, turf and woody ornamentals to control grasses and broadleaf weeds. It is strongly absorbed to organic matter and clay and therefore does not leach. (26399-36-0) (PE)

Propane side chain: Polymers may have side chains that are other hydrocarbons. One such side chain is the hydrocarbon propane, C₃H₈. On its own, propane is a colourless gas found in natural gas and petroleum that is used as a fuel. (PP)

Propoxur: 2-isopropoxyphenyl methyl carbamate (C₁₁H₁₅NO₃). A carbamate contact insecticide used against silverfish, hornets and wasps. (114-26-1) (PE)

Prospective cohort: Any designated group of persons who are followed or traced over a period of time.

Proteases: A class of enzymes capable of splitting the peptide bonds of a protein. (MM)

Proxy/surrogate respondent: One who speaks for a subject in a study (e.g., when a subject has died or is too ill to participate).

Pulsed electromagnetic field exposure: Electromagnetic fields that deliver their exposures in short pulses as opposed to a continuous flow. (EF)

Pyrethroids: Synthetic forms of pyrethrins. Pyrethrins are two highly insecticidal compounds that were isolated from pyrethrum flower heads in 1924: Pyrethrin I (C₂₁H₂₈O₃) (121-21-1) and Pyrethrin II (C₂₂H₂₈O₅) (121-29-9). Natural pyrethroids are expensive and unstable in sunlight. Synthetic pyrethroids are very stable in sunlight and are effective at extremely low rates of application. They function as axonic poisons. Type I Pyrethroids include allethrin, tetramethrin, resmethrin, d-phenothrin, bioresmethrin, and permethrin. Type II Pyrethroids include cypermethrin, cyfluthrin, deltamethrin, cyphenothrin, fenvalerate and fluvinate. (PE)

Pyrite: (FeS2). A common mineral consisting of iron sulphide having a yellow colour and a metallic glitter that suggests gold; “fool’s gold”. (MM)

Pyrrhotite: A bronze-coloured, slightly magnetic iron sulphide, sometimes containing nickel. (MM)

Quasi-controls: A control group in which members have not been assigned randomly along with the experimental group. Quasi controls are used when it is impossible to achieve random assignment of subjects to both experimental and control groups.

Quetelet index: An anthropometric measure of body mass defined as (weight)/(height)². This measure has the highest correlation with skinfold thickness or body density. Also known as body mass index (BMI).

Radiation: The emission and propagation of energy by means of electromagnetic waves or particles. (R)

Radical: An atom or group of atoms acting as a unit in reactions. For example, ammonium (NH₄) is a radical in ammonium hydroxide (NH₄OH) and ammonium chloride (NH₄Cl). (OC, DB, PP)

Radioactive decay: Breakdown of atoms of radioactive substances into other radioactive products (e.g., radium 226 decays to radon-222). Atoms in a radioactive substance decay in a random fashion but at a characteristic rate. The length of time this takes, the number of steps required and the kinds of radiation released at each step are well known. (R)

Radioactivity: The spontaneous decay of an unstable atomic nucleus, giving rise to the emission of radiation. (R)

Radioisotope: A radioactive isotope, i.e., one whose atoms undergo radioactive decay emitting alpha, beta or gamma radiation. Radioisotopes are produced by decay of other radioisotopes or irradiation of a stable isotope. (MM)

Radium: (Ra). A radioactive metallic element with atomic number 88. As found in nature, the most common isotope has a mass number of 226. It occurs in minute quantities associated with uranium in pitchblende, camotite, and other minerals. (MM, R)

Radon: (Rn). A radioactive element that is one of the heaviest gases known. Its atomic number is 86. It is a decay product of radium. (MM, R)

Radon daughters/progeny: Short-lived decay products of radon-222. Radon progeny are gasses that become attached (adsorbed) to solid particles that are inhaled and trapped within the lungs. The progeny can thereby irradiate cells in the immediate vicinity of the particles to which they are attached. While most of the progeny attach to larger aerosols immediately after forming, a variable proportion remains unattached and is referred to as the “unattached fraction”. (R, MM)

Random-digit dialling: The procedure for selecting a population sample from telephone subscribers in a region. It is based on every possible permutation and combination of seven digits from a set of 10 (0-9). The area code is constant and unlisted numbers can be accessed.

Rat liver activation system: In a standard Ames assay a rat liver homogenate is used to provide the P450 cytochromes necessary for activation of mutagens to their reactive forms. (PE)

Raw water: Water that has not been treated in any way; it is generally considered to be unsafe to drink. (DB)

Recall bias: The distortion in the results respondents’ foggy memories about their exposure history.

