Biological test method for measuring terrestrial plants 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

Adventitious roots are thin, moderately branching roots that arise from somewhere other than the primary root; for example, roots that arise from the stem or leaves.

Angiosperm is a term used in plant classification referring to plants that flower, and whose ovules (young seeds) are enclosed in an ovary. The ovary matures into a fruit with seeds, following fertilization. The Phylum Magnoliophyta (or Anthophyta) contains all angiosperms and is the largest and most diverse group within the Kingdom Plantae. Two Classes of angiosperms include the Class Magnoliopsida (Dicotyledons) and the Class Liliopsida (Monocotyledons).

Annual is a plant that completes its entire life cycle in a single growing season. (See also biennial and perennial.)

Biennial is a plant that normally requires two seasons to complete its life cycle, growing only roots and leaves in the first season and producing flowers and fruits and then dying in the second season. (See also annual and perennial.)

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

Canopy for the purpose of this method is the more or less continuous cover produced by the foliage of plants.

Cespitose means growing in dense clumps or tufts.

Chlorosis is a condition in which the green parts of plants have depressed concentrations of chlorophyll and the leaves are pale green or yellow in colour. This might result from disease, exposure to toxic substances, nutrient deficiencies, or senescence.

Coleoptile is the protective tissue surrounding the growing shoot in a monocotyledonous plant.

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.

Cotyledon is a primary leaf of the developing embryo in seeds; there is only one in monocotyledonous plants, and two in dicotyledonous plants. In many dicotyledonous species, such as the bean, the cotyledons emerge above ground and appear as the first leaves.

Cultivar means a race or variety of plant that has been created or selected intentionally and maintained through cultivation.

Defoliation is the condition in which a plant does not have a normal complement of leaves due to some internal or external cause.

Dessication is when the plant, or portion of plant, is dried.

Dicotyledon is a term used in the classification of plants, that refers to those species having two seed leaves (cotyledon).

Ecological risk assessment (ERA) is the process of identifying and quantifying risks to nonhuman organisms and determining the acceptability of those risks.

Emergence occurs following the germination of a plant, wherein the early growth of a seedling pushes the epicotyl through the soil surface. In this test method, emergence refers to the appearance of the seedling shoot 3 mm above the surface of the soil.

Epicotyl is that portion of an embryo or seedling containing the shoot. It is delineated anatomically by the tissue transition zone which separates the epicotyl from the hypocotyl.

Epigeal (germination) refers to a type of germination where the hypocotyl is active and pulls the cotyledons above ground during its growth. Germination begins with the imbibition of water and proceeds with emergence of the radicle from the seed to form the primary root and secondary roots; elongation of the active hypocotyl follows with the hypocotyl arch penetrating through the soil surface. Epigeal-emerging dicots (e.g., 90% of dicotyledonous plants) have the advantages of being able to commence photosynthesis as soon as the cotyledons emerge, and of being able to expand leaf area rapidly.

Germination refers to the process by which the plant embryo within the seed resumes growth after a period of dormancy and the seedling emerges from the seed. (See also epigeal and hypogeal.)

Growth is the increase in size or weight as the result of proliferation of new tissues. In this test method, growth refers to an increase in shoot and root length, as well as an increase in shoot and root dry and wet weights.

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

Hull is the dry outer covering of a seed.

Hypogeal (germination) refers to a type of germination where the hypocotyl is inactive and the scutellum (cotyledon) remains below the ground. The radicle emerges first to form the primary root, followed by the coleoptile. Emergence is largely dependent on elongation of the coleoptile and the first internode. When the soil surface is reached, light inhibits further growth and true leaves emerge through the hollow sheath. All grasses (e.g., barley) are characterized by hypogeal germination.

Hypocotyl is that portion of an embryo or seedling containing the root or radicle. It is delineated anatomically by the tissue transition zone which separates the epicotyl from the hypocotyl.

