Biological test method for measuring survival of springtails exposed to contaminants in soil: terminology

Terminology

Note: All definitions are given in the context of the procedures in this report, and might not be appropriate in another context.

Grammatical Terms

Must is used to express an absolute requirement.

Should is used to state that the specified condition or procedure is recommended and ought to be met if possible.

May is used to mean “is (are) allowed to.”

Can is used to mean “is (are) able to.”

Might is used to express the possibility that something could exist or happen.

Technical Terms

Acclimation is physiological adjustment to a particular level of one or more environmental factors such as temperature. The term usually refers to the adjustment to controlled laboratory conditions.

Adult (springtail) is a Collembola that is sexually mature. (See also juvenile.)

Anal spines are chitinous structures extending from the anal segment of the Collembola.

Biomass is the total weight (mass) of a group of animals or plants.

Collembola refers to springtails that are members of the family Collembola.

Compliance means in accordance with governmental regulations or requirements for issuing a permit.

Conductivity is a numerical expression of the ability of an aqueous solution to carry an electric current. This ability depends on the concentrations of ions in solution, their valence and mobility, and on the solution’s temperature. Conductivity is measured at 25°C, and is reported as micromhos per centimetre (μmhos/cm) or as millisiemens per metre (mS/m); 1 mS/m = 10 μmhos/cm.

Culture, as a noun, means the stock of organisms raised in the laboratory under defined and controlled conditions through one or more generations, to produce healthy test organisms. As a verb, it means to carry out the procedure of raising healthy test organisms from one or more generations, under defined and controlled conditions.

Dentes (Dens, singular) is the pair of structures protruding from the manubrium (i.e., two arms forming the distal part of the furca).

Eclosion refers to hatching or escape of a larva (i.e., springtail) from its egg.

Ecological risk assessment (ERA) is the process of risk analyses and evaluation of the adverse effects of contaminated environmental media (e.g., air, soil, water) on non-human organisms with respect to the nature, extent and probability of the occurrence of these effects (ISO, 2005).

Empodium is a small appendage on the pretarsus opposite the claw.

Euedaphic means permanent soil dwellers and refers to those species that live within the interstitial spaces of the soil. (See also hemiedaphic.)

Fungal hyphae are the long, slender, usually branched filaments of fungal mycelium.

Furca or jumping organ, evolved through the basal fusion of a pair of appendages on the fourth abdominal segment, and is capable of propelling some springtails many times their own body length in a fraction of a second. It evolved as an escape mechanism to avoid predators. Soil-dwelling species have reduced furca or have lost the structure entirely.

Hemiedaphic means living in the superficial soil layers and leaf litter. (See also euedaphic.)

Hormesis is an observed stimulation of performance (e.g., reproduction) among organisms, compared to the control organisms, at low concentrations in a toxicity test.

Instar refers to a stage of an insect or other arthropod between molts.

Juvenile (springtail) is a Collembola that is sexually immature. (See also adult.)

L, F and H layers refer to the combined LFH layer of a soil. This is an organic layer that occurs on the surface of the mineral soil, and is usually composed of the accumulation of leaves, twigs and woody materials. The components of the L (leaf) layer, which is at the top, are usually identifiable. The next layer down (F) is distinguished by the original materials being difficult to identify as a result of the initiation of decomposition, while the H layer is composed of decomposed organic materials that are indiscernible. The H layer may be intermixed with mineral particles from the mineral soil below.

Lamella refers to a thin sheet or plate of tissue.

Lux is a unit of illumination based on units per square metre. One lux = 0.0929 foot-candles and one foot-candle = 10.76 lux. For conversion of lux to quantal flux [μmol/(m²· s)], the spectral quality of the light source must be known. Light conditions or irradiance are properly described in terms of quantal flux (photon fluence rate) in the photosynthetically effective wavelength range of approximately 400−700 nm. The relationship between quantal flux and lux or foot-candles is highly variable and depends on the light source, the light meter used, the geometrical arrangement, and the possibilities of reflections (see ASTM, 2008). Approximate conversions between quantal flux and lux, however, are:

• for cool-white fluorescent light: 1 lux ≈ 0.014 μmol/(m²· s);
• for full-spectrum fluorescent light (e.g., Vita-Lux® by Duro-Test®): 1 lux ≈ 0.016 μmol/(m²· s); and
• for incandescent light: 1 lux ≈ 0.019 μmol/(m²· s) (Deitzer, 1994; Sager and McFarlane, 1997).