Receptor: A cellular protein that binds with a specific drug, chemical or hormone, effecting a change in the cell’s function.

Recovery furnace/power boiler: Spent digester liquors are sent here to recover and reconstitute digestion chemicals from the spent cooking liquor, and to recover heat energy by burning the dissolved organic material from the wood. (PP)

Reduced sulphur compounds: The vile-smelling gases emitted from the kraft process. They include include hydrogen sulfide (H₂S), Methyl mercaptan (CH₃-SH), Dimethyl sulfide (CH₃-S-CH₃), and Dimethyl disulfide (CH₃-S-S-CH₃). (PP)

Regionalized variable: A variable that has properties that are intermediate between a fully random variable and a fully deterministic one. This means that although they are continuous over an entire surface, the complexity of the surface is such that it cannot be described easily by a deterministic function such as a trend surface. (AP)

Regression statistics: The relationship between the mean value of a random variable and the corresponding values of one or more independent variables.

Relative risk: A ratio of the risk of disease or death among the exposed to the risk among the unexposed.

Repeated sampling paradigm: A sequence of two or more cross-sectional studies conducted within the same dynamic target population generally spaced at least a few years apart. In this model the investigator follows the population rather than individuals. It is unlikely that a single respondent will appear in more than one sample.

Resins: Sticky yellow or brown substances that flow from certain plants and trees, especially the pine and fir, and normally harden upon exposure to air into brittle, amorphous, solids that are insoluble in water. They are soluble, however, in alcohol, ether and other organic solvents. There are three types of resins: hard resins, oleoresins, and gum resins. The oleoresins are perhaps the most commercially important. The most widely used of the oleoresins being rosin, used in sizing paper, soap making and for the bows of stringed instruments. It is obtained by the distillation of the oleoresin, turpentine.

Resmethrin: 5-benzyl-3-furylmethyl (1RS, 2RS; 1RS, 3SR)-2,2-dimethyl-3-(2-methylprop-1-enyl) cyclopropane carboxylate (C22H26O3). A pyrethroid ester insecticide used to control flying and crawling insects and for fabric protection, pet sprays and shampoos.  (10453-86-8) (PE)

Robertson-Berger metre: A metre used to measure ultraviolet radiation. (UR)

Saccharomyces cerevisiae: A yeast that is an ideal eukaryotic (having a nucleus) micro-organism for biological studies because the complete sequence of its genome is known and genetic manipulation is relatively easy. It can be used to functionally dissect gene produces from other eukaryotes. (PE)

Salmonella typhimurium: A strain of gram negative bacteria belonging to genus Salmonella. It is responsible for food poisoning in man. (PE)

SCE: See Sister chromatid exchange.

Schist: A crystalline metamorphic rock that splits easily into layers. (MM)

Serum: The clear portion of any liquid separated from its solid particles. The pale yellowish fluid which exudes from the clot formed in the coagulation of the blood; the liquid portion of the blood, after removal of the blood corpuscles and the fibrin.

Siderite: (FeCO₃). An iron ore composed of iron carbonate. Siderite occurs in various forms and colours. (MM)

Sidestream smoke: The stream of smoke from the burning end of a cigar, cigarette, or pipe. (ET)

Sievert (Sv): The international system (SI) unit for equivalent dose equal to 1 Joule/kilogram.

Silica: Silicon dioxide (SiO₂). The main ingredient in sand and a compound of the two most abundant elements in the Earth’s crust, silicon and oxygen. The crystalline form exits in three different forms or morphs (i.e., it is polymorphic) namely quartz, cristobalite, and tridymite. Quartz is mainly diffused in the planet as sand. The other two occur in lava and are formed by heating quartz or amorphous silica. (MM, R)

Silicosis: A disease of the lungs caused by continued inhalation of the dust of minerals containing silicon; characterized by progressive fibrosis and a chronic shortness of breath. (R)

Sintering: Fusing together fine particles to form larger masses by the combined action of heat and pressure. (MM)

Sister chromatid exchange (SCE): A genetic exchange between two sister chromatids or genetic material in the prophase of mitosis (cell division in the body cells – as opposed to the germ cells) thereby producing different genetic architecture between the two daughter cells. The frequency of such exchanges in an experimental biological system (e.g., Chinese hamster cells) indicates the degree of carcinogenicity of an exposure.

