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GLOSSARY OF EXPOSURE ASSESSMENT-RELATED TERMS: A COMPILATION Prepared by the Exposure Terminology Subcommittee of the IPCS Exposure Assessment Planning Workgroup for the International Programme on Chemical Safety Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals November 1, 2001 This document is a compilation (a secondary reference). Citations should be made to the original documents, which are referenced herein. This compilation has been developed for the IPCS Exposure Terminology Subcommittee. It does not necessarily represent the views or stated policy of UNEP, ILO or WHO.
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GLOSSARY OF EXPOSURE ASSESSMENT-RELATED TERMS:A COMPILATION

Prepared by the Exposure Terminology Subcommitteeof the

IPCS Exposure Assessment Planning Workgroup

for theInternational Programme on Chemical Safety

Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals

November 1, 2001

This document is a compilation (a secondary reference).Citations should be made to the original documents, which are referenced herein.

This compilation has been developed for the IPCS Exposure Terminology Subcommittee.It does not necessarily represent the views or stated policy of UNEP, ILO or WHO.

The International Programme on Chemical Safety (IPCS)Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals

GLOSSARY OF EXPOSURE ASSESSMENT-RELATED TERMS: A COMPILATION

PreambleThis is an unedited selection of exposure assessment related terms taken from a combination of 57

glossaries for exposure and related fields (references below). It has been prepared for the IPCS ExposureTerminology Subcommittee as a research paper for discussion purposes. It makes no pretense at beingcomprehensive; the 57 glossaries were those that were available to the Subcommittee when the project was inprogress. Efforts to obtain several other glossaries were unsuccessful in the period when the work was being done.This compilation is being made available on the IPCS Harmonization website to aid researchers in findingdifferences in definitions for exposure-related terms, which is part of the original intent of the ExposureTerminology Subcommittee.

Selections of terms in this glossary were based on the IPCS Exposure Terminology Subcommittee’sopinion of relevance to exposure assessment. Toxicological terms, risk-related terms, chemical names, proceduralterms, and risk management terms were generally excluded from this list, as were terms clearly outside the riskassessment paradigm altogether.

The definitions are presented as they were worded in the references, with minor adjustments to reflectagreement among several definitions as to singular vs. plural definitions (e.g., source vs. sources).

The order in which the definitions are presented is alphabetical by reference, and should not imply order ofimportance or “correctness.” Where several references give the same definition, the references are listed in order ofdates, with oldest first.

The International Programme on Chemical Safety (IPCS)Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals

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GLOSSARY OF EXPOSURE ASSESSMENT-RELATED TERMS: A COMPILATION

Absorbed dose - a. See internal dose. [REAP,1995: Residential Exposure AssessmentProject][USEPA, 1992: GL for ExposureAssessment]; b. 1.The energy imparted to aunit mass of matter by ionizing radiation. Theunit of absorbed dose is the rad. One radequals 100 ergs per gram. 2.The amount of asubstance absorbed into the body, usually perunit of time. The most common unit of dose ismg per kg body weight per day (mg/kg_day).[SRA, 1999: Glossary of Risk Analysis Terms,attributed to Stephen L. Brown]; c. Energyabsorbed by matter from ionizing radiationper unit mass of irradiated material at the placeof interest in that material. The absorbed doseis expressed in units of rad (or gray) (1 rad =0.01 gray). [USDOE, 1998: RadiologicalControl Manual]; d. The energy imparted to aunit mass of matter by ionizing radiation. Theunit of absorbed dose is the rad or gray. Onerad equals 100 ergs per gram. The amount of asubstance absorbed into the body, usually perunit of time. The most common unit of dose ismg per kg body weight per day (mg/kg_day).[USDOE, 2000: RAIS Glossary]; e. Theamount of a substance penetrating across anabsorption barrier (the exchange boundaries)of an organism, via either physical orbiological processes. Sometimes calledinternal dose. [USEPA, 1992a: DermalExposure Assessment]; f. In exposureassessment, the amount of a substance thatpenetrates an exposed organism's absorptionbarriers (e.g.,, skin, lung tissue,gastrointestinal tract) through physical orbiological processes. The term is synonymouswith internal dose. [USEPA, 1997a: EPATerms of Environment]; g. The amount ofpesticide entering systemic circulation aftercrossing a specific absorption barrier (e.g., theexchange boundary of the skin, lung, ordigestive tract); normally expressed as massper unit body weight per unit time (e.g.,mg/kg/day). Internal dose is a more generalterm denoting the amount absorbed withrespect to specific absorption barriers orexchange boundaries [USEPA, 1998: Postapp.Exposure Test GL., attributed to USEPA,1992]; h. Dose resulting from the agentcrossing the contact boundary and diffusingthrough a resisting boundary layer [Zartarian,et al., 1997: Quant. Def. of Exp. & RelatedConcepts] [Cf. internal dose]

Absorption - a. The process of taking in, aswhen a sponge takes up water. Chemicals canbe absorbed through the skin into thebloodstream and then transported to otherorgans. Chemicals can also be absorbed intothe bloodstream after breathing or swallowing.[ATSDR, 1999: Online Glossary][New YorkDepartment of Health, 1999: Glossary of

Environmental Health Terms]; b. Thepenetration of a substance through a barrier(e.g., the skin, gut, or lungs). [REAP, 1995:Residential Exposure Assessment Project]; c.1. The penetration of one substance into orthrough another. 2. Specifically, thepenetration of a substance into the body fromthe skin, lungs, or digestive tract. [SRA, 1999:Glossary of Risk Analysis Terms, attributed toStephen L. Brown][USDOE, 2000: RAISGlossary]; d. The taking in of water anddissolved minerals and nutrients across cellmembranes. Contrast with ingestion. [UCMP,1998: Glossary of Ecological Terms]; e. Amode of entry of a toxic substance into thebody in which the substance enters through theunbroken skin. [University of Kentucky, 1999:Glossary of Safety Terms]; f. The process bywhich a substance is transported across theskin permeability surface barrier and taken upinto the living tissue of the body; generallysynonymous with percutaneous absorption andwith dermal uptake. [USEPA, 1992a: DermalExposure Assessment]; g. The uptake ofwater , other fluids, or dissolved chemicals bya cell or an organism (as tree roots absorbdissolved nutrients in soil.) [USEPA, 1997a:EPA Terms of Environment]

Absorption barrier - a. Any of the exchangebarriers of the body that allow differentialdiffusion of various substances across aboundary. Examples of absorption barriers arethe skin, lung tissue, and gastrointestinal tractwall. [USEPA, 1992: GL for ExposureAssessment][USEPA, 1992a: DermalExposure Assessment]; b. Any of theexchange sites of the body that permit uptakeof various substances at different rates (e.g.,skin, lung tissue, and gastrointestinal tractwall) [USEPA, 1997a: EPA Terms ofEnvironment]

Absorption cross section - A measurement ofan atom or molecule's ability to absorb light ata specified wavelength, measured in squarecm/particle. [SHSU, 2000: AtmosphericChemistry Glossary, attributed to Journal ofAtmospheric Sciences 50:941-950 (1994) andJournal of Chemical Education 71:105-108(1994)]

Absorption factor - The fraction of an agent(e.g., a chemical) making contact with anorganism that is systemically distributed in theorganism. [REAP, 1995: Residential ExposureAssessment Project]

Absorption fraction - The relative amount ofa substance on the skin that penetrates throughthe epidermis into the body; reported as the

unitless fraction of the applied dose or as thepercent absorbed. [USEPA, 1992a: DermalExposure Assessment]

Absorption percent - (percent absorbed) Therelative amount of a substance that penetratesthrough a barrier into the body, reported as aunitless fraction. [USEPA, 1997b: ExposureFactors Handbook];

Absorption of radiation - The uptake ofradiation by a solid body, liquid or gas. Theabsorbed energy may be transferred orre_emitted. [USEPA, 2000: Global WarmingGlossary]

Acceptable daily intake (ADI) - a. Thehighest daily amount of a substance that maybe consumed over a lifetime without adverseeffects. [CARB, 2000: Glossary of AirPollution Terms]; b. This is an estimate ofthe amount of a substance in food that can beingested daily over a lifetime by humanswithout appreciable health risk. The concept ofthe ADI has been developed principally byWHO and FAO and is relevant to chemicalssuch as additives to foodstuffs, residues ofpesticides and veterinary drugs in foods. ADIsare derived from laboratory toxicity data, andfrom human experiences of such chemicalswhen this is available, and incorporate a safetyfactor. The ADI is thus an estimate of theamount of a substance in food that can beingested over a lifetime by humans withoutappreciable health risk (for contaminants infood and drinking water, Tolerable Intakes _daily or weekly _ are used). See TolerableDaily Intake. [Duffus, 2000: Univ. EdinburghMed School On-line Chemical SafetyGlossary]; c. The ADI of a chemical is theestimate of the amount of a substance in foodand/or drinking water, expressed on a body-weight basis, that can be ingested daily over alifetime without appreciable health risk to theconsumer on the basis of all the known facts atthe time of the evaluation. It is usuallyexpressed in milligrams of the chemical perkilogram of body weight. [FAO/WHO, 1997:Food Consumption & Exp. Assessment ofChemicals]; d. The amount of a chemical aperson can be exposed to on a daily basis overan extended period of time (usually a lifetime)without suffering deleterious effects. [IRIS,1999: Glossary of IRIS Terms]; e. Same as"Reference Dose". Estimate of largest amountof exposure to an agent on a daily basis notexpected to result in adverse effects. [REAP,1995: Residential Exposure AssessmentProject]; f. An estimate of the daily exposuredose that is likely to be without deleteriouseffect even if continued exposure occurs overa lifetime. [USDOE, 2000: RAIS Glossary]

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Accumulation - Repeated doses of a chemicalmay result in its concentration in an organism,organ or tissue increasing progressively andthe toxic effects may become more markedwith successive doses. Factors involved inaccumulation include selective binding of thechemical to tissue molecules, concentration offat soluble chemicals in body fat, absent orslow metabolism, and slow excretion.Accumulation is a mass balance effect whereinput exceeds output. [Duffus, 2000: Univ.Edinburgh Med School On-line ChemicalSafety Glossary]

Accuracy - a. The extent to which results ofa calculation or the readings of an instrumentapproach the true values of the calculated ormeasured quantities, and are free from error.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; b. The degree towhich a measurement, or an estimate based onmeasurements, represents the true value of theattribute that is being measured. [Last, 1983: ADictionary of Epidemiology]; c. The degreeof agreement between a measured value andthe true value; usually expressed as +/_percent of full scale. [SRA, 1999: Glossary ofRisk Analysis Terms][USDOE, 2000: RAISGlossary]; d. The measure of the correctnessof data, as given by the difference between themeasured value and the true or standard value.[USEPA, 1992: GL for ExposureAssessment][USEPA, 1997b: ExposureFactors Handbook] [Cf. precision]

Activity - A specific action related to a task orbehavior that may result in an exposure event(e.g., harvesting pesticide treated crops,crawling on pesticide treated lawn) [USEPA,1998: Postapp. Exposure Test GL.]