Manubrium refers to the basal part of the furca.

Monitoring is the routine (e.g., daily, weekly, monthly, quarterly) checking of quality or collection and reporting of information. In the context of this report, it means either the periodic (routine) checking and measurement of certain biological or soil quality variables, or the collection and testing of soil samples for toxicity.

Mucro is the hook-like (i.e., modified claw) structure on the ends of each of the dens. Springtails use these structures to push or hook against the ground, providing the leverage to enable them to jump.

Mycorrhizae is symbiotic association of the mycelium of a fungus with the roots of certain plants.

Ocelli is one of the types of photoreceptor organs in animals. Also called “simple eyes,” Ocelli are miniature eyes, capable of just sensing light but not of distinguishing its direction.

Papillae are protuberances on the cuticle of Collembola that serve a sensory function.

Parthenogenetic means asexual, and refers to organisms in which females lay unfertilized eggs that develop into viable offspring and males are completely absent from the population.

pH is the negative logarithm of the activity of hydrogen ions in gram equivalents per litre. The pH value expresses the degree or intensity of both acidic and alkaline reactions on a scale from 0−14, with 7 representing neutrality, numbers < 7 indicating increasingly greater acidic reactions, and numbers > 7 indicating increasingly basic or alkaline reactions.

Photoperiod is the duration of illumination and darkness within a 24-hour period.

Pollution is the addition of a substance or material, or a form of energy such as heat, to some component of the environment, in such an amount as to cause a discernible change that is deleterious to some organism(s) or to some human use of the environment. Some national and international agencies have formal definitions of pollution, which should be honoured in the appropriate contexts.

Post antennal organ (PAO) is dorsally located on the head at the base (posteriorally) of the antennae and is believed to have an olfactory function.

Pretreatment means treatment of a sample of soil, or portion thereof, before exposure of the test organisms.

Progeny means the young or offspring (i.e., immediate descendants) of sexually mature (adult) springtails.

Protocol is an explicit set of procedures for a test, formally agreed upon by the parties involved, and described precisely in a written document.

Pseudocelli are small areas of thin cuticle through which defensive fluid can be extruded. Pseudocelli can be distributed over the entire surface of the body including appendages. They are made from epicuticle, and the glands located below each one are composed of secretory cells in direct contact with the haemolymph. The defensive fluid secreted by the pseudocelli will repel predators and other Collembola.

Quality assurance (QA) is a program within a laboratory, intended to provide precise and accurate results in scientific and technical work. It includes selection of proper procedures, sample collection, selection of limits, evaluation of data, quality control, and qualifications and training of personnel.

Quality control (QC) consists of specific actions within the program of quality assurance. It includes standardization, calibration, replication, control samples and statistical estimates of limits for the data.

Redox potential (also known as the oxidation-reduction potential) is a measure (in volts) of the affinity of a substance for electrons relative to hydrogen.

Reference method refers to a specific protocol for performing a toxicity test, i.e., a biological test method with an explicit set of test procedures and conditions, formally agreed upon by the parties involved and described precisely in a written document. Unlike other multi-purpose (generic) biological test methods published by Environment Canada, the use of a reference method is frequently restricted to testing requirements associated with specific regulations.

Remediation is the management of a contaminated site to prevent, minimize, or mitigate damage to human health or the environment. Remediation can include both direct physical actions (e.g., removal, destruction and containment of toxic substances) and institutional controls (e.g., zoning designations or orders).

Risk is the probability or likelihood that an adverse effect will occur.

Risk assessment - see ecological risk assessment.

Sensilla (sing. sensillum) are smooth blunt setae located on the antennae, which serve as chemosensory receptors.