Sister chromatids: In the prophase of mitosis of eukaryote organisms (cells containing nuclei), each chromosome in each cell replicates to constitute a pair of daughter chromosomes, called sister chromatids at this stage, that are in close association with each other.

Skarn: A rock, created from limestone or dolomite by contact metamorphism, that contains large amounts of silicon, aluminum, iron and magnesium that have moved from the adjacent igneous rock (typically granite). Skarns can be economically mined for iron and copper. (MM)

Small cell carcinoma: A type of cancer in which the tumour cells have endocrine-like characteristics and may secrete one or more of a wide range of hormones.

Smelting: A complex set of chemical reactions that result in the formation of slag (waste) and a valuable matte (an impure mixture of sulphides that is processed further). (MM)

Smelting dissolving tanks: The unburned inorganic component that collects at the bottom of the recovery boiler/furnace is molten smelt. The smelt flows out of the furnace and is dissolved in a weak caustic solution producing “green liquor”. (PP)

Sodium hydroxide: A brittle, white, opaque solid with the chemical formula NaOH. It is strongly alkaline, and is used in the making of wood pulp for paper, and in the manufacture of soap. Sodium hydroxide is also known as sodium hydrate, caustic soda, and lye. (PP)

Sodium sulphide (Na₂S): A reddish brown amorphous solid that is deliquescent (becomes liquid by absorbing moisture from the air) and is used in the manufacture of dyes. (PP)

Soil sterilant: A chemical that kills everything growing in the soil where it is applied. Can be carried by water and persist in the soil for several years. (PE)

Soluble nickel: All forms of soluble nickel salts: nitrates, citrates, acetate, sulfamates.

Somatic mutation: A change in the genetic material in the somatic cells (or body cells) which does not transmit to the next generation.

Spatial interpolation: Interpolation carried out on a spatial or geographic domain.

Sprague-Dawley rats: A strain of rats commonly used to conduct toxicological experiments into the health effects of various exposures.

Squamous cell carcinoma: A skin cancer that is less common than basal cell carcinoma but has a higher rate of metastasis (spread). It is estimated that 90-95% of SCCs are caused by sunlight exposure. Squamous cell carcinoma is also an occupational hazard, occurring in workers who distill tar vapour in the manufacture of coal gas and in machinery operators whose clothes and skin become soaked in mineral oil.

Standardized (standardised) incidence/morbidity/mortality ratio (SIR/SMR): The ratio of the number of events observed in the study group or population to the number that would be expected if the study group had the same age-specific rates as the standard population.

Statistical power/power of a statistical test: A gauge of the sensitivity of a statistical test; i.e., its ability to detect effects of a specific size, given the particular variance and sample sizes of the study.

Statistical significance: The probability, expressed as a p-value, that an observed effect has occurred purely as a result of chance. The smaller the p-value, the less likely the observed effect is the result of chance, and the greater the statistical significance.

Sub-multiplicative interaction: Unmeasurable and complex interaction between two or more factors (e.g., between smoking and radon exposure in lung cancer).

Substituted amides: A class of herbicide also known as chloracetamides that act as shoot inhibitors, and are used as pre-emergence herbicides. The leading examples of amide herbicides used in Canada are alachlor and metolachlor. (PE)

Sulphallate: 2-chloroallyl diethyldithiocarbamate (C₈H₁₄ClNS₂). A thiocarbamate herbicide. (95-06-7) (PE)

Sulphanilamide: p-aminobenzenesulphonamide (C₆H₈N₂O₂S). The amide of sulphanilic acid (sulphanilamide) and certain related substituted amides are of importance as the sulpha drugs. Anti-bacterial activity and toxicity of the substituted sulphanilamides depend on the nature of the group attached to the amido nitrogen. It is nearly always heterocyclic-a ring structure in which one or more of the carbon atoms is replaced by a different atom (nitrogen, oxygen or sulphur). (63-91-2) (PE)

Sulphates: Salts of sulphuric acid (H₂SO₄) that occur naturally in numerous minerals and have numerous practical uses (e.g., in the manufacture of chemicals, dyes and fertilizers). (AP)

Sulphide matrix breccias: A sedimentary rock containing very large angular grains held together by a matrix (thick glue) of very small grains of some type of sulphide. Some common sulphides are galena (PbS), sphalerite (ZnS), pyrite (FeS₂). (MM)

Sulphidic nickel: Nickel compounds that contain sulphur, including nickel subsulphide and nickel sulphide. (MM)