Actual dermal exposure - The amount ofpesticide coming into contact with bare(uncovered) skin and the fraction transferringthrough protective and work clothing or viaseams to the underlying skin, and which istherefore available for percutaneousabsorption. [OECD, 1997: OccupationalExposure to Pesticides]

Acute - a. Occurring over a short time,usually a few minutes or hours. An acuteexposure can result in short-term or long-termhealth effects. An acute effect happens a shorttime (up to 1 year) after exposure. [ATSDR,1999: Online Glossary]; b. Occurring over ashort time, usually a few minutes or hours. Anacute exposure can result in short term or longterm health effects. An acute effect happenswithin a short time after exposure. [New YorkDepartment of Health, 1999: Glossary ofEnvironmental Health Terms]; c.Acute_diseases or responses with short andgenerally severe course (often due to high

pollutant concentrations). [SRA, 1999:Glossary of Risk Analysis Terms]; d. Ahealth effect that is the result of a short timeexposure to a very high concentration of atoxic material. The effect is usuallyimmediately seen, not more than several hoursafter the exposure. [University of Kentucky,1999: Glossary of Safety Terms]; e. Diseasesor responses with short and generally severecourse (often due to high pollutantconcentrations). [USDOE, 2000: RAISGlossary]

Acute exposure - a. One or a series ofshort_term exposures generally lasting lessthan 24 hours. [CARB, 2000: Glossary of AirPollution Terms]; b. One dose or multipledoses of short duration spanning less than orequal to 24 hours. [IRIS, 1999: Glossary ofIRIS Terms]; c. A short-term exposure to achemical, usually consisting of a singleexposure or dose administered for a period ofless than 24 hours. [OFA, 2000: OxyfuelsGlossary]; d. An exposure of short durationand/or rapid onset. An acute toxic effect is onethat develops during or shortly after an acuteexposure to a toxic substance. [REAP, 1995:Residential Exposure Assessment Project]; e.A single exposure to a toxic substance whichmay result in severe biological harm or death.Acute exposures are usually characterized aslasting no longer than a day, as compared tolonger, continuing exposure over a period oftime. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAIS Glossary]

Administered dose - a. The amount of asubstance given to a test subject (human oranimal) in determining dose-responserelationships, especially through ingestion orinhalation. In exposure assessment, sinceexposure to chemicals is usually inadvertent,this quantity is called potential dose. [USEPA,1992: GL for Exposure Assessment][REAP,1995: Residential Exposure AssessmentProject]; b. The amount of a substance givento a test animal in determining dose_respon.serelationships, esp. through ingestion orinhalation. In exposure assessment, sinceexposure to chemicals is usually inadvertent.this quantity is called applied dose. [USEPA,1992a: Dermal Exposure Assessment]; c. Inexposure assessment, the amount of asubstance given to a test subject (human oranimal) to determine dose_responserelationships. Since exposure to chemicals isusually inadvertent, this quantity is often calledpotential dose. [USEPA, 1997a: EPA Termsof Environment]

Adsorption - a. The attachment of themolecules of a liquid or gaseous substance tothe surface of a solid. [SRA, 1999: Glossaryof Risk Analysis Terms]; b. The retention ofa substance by soil particles. [USDOE, 2000:

RAIS Glossary]; c. Adherence of a solid orliquid to a surface without penetrating throughthe surface layer. Also, the adherence of ionsor organic chemicals onto the surface layer ofother materials without being incorporated intoor absorbed by the surface of the material.[USEPA, 1992a: Dermal ExposureAssessment]; d. Removal of a pollutant fromair or water by collecting the pollutant on thesurface of a solid material; e.g., an advancedmethod of treating waste in which activatedcarbon removes organic matter fromwaste_water. [USEPA, 1997a: EPA Terms ofEnvironment]

Advection - a. In meteorology, the transferof heat, cold, or other atmospheric propertiesby the horizontal motion of an air mass; inoceanography, the process of transport ofwater, or of an aqueous property, solely by themass motion of the oceans, most typically viahorizontal currents. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]; b. To transport or carry. In airquality, the rate at which particulate matter istransported. [SHSU, 2000: AtmosphericChemistry Glossary, attributed to Journal ofthe Atmospheric Sciences 51:3109-3121(1994) and Deep-Sea Research 41:243-261(1994)]; c. Process of transport of anatmospheric property, or substance within theatmosphere, solely by the mass motion of theatmosphere. [SRA, 1999: Glossary of RiskAnalysis Terms]

Aerodynamic diameter - a. The diameter ofa sphere with unit density that hasaerodynamic behavior identical to that of theparticle in question; an expression ofaerodynamic behavior of an irregularly shapedparticle in terms of the diameter of anidealized particle. Particles having the sameaerodynamic diameter may have differentdimensions and shapes. [IRIS, 1999:Glossary of IRIS Terms]; b. Expression ofaerodynamic behavior of an irregularly shapedparticle in terms of the diameter of anidealized particle; that is, aerodynamicdiameter is the diameter of a sphere of unitdensity that has aerodynamic behavioridentical to that of the particle in question.Thus, particles having the same aerodynamicdiameter may have different dimensions andshapes. [SRA, 1999: Glossary of RiskAnalysis Terms]

Aerosol - a. Particles of solid or liquid matterthat can remain suspended in air from a fewminutes to many months depending on theparticle size and weight. [CARB, 2000:Glossary of Air Pollution Terms]; b. This isa very broad term applied to any suspension ofsolid or liquid particles in a gas. Particlediameters may range from about 0.001micrometres to about 100 micrometres. Mass

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concentrations may range from 10_9 to 10grams per cubic metre of gas. [Duffus, 2000:Univ. Edinburgh Med School On-lineChemical Safety Glossary]; c. A suspensionof liquid or solid particles in air. [IRIS, 1999:Glossary of IRIS Terms]; d. A suspension ofmicroscopic solid or liquid particles in air. Seealso haze, particulate matter. [ODEQ, 1999:Air Quality Glossary]; e. System in whichthe dispersion medium is a gas and thedispersed phase (composed of solid particlesor liquid droplet) does not settle out under theinfluence of gravity. [SRA, 1999: Glossary ofRisk Analysis Terms]; f. 1. Small droplets orparticles suspended in the atmosphere,typically containing sulfur. They are usuallyemitted naturally (e.g., in volcanic eruptions)and as the result of anthropogenic (human)activities such as burning fossil fuels. 2. Thepressurized gas used to propel substances outof a container. 3. A finely divided materialsuspended in air or other gaseous environment.[USEPA, 1997a: EPA Terms of Environment];g. [aerosols] Particles of matter, solid orliquid, larger than a molecule but small enoughto remain suspended in the atmosphere.Natural sources include salt particles from seaspray and clay particles as a result ofweathering of rocks, both of which are carriedupward by the wind. Aerosols can alsooriginate as a result of human activities and inthis case are often considered pollutants. Seealso Sulfate Aerosols. [USEPA, 2000: GlobalWarming Glossary]

Aerosol particles - One of the components ofan atmospheric air parcel, comprised of minutesolids particles part of which is almostcertainly water.[SHSU, 2000: AtmosphericChemistry Glossary, attributed to TheCharacter and Origins of Smog Aerosols, Vol.9 - Advances in Environmental Science andTechnology Series; Hidey, ed.; page 234(1980) Wiley; New York, and EnvironmentalParticles, Vol. 1 - Environmental Analyticaland Physical Chemistry Series; pages 7, 30, 33(1992)]; b. Solid particles <10_6 m indiameter, dispersed in gas. [SRA, 1999:Glossary of Risk Analysis Terms]

Agent - a. A chemical, physical,mineralogical, or biological entity that maycause deleterious effects in an organism afterthe organism is exposed to it. [USEPA, 1992:GL for Exposure Assessment]; b. Achemical, radiological, mineralogical, orbiological entity that may cause deleteriouseffects an organism after the organism isexposed to it. [USEPA, 1992a: DermalExposure Assessment] [REAP, 1995:Residential Exposure Assessment Project][AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; c. Suter et al. 1994suggested it as an alternative for the term

stressor. It is considered to be more neutralthan stressor, and is used in EPA's Guidelinesfor Exposure Assessment. [USEPA, 1997:Guidance on Cumulative Risk Assessment,Planning and Scoping]; d. Any physical,chemical, or biological entity that can beharmful to an organism (synonymous withstressor). [USEPA, 1997a: EPA Terms ofEnvironment]; e. Any physical, chemical, orbiological entity that can induce an adverseresponse (synonymous with stressor).[USEPA, 1998a: Guidelines for EcologicalRisk Assessment]; f. A chemical, physical,mineralogical, or biological entity that maycause deleterious effects in a target aftercontacting the target [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts] [Cf.stressor]

Agent (of disease) - A factor, such as amicroorganism, chemical substance, or form ofradiation, whose presence, excessive presence,or (in deficiency diseases) relative absence isessential for the occurrence of a disease. Adisease may have a single agent, a number ofindependent alternative agents (at least one ofwhich must be present), or a complex of two ormore factors whose combined presence isessential for the development of the disease.See also causality. [Last, 1983: A Dictionaryof Epidemiology]

Aggregate exposure - The sum of exposuresto pesticide chemical residues with a commonmechanism of toxicity from multiple sourcesand multiple routes of exposure (Food QualityProtection Act, 1996). [USEPA, 1997:Guidance on Cumulative Risk Assessment,Planning and Scoping]

Air exchange rate - a. The rate at whichoutside air replaces indoor air in a given space.[USEPA, 1997a: EPA Terms of Environment];b. Rate of air leakage through windows,doorways, intakes, exhausts, and “adventitiousopenings" (i.e. cracks and seams) that combineto form the leakage configuration of thebuilding envelope plus natural and mechanicalventilation. [USEPA, 1997b: Exposure FactorsHandbook]

ALARA - a. As Low As ReasonablyAchievable; concept utilized in relation tointervention levels following the release ofdangerous chemical or nuclear materials.[PDM, 2000: Disaster Terminology; fromDebacker, et al., 1999]; b. An approach toradiological control to manage and controlexposures (individual and collective) to thework force and to the general public at levelsas low as is reasonable, taking into accountsocial, technical, economic, practical andpublic policy considerations. As used in thisManual, ALARA is not a dose limit but a

process that has the objective of attainingdoses as far below the applicable controllinglimits as is reasonably achievable. [USDOE,1998: Radiological Control Manual]; c.Acronym for "As Low As ReasonablyAchievable," means making every reasonableeffort to maintain exposures to ionizingradiation as far below the dose limits aspractical, consistent with the purpose forwhich the licensed activity is undertaken,taking into account the state of technology, theeconomics of improvements in relation to stateof technology, the economics of improvementsin relation to benefits to the public health andsafety, and other societal and socioeconomicconsiderations, and in relation to utilization ofnuclear energy and licensed materials in thepublic interest. (see 10 CFR 20.1003).[USDOE, 2000: RAIS Glossary]