Setae are slender, usually rigid, bristles, hair or spines distributed in characteristic patterns on the exoskeleton that function as sensory receptors or in locomotion.

Spermatophore is a capsule or compact mass of spermatozoa extruded by the males of certain invertebrates.

Ventral tube is comprised of eversible sacs derived from a pair of appendages on the first abdominal segment. It is an organ that is important in fluid balance and as a means of adhering to surfaces.

Terms for Test Materials or Substances

Artificial soil is a laboratory-formulated soil, prepared to simulate a natural soil using a specific ratio of natural constituents of sand, clay and peat. Artificial soil may be used as a negative control soil, and as a diluent to prepare multiple concentrations of site soil(s) or chemical-spiked soil(s).

Batch means the total amount of a particular test soil (or specific concentration thereof) prepared for each treatment (concentration) in a test. A batch is any hydrated test soil ready for separation into replicates.

Bulk soil samples are unconsolidated, typically large (> 1 L) point samples that consist of more than one individual block of soil removed from one sample location by a sampling device, and therefore are point samples, not composite samples (see point and composite samples). Bulk soil samples are often collected to satisfy the large volume requirements for biological testing.

Cation exchange capacity is the sum total of exchangeable cations that a soil can adsorb. It is sometimes called total-exchange capacity, base-exchange capacity or cation-adsorption capacity. It is expressed in milliequivalents per 100 grams of soil (or other adsorbing material such as clay) (AAFC, 1998).

Chemical is any element, compound, formulation, or mixture of a substance that might be mixed with, deposited in, or found in association with soil or water, or enter the environment through spillage, application, or discharge.

Chemical-spiked soil is natural or artificial soil (usually negative control soil, reference soil or other clean soil) to which one or more chemicals or chemical products have been added, and mixed thoroughly to evenly distribute the substance(s) throughout the soil at a specific concentration to form a batch for use in a soil toxicity test. (See also spiked soil.)

Clean soil is soil that does not contain concentrations of any substance(s) or material(s) causing discernible toxic effects to the test organisms.

Composite sample(s) are soil samples consisting of point or bulk samples combined from two or more sample locations at a site (Crépin and Johnson, 1993).

Concentration means the ratio of the weight of test substance or material to the weight of soil, and is frequently expressed as the weight of test substance or material per kg of dry soil (mg/kg). Concentration might also be expressed as a percentage of the test substance (e.g., contaminated site soil) or material per dry weight of soil.

Consolidated soil sample (see also unconsolidated soil sample) is synonymous with undisturbed sample and is a sample obtained from soil using a method designed to preserve the soil structure (ISO, 2005).

Contaminant is a substance or material that is present in a natural system, or present at increased concentration, often because of some direct or indirect human activity. The term is frequently applied to substances or materials present at concentrations that have the potential to cause adverse biological effects.

Contaminated (soil) means (soil) containing chemical substances or materials at concentrations that pose a known or potential threat to environmental or human health.

Control is a treatment in an investigation or study that duplicates all the conditions and factors that might affect results, except the specific condition being studied. In toxicity tests, the control must duplicate all the conditions of the exposure treatment(s), but must contain no contaminated test material or substance. The control is used as a check for the absence of measurable toxicity due to basic test conditions such as temperature, health of test organisms or effects due to their handling. Control is synonymous with negative control, unless indicated otherwise.

Control soil - see negative control soil.

Core sample is a sample of soil that has been collected using a corer.

Data quality objectives (DQOs) are pre-defined criteria for the quality of data generated or used in a particular study so as to ensure that the data are of acceptable quality to meet the needs for which they were collected.

Definitive (soil toxicity test) means decisive (as opposed to a preliminary, range-finding test). [See also range-finding (test).]

De-ionized water is water that has been purified by passing it through resin columns or a reverse osmosis system, for the purpose of removing ions such as Ca⁺⁺and Mg⁺⁺.

Distilled water is water that has been passed through a distillation apparatus of borosilicate glass or other material, to remove impurities.