Sulphite pulping process: An alternative to the Kraft (sulphate) pulping process, that uses sulphuric acid and one of its base salts. One of the major drawbacks of this alternative is that it creates more pollutants, uses more water, and produces a poorer quality product than the sulphate process. (PP)

Sulphonation: Treating wood chips with hydrosulphide, and exposing them to increased acidity in a bisulphate solution to remove the lignin. (PP)

Sulphonyl ureas: Herbicides with a urea functional group having a sulfonyl substituent. Examples include Bensulfuron-methyl and Chlorsulphuron ((C₁₂H₁₂ClN₅O₄S) 1-(chlorophenylsulphonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl) urea) (6490-27-23), trade names Glean^® and Telar^®. Used to control many broadleaf weeds and some annual grass weeds, sulphonyl urea herbicides block the synthesis of essential branched chain amino acids. They have a high potential to contaminate ground water. (PE)

Sulphur: A lemon-yellow-coloured non-metallic element sometimes known as “brimstone”. (PP)

Sulphur dioxide: (SO₂). A colourless, non-flammable, extremely irritating gas or liquid used in many industrial processes. (MM, PP)

Summary relative risks: Relative risk calculated by pooling relative risks emerging from meta-analysis.

Suppressor T-cells: Antigen-specific suppressor T lymphocytes (white blood cells) that diminish an organism’s immune response.

Surface water: Water which is open to the atmosphere and subject to surface runoff; generally lakes, streams, rivers. (DB)

Surfactants: Surface-active lipoproteins that normally serve to decrease the surface tension of fluids. In the lung, they thereby permit the pulmonary tissues to expand during inspiration. (PE)

Susceptibility genes: Genetic loci that put individuals into a higher risk of morbidity or mortality from a specific condition.

Synergistic effect: A situation in which the combined effect of two or more factors is greater than the sum of their solitary effects.

Tankhouse: Where the electrolytic tanks are located in a smelter. (MM)

TCDD: See 2,3,7,8-tetrachlorodibenzo-p-dioxin.

TCP: See 2,4,5-trichlorophenol.

Terbuphos: S-tert-butylthiomethyl-0,0-diethyl phosphorodithioate (C₉H₂₁O₂PS₃). A highly toxic aliphatic organo thiophosphate insecticide and nematicide used to control soil pests on corn and sugar beets. Primarily formulated as granules, it is applied at planting. Terbufos controls wireworms, seedcorn maggots, white grubs, corn rootworm larvae and other pests. It breaks down rapidly. Two of the primary degradation products, terbufos sulphoxide and terbufos sulphone are highly toxic and more persistent in terrestrial and aquatic environments than the terbufos itself. Use is being phased out in Canada. (13071-79-9) (PE)

Tesla: The unit of magnetic flux density, equal to one weber per square meter and symbolized as T. A micro-tesla (µT) is one millionth of a tesla. (EF)

Tetrachlorodioxins: Pesticide by-products/contaminants. (PE)

Tetrachloroethylene: (CCl2; CCl2). A halogenated volatile organic compound (VOC) organic solvent that can become airborne from pulp and paper mill waste water. (PP)

Thiocarbamate: Typically herbicides with a carbamate structure where sulfur replaces one of the oxygens in the amide functional group (-S-CO-N- instead of -OCO-N-). They are weak cholinesterase inhibitors. (PE)

Thiocyanate: A compound having the SCN group in its structure. (PE)

Thiol-containing molecules: An organic compound containing SH (sulphydryl). (MM)

Thiophanate methyl: Dimethyl 4,4’-(O-phenylene) bis (3-thioallophanate) (C₁₂H₁₄N₄O₄S₂). A carbamate fungicide. (23564-05-8) (PE)

Thiophosphate: A phosphate in which one of the oxygen atoms has been replaced by a sulphur atom. (PE)

THMs: See Trihalomethanes.

Threshold-limit value (TLV): Air borne concentration of substances which represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day, for the entire working life, without adverse effects. (MM)

Threshold-limit value time-weighted average (TLV-TWA): Average concentration of an airborne substance for a normal eight hour work day or 40-hour work week to which nearly all workers may be repeatedly exposed day after day without adverse effects. (MM)

TLV: See Threshold limit value.

