Endpoint - A response measure in a toxicity study.

Emission - Like effluent but used in regard to air pollution.

Emission rate - The amount of pollutant emitted per unit of time.

Environment - Water, air, land, and all plants and man and other animals living therein, and the interrelationships which exist among them.

Environmental monitoring - Continuous or repeated measurement of agents in the environment to evaluate environmental exposure and possible damage by comparison with appropriate reference values based on knowledge of the probable relationship between ambient exposure and resultant adverse effects.

Environmental pathway - All routes of transport by which a toxicant can travel from its release site to human populations including air, food chain, and water.

Epidemiology - The study of the distribution and determinants of health-related states or events in populations, and the application of this study to control of health problems.

Equilibrium - State of a system in which the defining variables (temperature, pressure, chemical potential) have constant values.

Estimated Exposure Dose (LEO) - The measured or calculated dose to which humans are likely to be exposed considering exposure by all sources and routes.

Event - Occurrence of a particular set of circumstances 1.  The event may be certain or uncertain 2.  The event can be singular or multiple 3.  The probability associated with the event can be estimated for a given period of time.

Excess deaths - The excess over statistically expected deaths in a population within a given time interval. Attempts are made to relate excess deaths to specific causes. Note that since every person can (and must) die only once; there can be no excess deaths over all time.

Expected deaths - The number of deaths statistically expected in a population in a given time interval obtained by summing the product of age-, sex-, and race-specific mortality rates from a standard population and person-years in each age, sex, and race category in the study population.

Expected loss - The quantity obtained by multiplying the magnitude of health or environmental effect loss by the probability (or risk) of that loss and adding the products. The expected loss is the average loss over a large number of trials; one must reflect on the appropriateness of its use in cases for which there will be only one, or a few, trials.

Extrapolation - In risk assessment, this process entails postulating a biologic reality based on observable responses and developing a mathematical model to describe this reality. The model may then be used to extrapolate to response levels which cannot be directly observed.

Excretion- Discharge or elimination of an absorbed or endogenous substance, or of a waste product, and/or its metabolites, through some tissue of the body and its appearance in urine, feces, or other products normally leaving the body.

Excretion rate - Amount of substance and/or its metabolites that is excreted divided by time of excretion.

Exposure - Concentration or amount of a particular agent that reaches a target organism, system, or (sub)population in a specific frequency for a defined duration.

Exposure Assessment - Evaluation of the exposure of an organism, system, or (sub)population to an agent (and its derivatives). Exposure assessment is the third step in the process of risk assessment.

Exposure Estimation - Estimation of the amount and duration of contact between a receptor and an agent.  May consider such factors as concentration, route, receptor, population, and timescale.

Exposure Identification - Identification of the conditions of contact between a receptor and an agent. May involve identification of concentration, route, receptor population, and timescale.

Exposure scenario - A set of conditions or assumptions about sources, exposure pathways, amounts or concentrations of agent(s) involved, and exposed organism, system, or (sub)population (i.e., numbers, characteristics, habits) used to aid in the evaluation and quantification of exposure(s) in a given situation.

Extrapolation - The calculation, based on quantitative observations in exposed test species, of predicted dose-effect and dose-response relationships for a chemical in humans and other environmental biota.

False negative results - Results which show no effect when one is there.

False positive results - Results which show an effect when one is not there.

Fate - Pattern of distribution of an agent, its derivatives, or metabolites in an organism, system, compartment, or (sub)population of concern as a result of transport, partitioning, transformation, or degredation.

First-order process
1. Chemical reaction where the rate is directly proportional to the concentration of reactant.
2. Any reaction changing at a constant fractional rate.
First-pass effect -   Biotransformation and, in some cases, elimination of a substance in the liver after absorption from the intestine and before it reaches the systemic circulation.

Food chain - Dependence of a series of organisms, one upon the other, for food. The chain begins with plants and ends with the largest carnivores.

Frank-Effect Level (FEL) - The exposure level which produces unmistak­able adverse effects, such as irreversible functional impairment or mortality, at a statistically or biologically significant increase in frequency or severity between an exposed population and its appropri­ate control.

Genetic effects - Effects that are inheritable and appear in the descendants of those exposed.

Genotoxic - Capable of causing a heritable change to the structure of DNA thereby producing a mutation.

Guideline - A guideline is a recommended exposure limit for a substance or an agent intended to protect human health or the environment, that is not legally enforceable.

Guidance value - Value, such as concentration in air or water, that is derived after allocation of the reference dose among the different possible media (routes) of exposure. The aim of the guidance value is to provide quantitative information from risk assessment to the risk managers to enable them to make decisions.

Half-life - The time in which half the molecules of a chemical substance disappear as a result of chemical or biochemical transformation.

Half-life, biological - The time required for a living organism to eliminate, by natural processes, half the amount of a substance that has entered it.

Half-life, effective - The time required for a radionuclide contained in a biological system to reduce its activity by half due to the combined result of radioactive decay and biological.

Harmonization - Harmonization represents the attempts by regulatory bodies at the provincial/state, federal, and international level to adopt identical or similar regulatory limits, including definitions of allowable limits, monitoring and measurement methods, and legal penalties.

Hazard – Inherent property of an agent or situation having the potential to cause adverse effects when an organism, system, or (sub)population is exposed to that agent.

Hazard assessment – A process designed to determine the possible adverse effects of an agent or situation to which an organism, system, or (sub)population could be exposed. The process focuses on the hazard identification and hazard characterization. The process focuses on the hazard, in contrast to risk assessment, where exposure assessment is a distinct additional step.

Hazard characterization – The qualitative and, wherever possible, quantitative description of the inherent property of an agent or situation having the potential to cause adverse effects. This should, where possible, include a dose-response assessment and its attendant uncertainties. Hazard characterization is the second stage in the process of hazard assessment and the second of four steps in risk assessment.

Hazard Identification - The identification of the type and nature of adverse effects that an agent has an inherent capacity to cause in an organism, system, or (sub)population. Hazard identification is the first stage in hazard assessment and the first of four steps in risk assessment.