Fertility (of soil) refers to the potential of a soil to supply nutrient elements in the amounts, forms and proportions required for optimal plant growth. Soil fertility is measured directly in terms of the ions and compounds important for plant nutrition. The fundamental components of fertility are the essential nutrients (macronutrients including C, H, O, N, P, K, Ca, Mg, S and micronutrients including Fe, Mn, Mo, B, Cu, Zn and Cl). Indirectly, soil fertility is measured by demonstrating its productivity (i.e., the capacity of the soil to produce plants that supply essential food and fibre; Hausenbuiller, 1985).

Horizon - see soil horizon.

Hydration water means water used to hydrate test soils, to create a specific moisture content suitable for the test organisms. The water used for hydration is normally test water, and is frequently de-ionized or distilled water, reverse-osmosis water, or de-chlorinated tap water. Depending on study design and intent, a surface water or groundwater from the site might be used instead of de-ionized or distilled water for the hydration of each test soil (including negative control soil). (See also test water, de-ionized water and distilled water.)

Material is the substance or substances from which something is made. A material would have more or less uniform characteristics. Soil, sediment or surface water are materials. Usually, the material would contain several or many substances.

Moisture content is the percentage of water in a sample of test soil, based on its wet or dry mass. It is determined by measuring both the wet and dry weights of a subsample of the soil. The soil’s moisture content is then calculated and expressed on a dry-weight basis, by dividing the mass of water in the subsample (wet mass - dry mass) by the mass of dry soil, and then multiplying by 100. Units for mass (i.e., g or mg) must be the same in each instance.

Negative control - see control.

Negative control soil is clean soil that does not contain concentrations of one or more contaminants that could affect the survival or reproduction of the test organisms. Negative control soil might be natural soil from an uncontaminated site, or artificial (formulated) soil. This soil must contain no added test material or substance, and must enable acceptable survival and performance of the test organisms during the test. The use of negative control soil provides a basis for interpreting data derived from toxicity tests using test soil(s) and gives information about the state of health (i.e., quality) of the test individuals coming from a culture.

Organic matter (OM) in soil consists primarily of plant and animal residues, at different stages of decomposition, including soil humus. The accumulation of OM within soil is a balance between the return or addition of plant and animal residues and their subsequent loss due to the decay of these residues by soil micro-organisms. For many types of soil, the following equation (from AESA, 2001) is suitable for estimating the total OM content of soil from total organic carbon (TOC) measurements: % OM = % TOC 1.78; however, the relationship between TOC and OM is slightly different among soils, and therefore the total organic carbon content should also be determined by laboratory analysis. (See also total organic carbon.)

Point sample(s) are individual blocks of soil removed from one sample location by a sampling device (e.g., a soil core).

Positive control soil is contaminatedsoil that contains concentrations of one or more contaminants that adversely affect the survival and reproduction of the test organisms using the biological test method defined herein. Positive control soil might be used as a reference toxicant to assess the sensitivity of the test organisms at the time the test material or substance is evaluated, and to determine the precision of results obtained by the laboratory for that reference toxicant.

Product is a commercial formulation of one or more chemicals. (See also chemical.)

Range-finding (test) means a preliminary soil toxicity test, performed to provide an initial indication of the toxicity of the test material under defined conditions and to assist in choosing the range of concentrations to be used in a definitive multi-concentration test. [See also definitive (soil toxicity test).]

Reference soil is typically cleanfield-collected soil or formulated (artificial) soil that is selected for use in a particular toxicity test together with a negative control soil and one or more samples of test soil. The test soil might be either field-collected site soil that is contaminated or potentially so, or chemical-spiked soil. Reference soil used in a test frequently exhibits physicochemical properties (e.g., texture, organic matter content, total organic carbon content, pH and conductivity) closely matching those of the test soil sample(s), except that it is free from the source of contamination being assessed. In tests involving samples of site soil, one or more samples of reference soil are often selected from the general location of test soil sampling, and thus might be subject to other sources of contamination aside from the one(s) being studied. Reference soil is used to describe matrix effects in the test, and may also be used as a diluent to prepare concentrations of the test soil. In tests involving chemical-spiked soil, one or more samples of artificial (formulated) soil with differing physicochemical characteristics might be chosen to investigate the influence of certain soil properties (e.g., soil texture, or percent organic matter) on the toxicity of a chemical mixed in each of these soil types. (See also negative control soil, site soil, test soil, clean, artificial soil and chemical-spiked soil.)