ALARA Committee - Multidisciplined forumthat reviews and advises management onimproving progress toward minimizingradiation exposure and radiological releases.[USDOE, 1998: Radiological Control Manual]

Ambient measurement - a. A measurement(usually of the concentration of a chemical orpollutant) taken in an ambient medium,normally with the intent of relating themeasured value to the exposure of an organismthat contacts that medium. [USEPA, 1992: GLfor Exposure Assessment]; b. Ameasurement of the concentration of asubstance or pollutant within the immediateenvirons of an organism; taken to relate it tothe amount of possible exposure. [USEPA,1997a: EPA Terms of Environment]

Ambient monitoring - a. Monitoring that isdone to determine existing environmentalconditions, contaminant levels, rates, orspecies in the environment, against whichfuture conditions can be compared. [NCSU,1997: Watershedds Glossary]; b. A methodof measuring the amount of a substance that isavailable for uptake: composed ofenvironmental monitoring and personalmonitoring. [OECD, 1997: OccupationalExposure to Pesticides]

Analysis of variance - A statistical techniquethat isolates and assesses the contribution ofcategorical factors to variation in the mean of acontinuous outcome variable. The data aredivided into categories based on their valuesfor each of the independent variables, and thedifferences between the mean outcome valuesof these categories are tested for statisticalsignificance. [Last, 1983: A Dictionary ofEpidemiology]

Antagonism - a. When the adverse effect orrisk from two or more chemicals interacting

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with each other is less than what it would be ifeach chemical was acting separately. [ED,2000: Environmental Scorecard Glossary]; b.Opposite of synergism. The situation in whichthe combined effect of two or more factors issmaller than the solitary effect of any one ofthe factors. In bioassay, the term may be usedto refer to the situation when a specifiedresponse is produced by exposure to either oftwo factors but not by exposure to bothtogether. [Last, 1983: A Dictionary ofEpidemiology]; c. Interference or inhibitionof the effect of one chemical by the action ofanother. [USDOE, 2000: RAIS Glossary]; d.Interference or inhibition of the effect of onechemical by the action of another. [USEPA,1997a: EPA Terms of Environment] [Cf.synergism]

Antagonistic effect - This is the consequenceof one chemical (or group of chemicals)counteracting the effects of another: in otherwords, the situation where exposure to twochemicals together has less effect than thesimple sum of their independent effects; suchchemicals are said to show antagonism.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary]

Applied dose - a. The amount of a substancein contact with the primary absorptionboundaries of an organism (e.g., skin, lung,gastrointestinal tract) and available forabsorption. [USEPA, 1992: GL for ExposureAssessment] [REAP, 1995: ResidentialExposure Assessment Project]; b. Inexposure assessment, the amount of asubstance in contact with the primaryabsorption boundaries of an organism (e.g.,skin, lung tissue, gastrointestinal track) andavailable for absorption. [USEPA, 1997a:EPA Terms of Environment]; c. The amountof a substance presented to an absorptionbarrier (i.e., skin, lung, or digestive tract) andavailable for absorption, but not yet havingcrossed the outer boundary of an organism(U.S. EPA, 1992). [USEPA, 1998: Postapp.Exposure Test GL.]; d. The amount of asubstance in contact with the primaryabsorption boundaries of an organism (e.g.,skin, lung, gastrointestinal tract) and availablefor absorption. [USEPA, 1992a: DermalExposure Assessment]

Arithmetic mean - [also called simply the“mean”] a. The arithmetic average of all thevalues in the data set. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist] b. Average. [CARB, 2000:Glossary of Air Pollution Terms]; c. Ameasure of central tendency. It is computed byadding all the individual values together anddividing by the number in the group. [Last,1983: A Dictionary of Epidemiology]; d. The

arithmetic average, or the sum of all the valuesdivided by the number of values. [NIAID,1997: HIV Vaccine Glossary] e. The sum ofall the measurements in a data set divided bythe number of measurements in the data set.[USEPA, 1992: GL for Exposure Assessment]

As consumed intake rates - Intake rates thatare based on the weight of the food in the formthat it is consumed. [USEPA, 1997b: ExposureFactors Handbook]As low as reasonably achievable - seeALARA

Assessment - a. Survey of a real or potentialdisaster to estimate the actual or expecteddamages and to make recommendations forpreparedness, mitigation and relief action[PDM, 2000: Disaster Terminology; fromGunn, 1990]; b. Evaluation or appraisal of aprocess, program or activity to estimate itsacceptability. [USDOE, 1998: RadiologicalControl Manual]

Assessment of exposure - see exposureassessment

Atmospheric lifetime - see lifetime

Autocorrelation - The correlation betweenadjacent observations in time or space.[NCSU, 1997: Watershedds Glossary]

Average daily dose (ADD) - The average dosereceived on any given day during a period ofexposure, expressed in mg/kg bodyweight/day. Ordinarily used in assessingnoncancer risks. [REAP, 1995: ResidentialExposure Assessment Project]; b. Dose rateaveraged over a pathway specific period ofexposure expressed as a daily dose on a per-unit-body-weight basis. The ADD is used forexposure to chemicals with non-carcinogenic,non-chronic effects. The ADD is usuallyexpressed in terms of mg/kg-day or othermass/mass-time units. [USEPA, 1997b:Exposure Factors Handbook] [IRIS, 1999:Glossary of IRIS Terms]; c. Dose that isaveraged over a specified time period takinginto account the frequency, duration, andintensity of exposure during that time period.ADDs are usually expressed in units ofmg/kg/day. [USEPA, 1998: Postapp. ExposureTest GL.]

Average life expectancy - [expectation of life]The average number of years an individual isexpected to live if current mortality trendscontinue to apply. A statistical abstractionbased on existing, age_specific death rates.Life expectancy at birth (0): Average number ofyears a newborn baby can be expected to liveif current mortality trends continue.Corresponds to the total number of years a

given birth cohort can be expected to live,divided by the number of children in thecohort. Life expectancy at birth is partlydependent on mortality in the first year of lifeand is lower in poor than in rich countriesbecause of the higher infant mortality rates inthe former. Life expectancy at a given age, agex (x): The average number of additional years aperson age x would live if current mortalitytrends continue to apply, based on theage_specific death rates for a given year. Lifeexpectancy is a hypothetical measure andindicator of current health and mortalityconditions. It is not a rate. [Last, 1983: ADictionary of Epidemiology]

Background level (or levels) - a. (1)anthropogenic: concentrations of chemicalsthat are present in the environment due tohuman-made, non-site sources; (2) naturallyoccurring: ambient concentrations ofchemicals that are present in the environmentaland have not been influenced by humans.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist, attributed to the RiskAssessment Guidance for Superfund, USEPA1989]; b. A typical or average level of achemical in the environment. Backgroundoften refers to naturally occurring oruncontaminated levels. [ATSDR, 1999: OnlineGlossary] [New York Department of Health,1999: Glossary of Environmental HealthTerms]; c. Two types of background levelsmay exist for chemical substances:. (1)Naturally occurring levels: Ambientconcentrations of substances present in theenvironment, without human influence; (2)Anthropogenic levels: Concentrations ofsubstances present in the environment due tohuman_made, non_site sources (e.g.,automobiles, industries). [IRIS, 1999:Glossary of IRIS Terms]; d. (1) In airpollution, the level of pollutants present inambient air from natural sources. (2) Moregenerally, the level of pollution present in anyenvironmental medium attributable to naturalor ubiquitous sources. [SRA, 1999: Glossaryof Risk Analysis Terms, attributed to StephenL. Brown] [USDOE, 2000: RAIS Glossary];e. The concentration of substance in a definedcontrol area during a fixed period of timebefore, during, or after a data-gatheringoperation. [USEPA, 1992: GL for ExposureAssessment]; f. (1) The concentration of asubstance in an environmental media (air,water, or soil) that occurs naturally or is notthe result of human activities. (2) In exposureassessment the concentration of a substance ina defined control area, during a fixed period oftime before, during, or after a data_gatheringoperation.. [USEPA, 1997a: EPA Terms ofEnvironment]

Benchmark dose (BMD) - a. A statistical

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lower confidence limit on the dose producing apredetermined, altered response for an effect.[USEPA, 1995: Benchmark Dose]; b. (alsobenchmark concentration, BMC) Astatistical lower confidence limit on the dosethat produces a predetermined change inresponse rate of an adverse effect (called thebenchmark response or BMR) compared tobackground. [IRIS, 1999: Glossary of IRISTerms]

Bias - a. A technical term for playingfavorites in choosing study subjects or inassessing exposure. [FACS, 2000:Epidemiology for Journalists]; b. Any effectat any stage of investigation or inferencetending to produce results that departsystematically from the true values (to bedistinguished from random error). The term"bias" does not necessarily carry an imputationof prejudice or other subjective factor, such asthe experimenter's desire for a particularoutcome. This differs from conventional usagein which bias refers to a partisan point of view.Many varieties of bias have been described.[attributed to Sackett, D. L., Bias in analyticresearch, J. Chron. Dis. 32:51-53 (1979)]...ascertainment bias - Systematic error, arisingfrom the kind of individuals or patients (e.g.,slightly ill, moderately ill, acutely ill) that theindividual observer is seeing. Also systematicerror arising from the diagnostic process(which may be determined by the culture,customs, or individual idiosyncrasy of theperson providing care for the patient)... biasdue to instrumental error - Systematic errordue to faulty calibration, inaccurate measuringinstruments, contaminated reagents, incorrectdilution or mixing of reagents, etc.... bias dueto withdrawals - A difference between thetrue value and that actually observed in a studydue to the characteristics of those subjects whochoose to withdraw.... bias, in assumption -(Syn: conceptual bias) Error arising fromfaulty logic or premises or mistaken beliefs onthe part of the investigator. False conclusionsabout the explanation for associations betweenvariables. Example: Having correctly deducedthe mode of transmission of cholera, JohnSnow concluded that yellow fever wastransmitted by similar means. In fact, the"miasma" theory would better fit the facts ofyellow fever transmission.... bias in autopsyseries - Systematic error resulting from thefact that autopsies represent a nonrandomsample of all deaths.... bias in handlingoutliers - Error arising from a failure todiscard an unusual value occurring in a smallsample, or due to exclusion of unusual valuesthat should be included.... bias in publication- An editorial predilection for publishingparticular findings, e.g., positive results, whichleads to the failure of authors to submitnegative findings for publication. This can