Hazardous waste - Any waste or combination of wastes which pose a substantial present or potential hazard to human health or living organisms because such wastes are nondegradable or persistent in nature or because they can be biologically magnified, or because they can be lethal, or because they may otherwise cause or tend to cause detrimental cumulative effects; also, a waste or combination of wastes of a solid, liquid, contained gaseous, or semisolid form which may cause, or contribute to, an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness, taking into account the toxicity of such waste, its persistence and degradability in nature, its potential for accumulation or concentration in tissue, and other factors that may otherwise cause or contribute to adverse acute or chronic effects on the health of persons or other organisms.

Health and safety study - Any study of any effect of a chemical substance or mixture on health or the environment or on both, including underlying data and epidemiological studies, studies of occupational exposure to a chemical substance or mixture, toxicological, clinical, and ecological studies of a chemical substance or mixture, and any test performed pursuant to this [TSCA] Act.

Health effect - A deviation in the normal function of the human body.

Health risk - Risk in which an adverse event affects human health.

Healthy worker effect - The difference in mortality risk due to selection forces between a population of active workers healthy enough to have been (and remain) employed and the general population which includes sick and disabled persons. If working in a safe environment, such a population of active workers has been variously estimated to have a mortality risk 60-90% that of the general population.

Human Equivalent Dose - The human dose of an agent that is believed to induce the same magnitude of toxic effect as that which the known animal dose has induced.

Hypersensitivity - A hyper susceptible individual is one who will experience an adverse health effect significantly before the general population, because of one or more factors which predispose the individual to the harmful effects of pollutant exposure.

Idiosyncratic Reaction - A genetically-determined abnormal reactivity to a chemical.  

Idiosyncrasy - The increased individual sensitivity of an organism to the effect of certain substances.

Immediate versus Delayed Toxicity - Immediate effects occur or develop rapidly after a single administration of a substance, while delayed effects are those that occur after the lapse of some time. These effects have also been referred to as acute and chronic, respectively.

Impact - The force of impression of one thing on another.

Incidence - The number of instances of illness commencing, or of persons falling ill, during a given period in a specific population.  Incidence is usually expressed as a rate, the denominator being the average number of persons in the specified population during a defined period or the estimated number of persons at the mid-point of that period.  The basic distinction between incidence and prevalence is that whereas incidence refers only to new cases, prevalence refers to all cases, irrespective of whether they are new or old.  When the terms incidence and prevalence are used, it should be stated clearly whether the data represent the numbers of instances of the disease recorded or the numbers of persons ill.

Incidence Rate - The rate at which new events occur in a population.  The numerator is the number of new events that occur in a defined period; the denominator is the population at risk of experiencing the event during this period, sometimes expressed as person-time.  The incidence rate most often used in public health practice is calculated by the formula
Number of new events in a specified period       X   10n
    Number of persons exposed to risk during the period                      

In a dynamic population, the denominator is the average size of the population, often the estimated population at the mid-period.  If the period is a year, this is the annual incidence rate.  This rate is an estimate of the person-time incidence rate, i.e., the rate per 10n person-years.  If the rate is low, as with many chronic diseases, it is also a good estimate of the cumulative incidence rate.  In follow-up studies with no censoring, the incidence rate is calculate by dividing the number of new cases in a specified period by the initials size of the cohort of person being followed; this is equivalent to the cumulative incidence rate during the period.  If the number of new cases during a specified period is divided by the sum of the person-time units at risk for all persons during the period, the result is the person-time incidence rate.

Individual Risk - The probability that an individual person will experience an adverse effect.  This is identical to population risk unless specific population subgroups can be identified that have different (higher or lower) risks.

Individual susceptibility - The marked variability in the manner in which individuals will respond to a given exposure to a toxic agent.

Initiator - An agent that causes a cell to become immortalized. This is the first step in the multi-step process of carcinogenesis in which a cell continues to divide and fails to terminally differentiate. This step may be referred to as anti-differentiation.

Intake – The process by which an agent crosses an outer exposure surface of a target without passing an absorption barrier, i.e., through ingestion or inhalation.

Interspecies Dose Conversion - The process of extrapolating from animal doses to equivalent human doses.

In vitro - Outside the living organism.

In vivo - Within the living organism.

Involuntary Risks - Exposures which are not under individual control, for example, exposure to air or water pollutants.  In general, voluntary risks (such as smoking) are more seen as more acceptable than involuntary risks.

Iterative Process - A process that is repeated periodically in a systematic fashion.  Some or all of the steps in the risk management process can be revisited as new information becomes available, allowing for more informed decisions to be considered as uncertainty is reduced by further study and analysis.

Kinetics (in chemistry) - Branch of chemistry concerned with measuring and studying rates of chemical reactions.

Latent Period - Delay between exposure to a disease-causing agent and the appearance of manifestation of the disease.  After exposure to ionizing radiation, for instance, there is a latent period of five years, on average, before development of leukemia, and more than 20 years before development of certain other malignant conditions.  The term Alatent period@ is often used synonymously with Ainduction period@, that is, the period between exposure to a disease-causing agent and the appearance of manifestations of the disease.  It has also been defined as the period from disease initiation to disease detection.

Lethal concentration, LC - Concentration of a substance in an environmental medium that causes death following a certain period of exposure.

Lethal concentration fifty (LC50)

• A calculated concentration [in air] which when administered by the respiratory route is expected to kill 50% of a population of experimental animals during an exposure of four hours. Ambient concentration is expressed in milligrams per liter.

Lethal dose, LD - Amount of a substance or physical agent (e.g., radiation) that causes death when taken into the body.

Lethal dose fifty (LD50) - A calculated dose of a chemical substance which is expected to kill 50% of a population of experimental animals exposed through a route other than respiration. Dose is expressed in milligrams per kilogram of body weight.

Lethal synthesis - Metabolic formation of a highly toxic compound often leading to death of affected cells.