Toxaphene: (C₁₀H₁₀C₁₈). Polychlorcamphene, camphechlor. A reaction mixture of chlorinated camphenes containing 67-69% chlorine. A polychloroterpene (organochlorine) insecticide. The use of toxaphene on Canadian crops was discontinued in 1970. It is a common fish contaminant in the Yukon and NWT. For Canadians, the principal route of exposure is eating contaminated fish. (8001-35-2) (PE)

Transition: A mutation in which a chemical in DNA is replaced by a different chemical but of a similar type.

Translocation: An exchange of chromosomal fragments between two non-homologous chromosomes in a diploid organism during cell division.

Transversion: A mutation in which a chemical in DNA is replaced by a chemical of a different type.

Treated water: Disinfected and/or filtered water served to water system customers. (DB)

Triadimefon: 1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)butan-2-one. A triazole fungicide used to control powdery mildews, rusts, and other fungal pests on cereals, fruits, and vegetables. (43121-43-3) (PE)

Triallate: S-2,3,3-trichloroallyl di-isopropylthiocarbamate (C₁₀H₁₆Cl₃NOS). A thiocarbamate herbicide used to control wild oats, primarily in wheat and barley and one of the thiocarbamate herbicides used most commonly in Canada. (2303-17-5) (PE)

Triazines: Herbicides that act by stopping photosynthesis, used on fruit, grain and vegetable crops. They include Atrazine (AATREX), Cyanazine (BLADEX), Hexazinone (VELPAR), Metribuzin (LEXONE, SENCOR) and Simazine (PRINCEP). Triazine is a heterocyclic aromatic 6-membered ring made up of 3 nitrogen atoms and 3 carbon atoms. (PE)

Triazoles: A class of herbicide and fungicide/fumigant including Amitrole, Fluconazole, Guanazole, Itraconazole, and Trapidil. Triazole is a heterocyclic aromatic 5-membered ring made up of three nitrogen atoms and two carbon atoms. (PE)

Trichloroethylene: (CHCl; CCl2). A halogenated volatile organic compound (VOC) in the form of a heavy, stable toxic liquid with a chloroform aroma, slightly soluble in water. (PP)

Trichlorophenol: (C₆H₃Cl₃O). An organochlorine fungicide/fumigant. A man-made chemical no longer made in the US. It is a germicidal agent used to preserve wood and glue as well as to protect textiles against mildew. (88-06-2) (PE)

Trifluralin: α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (C13H16F3N3O4). One of the dinitroaniline herbicides most commonly used in Canada; a selective, pre-emergence herbicide used to control annual grasses and broadleaf weeds in a variety of crops. (1582-09-8) (PE)

Triflusulfuron: 2-[4-dimethylamino-6-(2,2,2-trifluoroethoxy)-1,3,5-triazin-2-ylcarbamoylsulfamoyl]-m-toluic acid (C₁₆H₁₇F₃N₆O₆S). A sulfonyl urea herbicide. (PE)

Trihalomethanes (THMs): Halogen-substituted single-carbon compounds with the general formula CHX₃, where X may be one or a combination of chlorine, bromine, fluorine, or iodine. These compounds are formed in treated water primarily as a result of chlorination of organic matter present naturally in raw water supplies. The THMs most commonly present in drinking water are chloroform, bromodichloromethane, chlorodibromomethane, and bromoform. (DB)

Trivalent arsenicals: Arsenic compounds possessing a valence of three (e.g., Arsenic trichloride (AsCl₃), Arsenic Trioxide (As₂O₃)). (MM)

Tumour-promoting agent: A stimulus or substance (chemical or otherwise) which has the potential to stimulate the growth of either benign or malignant tumours.

Turpenes: Any of the group of isomeric unsaturated hydrocarbons with the formula C₁₀H₁₆, also known as turpentines. They have a pleasant aromatic odour, and occur in essential oils and oleoresins of plants, especially conifers. Terpenes are emitted from outside chip piles in the pulp and paper industry and they constitute a group of volatile organic compounds that have no practical collection or disposal method. Forest trees also emit vast amounts of terpenes, and in the typical rural kraft mill, terpenes emitted by a chip pile are negligible compared to natural terpene emissions. (PP)

Turpenoids: A group of plant secondary metabolites based on one or more isoprene units, and constituents of many essential oils. (PP)

Ultraviolet radiation (UVR): That portion of the electromagnetic spectrum extending from the violet, or short wavelength, end of the visible light range to the X ray region. Ultraviolet (UV) radiation is undetectable by the human eye, although when it falls on certain materials it may cause them to fluoresce; i.e., emit electromagnetic radiation of lower energy, such as visible light. (UR)

Uncertainty factor: All those factors (or confounders) for which the investigator has only probabilistic data.