distort the general belief about what has beendemonstrated in a particular situation.... biasin the presentation of data - Error due toirregularities produced by digit preference,incomplete data, poor techniques ofmeasurement, or technically poor laboratorystandards.... bias of interpretation - Errorarising from inference and speculation.Sources of the error include (1) failure of theinvestigator to consider every interpretationconsistent with the facts and to assess thecredentials of each, and (2) mishandling ofcases that constitute exceptions to somegeneral conclusion.... design bias - Thedifference between a true value and thatactually obtained, occurring as a result offaulty design of a study. Some examples are(1) uncontrolled studies where the effects oftwo processes cannot be separated(confounding), (2) controlled studies whereobservations are based on a poorly definedpopulation, and (3) nonsimultaneouscomparisons.... detection bias - Due tosystematic error(s) in methods ofascertainment, diagnosis, or verification ofcases in an epidemiologic survey, study, orinvestigation. Example: Verification ofdiagnosis by laboratory tests in hospital cases,but failure to apply the same tests to casesoutside hospital.... information bias - (Syn:observational bias) A flaw in measuringexposure or outcome that results in differentialquality (accuracy) of information betweencompared groups.... interviewer bias -Systematic error due to interviewers'subconscious or even conscious gathering ofselective data.... length bias - A systematicerror due to the selection of a disproportionatenumber of long_duration cases (cases whosurvive longest) in one group and not in theother. Can occur when prevalent cases, ratherthan incident cases, are included in a casecontrol study.... "lead_time" bias - Asystematic error arising when follow_up of twogroups does not begin at strictly comparabletimes. Occurs especially when one group hasbeen diagnosed earlier in the natural history ofthe disease than the other group....measurement bias - Systematic error arisingfrom inaccurate measurement (orclassification) of subjects on the studyvariables.... observer bias - Systematicdifference between a true value and thatactually observed due to observer variation.Observer variation may be due to differencesamong observers (interobserver variation) or tovariation in readings by the same observer onseparate occasions (intraobserver variation)....recall bias - Systematic error due todifferences in accuracy or completeness ofrecall to memory of prior events orexperiences. Example: Mothers whose childrenhave had or have died of leukemia are morelikely than mothers of healthy living children

to remember details of diagnostic x_rayexaminations to which these children wereexposed in utero.... reporting bias - Selectivesuppression or revealing of information suchas past history of sexually transmitteddisease.... response bias - Systematic errordue to difference in characteristics betweenthose who choose or volunteer to participate ina study and those who do not.... samplingbias - Unless the sampling method ensuresthat all members of the "universe" or referencepopulation have a known chance of selectionin the sample, bias is possible. The best way toensure a known chance of selection for all is touse a probability sampling method such as atable of random numbers.... selection bias(Berkson’s bias) - Error due to systematicdifferences in characteristics between thosewho are selected for study and those who arenot. Examples include hospital cases or casesunder a physician's care, excluding those whodie before admission to hospital because thecourse of their disease is so acute, those notsick enough to require hospital care, or thoseexcluded by distance, cost, or other factors.Selection bias also invalidates generalizableconclusions from surveys which would includeonly volunteers from a healthy population. Aspecial example is Berkson's Bias, whichBerkson characterized as the set of selectivefactors that lead hospital cases and controls ina case control study to be systematicallydifferent from one another. This occurs whenthe combination of exposure and disease understudy increases the risk of hospital admission,thus leading to a systematically higherexposure rate among the hospital cases thanthe hospital controls. This in turn results insystematic distortion of the odds ratio. [fromBerkson, J., Limitations of the application offourfold table analysis to hospital data,Biometrics Bull, 2:47_53, 1946.] [Last, 1983:A Dictionary of Epidemiology]; c. Aninclination that influences judgment. The term"bias" may be used in a merely descriptiveway to mean an inclination, but more often itis used as a term of evaluation to mean aninclination that influences judgment and oughtnot to. "Prejudice" is a synonym for bias inthis pejorative sense. However, bias thatcannot be completely eliminated in the workof scientific investigators, in contrast to bias orprejudice that can and should be eliminated, isalso an important topic in research ethics. Forexample, the way disciplinary training inclinespeople to interpret the results of an experimentin terms of the established categories of thatdiscipline is a feature of research, and one thatmust be taken into account in assessingresponsible behavior in research. Sinceundertaking research requires undergoingadvanced training in a discipline, it isimpossible to eliminate all preconceptionsfrom one's interpretation of the data. Of

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course, researchers may hold disciplinarybiases and still be unbiased in other respects.For example, they may be impartial on thequestion of the truth or falsity of a particularresearch hypothesis. [OECES, 1998: OnlineEthics Glossary]; d. Any difference betweenthe true value and that actually obtained due toall causes other than sampling variability.[SRA, 1999: Glossary of Risk AnalysisTerms]; e. Any difference between the truevalue and that actually obtained due to allcauses other than sampling variability.[USDOE, 2000: RAIS Glossary]; f. Asystematic error inherent in a method orcaused by some feature of the measurementsystem. [USEPA, 1992: GL for ExposureAssessment]

Bimodal distribution - A distribution withtwo regions of high frequency separated by aregion of low frequency of observations. Atwo_peak distribution. [Last, 1983: ADictionary of Epidemiology]

Bioaccumulants - Substances that increase inconcentration in living organisms as they takein contaminated air, water, or food because thesubstances are very slowly metabolized orexcreted. (See: biological magnification.)[USEPA, 1997a: EPA Terms of Environment]

Bioaccumulation - a. In ecology, theaccumulation of toxic chemicals in livingthings through the consumption of food orwater. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]; b.Bioaccumulation is the process by whichchemicals concentrate in an organism. Forexample, DDT concentrates in fish and birdsthat eat fish. This concentration effect isexpressed as the ratio of the concentration ofthe chemical in an organism (like a fish) to itsconcentration in the surrounding medium(usually water). Bioaccumulation refers to theuptake of chemicals both from water(bioconcentration) and from ingested food andsediment. [ED, 2000: EnvironmentalScorecard Glossary]; c. The process bywhich a contaminant accumulates in thetissues of an organism. [NCSU, 1997:Watershedds Glossary]; d. The processwhereby certain toxic substances collect inliving tissues, thus posing a substantial hazardto human health or the environment. [SRA,1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary]

Bioavailability - a. The state of beingcapable of being absorbed and available tointeract with the metabolic processes of anorganism. Typically a function of chemicalproperties, physical state of the material towhich an organism is exposed, and the abilityof the individual organism to physiologically

take up the chemical. Also, the term used forthe fraction of the total chemical in theenvironmental which is available for uptake byorganisms. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist,attributed to USEPA 1992a]; b. The degreeto which a substance becomes available to thetarget tissue after administration or exposure.[IRIS, 1999: Glossary of IRIS Terms]; c. Thestate of being capable of being absorbed andavailable to interact with the metabolicprocesses of an organism. Bioavailability istypically a function of properties of agents,physical state of the material to which anorganism is exposed, and the ability of theindividual organism to physiologically take upthe agent. [REAP, 1995: Residential ExposureAssessment Project]; d. The state of beingcapable of being absorbed and available tointeract with the metabolic processes of anorganism. Bioavailability is typically afunction of chemical properties, physical stateof the material to which an organism isexposed, and the ability of the individualorganism to physiologically take up thechemical. [USEPA, 1992: GL for ExposureAssessment] [USEPA, 1992a: DermalExposure Assessment]; e. Degree of abilityto be absorbed and ready to interact inorganism metabolism. [USEPA, 1997a: EPATerms of Environment]

Bioconcentration - a. The tendency of achemical to accumulate in a living organism tolevels in excess of the concentration in itssurrounding environment. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]; b. The accumulation of achemical in tissues of a fish or other organismto levels greater than in the surroundingmedium. [USEPA, 1997a: EPA Terms ofEnvironment]

Bioconcentration factor (BCF) - provides ameasure of the extent of chemical partitioningat equilibrium between a biological mediumsuch as fish tissue or plant tissue and anexternal medium such as water. The higher theBCF, the greater the likely accumulation inliving tissue. (Source: RAGS, 1989) [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]

Biodegradation - decomposition [by livingorganisms], especially by bacterial action. Oneof the most important degradation pathwaysfor chemicals in the soil or aqueousenvironments. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]

Bioindicators - Organisms that are used todetect changes in environmental pollutantlevels. [NCSU, 1997: Watershedds Glossary]

Biological half_life (t1/2) - a. The termwhich is used for the time required for theamount of a particular substance in abiological system to be reduced to one half ofits value by biological processes when the rateof removal is approximately exponential.Substances with a long biological half_life willtend to accumulate in the body and are,therefore, particularly to be avoided.Substances with a short biological half_lifemay accumulate if some becomes tightlybound, even if most is cleared from the bodyrapidly. There is also the possibility ofcumulative effects of chemicals which have ashort residence time in the body. [Duffus,2000: Univ. Edinburgh Med School On-lineChemical Safety Glossary]; b. The timerequired for a biological system (such as ahuman or animal) to eliminate, by naturalprocesses, half the amount of a substance(such as a radioactive material) that has beenabsorbed into that system. [SRA, 1999:Glossary of Risk Analysis Terms] [USDOE,2000: RAIS Glossary] [cf. half-life]

Biomagnification (biological magnification)- a. The process by which impurities found inwater are concentrated in lower forms of lifeand reconcentrated substantially during theirmovement through the food chain. Due also touptake of food which has progressivelybioconcentrated that chemical in itsenvironment. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]; b.This is a general term applied to the sequenceof processes in an ecosystem by which higherconcentrations are attained in organisms ofhigher trophic level, i.e., of higher levels in thefood chain. The process by which xenobioticsincrease in body concentration in organismsthrough a series of prey_predator relationshipsfrom primary producers to ultimate predators,often human beings. [Duffus, 2000: Univ.Edinburgh Med School On-line ChemicalSafety Glossary]; c. An increase in theconcentration of a substance in eachprogressive link of the food chain. [NCSU,1997: Watershedds Glossary]; d. Theconcentration of certain substances up a foodchain. A very important mechanism inconcentrating pesticides and heavy metals inorganisms such as fish. [SRA, 1999: Glossaryof Risk Analysis Terms]; e. Refers to theprocess whereby certain substances such aspesticides or heavy metals move up the foodchain, work their way into rivers or lakes, andare eaten by aquatic organisms such as fish,which in turn are eaten by large birds, animalsor humans. The substances becomeconcentrated in tissues or internal organs asthey move up the chain. [USDOE, 2000:RAIS Glossary]; f. Refers to the processwhereby certain substances such as pesticidesor heavy metals move up the food chain, work