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-candle is highly variable and depends on the light source, the light meter used, the geometrical arrangement, and the possibility of reflections (see ASTM, 1999a). The approximate conversion between quantal flux and lux, however, for full-spectrum fluorescent light (e.g., Vita-Lite® by Duro-Test®), is 1 lux 0.016 µmol/(m₂ · s) (Deitzer, 1994; Sager and McFarlane, 1997).

Malformation is a structural defect that occurs infrequently and is due to abnormal development.

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.

Monocotyledon is a term used in the classification of plants, that refers to those species having a single seed leaf (cotyledon).

Mottling means marked with spots or streaks of different colors (e.g., blotched). This includes the discoloration of leaf margins.

Necrosis refers to dead tissue.

Nodulate is the process of forming nodules, which are small, cylindrical growths, often found on the roots of leguminous plants. These nodules house symbiotic bacteria (Rhizobia) that fix atmospheric nitrogen, making it available to the plant.

Perennial is a plant that, under natural conditions, lives for several to many growing seasons. (See also annual and biennial.)

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 14, with 7 representing neutrality, numbers less than 7 indicating increasingly greater acidic reactions, and numbers greater than 7 indicating increasingly basic or alkaline reactions.

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

Phytomass is the total weight (mass), either above and/or below ground, of a group of plants.

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.

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

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

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.

Rachis is the central stalk or mid-rib of a compound leaf.

Radicle is the end of a plant embryo that gives rise to the first root.

Reference method refers to a specific protocolfor 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).

Rhizobia are soil bacteria that fix nitrogen after becoming established inside the root nodules of legumes.

Rhizome is a fleshy, creeping, horizontal, underground stem that often sends out roots and shoots from its nodes. Certain plants reproduce vegetatively by means of their rhizome.

Rhizomatous - see rhizome.

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

Risk assessment see Ecological risk assessment.

Root is usually the below-ground portion of a plant that serves as support, draws minerals from surrounding soil, and sometimes stores food. There are two main types of root systems: the tap root system, in which there is a main primary root larger than the other branching roots, and the fibrous root system, in which there are many slender roots with numerous smaller root branches. (See also shoot.)

Seed is a fertilized and ripened plant ovule consisting of the plant embryo, varying amounts of stored food material, and a protective outer seed coat.

Seedling is a young plant that is grown from a seed.

Seed pretreatment is a coating of fungicide applied to seeds before water imbibition.

Seminal root is a seed-born root that develops directly from root growing points present in the seed. Seminal roots consist of the radicle and lateral seminal roots, and are the first seedling roots to emerge from the seed. These roots serve to anchor and support the young seedling and absorb small amounts of water and nutrients until the permanent root system takes over.

Shoot is the usually above-ground portion of the plant such as the stems and leaves.

Staining is the discoloration of plant parts (roots, vegetative growth) caused by the test substance.

Tetraploid means having four-times the haploid number of chromosomes (i.e., a single set of chromosomes) in the cell nucleus.

Waterlogging is the over-saturation or soaking of agricultural land caused by a rising water table or excessive irrigation. Waterlogging compacts soil and deprives roots of oxygen.

Wilting occurs when plant tissues lose their turgidity and the plant becomes limp.

Withering is the process of drying; plants become limp and desiccated. This frequently is the result of root damage.

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.

Chemical is, in this report, any element, compound, formulation, or mixture of a substance that might be mixed with, deposited in, or found in association with soil or water.

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 on the test organisms.

Concentration means, for this biological test method, 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.

Contaminant is a substance or material that is present in a natural system, or present at increased concentrations, often because of some direct or indirect human activity. The term is frequently applied to substances or materials present at concentrations having 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. The control is used as a check for the absence of 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.

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 man with essential food and fibre; Hausenbuiller, 1985).

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, de-chlorinated tap water, or nutrient solution, where applicable. 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 which could affect the emergence, survival, or growth 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 emergence, survival, and growth of the test plants during the test. The use of negative control soil provides a basis for interpreting data derived from toxicity tests using test soil(s).