Lifetime Risk – Lifetime Risk is the risk of developing a disease during an individual’s lifetime.

Linearized multistage model - Sequence of steps in which (a) a multistage model is fitted to tumor incidence data; (b) the maximum linear term consistent with the data is calculated; (c) the low-dose slope of the dose–response function is equated to the coefficient of the maximum linear term; and (d) the resulting slope is then equated to the upper bound of potency.

Linear No-Threshold Model (LNT) - The simplest of toxicological dose-response relationships in which a doubling of the original dose would be expected to result in a doubling of the response frequency, and a halving of the original dose would produce a halving of the response frequency and so on down the dose ladder all the way to zero dose.  Used primarily for carcinogenic or mutagenic environmental contaminants.

Local effect - Change occurring at the site of contact between an organism and a toxicant.

Local versus Systemic Toxicity - Local effects refer to those that occur at the site of first contact between the biological system and the toxicant: systemic effects are those that are elicited after absorption and distribution of the toxicant from its entry point to a distant site.

Lowest effective dose, LED - Lowest dose of a chemical inducing a specified effect in a specified fraction of exposed individuals.

Lowest-observed-adverse-effect level, LOAEL - Lowest concentration or amount of a substance (dose), found by experiment or observation, which causes an adverse effect on morphology, functional capacity, growth, development, or life span of a target organism distinguishable from normal (control) organisms of the same species and strain under defined conditions of exposure.

Lowest-observed-effect level, LOEL - Lowest concentration or amount of a substance (dose), found by experiment or observation, that causes any alteration in morphology, functional capacity, growth, development, or life span of target organisms distinguishable from normal (control) organisms of the same species and strain under the same defined conditions of exposure.

Margin of exposure, MOE - Ratio of the no-observed-adverse-effect level (NOAEL) for the critical effect to the theoretical, predicted, or estimated exposure dose or concentration.

Margin of Safety – For some experts, margin of safety has the same meaning as margin of exposure, while for others, margin of safety means the margin between the reference dose and the actual exposure.

Maximum tolerable concentration, MTC - Highest concentration of a substance in an environmental medium that does not cause death of test organisms or species (denoted by LC0).

Maximum tolerable dose, MTD - Highest amount of a substance that, when introduced into the body, does not kill test animals (denoted by LD0).

Maximum tolerable exposure level, MTEL - Maximum amount (dose) or concentration of a substance to which an organism can be exposed without leading to an adverse effect after prolonged exposure time.

Measurement end-point - Measurable (ecological) characteristic that is related to the valued characteristic chosen as an assessment point.

Median effective concentration, EC50 - Statistically derived concentration of a substance in an environmental medium expected to produce a certain effect in test organisms in a given population under a defined set of conditions.
Note: ECn refers to the median concentration that is effective in n % of the test population.

Median effective dose, ED50 - Statistically derived dose of a chemical or physical agent (radiation) expected to produce a certain effect in test organisms in a given population or to produce a half-maximal effect in a biological system under a defined set of conditions.
Note: EDn refers to the median dose that is effective in n % of the test population.

Median lethal concentration, LC50 - Statistically derived concentration of a substance in an environmental medium expected to kill 50 % of organisms in a given population under a defined set of conditions.

Median lethal dose, LD50 - Statistically derived dose of a chemical or physical agent (radiation) expected to kill 50 % of organisms in a given population under a defined set of conditions.

Median lethal time, TL50 - Statistically derived average time interval during which 50 % of a given population may be expected to die following acute administration of a chemical or physical agent (radiation) at a given concentration under a defined set of conditions.

Medium - Material (e.g., air, water, soil, food, consumer products) surrounding or containing an agent.

Medium intake rate - The rate at which the medium crosses the outer exposure surface of a target during ingestion or inhalation.

Metabolic activation - Biotransformation of a substance to a more biologically active derivative.
Synonym: bioactivation

Metabolic Model - An analysis and theoretical reconstruction of the way in which the body deals with a specific substance, showing the proportion of the intake that is absorbed, the proportion that is stored and in what tissues, the proportion and rate of breakdown in the body and the subsequent fate of the metabolic products, and the proportion of the substance and the rate at which it is eliminated by different organs.

Metabolic transformation - Biotransformation of a substance that takes place within a living organism.

Metabolism - Sum total of all physical and chemical processes that take place within an organism; in a narrower sense, the physical and chemical changes that take place in a substance within an organism.

Metabolite - Intermediate or product resulting from metabolism.

Metabonomics - Evaluation of tissues and biological fluids for changes in metabolite levels that follow exposure to a given substance, in order to determine the metabolic processes involved and to evaluate the disruption in intermediary metabolic processes that results from exposure to that substance.

Microenvironment - Surroundings that can be treated as homogeneous or well characterized in the concentrations of an agent (e.g., home, office, automobile, kitchen, store). This term is generally used for estimating inhalation exposures.

Mitigation - Limitation of any negative consequence of a particular event.

Model - A formalized expression of a theory or the causal situation which is regarded as having generated observed data.  In statistical analyses the model is generally expressed in symbols, that is to say in a mathematical from, but diagrammatic models are also found.

Modifying Factor (MF) - An uncertainty factor that is greater than zero and less than or equal to 10; the magnitude of the MF depends upon the professional assessment of scientific uncertainties of the study and data base not explicitly treated with the standard uncer­tainty factors (e.g., the number of animals tested); the default value for the MF is 1.

Monitoring - Continuous or repeated observation, measurement, and evaluation of health and/or environmental or technical data for defined purposes, according to prearranged schedules in space and time, using comparable methods for sensing and data collection.

Morbidity - A departure from a state of physical or mental well-being, resulting from disease or injury. Frequently used only if the affected individual is aware of the condition. Awareness itself connotes a degree of measurable impact. Frequently, but not always, there is a further restriction that some action has been taken such as restriction of activity, loss of work, seeking of medical advice, etc.

Mortality - Death; the death rate; ratio of number of deaths to a given population.