Reference toxicant is a standard chemical used to measure the sensitivity of the test organisms to establish confidence in the toxicity data obtained for a test material or substance. In most instances, a toxicity test with a reference toxicant is performed to assess the sensitivity of the organisms at the time the test material or substance is evaluated, and the precision and reliability of results obtained by the laboratory for that chemical.

Reference toxicity test is a test conducted using a reference toxicant in conjunction with a soil toxicity test, to appraise the sensitivity of the organisms and the precision and reliability of results obtained by the laboratory for that chemical at the time the test material or substance is evaluated. Deviations outside an established normal range indicate that the sensitivity of the test organisms, and the performance and precision of the test are suspect and should be investigated as to the cause. A reference toxicity test with springtails is performed as a spiked-soil test, using a standard chemical.

Sampling location means a specific location, within a site, where the sample(s) of field-collected soil are obtained for toxicity tests and associated physicochemical analyses (and is considered the same as a sampling station).

Site means a delineated tract of land that is being used or considered as a study area, usually from the perspective of its being contaminated or potentially contaminated by human activity. A reference site is a site uninfluenced by the source(s) of contamination but within the general vicinity of the sites where samples of test soil are collected.

Site soil is a field-collected sample of soil, taken from a location thought to be contaminated with one or more chemicals, and intended for use in the toxicity test with springtails. In some instances, the term includes reference soil or negative control soil from a site.

Soil is whole, intact material representative of the terrestrial environment, that has had minimal manipulation following collection or formulation. In the natural environment, it is formed by the physical, chemical, and biological weathering of rocks and the decomposition and recycling of nutrients from organic matter originating from plant and animal life. Its physicochemical characteristics are influenced by biological activities (e.g., microbial, invertebrate [including springtail], and plants) therein, and by anthropogenic activities.

Soil horizon is a layer of mineral or organic soil material approximately parallel to the land surface that has characteristics altered by processes of soil formation. It differs from adjacent horizons in properties such as colour, structure, texture, and consistence and in chemical, biological, or mineralogical composition.

Solvent control soil is a sample of (usually artificial) soil included in a test involving chemical-spiked soil, in which an organic solvent is required to solubilize the test chemical before mixing it in a measured quantity of negative control soil. The amount of solvent used when preparing the solvent control soil must contain the same concentration of solubilizing agent as that present in the highest concentration of the test chemical(s) in the sample of chemical-spiked soil to be tested. This concentration of solvent should not adversely affect the performance of springtails during the test. Any test that uses an organic solvent when preparing one or more concentrations of chemical-spiked soil must include a solvent control soil in the test. (See also artificial soil, negative control soil and chemical-spiked soil.)

Spiked soil is natural or artificial soil (usually negative control soil, reference soil or other clean soil) to which one or more chemicals, chemical products, or other test substances or materials (e.g., a sample of sludge or drilling mud) have been added in the laboratory, and mixed thoroughly to evenly distribute the substance(s) or material(s) throughout the soil at a specific concentration to form a batch for use in a soil toxicity test. (See also chemical-spiked soil and spiking.)

Spiking refers to the addition of a known amount of chemical(s), chemical product(s), or other test substance(s) or material(s) (e.g., a sample of sludge or drilling mud) to a natural or artificial soil. The substance(s) or material(s) is usually added to negative control soil, reference soil, or another clean soil, but sometimes to a contaminated or potentially contaminated soil. After the addition (“spiking”), the soil is mixed thoroughly. If the added test material is a site soil, Environment Canada documents typically do not call this spiking, but instead refer to the manipulation as “dilution,” “amendment,” or simply “addition.” (See also chemical-spiked soil and spiked soil.)