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their way into rivers or lakes, and are eaten byaquatic organisms such as fish, which in turnare eaten by large birds, animals or humans.The substances become concentrated in tissuesor internal organs as they move up the chain.(See: bioaccumulants.) [USEPA, 1997a: EPATerms of Environment]

Biological marker (biomarker) - Indicatorsof changes or events in human biologicalsystems. Biological markers of exposure referto cellular, biochemical, or molecularmeasures that are obtained from biologicalmedia such as human tissues, cells, or fluidsand are indicative of exposure toenvironmental contaminants. [NRC, 1991:Human Exp. for Airborne Pollutants]

Biological marker (biomarker) of exposure- Exogenous chemicals, their metabolites, orproducts of interactions between a xenobioticchemical and some target molecule or cell thatis measured in a compartment within anorganism. [USEPA, 1992: GL for ExposureAssessment] [USEPA, 1992a: DermalExposure Assessment] [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]

Biological measurement - a. A measurementtaken in a biological medium. For the purposeof exposure assessment via reconstruction ofdose, the measurement is usually of theconcentration of a chemical/metabolite or thestatus of a biomarker, normally with the intentof relating the measured value to the internaldose of a chemical at some time in the past.(Biological measurements are also taken forpurposes of monitoring health status andpredicting effects of exposure.) (See alsoambient measurement) [USEPA, 1992: GL forExposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment]; b. Ameasurement taken in a biological medium.For exposure assessment, it is related to themeasurement is taken to related it to theestablished internal dose of a compound.[USEPA, 1997a: EPA Terms of Environment]

Biological medium - a. One of the majorcategories of material within an organism, e.g.,blood, adipose tissue, or breath, through whichchemicals can move, be stored, or bebiologically, physically, or chemicallytransformed. (See also ambient medium,environmental medium) [USEPA, 1992: GLfor Exposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment]; b. One ofthe major component of an organism; e.g.,blood, fatty tissue, lymph nodes or breath, inwhich chemicals can be stored or transformed.(See: ambient medium, environmentalmedium.) [USEPA, 1997a: EPA Terms ofEnvironment]

Biological monitoring (biomonitoring) - a.Measuring chemicals in biological materials(blood, urine, breath, etc.) to determinewhether chemical exposure in humans,animals, or plants has occurred. [ATSDR,1999: Online Glossary] [New YorkDepartment of Health, 1999: Glossary ofEnvironmental Health Terms]; b. This is aprocedure of periodic examination ofbiological specimens for the purposes ofmonitoring). It is usually applied to exposuremonitoring but can also apply to effectmonitoring. Analysis of the amounts ofpotentially toxic substances or theirmetabolites present in body tissues and fluids,as a means of assessing exposure to thesesubstances and aiding timely action to preventadverse effects. The term is also used to meanassessment of the biological status ofpopulations and communities of organisms atrisk, in order to protect them and to have earlywarning of possible hazards to human health.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary]; c. Amethod of assessing the absorption ofchemicals by measuring the parent compoundor its metabolites in body fluids, usually blood,urine or exhaled breath. Woollen (1993)refined this term in the context of pesticidesand assessment of absorbed dose for riskassessment: Measurement of a pesticide or itsmetabolites in the body fluids of exposedpersons and conversion to an equivalentabsorbed dose of the pesticide based on aknowledge of its human metabolism andpharmacokinetics. [OECD, 1997: OccupationalExposure to Pesticides]; d. 1. The use ofliving organisms to test the suitability ofeffluents for discharge into receiving watersand to test the quality of such watersdownstream from the discharge. 2. Analysis ofblood, urine, tissues, etc., to measure chemicalexposure in humans. [USEPA, 1997a: EPATerms of Environment]

Biological stressor - a. As used in this report,synonymous with non-indigenous species - aspecies introduced (intentionally orunintentionally) beyond its natural range ornatural zone of potential dispersal. Biologicalstressors may also include geneticallyengineered organisms. [CENR, 1999: Ecoriskin the Federal Government]; b. [biologicalstressors] Organisms accidently orintentionally dropped into habitats in whichthey do not evolve naturally; e.g. gypsy moths,Dutch elm disease, certain types of algae, andbacteria. [USEPA, 1997a: EPA Terms ofEnvironment]

Biological uptake - The transfer of hazardoussubstances from the environment to plants,animals, and humans. This may be evaluated

through environmental measurements, such asmeasurement of the amount of the substance inan organ known to be susceptible to thatsubstance. More commonly, biological dosemeasurements are used to determine whetherexposure has occurred. The presence of acontaminant, or its metabolite, in humanbiologic specimens, such as blood, hair, orurine, is used to confirm exposure and can bean independent variable in evaluating therelationship between the exposure and anyobserved adverse health effects. [ATSDR,1999: Online Glossary]

Biologically Based Dose Response (BBDR)model - A predictive tool used to estimatepotential human health risks by describing andquantifying the key steps in the cellular, tissueand organismal responses as a result ofchemical exposure. [IRIS, 1999: Glossary ofIRIS Terms]

Biologically effective dose - a. The amountof the deposited or absorbed contaminant thatreaches the cells or target site where anadverse effect occurs or where an interactionof that contaminant with a membrane surfaceoccurs. [NRC, 1991: Human Exp. for AirbornePollutants]; b. The amount of a deposited orabsorbed chemical that reaches the cells ortarget site where an adverse effect occurs, orwhere that chemical interacts with a membranesurface. [USEPA, 1992: GL for ExposureAssessment] [REAP, 1995: ResidentialExposure Assessment Project] [USEPA,1997a: EPA Terms of Environment]

Biomarker - see biological marker

Biomonitoring - see biological monitoring

Biosensor - Analytical device comprising abiological recognition element (e.g., enzyme,receptor, DNA, antibody, or microorganism)in intimate contact with an electrochemical,optical, thermal, or acoustic signal transducerthat together permit analyses of chemicalproperties or quantities. Shows potentialdevelopment in some areas, includingenvironmental monitoring. [USEPA, 1997a:EPA Terms of Environment]

Biotransformation - a. The transformationof chemical compounds within a livingsystem. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]; b. Inthis process, a chemical is modified by a livingorganism in contrast to abiotic processesreferred to earlier. The enzyme_mediatedtransformation of xenobiotics, frequentlyinvolving phase 1 and phase 2 reactions.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary]; c.Conversion of a substance into other

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compounds by organisms; includesbiodegradation. [USEPA, 1997a: EPA Termsof Environment]

Body burden - a. The amount of a particularchemical stored in the body at a particulartime, especially a potentially toxic chemical inthe body as a result of exposure. [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]; b. The total amount ofa chemical in the body. Some chemicals buildup in the body because they are stored in fat orbone or are eliminated very slowly. [ATSDR,1999: Online Glossary]; c. The total amountof a chemical in the body. Some chemicalsbuild up in the body because they are stored inbody organs like fat or bone or are eliminatedvery slowly. [New York Department ofHealth, 1999: Glossary of EnvironmentalHealth Terms]; d. The amount of a substancestored in the body a particular time, in thebody as a result of exposure. Body burdenscan be the result of long term or short termstorage, for example, the amount of metal inbone, the amount of a lipophilic substancesuch as PCB is adipose tissue, or the amountof carbon monoxide (as carboxyhemoglobin)in the blood. [REAP, 1995: ResidentialExposure Assessment Project]; e. The totalamount of a specific substance (for example,lead) in an organism, including the amountstored, the amount that is mobile, and theamount absorbed. [SRA, 1999: Glossary ofRisk Analysis Terms] [USDOE, 2000: RAISGlossary]; f. The amount of a particularchemical stored in the body at a particulartime, especially a potentially toxic chemical inthe body as a result of exposure. Bodyburdens can be the result of long-term or short-term storage, for example, the amount of ametal in bone, the amount of a lipophilicsubstance such as PCB in adipose tissue, or theamount of carbon monoxide (ascarboxyhemoglobin) in the blood. [USEPA,1992: GL for Exposure Assessment] [USEPA,1992a: Dermal Exposure Assessment]; g.The amount of a chemical stored in the body ata given time, especially a potential toxin in thebody as the result of exposure. [USEPA,1997a: EPA Terms of Environment]

Bounding estimate - An estimate of exposure,dose, or risk that is higher than that incurredby the person in the population with thehighest exposure, dose, or risk. Boundingestimates are useful in developing statementsthat exposures, doses, or risks are "not greaterthan" the estimated value. [USEPA, 1992: GLfor Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project][USEPA, 1997a: EPA Terms of Environment]

Breathing zone - a. The area around the noseand mouth from which air is inhaled. [OECD,

1997: Occupational Exposure to Pesticides];b. A zone of air in the vicinity of an organismfrom which respired air is drawn. Personalmonitors are often used to measure pollutantsin the breathing zone. [USEPA, 1992: GL forExposure Assessment]; c. Area of air inwhich an organism inhales. [USEPA, 1997a:EPA Terms of Environment]

Characterization of exposure - a. A portionof the analysis phase of ecological riskassessment that evaluates the interaction of thestressor with one or more ecological entities.Exposure can be expressed as co-occurrence orcontact, depending on the stressor andecological component involved. [CENR, 1999:Ecorisk in the Federal Government]; b. Aportion of the analysis phase of ecological riskassessment that evaluates the interaction of thestressor with one or more ecological entities.Exposure can be expressed as co-occurrence orcontact, depending on the stressor andecological component involved. [USEPA,1998a: Guidelines for Ecological RiskAssessment]; c. Portion of an ecological riskassessment that evaluates interaction of astressor with one or more ecological entities.[USEPA, 1997a: EPA Terms of Environment]

Chemical stressors - Chemicals released tothe environment through industrial waste, autoemissions, pesticides, and other human activitythat can cause illnesses and even death inplants and animals. [USEPA, 1997a: EPATerms of Environment]

Chronic - a. Occurring over a long period oftime (more than 1 year). [ATSDR, 1999:Online Glossary]; b. Occurring over a longperiod of time, several weeks, months or years.[New York Department of Health, 1999:Glossary of Environmental Health Terms]; c.Having a persistent, recurring or long_termnature. As distinguished from acute. [SRA,1999: Glossary of Risk Analysis Terms]; d.A toxic effect that occurs only after exposureto a material for a long time, usually months oryears. The amount of exposure is usually verylow, and often symptoms are not immediatelynoticeable. [University of Kentucky, 1999:Glossary of Safety Terms]; e. Having apersistent, recurring or long_term nature. Asdistinguished from acute. [USDOE, 2000:RAIS Glossary]; f. A disease or conditionthat has been present for several weeks orlonger. [WSU, 1999: Definitions andAbbreviations of Veterinary Terms]

Chronic daily intake - see intake, chronicdaily. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]