Mortality rate - The number of deaths that occur in a given population during a given time interval; usually deaths per l03 or l05 people per year. Can be age, sex, race, and cause specific.

Mutagen - Agent that can induce heritable changes (mutations) of the genotype in a cell as a consequence of alterations or loss of genetic material.

Mutation - Any heritable change in genetic material.  This may be a chemical transformation of an individual gene (a gene or point mutation), which alters its function.  On the other hand, this change may involve a rearrangement, or a gain or loss of part of a chromosome, which may be microscopically visible.  This is designated a chromosomal mutation.

Negligible risk
1. Probability of adverse effects occurring that can reasonably be described as trivial.
2. Probability of adverse effects occurring that is so low that it cannot be reduced appreciably by increased regulation or investment of resources.

No-effect level, NEL - Maximum dose (of a substance) that produces no detectable changes under defined conditions of exposure.
Note: This term tends to be substituted by no-observed-adverse-effect level (NOAEL) or no-observed- effect level (NOEL).

No-Observed-Adverse-Effect Level (NOAEL) - The greatest concentration or amount of a chemical, found by experiment or observation, that causes no detectable adverse alteration of morphology, functional capacity, growth, development, or life span of the target.

No Observed Effect Level (NOEL) - The highest dose level, in a toxicological dose-response study, where no detectable biological effect is found (usually in test animals).  Used as an experimental estimate of the threshold dose at which toxic effects begin to appear in the dose-response relationship.

Non-Threshold Toxicity - A class of toxicity mechanisms where the damaging biological processes are thought to occur at any exposure level above zero dose, often in a linear dose-response relationship.  Usually applied to environmental substances (ionizing radiation, genotoxic chemicals) that are thought to act by a carcinogenic or mutagenic mechanism involving genetic damage to body (somatic) cells or reproductive (germ) cells.

Odds Ratio - The statistical odds or probability of disease occurrence in the exposed group of individuals compared with the unexposed group of individuals in case-control studies.

Oncogenic - A substance that causes tumors, whether benign or malignant.

One-compartment model - Kinetic model, where the whole body is thought of as a single compartment in which the substance distributes rapidly, achieving an equilibrium between blood and tissue immediately.

Option Evaluation - The process of developing and analysing options for risk management.   Development of options may involve consideration of program objectives and current institutional policies, and the regulatory environment.  Option analysis may involve consideration of risks and benefits; uncertainties in risk estimations; public awareness and perception; technical feasibility; and economic, social, political, and cultural impacts.  

Organoleptic - Affecting or involving a sense organ as of taste, smell, or sight.

Other Supportive Data - In the weight-of-evidence determination of the Agency's hazard identification process this phrase refers to informa­tion on structure activity relationships (SARs), results of short-term in vitro studies, mechanistic studies and pharmacokinetics.

Ozone (O3) - A pungent, colorless, toxic gas that contributes to photochemical smog.

Particulates - Fine liquid or solid particles such as dust, smoke, mist, fumes, or smog, found in the air or emissions.

Particulate matter (in atmospheric chemistry)
1. General term used to describe airborne solid or liquid particles of all sizes.
   Note: The term aerosol is recommended to describe airborne particulate matter.
2. Particles in air, usually of a defined size and specified as PMn

Persistence, Persistent Pollutant - A persistent pollutant is one that remains for a long time in the environment.  For example, under the Canada/U.S. Great Lakes Water Quality Agreement, a persistent pollutant is one with a half-life of eight weeks or longer.

Person-year  - The sum of the number of years each person in the study population is at risk; a metric used to aggregate the total population at risk assuming that 10 people at risk for one year is equivalent to 1 person at risk for 10 years.

Pharmacodynamics - The study of the actions of drugs on the living organism. It involves the biochemical and physiological effects of drugs and the mechanisms of their actions, including the correlation of actions and effects of drugs with their chemical structure. The pharmacodynamics of a toxic substance is called toxicodynamics.

Pharmacogenetics - Study of the influence of genetic factors on the effects of drugs on individual organisms.

Pharmacokinetics - The study of the movement of drugs within biologi­cal systems. The absorption, distribution, biotransformation and excretion of substances in the organism are examined. The p­harmacokinetics of a toxic substance is called toxicokinetics.

Phenotype - Observable structural and functional characteristics of an organism determined by its genotype and modulated by its environment.

Physiologically based pharmacokinetic modeling, PBPK - Mathematical modeling of kinetic behavior of a substance, based on measured physiological parameters.
Synonym: toxicologically based pharmacokinetic modeling

PMR - Proportionate mortality ratio.

Poison (in toxicology) - Substance that, taken into or formed within the organism, impairs the health of the organism and may kill it.

Point source - A single isolated stationary source of pollution.

Pollutant - Any undesirable solid, liquid, or gaseous matter in a gaseous, liquid, or solid medium. 

Pollution - The presence of matter or energy whose nature, location or quantity produces undesired environmental effects

Population at Risk - The number of people who can develop the adverse health effect under study and who are potentially exposed to the risk factor of interest.  For example, all people in a population who have not developed immunity to an infectious disease are at risk of developing the disease, if they are exposed.  Similarly, people already having chronic disease are excluded from the population at risk in studies of the incidence of the disease.

Potency (in toxicology) - Expression of relative toxicity of an agent as compared to a given or implied standard or reference

Potential Years of Life Lost (PYLL) – Potential Years of Life Lost (PYLL) is an indicator that measures the number of years of life lost when a person dies prematurely.

ppm (Parts per million) - A measurement of concentration such as 1 µg per gram.

Precautionary Principle - A decision criterion that impels decision-makers towards action in situations where a health or ecological hazard is believed to exist as a possibility, although the exact probability of the suspected hazard is imperfectly understood.

Precision - A measure of how consistently the result is determined by repeated determinations without reference to any "true" value.

Premature death - A death that occurs before statistical expectation, usually attributable to a specific cause, and usually referring to deaths statistically estimated in a population rather than to individuals.