Stock solution means a concentrated solution of the substance(s) to be tested, following the addition of a measured quantity of this solution to a sample of natural or artificial soil and thorough mixing to prepare a batch of chemical-spiked soil. To prepare the required strength of the stock solution, measured weights or volumes of test chemical(s) or chemical product(s) are added to test water (de-ionized, distilled water or equivalent), with or without the inclusion of an organic solvent.

Substance is a particular kind of material having more or less uniform properties. The word substance has a narrower scope than material, and might refer to a particular chemical (e.g., an element) or chemical product.

Test soil is a sample of field-collected soil or chemical-spiked soil to be evaluated for toxicity to springtails. Boreal and taiga test soils are collected as separate soil horizons. In some instances, the term also applies to any solid-phase sample or mixture thereof (e.g., negative control soil, positive control soil, reference soil, sludge, drilling mud) used in a soil toxicity test.

Test water is water used to prepare stock solutions, rinse test organisms, or rinse glassware and other apparatus used for culturing springtails and for other purposes associated with the biological test method (e.g., to hydrate samples of test soil). Test water must be de-ionized or distilled water or better (e.g., reagent-grade water produced by a system of reverse osmosis, carbon and ion-exchange cartridges). (See also hydration water.)

Texture is defined based on a measurement of the percentage by weight of sand, silt and clay in the mineral fraction of soils. Classification as to texture confers information on the general character and behaviour of substances in soils, especially when coupled with information on the structural state and organic matter content of the soil. Texture in the context of this guidance document is described according to the Canadian System of Soil Classification (AAFC, 1998), not the Unified Soil Classification, the United States Soil Conservation Service Classification or any other soil classification system used for soil science, engineering or geology. Soil texture is determined in the laboratory by measuring the particle-size distribution using a two-step procedure whereby the sand particles (coarse fragments) are initially separated by sieving from the silt and clay particles, followed by separation of the silt and clay particles by their sedimentation in water. Textural classification systems typically refer to groupings of soil based on specific ranges in relative quantities of sand, silt and clay.

There are three main textural classes:

1. coarse texture (sands, loamy sands, sandy loams);
2. medium texture (loams, silt loams, silts, very fine sandy loams); and
3. fine texture (clays, silty clay loams, sandy clay loams, silty clays, sandy clays).

Further distinction as to texture (e.g., “sandy clay,” “silt loam,” “loam”) can be made based on the Canadian classification scheme using the relative amounts of percent sand, percent silt and percent clay in the soil (AAFC, 1998).

Total organic carbon (TOC) refers to the organic carbon content of soil exclusive of carbon from undecayed plant and animal residues, as determined by dry combustion analysis (ISO, 1995). (See also organic matter.)

Unconsolidated soil sample (see also consolidated soil sample) is synonymous with disturbed sample and is a sample obtained from soil without any attempt to preserve the soil structure (ISO, 2005).

Water-holding capacity (WHC) refers to the maximum quantity of water that a soil can retain, following complete saturation. It is usually determined gravimetrically, and is generally expressed as the percentage of water (by mass; water weight:dry soil weight) retained in a sample of soil that has been saturated with water.

Statistical and Toxicological Terms

A priori literally refers to something that is independent of experience. In the context of test design and statistics, a priori tests are ones that have been planned before the data were collected. Test objectives and test design would influence the decisions on which a priori tests to select.

Acute means within a short period (seconds, minutes, hours or a few days) in relation to the life span of the test organism and is generally used to describe the length of a test or exposure duration.

Acute toxicity is a discernible adverse effect (lethal or sublethal) induced in the test organisms within a short period (usually a few days, and for purposes of this document within 7 or 14 days) of exposure to test soil(s).

Battery of toxicity tests is a combination of several toxicity tests, normally using different species of test organisms (e.g., a series of soil toxicity tests using springtails, plants or earthworms), different biological endpoints (e.g., lethal and various sublethal), and different durations of exposure (e.g., acute and chronic).