Unit risk: The excess probability of developing a disease, given continuous exposure to one unit (e.g. 1 µg/m³) of a substance over a lifetime. (MM)

Uracil: (C₄H₄N₂O₂). One of the bases in RNA. It is a pyrimidine(1,3-diazine), an aromatic heterocyclic compound that is a six-membered ring made up four carbon atoms and two nitrogen atoms. There are two oxygen atoms attached to two of the carbons in the ring. Uracil herbicides, derived from Uracil, can cause ground water contamination. Examples of Uracil herbicides include Bromacil (314-40-9 ) and Teracil (5902-51-2 ). (PE)

Uranium: (U). A heavy silvery-white metallic element with the atomic number 92, radioactive and toxic, easily oxidized, and having 14 known isotopes of which U 238 is the most abundant in nature. The element occurs in several minerals from which it is extracted and processed for use in research and nuclear fuels and weapons. (R)

Urea: (CO(NH₂)₂). A water-soluble crystalline compound, that is the major nitrogenous end product of protein metabolism and is the chief nitrogenous component of the urine of mammals and other organisms. Also called carbamide. Urea is manufactured synthetically for use in making fertilizers. (57-14-7) (PE, PP)

Uvea: The portion of the eye composed of the iris and ciliary bodies together with the choroid coat.

Uveal melanoma: Melanoma which occurs in human uvea.

UVR: See Ultraviolet radiation.

Valence: A measure of the possible ways an atom can combine with other atoms. It is dependent on the electron configurations of the reacting elements.

Variable penetrance: In the medical context, penetrance is the proportion of individuals with a given genotype who present with any phenotypic features of the disorder (i.e., it is an all-or-none phenomenon). However, in one sense penetrance may vary with age, as in the case of Huntington’s disease. Variation in age of onset is most often considered as an aspect of variable expression.

Variance: A measure of the variation shown by a set of observations.

Variogram: A plot reflecting several measurements of a spatial or regionalized variable along a specified area or distance. Measurements are taken at a number of locations and the relationship between observations at the various locations can be explored by variogram analysis. (AP)

Vitamin D photochemistry: Cutaneous exposure to UV-B converts epidermal previtamin D3 (7-dehydrocholesterol) to the stable hormone vitamin D3. This compound then diffuses through the skin to blood vessels and circulates systemically, where it is converted to the functional hormone 1,25-dihydroxy vitamin D3[1,25(OH)₂D3]. Aging substantially decreases the ability of human skin to produce vitamin D3. This, coupled with the widespread use of sunscreens that filter out UV-B, has led to concern that vitamin D deficiency may become a significant clinical problem in the elderly. Indeed, studies have shown that the use of sunscreens can prevent the production of vitamin D3 in human skin. (UR)

VOCs: See Volatile organic compounds.

Volatile organic compounds (VOCs): Organic compounds that convert into vapour or gas without a chemical reaction. (DB, AP, PP)

Volt: The electrical unit equal to the potential difference between two points on a conductor carrying a current of 1 ampere when the power dissipated between the two points is 1 watt; equivalent to the potential difference across a resistance of 1 ohm when 1 ampere of current flows through it. (EF)

Watt: The unit for measuring electric power or energy available per second. One watt is equal to one joule of energy per second. (EF)

Weber: The unit of magnetic flux. (EF)

Wertheimer-Leeper wire code: A categorization of wiring configurations developed by Nancy Wertheimer and Ed Leeper. Power lines close to residences are categorized according to the number of conductors and their diameters, location of transformers and service drops, as well as the distance of the conductors from the home. (EF)

Wood volatiles: Extractives naturally present in wood that vapourize over time. (PP)

Working level month: A WL (Working Level) is any combination of radon progeny in one litre of air that results in the average emission of 1.3 X 10⁵ MeV of alpha energy during decay. Exposure to 1 WL for 170 hours equals 1 Working Level Month (WLM) of exposure, a unit developed to describe exposure sustained by miners during the average number of hours spent underground. (R)

Xenoestrogen hypothesis: A convention that states: “some environmental chemicals (e.g., organochlorines) exhibit estrogen receptor agonistic activity.” It is unclear whether this is an important mechanism whereby cancer is induced in humans. (PE)

Xiphophorus fish model: Heavily pigmented backcross hybrids of the genus Xiphophorus (platyfish and swordtails) are very sensitive to melanoma induction by single exposures to UVR. They are therefore used in experiments involving melanoma induction by UVR. (UR)