Chronic exposure - a. Long_term exposure,usually lasting one year to a lifetime. [CARB,

2000: Glossary of Air Pollution Terms]; b.Multiple exposures occurring over an extendedperiod of time, or a significant fraction of theanimal's or the individual's lifetime. [IRIS,1999: Glossary of IRIS Terms]; c. A long-term exposure to a chemical for a period ofone year or more in animals and more thanseven years in humans. [OFA, 2000: OxyfuelsGlossary]; d. A persistent, recurring, or long-term exposure, as distinguished from acute.Chronic exposure may result in health effects(such as cancer) that are delayed in onset,occurring long after exposure has ceased.[REAP, 1995: Residential ExposureAssessment Project]; e. Multiple exposuresoccurring over an extended period of time, or asignificant fraction of the animal's or theindividual's life_time. [USDOE, 2000: RAISGlossary]; f. Long_term exposure usuallylasting 6 months to a lifetime. [USEPA, 1995:Benchmark Dose]; g. Multiple exposuresoccurring over an extended period of time orover a significant fraction of an animal's orhuman's lifetime (Usually seven years to alifetime.) [USEPA, 1997a: EPA Terms ofEnvironment]; h. Exposure to the poisonoccurs over a period of weeks, months, oryears; onset of signs may be sudden anddramatic, or can be insidious like a slow lossin body condition or reduced productivity.[WSU, 1999: Definitions and Abbreviations ofVeterinary Terms]

Chronic intake - The long term period overwhich a substance crosses the outer boundaryof an organism without passing an absorptionbarrier. [USEPA, 1997b: Exposure FactorsHandbook]

Climate model - A quantitative way ofrepresenting the interactions of theatmosphere, oceans, land surface, and ice.Models can range from relatively simple toquite comprehensive. Also see GeneralCirculation Model. [USEPA, 2000: GlobalWarming Glossary]

Climate modeling - The simulation of theclimate using computer_based models. Alsosee General Circulation Model. [USEPA,2000: Global Warming Glossary]

Coefficient of variation - The ratio of thestandard deviation to the mean. This ismeaningful only if the variable is measured ona ratio scale. [Last, 1983: A Dictionary ofEpidemiology]

Collective dose - a. The sum of the totaleffective dose equivalent values for allindividuals in a specified population.Collective dose is expressed in units of person-rem (or person-sievert). [USDOE, 1998:Radiological Control Manual]; b. The sum

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of the individual doses received on a givenperiod of time by a specified population fromexposure to a specified source of radiation.[USDOE, 2000: RAIS Glossary]

Composite sample - a. A sample of water,soil or other medium which is made bycombining samples from two or morelocations. [New York Department of Health,1999: Glossary of Environmental HealthTerms]; b. A series of water samples takenover a given period of time and weighted byflow rate. Or a soil sample that consists of soiltaken from various depths or various locations.[USDOE, 2000: RAIS Glossary]; c. A seriesof water samples taken over a given period oftime and weighted by flow rate. [USEPA,1997a: EPA Terms of Environment]

Concentration - a. The amount of onesubstance dissolved or contained in a givenamount of another. For example, sea watercontains a higher concentration of salt thanfresh water. [ATSDR, 1999: Online Glossary][New York Department of Health, 1999:Glossary of Environmental Health Terms]; b.The amount of material in the air, eg., 50 partsper million. May also refer too the amount of asubstance in a mixture, eg., 10% ammonia inwater. [University of Kentucky, 1999:Glossary of Safety Terms]; c. The relativeamount of a substance mixed with anothersubstance. An example is five ppm of carbonmonoxide in air or 1 mg/l of iron in water.[USEPA, 1997a: EPA Terms of Environment];d. Amount of agent per unit volume[Zartarian, et al., 1997: Quant. Def. of Exp. &Related Concepts]

Concentration_effect curve - This is a graphproduced to show the relationship between theexposure concentration of a drug or xenobioticand the magnitude of graded effect that itproduces. [Duffus, 2000: Univ. EdinburghMed School On-line Chemical SafetyGlossary]

Concentration ratio - The ratio of theconcentration of a compound or radionuclidein an organism or its tissues to theconcentration in the surrounding underequilibrium, or steady_state conditions. [SRA,1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary]

Concentration_response curve- This is agraph produced to show the relation betweenthe exposure concentration of a drug orxenobiotic and the degree of response itproduces, as measured by the percentage of theexposed population showing a defined, oftenquantal, effect. If the effect determined isdeath, the curve may be used to estimate anLC50 value. [Duffus, 2000: Univ. Edinburgh

Med School On-line Chemical SafetyGlossary]

Conceptual model - a. The conceptual modeldescribes a series of working hypotheses ofhow the stressor might affect ecologicalentities. The conceptual model also describesthe ecosystem potentially at risk, therelationship between measures of effect andassessment endpoints, and exposure scenarios.[CENR, 1999: Ecorisk in the FederalGovernment]; b. A diagram or writtendescription of the predicted key relationshipsbetween the stressor(s) and the assessmentendpoint(s) for a risk assessment. [USEPA,1997: Guidance on Cumulative RiskAssessment, Planning and Scoping]; c. Aconceptual model in problem formulation is awritten description and visual representation ofpredicted relationships between ecologicalentities and the stressors to which they may beexposed. [USEPA, 1998a: Guidelines forEcological Risk Assessment]

Confidence interval - a. A range of valueswhich bracket a point estimate; e.g., there is a95% probability that the true value is containedin the 95% confidence interval. [AIHA, 2000:Risk Assessment Principles for the IndustrialHygienist]; b. A range of values (a1 < a < a2)determined from a sample of definite rules sochosen that, in repeated random samples fromthe hypothesized population, an arbitrarilyfixed proportion of that range will include thetrue value, x, of an estimated parameter. Thelimits, a1 and a2, are called confidence limits;the relative frequency with which these limitsinclude a is called the confidence coefficient;and the complementary probability is calledthe confidence level. As with significancelevels, confidence levels are commonly chosenas 0.05 or 0.01, the corresponding confidencecoefficients being 0.95 or 0.99. Confidenceintervals should not be interpreted as implyingthat the parameter itself has a range of values;it has only one value, a. On the other hand, theconfidence limits (a1, a2) being derived from asample, are random variables, the values ofwhich on a particular sample either do or donot include the true value a of the parameter.However, in repeated samples, a certainproportion of these intervals will include aprovided that the actual population satisfied theinitial hypothesis. [SRA, 1999: Glossary ofRisk Analysis Terms] [USDOE, 2000: RAISGlossary]

Confidence limit - A confidence interval for aparameter is a range of values that has aspecified probability (e.g., 95 percent) ofcontaining the parameter. The confidence limitrefers to the upper or lower value of the range(e.g., upper confidence limit). [USEPA, 1995:Benchmark Dose]

Contact boundary - a surface in spacecontaining at least one exposure point on thetarget of interest [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Contact boundary element - Surface elementof a contact boundary [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Contact, direct - see direct contact

Contact, indirect - see indirect contact

Contact rate - a. Amount of medium (water,soil) contacted per unit of time or event.(Source: RAGS, 1989) [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]; b. The rate at which susceptiblesmeet infecteds. Usually measured asindividuals per unit time. [Swinton, 1999: ADictionary of Epidemiology]

Contact zone - a volume adjoining a contactboundary in which agent has a high probabilityof contacting the contact boundary in the timeinterval of interest [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Contact zone element - Volume element thatcontains only one type of carrier medium (e.g.,air, liquid, soil, particles) and is contained in acontact zone [Zartarian, et al., 1997: Quant.Def. of Exp. & Related Concepts]

Contact zone thickness - The distance (fromthe contact boundary) in which a particle ofagent has at least a pre-specified probability pof intersecting the contact boundary within apre-specified time interval t [Zartarian, et al.,1997: Quant. Def. of Exp. & RelatedConcepts]

Continuous sample - a. A flow of water froma particular place in a plant to the locationwhere samples are collected for testing; maybe used to obtain grab or composite samples.[USDOE, 2000: RAIS Glossary]; b. A flowof water, waste or other material from aparticular place in a plant to the location wheresamples are collected for testing. May be usedto obtain grab or composite samples.[USEPA, 1997a: EPA Terms of Environment]

Continuous time model - A model in whichthe system changes continuously over time.Derivatives (e.g. dY/dt) are the mathematicalformalism for describing such continuouschange. The differential equation whichembodies a model provides the values of thesederivatives at any particular time point;calculus or a computer can then be used tomove the state of the model forwards in time.Continuous models have the advantage over

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discrete time models in that they are moreamenable to algebraic manipulation, althoughthey are slightly harder to implement on acomputer. The same as a differential equationmodel. [Swinton, 1999: A Dictionary ofEpidemiology]

Correlation - relationship that results when achange in one variable is consistentlyassociated with a change in another one[EDVCB, 2000: Environmental EconomicsGlossary]

Correlation coefficient - A measure ofassociation that indicates the degree to whichtwo or more sets of observations fit a linearrelationship. This coefficient, represented bythe letter r, can vary between + 1 and _1. If r =+ 1, there is a perfect linear relationship inwhich one variable varies directly with theother. If r = _1, there is again a perfect linearassociation, but one variable varies inverselywith the other. [Last, 1983: A Dictionary ofEpidemiology]

Cumulative distribution function (CDF) -Cumulative distribution functions areparticularly useful for describing thelikelihood that a variable will fall withindifferent ranges of x. F(x) (i.e., the value of yat x in a CDF plot) is the probability that avariable will have a value less than or equal tox . Note: the original has a sample CDF plotthat is not reproduced here. [USEPA, 1998a:Guidelines for Ecological Risk Assessment]

Cumulative dose - The total dose resultingfrom repeated exposures of ionizing radiationto an occupationally exposed worker to thesame portion of the body, or to the wholebody, over a period of time (see 10 CFR20.1003). [USDOE, 2000: RAIS Glossary]

Cumulative exposure - The sum ofexposures of an organism to a pollutant over aperiod of time. [USEPA, 1997a: EPA Termsof Environment]

Cutaneous - Of, relating to, or affecting theskin. [USEPA, 1992a: Dermal ExposureAssessment]

Delivered dose - The amount of a chemicalavailable for interaction by any particularorgan or cell (U.S. EPA, 1992). [USEPA,1998: Postapp. Exposure Test GL.]