Prevalence - The proportion of a population that has a specified disease at a particular time.  Both previous and newly occurring cases of the disease are counted, so prevalence for a chronic disease usually exceeds its annual incidence.

Prevalence, annual (an occasionally used index) - the total number of persons with the disease or attribute at any time during a year.  It includes cases of the disease arising before but extending into or through the year as well as those having their inception during the year.

Prevalence, lifetime - The total number of persons known to have had the disease or attribute for at least part of their life.

Prevalence, period - The total number of persons known to have had the disease or attribute at any time during a specified period.

Prevalence, point - The number of persons with a disease or an attribute at a specified point in time.

Prevalence Rate - The total number of individuals who have an attribute or disease at a particular time (or during a particular period) divided by the population at risk of having the attribute or disease at this point in time or midway through the period.  A problem may arise with calculating period prevalence rates because of the difficulty of defining the most appropriate denominator.

Principal Study - The study that contributes most significantly to the qualitative and quantitative risk assessment.

Probability - The likelihood or frequency of occurrence of an event.  

Probable error - The magnitude of error which is estimated to have been made in determination of results.

Procarcinogen - Substance that has to be metabolized before it becomes a carcinogen.

Progressor/Completer - A factor that acts synergistically with carcinogens, initiators, promotors to induce the neoplastic state.

Promoter - An agent, usually chemical, that causes an initiated cell to become malignant. This is one of the final steps in carcinogenesis and leads to the formation of a tumour and may ultimately result in metastasis.

Proportionate mortality ratio (PMR) - The fraction of all deaths from a given cause in the study population divided by the same fraction from a standard population. A tool for investigating cause-specific risks when only data on deaths are available. If data on the population at risk are also available, SMRs are preferred.

Prospective Study - A way in which subjects are followed forward in time from initiation of the study.  This is often called a longitudi­nal or cohort study.

Public accident - Any accident other than motor vehicle that occurs in the public use of any premises. Includes deaths in recreation (swimming, hunting, etc.), transportation except motor vehicle, public buildings, etc., and deaths from widespread natural disasters even though some may have happened on home premises. Excludes accidents to persons in the course of gainful employment.

Pulmonary - Pertaining to the lung(s).

Quality Adjusted Life Year (QALY) – A quality-adjusted life year (QALY) measures both the quantity and the quality of life achieved by an intervention.

Quantal Data - specify the number of animals affected as a function of dose rate (e.g., mg/kg bw/day) for a single type of effect.  The numbers of animals with tumors or that die from a chemical exposure are examples.  Quantal data are often reported as an incidence (percent response) and, thus, can be used to construct a dose-response curve.

Quantal Effect - An effect that can be expressed only as Aoccurring@ or Anot occurring”. Typical examples of quantal effects are death or occurrence of a tumour.

Rate - A measure of the frequency of a phenomenon.  An expression of the frequency with which an event occurs in a defined population.

Rate Difference (RD) - The absolute difference between two rates, for example, the difference in incidence rate between a population group exposed to a causal factor and a population group not exposed to the factor:   RD = Ie - Iu   where Ie = incidence rate among exposed, and Iu = incidence rate among unexposed.  In comparisons of exposed and unexposed groups, the term excess rate may be used as a synonym for rate difference.

Rate Ratio (RR) - The ratio of two rates.  The term is used in epidemiologic research with a precise meaning, i.e., the ratio of the rate in the exposed population to the rate in the unexposed population:  RR=  Ie / Iu where Ie is the incidence rate among exposed and Iu is the incidence rate among unexposed.

Reasonably Consistent - In the weight-of-evidence determination of the Agency's hazard identification process this phrase refers to evidence of an effect in most species adequately tested.

Reference Dose (RfD) - An estimate of the daily exposure dose that is likely to be without deleterious effect even if continued exposure occurs over a lifetime.

Regression analysis - Statistical methods for modeling a set of dependent variables, Y, in terms of combinations of predictors, X.

Relative Risk - i) the ratio of the risk of disease or death among the exposed to the risk among the unexposed; this usage is synonymous with risk ratio; ii) alternatively, the ratio of the cumulative incidence rate in the exposed to the cumulative incidence rate in the unexposed, i.e., the cumulative incidence ratio, and iii) the term Arelative risk@ has also been used synonymously with Aodds ratio@ and, in some biostatistical articles, has been used for the ratio of forces of morbidity.  The use of the term Arelative risk@ for several different quantities arises from the fact that for Arare@ diseases (e.g., most cancers) all the quantities approximate one another.  For common occurrences (e.g., neonatal mortality in infants under 1500 g birth weight), the approximations do not hold.

Relative excess risk, RER - Measure that can be used in comparison of adverse reactions to drugs, or other exposures, based solely on the component of risk due to the exposure or drug under investigation, removing the risk due to background exposure experienced by all in the population. The relative excess risk, R, is given by
R = (R1 – R0)/(R2 – R0)
where R1 is the rate in the population, R2 is the rate in the comparison population, and R0 is the rate in the general population.
Note: Rate is used here as in epidemiology

Reliability - The probability a system performs a specified function or mission under given conditions for a prescribed time.

Reproducibility - The degree of variation obtained when the same measurement is made with similar instruments and many operators.

Reservoir (in biology) - Storage compartment from which a substance may be released with subsequent biological effects.

Residence time - The period of time during which a substance resides in a designated area.

Residual risk - Health risk remaining after risk reduction actions are implemented.

Respirable particle - Particle of the size (<5.0 µm) most likely to be deposited in the pulmonary portion of the respiratory tract.

Response - Change developed in the state or dynamics of an organism, system, or (sub)population in reaction to exposure to an agent.

Retention
1. Amount of a substance that is left from the total absorbed after a certain time following exposure.
2. Holding back within the body or within an organ, tissue or cell of matter that is normally eliminated.

Reversible versus Irreversible Toxicity - Reversible toxic effects are those that can be repaired, usually by a specific tissue's ability to regenerate or mend itself after chemical exposure, while irreversible toxic effects are those that cannot be repaired.