Bioassay is a test (= assay) in which the strength or potency of a substance is measured by the response of living organisms. In standard pharmacological usage, a bioassay assesses the unknown potency of a given preparation of a drug, compared to the known potency of a standard preparation. Toxicity testis a more specific and preferred term for environmental studies.

Chronic means occurring during a relatively long period of exposure (weeks, months or years), usually a significant portion of the life span of the organism such as 10% or more, and is generally used to describe the length of a test or exposure duration.

Chronic toxicity refers to discernable adverse effects observed during or after relatively long-term exposures to one or more contaminants, which are related to changes in reproduction, growth, metabolism, ability to survive or other biological variables (e.g., behaviour) being observed.

Coefficient of Variation (CV) is the standard deviation (SD) of a set of data divided by the mean of the data set, expressed as a percentage. It is calculated according to the following formula: CV (%) = 100 (SD ÷ mean).

Endpoint means the response(s) of the test organism that is measured (e.g., death or number of progeny), or the value(s) that characterize the results of a test (e.g., LC50, IC25).

Environmental toxicology is a branch of toxicology with the same general definition. However, the focus is on ecosystems, natural communities and wild living species, without excluding humans as part of the ecosystems.

Geometric mean is the mean of repeated measurements, calculated logarithmically. It has the advantage that extreme values do not have as great an influence on the mean as is the case for an arithmetic mean. The geometric mean can be calculated as the n^th root of the product of the “n” values, and it can also be calculated as the antilogarithm of the mean of the logarithms of the “n” values.

Heteroscedasticity refers herein to data showing heterogeneity of the residuals within a scatter plot (see EC, 2005b). This term applies when the variability of the residuals changes significantly with that of the independent variables (i.e., the test concentrations or treatment levels). When performing statistical analyses and assessing residuals (e.g., using Levine’s test), for test data demonstrating heteroscedasticity (i.e., non-homogeneity of residuals), there is a significant difference in the variance of residuals across concentrations or treatment levels. (See also homoscedasticity and residual.)

Homoscedasticity refers herein to data showing homogeneity of the residuals within a scatter plot (see EC, 2005b). This term applies when the variability of the residuals does not change significantly with that of the independent variables (i.e., the test concentrations or treatment levels). When performing statistical analyses and assessing residuals (e.g., using Levine’s test), for test data demonstrating homoscedasticity (i.e., homogeneity of residuals), there is no significant difference in the variance of residuals across concentrations or treatment levels. (See also heteroscedasticity and residual.)

ICp is the inhibiting concentration for a (specified) percent effect. It represents a point estimate of the concentration of test substance or material that causes a designated percent inhibition (p) compared to the control, in a quantitative (continuous) biological measurement such as number of progeny produced by individuals at the end of the test (e.g., IC25 or IC50).

LC50 is the median lethal concentration, i.e., the concentration (e.g., % or mg/kg) of substance(s) or material(s) in soil that is estimated to be lethal to 50% of the test organisms. The LC50 and its 95% confidence limits are usually derived by statistical analysis of percent mortalities in five or more test concentrations, after a fixed period of exposure. The duration of exposure must be specified (e.g., 28-day LC50). Depending on the study objectives, an LCp other than LC50 (e.g., an LC25) might be calculated instead of or in addition to the LC50.

Lethal means causing death by direct action. Death of test organisms is defined as the cessation of all visible signs of movement or other activity indicating life.

LOEC is the lowest-observed-effectconcentration. This is the lowest concentration of a test substance or material for which a statistically significant adverse effect on the test organisms was observed, relative to the control.

NOEC is the no-observed-effectconcentration. This is the highest concentration of a test substance or material at which no statistically significant adverse effect on the test organisms was observed, relative to the control.

Normality (or normal distribution) refers to a symmetric, bell-shaped array of observations. The array relates frequency of occurrence to the magnitude of the item being measured. In a normal distribution, most observations will cluster near the mean value, with progressively fewer observations toward the extremes of the range of values. The normal distribution plays a central role in statistical theory because of its mathematical properties. It is also central in biological sciences because many biological phenomena follow the same pattern. Many statistical tests assume that data are normally distributed, and therefore it can be necessary to test whether that is true for a given set of data.