Demography - a. The study of populations,especially with reference to size and density,fertility, mortality, growth, age distribution,migration, and VITAL STATISTICS, and theinteraction of all these with social andeconomic conditions. [Last, 1983: ADictionary of Epidemiology]; b. The rate of

growth and the age structure of populations,and the processes that determine theseproperties. [WRI, 1992: Biodiversity Glossaryof Terms]

Dermal - Referring to the skin. Dermalabsorption means absorption through the skin.[ATSDR, 1999: Online Glossary] [ED, 2000:Environmental Scorecard Glossary] [NewYork Department of Health, 1999: Glossary ofEnvironmental Health Terms]

Dermal absorption (dermal penetration) - a.The transfer of contaminant across the skin,and subsequent incorporation into the body.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; b. Movement of apesticide into and through the skin; includesthat taken up into the systemic circulation andthat retained in the skin compartment. [OECD,1997: Occupational Exposure to Pesticides];c. Process by which a chemical penetrates theskin and enters the body as an internal dose.[USEPA, 1997a: EPA Terms of Environment]

Dermal adherence capacity - The maximumamount of a specified matrix that can becontained on the skin. [USEPA, 1992a: DermalExposure Assessment]Dermal adsorption - The process by whichmaterials come in contact with the skinsurface, but are then retained and adhered tothe permeability barrier without being takeninto the body. [USEPA, 1992a: DermalExposure Assessment]

Dermal exposure - a. Contact with the skinby any medium containing chemicals,quantified as the amount on the skin andavailable for adsorption and possibleabsorption. [USEPA, 1992a: Dermal ExposureAssessment]; b. Contact between a chemicaland the skin. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAISGlossary]; c. This term refers to aquantifiable measure of the amount of residuedeposited on skin; normally expressed as adensity, or mass per unit time, deposited on adefined skin surface area (e.g., mg/hr handexposure); equivalent to potential dose for thedermal route. [USEPA, 1998: Postapp.Exposure Test GL.]

Dermally absorbed dose - The amount of theapplied material (the dose) which becomesabsorbed into the body. [USEPA, 1992a:Dermal Exposure Assessment]

Deterministic analysis - Calculation andexpression of health risks as single numericalvalues or "single point" estimates of risk. Inrisk assessments, the uncertainty andvariability are discussed in a qualitativemanner. [USEPA, 1999: Superfund Risk

Assessment Glossary]

Deterministic model - A mathematical modelin which the parameters and variables are notsubject to random fluctuations, so that thesystem is at any time entirely defined by theinitial conditions chosen. Contrast with astochastic model. [Swinton, 1999: ADictionary of Epidemiology]

Diary study - Survey in which individuals areasked to record food intake activities, or otherfactors in a diary which is later used toevaluate exposure factors associated withspecific populations. [USEPA, 1997b:Exposure Factors Handbook]

Direct contact - A mode of transmission ofinfection between an infected host andsusceptible host. Direct contact occurs whenskin or mucous surfaces touch, as in shakinghands, kissing, and sexual intercourse. [Last,1983: A Dictionary of Epidemiology]

Direct exposure - Exposure to a subject whocomes into contact with an agent via themedium in which it was initially released tothe environment. Examples include exposuresmediated by cosmetics, other consumerproducts, some food and beverage additives,medical devices, over-the-counter drugs, andsingle-medium environmental exposures.[REAP, 1995: Residential ExposureAssessment Project]

Dislodgeable residue - a. Residue of anapplied pesticide that may be removed from atreated or untreated surface by solvent rinse.[OECD, 1997: Occupational Exposure toPesticides]; b. The amount of chemicalresidues deposited onto the leaf surface thathave not been absorbed into the leaf ordissipated from the surface, and that can bedislodged by shaking leaf samples in adetergent solution ( g/cm2). [USEPA, 1998:Postapp. Exposure Test GL.]

Dispersion model - See air quality simulationmodel above. [CARB, 2000: Glossary of AirPollution Terms]

Distribution - a. This is a general term for thedispersal of a xenobiotic and its derivativesthroughout an organism or environmentalsystem. [Duffus, 2000: Univ. Edinburgh MedSchool On-line Chemical Safety Glossary];b. The complete summary of the frequenciesof the values or categories of a measurementmade on a group of persons. The distributiontells either how many or what proportion ofthe group were found to have each value (oreach range of values) out of all the possiblevalues that the quantitative measure can have.[Last, 1983: A Dictionary of Epidemiology];

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c. The pattern by which parasite numbers arepartitioned amongst available hosts. If thefraction of the population who have i parasitesis p(i) then the distribution is the set ofnumbers p(0),p(1), p(2), ... . Summarystatistics of this distribution include prevalence(1_p(0)) and mean intensity ( p(1)+ 2p(2)+3p(3)+...). Useful distributions include thePoisson and negative binomial. [Swinton,1999: A Dictionary of Epidemiology]; d. Aset of values derived from a specificpopulation or set of measurements thatrepresents the range and array of data for thefactor being studied. [USEPA, 1997b:Exposure Factors Handbook]

Distribution_free method - (Syn:nonparametric method) A method of testing ahypothesis or of setting up a confidenceinterval that does not depend on the form ofthe underlying distribution; in particular, itdoes not depend upon the variable following anormal distribution. [Last, 1983: A Dictionaryof Epidemiology]

Domestic waste - see household waste

Dosage - see dose rate

Dose - a. (1) absorbed: amount of asubstance penetrating the exchange boundariesof an organism after contact. Calculated fromintake and absorption efficiency, andexpressed as mg/kg-day. (2) administered:mass of a substance given to an organism andin contact with an exchange boundary,expressed as mg/kg-day. (3) applied: amountof a substance given to an organism, especiallythrough dermal contact. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist, attributed to USEPA RAGS, 1989];b. The amount of substance to which a personis exposed. Dose often takes body weight intoaccount. [ATSDR, 1999: Online Glossary]; c.The amount of a pollutant that is absorbed. Alevel of exposure which is a function of apollutant's concentration, the length of time asubject is exposed, and the amount of thepollutant that is absorbed. The concentrationof the pollutant and the length of time that thesubject is exposed to that pollutant determinedose. [CARB, 2000: Glossary of Air PollutionTerms]; d. (1) pharmacology. A quantity tobe administered at one time, such as aspecified amount of medication. (2)radiobiology. A general term denoting thequantity of radiation or energy absorbed. Forspecial purposes it must be appropriatelyqualified. If unqualified, it refers to absorbeddose. Unit of absorbed dose is the rad. The SIunit is the gray (1 Gy = 1 J kg_1 = 100 R).Origin: Gr. Dosis = a giving [Graham, 1998:The On Line Medical Dictionary]; e. Theamount of substance to which a person is

exposed. Dose often takes body weight intoaccount. For example, to receive equivalentdoses of medicine, children are given smalleramounts than adults. [New York Departmentof Health, 1999: Glossary of EnvironmentalHealth Terms]; f. The amount of acontaminant that is absorbed or deposited inthe body of an exposed organism for anincrement of time—usually from a singlemedium. Total dose is the sum of dosesreceived by a person from a contaminant in agiven interval resulting from interaction withall environmental media that contain thecontaminant. Units of dose and total dose(mass) are often converted to units of mass pervolume of physiological fluid or mass oftissue. [NRC, 1991: Human Exp. for AirbornePollutants]; g. The amount of a pesticidesystemically available. [OECD, 1997:Occupational Exposure to Pesticides]; h. Theamount of substance available for interactionwith metabolic processes or biologicallysignificant receptors after crossing the outerboundary of an organism (see potential dose,applied dose, and internal dose definitions).The amount of the agent available forinteraction by any particular organ or cell istermed the delivered dose for that organ orcell. [REAP, 1995: Residential ExposureAssessment Project]; i. The amount orconcentration of undesired matter or energydeposited at the site of effect. See alsoabsorbed dose. [SRA, 1999: Glossary of RiskAnalysis Terms]; j. The amount of asubstance that enters the body. The amountdepends on the rate at which the substanceenters the body and the length of time thesubstance continues to enter the body, eg., aworker may inhale 10 milligrams of dust perday for 10 days. The total dose is 100milligrams. Not all of the substance mayremain in the body; some is eliminated,possibly as fast as it enters. [University ofKentucky, 1999: Glossary of Safety Terms];k. The amount of energy deposited in bodytissue due to radiation exposure. Varioustechnical terms, such as dose equivalent,effective dose equivalent and collective dose,are used to evaluate the amount of radiation anexposed worker receives. These terms are usedto describe the differing interactions ofradiation with tissue as well as to assist in themanagement of personnel exposure toradiation. Some types of radiation, such asneutron and alpha, deposit their energy moredensely in affected tissue than gammaradiation and thereby causing more damage totissue. The term dose equivalent, measured inunits of rem, is used to take into account thisdifference in tissue damage. Therefore 1 remfrom gamma radiation causes damageequivalent to 1 rem from alpha radiation.However, it takes one-twentieth as muchenergy from alpha radiation, as compared with

gamma radiation, to produce this 1 rem doseequivalent. Definitions for dose termsnecessary for various exposure calculationsand recordkeeping purposes include thefollowing: [USDOE, 1998: RadiologicalControl Manual]; l. The absorbed dose,given in rads (or the international system ofunits, grays), that represents the energyabsorbed from the radiation in a gram of anymaterial. Furthermore, the biological dose ordose equivalent, given in rem or sieverts, is ameasure of the biological damage to livingtissue from the radiation exposure. [USDOE,2000: RAIS Glossary]; m. The amount of asubstance available for interaction withmetabolic processes or biologically significantreceptors after crossing the outer boundary ofan organism. The potential dose is the amountingested, inhaled, or applied to the skin. Theapplied dose is the amount of a substancepresented to an absorption barrier andavailable for absorption (although notnecessarily having yet crossed the outerboundary of the organism). The absorbeddose is the amount crossing a specificabsorption barrier (e.g., the exchangeboundaries of skin, lung, and digestive tract)through uptake processes. Internal dose is amore general term denoting the amountabsorbed without respect to specific absorptionbarriers or exchange boundaries. The amountof the chemical available for interaction byany particular organ or cell is termed thedelivered dose for that organ or cell.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1997b: Exposure FactorsHandbook]; n. The amount of a substanceavailable for interaction with metabolicprocesses after crossing the outer boundary ofan organism. The applied dose is the amountof a substance presented to an absorptionbarrier and available for absorption (althoughnot necessarily having yet crossed the outerboundary of the organism). The internal doseis the amount crossing an absorption barrier(e.g., the exchange boundaries of skin, lung,and digestive tract) through uptake processes.The amount of the chemical available forinteraction by any particular organ or cell istermed the delivered dose for that organ orcell. [USEPA, 1992a: Dermal ExposureAssessment]; o. (1) The actual quantity of achemical administered to an organism or towhich it is exposed. (2) The amount of asubstance that reaches a specific tissue (e.g.,the liver). (3) The amount of a substanceavailable for interaction with metabolicprocesses after crossing the outer boundary ofan organism. [USEPA, 1997a: EPA Terms ofEnvironment]; p. A term referringgenerically to the amount of chemical to whichan organism is exposed by any of severalroutes. Specifying the routes within theenvironmental context and especially the point