Risk - The probability of an adverse effect in an organism, system, or (sub)population caused under specified circumstances by exposure to an agent.

Risk Acceptance - a decision to accept a risk 1.The verb Ato accept@ is chosen to convey the idea that acceptance has its basic dictionary meaning 2. Risk acceptance depends on risk criteria.

Risk analysis - A process for controlling situations where an organism, system, or (sub)population could be exposed to a hazard. The risk analysis process consists of three components: risk assessment, risk management, and risk communication.

Risk Assessment - A process intended to calculate or estimate the risk to a given target organism, system, or (sub)population, including the identification of attendant uncertainties, following exposure to a particular agent, taking into account the inherent characteristics of the agent of concern as well as the characteristics of the specific target system. The risk assessment process includes four steps: hazard identification, hazard characterization, (related term: Dose-response assessment), exposure assessment, and risk characterization. It is the first component in a risk analysis process.

Risk Avoidance - Decision not to become involved in, or action to withdraw from a risk situation 1.  The decision may be taken based on the result of risk evaluation. 

Risk-Benefit Analysis (RBA) - Economic gains less the costs of a particular program. Essentially, the RBA is a CBA minus the qualitat­ive gains in health status.  It ignores aspects, such as human suffering which are difficult to quantify.

Risk Characterization - The qualitative and, wherever possible, quantitative determination, including attendant uncertainties, of the probability of occurrence of known and potential adverse effects of an agent in a given organism, system, or (sub)population, under defined exposure conditions. Risk characterization is the fourth step in the risk assessment process

Risk Communication - Interactive exchange of information about (health or environmental) risks among risk assessors, managers, news media, interested groups, and the general public.

Risk Control - the step in the Risk Management Framework which focuses on choosing a particular course of preventive or remedial action from an array of possible control options, all of which are intended to reduce health risks through various strategies identified by the stakeholders and the risk management team.

Risk Criteria - Terms of reference by which the significance of risk is assessed 1.  Risk criteria may include associated cost and benefits, legal and statutory requirements, socio-economic and environmental aspects, concerns of stakeholders, priorities and other inputs to the assessment.

Risk Estimation - Quantification of the probability, including attendant uncertainties, that specific adverse effects will occur in an organism, system, or (sub)population due to actual or predicted exposure.

Risk Evaluation - Establishment of a qualitative or quantitative relationship between risks and benefits of exposure to an agent, involving the complex process of determining the significance of the identified hazards and estimated risks to the system concerned or affected by the exposure, as well as the significance of the benefits brought about the agent. Risk evaluation is an element of risk management. Risk evaluation is synonymous with risk-benefit evaluation.

Risk Financing - Provision of funds to meet the cost of implementing risk treatment and related costs  1.  In some industries risk financing only relates to funding the financial consequences of risk.

Risk identification - Recognizing that a hazard exists and trying to define its characteristics. Often risks exist and are even measured for some time before their adverse consequences are recognized. In other cases, risk identification is a deliberate procedure to review, and it is hoped, anticipate possible hazards

Risk Management - Decision-making process involving considerations of political, social, economic, and technical factors with relevant risk assessment information relating to a hazard so as to develop, analyse, and compare regulatory and non-regulatory options and to select and implement appropriate regulatory response to that hazard. Risk management comprises three elements: risk evaluation; emission and exposure control; and risk monitoring.

Risk Management Framework - A systematic decision-making process for assessing and managing health risks.

Risk Management System - Set of elements of an organisation=s management system concerned with managing risk 1.  Management system elements may include: strategic planning; decision making; and other processes for dealing with risk 2.  Risk management systems reflect the culture of the organisation.

Risk Monitoring - Process of following up the decisions and actions within risk management in order to ascertain that risk containment or reduction with respect to a particular hazard is assured. Risk monitoring is an element of risk management.

Risk Optimization - Process, related to a risk, to minimize the negative and to maximize the positive consequences and their respective probabilities 1. In a safety context risk optimization is focused on reducing the risk 2.  Risk optimization follows risk criteria, including costs and legal requirements 3.  Risks associated with risk control may be considered.

Risk Perception - The significance assigned to risks by stakeholders.  This perception is derived form the stakeholders= expressed needs, issues, and concerns.

Risk Reduction - Actions taken to lessen the probability, negative consequences, or both, associated with a particular risk.

Risk Retention - Acceptance of the burden of loss or benefit of gain from a particular risk.  1.  Risk retention includes the acceptance of risks that have not been identified 2.  Risk retention does not include treatments involving insurance, or transfer by other means 3.  There may be variability in the degree of acceptance and dependence on risk criteria.

Risk Transfer - Share with another party the benefit of gain or burden of loss for a particular risk 1.  Risk transfer may be effected through insurance or other agreements 2.  Risk transfer may create new risks or modify existing risk 3.  Relocation of the source is not risk transfer 4.  Legal or statutory requirements may limit, prohibit, or mandate the transfer of certain risk.

Risk Treatment - Process of selection and implementation of measures to modify risk 1.  The term risk treatment is sometimes used for measures themselves 2.  Risk treatment measures may include avoiding, optimizing, transferring or retaining risk.

Safety - Practical certainty that adverse effects will not result from exposure to an agent under defined circumstances. It is reciprocal of risk.

Safety Factor - Composite (reductive) factor by which an observed or estimated no-observed-adverse-effect level (NOAEL) is divided to arrive at a criterion or standard that is considered safe or without appreciable risk.

Safety Factors (in food additives and contaminants) - A factor applied to the no-observed-effect level to derive acceptable daily intake (ADI) (the no-observed-effect level is divided by the safety factor to calculate the ADI).  The value of the safety factor depends on the nature of the toxic effect, the size and type of population to be protected, and the quality of the toxicological information available.

Sample (in statistics)
1. Group of individuals often taken at random from a population for research purposes.
2. One or more items taken from a population or a process and intended to provide information on the population or process.
3. Portion of material selected from a larger quantity so as to be representative of the whole.