Precision refers to the closeness of repeated measurements of the same quantity to each other, i.e., the degree to which data generated from replicate measurements are the same. It describes the degree of certainty around a result, or the tightness of a statistically derived endpoint such as an ICp.

Quantal effects in a toxicity test are those in which each test organism responds or does not respond. For example, an animal might respond by dying in or avoiding a contaminated test soil. Generally, quantal effects are expressed as numerical counts or percentages thereof. (See also quantitative.)

Quantitative effects in a toxicity test are those in which the measured effect is continuously variable on a numerical scale. An example would be number of progeny produced at test end. Generally, quantitative effects are determined and expressed as measurements. (See also quantal.)

Replicate (treatment, test vessel or test unit) refers to a single test vessel containing a prescribed number of organisms in either one concentration of the test material or substance, or in the control or reference treatment(s). A replicate of a treatment must be an independent test vessel; therefore, any transfer of organisms or test material from one test vessel to another would invalidate a statistical analysis based on the replication (see Sections 5.1 and 5.6.1 herein, and Section 2.5 of EC, 2005b).

Replicate samples are field-replicated samples of soil collected independently from the same sampling location, to provide an estimate of the sampling error or to improve the precision of estimation. A single soil sample from a sampling location is treated as one replicate. Additional samples are considered to be additional replicate samples when they are treated identically (regardless of whether they are pointor composite samples from the same location) but stored in separate sample containers (i.e., not composited or, if already composite samples, not composited further).

Residual, in the context of Section 4.8.2.1, refers to the difference between the predicted estimate (based on the model) and the actual value observed, as determined by subtracting the former from the latter. (See also heteroscedasticity and homoscedasticity.)

Static describes a toxicity test in which the test soil (or any chemical or chemical product therein) is not renewed or replaced during the test.

Sublethal (toxicity) means detrimental to the organism, but below the concentration or level of contamination that directly causes death within the test period.

Sublethal effect is an adverse effect on an organism, resulting from exposure to the concentration or level of contamination below that which directly causes death within the test period.

Toxic means poisonous. A toxic chemical or material can cause adverse effects on living organisms, if present in sufficient amounts at the right location (i.e., receptor/organ). Toxic is an adjective or adverb, and should not be used as a noun, whereas toxicant is a legitimate noun.

Toxicant is a toxic substance or material.

Toxicity is the inherent potential or capacity of a substance or material to cause adverse effect(s) on living organisms. These effect(s) could result from exposure to either lethal or sublethal concentrations of contaminants in soil.

Toxicity test is a determination of the adverse effect(s) of a substance or material that results from exposure of a group of selected organisms of a particular species (e.g., Folsomia candida, Orthonychiurus folsomi, Folsomia fimetaria or Proisotoma minuta), under defined conditions. A toxicity test involving samples of test soil usually measures (a) the proportions of organisms affected (quantal), and/or (b) the degree of effect observed (quantitative or graded), after exposure of the test organisms to the whole sample (e.g., undiluted site soil) or specific concentrations thereof.

Toxicology is a branch of science that studies the toxicity of substances, materials or conditions. There is no limitation on the use of various scientific disciplines, field or laboratory tools, or studies at various levels of organization, whether molecular, single species, populations, or communities. Applied toxicology would normally have a goal of defining the limits of safety of chemical or other agents. (See also environmental toxicology.)

Treatment refers to a specific test soil(e.g., a site soil, reference soil or negative control soil) from a particular sampling location, or a concentration of chemical-spiked soil(or a mixture of test soil diluted with clean soil) prepared in the laboratory. Test soils representing a particular treatment are typically replicated in a toxicity test. (See also replicate and replicate samples.)

Warning chart is a graph used to follow changes over time, in the endpoints for a reference toxicant. Date of the test is on the horizontal axis, and the effect-concentration is plotted on the vertical logarithmic scale.

Warning limit is plus or minus two standard deviations, calculated logarithmically, from a historic geometric mean of the endpoints from tests with a reference toxicant.