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 most types of soil, the following equation (AESA, 2001) is suitable for estimating the total OM content of soil from total organic carbon (TOC) measurements: % OM = % TOC × 1.78. (See also total organic carbon.)

Positive control soil is contaminated soil that contains known concentrations of one or more contaminants that adversely affect the emergence, survival, or growth 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, compactness, total organic carboncontent, pH) 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/or 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. A reference toxicity test with plants is performed as a spiked-soil test, using a standard chemical.

Sampling station means a specific location, within a site or sampling unit (depending on the study design), where the sample(s) of field-collected soil are obtained for toxicity tests and associated physicochemical analyses.

Site means a delineated tract of land that is being used or considered as a study area, usually from the perspective of it being contaminated or potentially contaminated by xenobiotics.

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 plants. 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, invertebrates, and plants) therein, and by anthropogenic activities.

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

Test soil is a sample of field-collected soil or chemical-spiked soil to be evaluated for toxicity to plants. 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 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. 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, and sandy clays).

Further distinction as to texture (e.g., “sandy clay”, “silt loam”, “loam”) can be made based on classification schemes using the relative amounts of percent sand, percent silt, and percent clay in the soil (Hausenbuiller, 1985; ACECSS, 1987).

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

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; wt water:wt dry soil) retained in a sample of soil that has been saturated with water.

Statistical and Toxicological Terms

Acute means within a short period of exposure (seconds, minutes, hours, or a few days) in relation to the life span of the test organism.

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 5-7 days) of exposure to test soil(s).

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 within 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.

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).

EC50 is the median effective concentration,i.e., the concentration (e.g., % or mg/kg) of substance(s) or material(s) in soil estimated to cause some defined toxic effect on 50% of the test organisms. In most instances, the EC50 and its 95% confidence limits are statistically derived by analyzing the percentages of organisms affected (e.g., % seeds emerged) at various test concentrations, after a fixed period of exposure. The duration of exposure must be specified (e.g., 7-day EC50). The EC50 describes quantal effects, lethal or sublethal, and is not applicable to continuous (i.e., quantitative) effects (see ICp). Depending on the study objectives, an ECx other than EC50 (e.g., an EC20) might be calculated instead of or in addition to the EC50.

Endpoint means the measurement(s) or value(s) that characterize the results of a test (e.g., EC50, IC25). It also means the response of the test organisms that is being measured (e.g., seedling emergence, or shoot/root length and weight).

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 nth 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 Figures I.2B and I.2C in Appendix I). 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 Figure I.2A in Appendix I). 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 length of shoots attained by individual seedlings at the end of the test.

LOEC is the lowest-observed-effect concentration. 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-effect concentration. 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.

Phytotoxicity means unwanted detrimental deviations from the normal pattern of appearance, growth, and/or function of plants in response to the test material. Phytotoxicity might occur during germination, growth differentiation, and/or maturation of plants.

Precision refers to the closeness of repeated measurements of the same quantity to each other, i.e., the degree to which data generated from repeated 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, a seedling might fail to emerge from 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. Examples would be shoot length of emerged seedlings or dry weight of roots at the end of the test. 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 unit; 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 5.5.1 herein, and Section 2.5 of EC, 2004a).

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

Residual, in the context of Section 4.8.3.1 and Appendix I, 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 (nor 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, below the concentration or level of contamination that 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 amount at the right location. Toxic is an adjective or adverb, and should not be used as a noun; whereas toxicantis 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 be lethal or sublethal.

Toxicity test is a determination of the effect of a substance or material on a group of selected organisms of a particular species, 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 shown (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 station, 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.)

Visual assessment represents the description of any visual damage to the test species based on observations of phytotoxicity (i.e., malformation, chlorosis, necrosis, defoliation, dessication, mottling, staining, wilting, or withering) observed in test vessels with contaminated soil compared to the controls.

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.