Severity - Connotes the toxicological significance attached to the continuum of effects, including adaptive, compensatory and adverse effects, potentially associated with exposure to xenobiotics.

Short-Term Exposure - Multiple or continuous exposures occurring over a week or so.

Short-term exposure limit, STEL - Fifteen-minute time-weighted average (TWA) exposure recommended by ACGIH which should not be exceeded at any time during a workday, even if the 8-h TWA is within the threshold limit value–timeweighted average, TLV–TWA.

SMR - Standardized mortality ratio.

Socioeconomic Impact Analysis (SEIA) - An assessment of both allocati­ve (market efficiency as measured by production and consumption) and non-allocative effects (income distribution, market structure, international trade, inflation etc.) on proposed regulations.

Socioeconomic Analysis - An analysis in monetary values of the costs and benefits of various actions to protect health or the environment.

Stakeholder - Any individual, group, or organization able to affect, be affected by, or believe it might be affected by, a decision or activity.  The decision-maker(s) is often, but not always, considered as a stakeholder.

Standard - A standard is a legally enforceable limit for a substance or an agent intended to protect human health or the environment.  Exceeding the standard could result in unacceptable harm.

Statistical significance - The statistical significance determined by using appropriate standard techniques of statistical analysis with results interpreted at the stated confidence level and based on data relating species which are present in sufficient numbers at control areas to permit a valid statistical comparison with the areas being tested.

Steady state (in toxicology) - State of a system in which the conditions do not change in time.

Stochastic - Pertaining to or arising from chance and hence obeying the laws of probability.

Stochastic Effect - Effect for which the probability of occurrence depends on the absorbed dose.  Hereditary effects and cancer induced by radiation are considered to be stochastic effects {ICRP 1977 434 /id}.  The term Astochastic@ indicates that the occurrence of effects so named would be random.  This means that, even for an individual, there is no threshold of dose below which the effect will not appear, but the chance of experiencing the effect increases with increasing dose.

Stochastic Process - A biological disease process that produces as an all-or-nothing outcome (e.g. cancer) through a series of stepwise cellular changes (e.g. gene mutations).  The likelihood of the disease is determined by the statistical probability of the occurrence of each of the underlying steps in the disease process.

Strength-of-Evidence - A common variant of the weight-of-evidence approach for Risk Identification, in which positive findings of harmful health effects are given greater weight than negative findings.  This may lead to the classification of many environmental agents as harmful, when the evidence from animal and human pollution studies is actually contradictory or inconclusive.    

Stressor - Any entity, stimulus, or condition that can modulate normal functions of the organism or induce an adverse response (e.g. agent, lack of food, drought).

Subacute Toxicity Test - An animal experiment serving to study the effects produced by the test material when administered in repeated doses (or continuously in food, drinking-water) over a period of up to about 90 days.

Subchronic - Repeated over a short period, usually about 10 % of the life span; an imprecise term used to describe exposures of intermediate duration.

Subchronic effect - Biological change resulting from an environmental alteration lasting about 10 % of the lifetime of the test organism.
Note: In practice with experimental animals, such an effect is usually identified as resulting from
multiple or continuous exposures occurring over 3 months (90 days).

Subchronic exposure - A contact between an agent and a target of intermediate duration between acute and chronic. (Other terms, such as “less-than-lifetime exposure,” are also used.)

Subchronic Study - A toxicity study designed to measure effects from subchronic exposure to a chemical.

Subchronic toxicity test - Animal experiment serving to study the effects produced by a test substance when administered in repeated doses (or continually in food, drinking-water, air) over a period of up to about 90 days.

Surrogate - Something that serves as a substitute. In risk analysis, surrogates are often used when data on the item of interest (a chemical, an industry, an exposure, etc.) is lacking. As an example, underground mining of coal and hardrock minerals can be used as a surrogate for underground oil shale mining.

Susceptible - Describing a group of organisms more vulnerable to a given exposure than the majority of the population to which they belong.
Note: Susceptibility may reflect gender, age, physiological status, or genetic constitution of the
organisms at risk.

Synergetic - Working together; an agent that works synergistically with one or more other agents.

Synergism - Co-ordinated or concerted action of two or more agents.  The effect observed from combined exposure is greater than the sum of effects of single exposure.  Also referred to as potentiation.

Synergism (in toxicology) - Pharmacological or toxicological interaction in which the combined biological effect of two or more substances is greater than expected on the basis of the simple summation of the toxicity of each of the individual substances

Systematic error - A reproducible inaccuracy introduced by faulty equipment, calibration, or technique.

Systemic - Relating to the body as a whole.

Systemic effect - Consequence that is either of a generalized nature or that occurs at a site distant from the point of entry of a substance.
Note: A systemic effect requires absorption and distribution of the substance in the body.

Target – Any biological entity that receives an exposure or a dose (e.g. a human, a human population, or a human organ).

Teratogen - An agent or factor that causes production of developmental anomalies and/or abnormalities in the developing embryo ie. in utero.

Teratogenic - Substances that are suspected of causing malformations or serious deviations from the normal type, which can not be inherited in or on animal embryos or fetuses.

Teratology - Science that deals with abnormal development of the fetus and congenital malformation.

Threshold - Dose or exposure concentration of an agent below which a stated effect is not observed or expected to occur.

Threshold Dose - The minimum exposure level which induces a statisti­cally significant response in the organism.

Threshold Level - A theoretical concept for the exposure level of a substance that represents the change from the maximum exposure producing no (adverse) effects to the minimum exposure producing an (adverse) effect under defined conditions.

Threshold Limit Value (TLV) - The concentration of a material to which most workers can be exposed daily without adverse effect - - - These values are time weighted concentrations for a 7-or 8-hour workday and a 40-hour workweek. For most materials, the value may be exceeded to a certain extent, provided there are compensatory periods of exposure below the value during the workday (or in some case the week). For a few materials, (mainly those that produce a rapid response) the limit is given as ceiling concentration (ie. a maximum permissible concen­tration) that should never be exceeded.

Threshold limit value-ceiling, TLV-C - Concentration of a potentially toxic substance that should not be exceeded during any part of the working exposure.

Threshold limit value–time-weighted average, TLV–TWA - Time-weighted average concentration for a conventional 8-h workday and a 40-h workweek, to which it is believed nearly all workers may be repeatedly exposed, day after day, without adverse effect.

Threshold limit value–short-term exposure limit, TLV–STEL - Concentration to which it is believed that workers can be exposed continuously for a short period of time without suffering from (1) irritation, (2) chronic or irreversible tissue damage, or (3) narcosis of sufficient degree to increase the likelihood of accidental injury, impair self rescue or materially reduce work efficiency, and provided that the daily TLV–TWA is not exceeded.
Note: It is not a separate independent exposure guideline; rather, it supplements the TLV–TWA
limit where there are recognized acute effects from a substance whose toxic effects are primarily
of a chronic nature. TLV–STELs are recommended only where toxic effects have been reported
from high short-term exposures in either humans or animals.

Time Weighted Average - An expression of permissible levels for occupational exposure.  Time weighted average permits exposure above the level, provided they are compensated by equivalent excursions below the level during the work-day shift. In some cases, the magnitude, duration and frequency of permissible excursions above these averages are specified.

Tolerable daily intake, TDI - Estimate of the amount of a potentially harmful substance (e.g., contaminant) in food or drinking water that can be ingested daily over a lifetime without appreciable health risk.
Note: Acceptable daily intake (ADI) is normally used for substances not known to be harmful, such as food additives.

Tolerable weekly intake, TWI - Estimate of the amount of a potentially harmful substance (e.g., contaminant) in food or drinking water that can be ingested weekly over a lifetime without appreciable health risk.

Tolerance - An adaptive state characterized by diminished responses to the same dose of a chemical.

Toxic - Able to cause injury to living organisms as a result of physicochemical interaction.

Toxicity – Inherent property of an agent to cause an adverse biological effect.
 
Toxicity test - Experimental study of the adverse effects of exposure of a living organism to a substance for a defined duration under defined conditions.

Toxicodynamics - Process of interaction of potentially toxic substances with target sites, and the biochemical and physiological consequences leading to adverse effects.

Toxicogenetics - Study of the influence of hereditary factors on the effects of potentially toxic substances on individual organisms.

Toxicokinetics - Process of the uptake of potentially toxic substances by the body, the biotransformation they undergo, the distribution of the substances and their metabolites in the tissues, and the elimination of the substances and their metabolites from the body.

Toxicology - Scientific discipline involving the study of the actual or potential danger presented by the harmful effects of substances on living organisms and ecosystems, of the relationship of such harmful effects to exposure, and of the mechanisms of action, diagnosis, prevention, and treatment of intoxications.

Toxin - Poisonous substance produced by a biological organism such as a microbe, animal, or plant.

Trace - A very small amount of a material. Usually used in reference to concentrations which are on the order of or less than 1-10 parts per million.

Tumor - Any abnormal mass of cells resulting from excessive cellular multiplication.

Two-compartment model - Product of compartmental analysis requiring two compartments.

Uncertainty - Imperfect knowledge concerning the present or future state of an organism, system, or (sub)population under consideration.

Uncertainty analysis - A detailed examination of the systematic and random errors of a measurement or estimate; an analytical process to provide information regarding the uncertainty

Uncertainty Factor - Reductive factor by which an observed or estimated no-observed-adverse-effect level (NOAEL) is divided to arrive at a criterion or standard that is considered safe or without appreciable risk.

Uptake (absorption) - The process by which an agent crosses an absorption barrier.
 
Validation - Process by which the reliability and relevance of a particular approach, method, process, or assessment is established for a defined purpose.

Virtually Safe Dose (VSD) - The VSD is an expression of the daily dose (exposure) over a lifespan that is predicted to produce no more than a pre-defined low level of risk, usually set according to an >acceptable risk level= (e.g. 10-6 cancer risk over a 70 year lifetime).

Volume of distribution - Apparent (hypothetical) volume of fluid required to contain the total amount of a substance in the body at the same concentration as that present in the plasma, assuming equilibrium has been attained.

Weight-of-Evidence - Considerations involved in assessing the reliability of available information about hazard; and the quality of testing methods, the size and power of the study design, the consistency of results across studies, and the biological plausibility of exposure-response relationships and statistical associations.

Willingness-to-Pay - An economic approach used to estimate the monetary value of avoiding an adverse health effect based on an individual=s willingness-to-pay (WTP) for risk reduction.  By summing many individuals= WTP to avoid small increases in risk over a large sample, the value of a statistical premature death avoided can be inferred.  This valuation is expressed as Adollars per mortality avoided@ or Avalue of a statistical life@ (VSL) even though the actual valuation represents small changes on mortality risk experience by a large number of people.  The VSL method estimates the dollar value of a given reduction in risk, in reference to an indivdual=s WTP to reduce that risk.  WTP is often based on wage-risk studies, which derive WTP values from estimates of the additional compensation demanded in the labour market for riskier jobs, or from contingent valuation (CV) studies which directly solicit WTP information from personal interviews.

Xenobiotic - Compound with a chemical structure foreign to a given organism.
Note: The term is frequently restricted to manmade compounds.

Years Lost due to Disability (YLD) – Years Lost due to Disability (YLD) gives the number of healthy years lost to a disability.

Years of Life Lost (YLL) – Years of Life Lost is simply the number of years lost due to premature mortality.

Zero order analysis - ­­The simplest approach to quantification of a risk with a limited treatment of each risk component (e.g. source terms, transport, health effects, etc.).

131I (Iodine – 131) - is a radioactive isotope of the chemical element Iodine with mass number 131. It is a beta-emitter with a half-life of 8 days.

137Cs (Cesium-137) -  is a radioactive isotope of the chemical element Cesium with mass number 137, which has a half life of 30.2 years and decays by beta-decay.