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of measurement is made possible viasubcategories of dose (see Potential Dose,Applied Dose, Absorbed Dose, Internal Dose,and Delivered Dose). Dose is normallyexpressed as a mass per unit body weight perunit time and is frequently expressed in unitsof mg/kg/day. [USEPA, 1998: Postapp.Exposure Test GL.]; q. The amount of agentthat enters the target over a specified timeinterval by crossing a contact boundary[Zartarian, et al., 1997: Quant. Def. of Exp. &Related Concepts]

Dose adjustment - Modification of doses usedin animal experimentation to equivalent levelsfor human beings. The usual method is tocalculate the ratio of body weights raised tosome power, which is roughly equivalent tothe ratio of surface areas; a simple ratio ofbody weights has also been used. [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]

Dose assessment - Process of determiningradiological dose and uncertainty included inthe dose estimate, through the use of exposurescenarios, bioassay results, monitoring data,source term information and pathway analysis.[USDOE, 1998: Radiological Control Manual]

Dose_effect - The relationship between dose(usually an estimate of dose) and the gradationof the effect in a population, that is abiological change measured on a graded scaleof severity, although at other times one mayonly be able to describe a qualitative effectthat occurs within some range of exposurelevels. [SRA, 1999: Glossary of Risk AnalysisTerms] [USDOE, 2000: RAIS Glossary]

Dose_effect curve - This is a graph drawn toshow the relationship between the dose of adrug or xenobiotic and the magnitude of thegraded effect that it produces. [Duffus, 2000:Univ. Edinburgh Med School On-lineChemical Safety Glossary]

Dose equivalent - a. The product of theabsorbed dose from ionizing radiation andsuch factors as account for differences inbiological effectiveness due to the type ofradiation and its distribution in the body asspecified by the International Commission onRadiological Units and Measurements (ICRU).[SRA, 1999: Glossary of Risk AnalysisTerms] [USDOE, 2000: RAIS Glossary]; b.The product of the absorbed dose (D) (in rador gray) in tissue, a quality factor (Q), and allother modifying factors (N). Dose equivalentis expressed in units of rem (or sievert) (1 rem= 0.01 sievert). [USDOE, 1998: RadiologicalControl Manual]; c. The product of theabsorbed dose from ionizing radiation andsuch factors as account for biological

differences due to the type of radiation and itsdistribution in the body in the body. [USEPA,1997a: EPA Terms of Environment]

Dose membrane - A barrier which offersresistance to flow of the agent after it crosses acontact boundary [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Dose rate - a. Dose per unit time, for examplein mg/day, sometimes also called dosage.Dose rates are often expressed on a per-unit-body-weight basis, yielding units such asmg/kg/day (mg/kg-day). They are also oftenexpressed as averages over some time period,for example a lifetime. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project]; b.In exposure assessment, dose per time unit(e.g., mg/day), sometimes also called dosage.[USEPA, 1997a: EPA Terms of Environment];c. The rate at which the agent passes through aunit area of the contact boundary [Zartarian, etal., 1997: Quant. Def. of Exp. & RelatedConcepts]

Dose_response - a. The relationship betweenthe dose of a pollutant and the response (oreffect) it produces on a biological system.[CARB, 2000: Glossary of Air PollutionTerms]; b. The relationship between the doseof a pollutant and its effect on a biologicalsystem [ODEQ, 1999: Air Quality Glossary];c. A dose response is a mathematical modelthat describes how a response variable__abiological measurement or epidemiologicpopulation statistic__depends on the level ofradiation dose. The dose_reponse model tellswhether the level of response increases ordecreases with dose and how rapidly it changesas a function of dose. [RERF, 1999: RadiationEffects Research Foundation Glossary]; d. Acorrelation between a quantified exposure(dose) and the proportion of a population thatdemonstrates a specific effect (response).[SRA, 1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary]; e. Shifts intoxicological responses of an individual (suchas alterations in severity) or populations (suchas alterations in incidence) that are related tochanges in the dose of any given substance.[USEPA, 1997a: EPA Terms of Environment]

Dose_response assessment - a. The amountof a chemical that an organism (such as aperson) is exposed to is called the dose, and theseverity of the effect of that exposure is calledthe response. A dose_response assessment is ascientific study to determine the relationshipbetween dose and response, and how muchdose is correlated with how much response.[ED, 2000: Environmental ScorecardGlossary]; b. A determination of the

relationship between the magnitude of anadministered, applied, or internal dose and aspecific biological response. Response can beexpressed as measured or observed incidence,percent response in groups of subjects (orpopulations), or as the probability ofoccurrence within a population. [IRIS, 1999:Glossary of IRIS Terms]; c. The process ofcharacterizing the relation between the dose ofan agent administered or received and theincidence of an adverse health effect inexposed populations and estimating theincidence of the effect as a function of humanexposure to the agent. It takes account ofintensity of exposure, age pattern of exposure,and possibly other variables that might affectresponse, such as sex, lifestyle, and othermodifying factors. A dose_responseassessment usually requires extrapolation fromhigh to low dose and extrapolation fromanimals to humans. A dose_responseassessment should describe and justify themethods of extrapolation used to predictincidence and should characterize thestatistical and biologic uncertainties in thesemethods. [NRC 1983: Risk Assessment in theFederal Government]; d. The second step inthe assessment of risks to humans frompotentially toxic agents, in which therelationship between the dose levels to whichanimals or humans are exposed and the health-effect responses at each dose level arecharacterized quantitatively. Often the close-response assessment is based on high-doseexperimental animal studies and applied tohumans who are exposed at much lower doses.(See risk assessment.) [OFA, 2000: OxyfuelsGlossary]; e. The process of characterizingthe relation between the dose of an agentadministered or received and the incidence ofan adverse health effect in exposedpopulations and estimating the incidence of theeffect as a function of human exposure to theagent. [SRA, 1999: Glossary of Risk AnalysisTerms] [USDOE, 2000: RAIS Glossary]; f.The determination of the relationship betweenthe magnitude of administered, applied, orinternal dose and a specific biologicalresponse. Response can be expressed asmeasured or observed incidence, percentresponse in groups of subjects (orpopulations), or the probability of occurrenceof a response in a population. [USEPA, 1992:GL for Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project]; g.The determination of the relationship betweenthe magnitude of administered, applied, orinternal dose and the probability of occurrenceof the health effects in question. [USEPA,1992a: Dermal Exposure Assessment]; h.(1) Estimating the potency of a chemical. (2)In exposure assessment, the process ofdetermining the relationship between the doseof a stressor and a specific biological response.

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(3) Evaluating the quantitative relationshipbetween dose and toxicological responses.[USEPA, 1997a: EPA Terms of Environment]

Dose-response curve - a. A mathematicalrelationship between the dose administered orreceived and the incidence of adverse healtheffects in the exposed population; toxicityvalues are derived from this relationship.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; b. This is a graphto show the relation between the dose of adrug or xenobiotic and the degree of responseit produces, as measured by the percentage ofthe exposed population showing a defined,often quantal, effect. If the effect determined isdeath, such a curve may be used to estimate anLD50 value. [Duffus, 2000: Univ. EdinburghMed School On-line Chemical SafetyGlossary]; c. A graphical representation ofthe quantitative relationship between potential,applied or internal dose of an agent, and aspecific biological response to that agent.[REAP, 1995: Residential ExposureAssessment Project]; d. A graphicalrepresentation of the quantitative relationshipbetween administered, applied, or internaldose of a chemical or agent, and a specificbiological response to that chemical or agent.[USEPA, 1992: GL for Exposure Assessment];e. A quantitative relationship betweenadministered, applied, or internal dose andprobability of occurrence of a health effect oreffects. Results are usually expressed in unitsof incidence per unit dose. [USEPA, 1992a:Dermal Exposure Assessment]; f. Graphicalrepresentation of the relationship between thedose of a stressor and the biological responsethereto. [USEPA, 1997a: EPA Terms ofEnvironment]

Dose response, linear - A linear doseresponse is a relationship between dose andbiological response that is a straight line. Inother words, the rate of change (slope) in theresponse is the same at any dose. A linear doseresponse is written mathematically as follows:if Y represents the expected, or averageresponse and D represents dose, then Y = aDwhere a is the slope, also called the linearcoefficient. [RERF, 1999: Radiation EffectsResearch Foundation Glossary]

Dose response, linear_quadratic - Alinear_quadratic dose response is arelationship between dose and biologicalresponse that is curved. This implies that therate of change in response is different atdifferent doses. The response may changeslowly at low doses, for example, but rapidlyat high doses. A linear_quadratic doseresponse is written mathematically as follows:if Y represents the expected, or averageresponse and D represents dose, then Y = aD +

bD2 where a is the linear coefficient (or slope)and b is the quadratic coefficient (orcurvature). [RERF, 1999: Radiation EffectsResearch Foundation Glossary]

Dose_response relationship - a. Arelationship in which a change in amount,intensity duration of exposure is associatedwith a change—either an increase or adecrease—in risk of a specified outcome.[Last, 1983: A Dictionary of Epidemiology];b. The relationship between the dose of avaccine and an immune or physiologicresponse. In vaccine research, a dose_responseeffect means that as the dose of the vaccineincreases, so does the level of the immuneresponse (antibodies and CTL activity).[NIAID, 1997: HIV Vaccine Glossary]; c.The resulting biological responses in an organor organism expressed as a function of a seriesof different doses. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1997b:Exposure Factors Handbook]; d. Arelationship between (1) the dose, either"administered dose" (i.e., exposure) orabsorbed dose, and (2) the extent of toxicinjury produced by that chemical. Responsecan be expressed either as the severity of injuryor proportion of exposed subjects affected. Adose_response assessment is one of the foursteps in a risk assessment. [USEPA, 1995:Benchmark Dose]; e. The quantitativerelationship between the amount of exposure toa substance and the extent of toxic injury ordisease produced. [USEPA, 1997a: EPATerms of Environment] [USDOE, 2000:RAIS Glossary]; f. The relationship betweena quantified exposure (dose), and theproportion of subjects demonstrating specific,biological changes (response). [IRIS, 1999:Glossary of IRIS Terms]

Dose, threshold - A threshold dose is a doselevel below which there is no effect ofradiation on the biological response. It is oftendifficult to distinguish between a threshold anda linear_quadratic dose response where theresponse changes only slightly at low doses. Athreshold model postulates that radiation doesnot cause the effect at any level below thethreshold. Radiation thresholds are generallythought to be limited to acute (short_term)effects that are called deterministic, becausethey require depletion of certain cells in thebody to below a critical number in a givenorgan or tissue. These effects include radiationsickness (nausea and vomiting), infection andbleeding, and loss of hair. [RERF, 1999:Radiation Effects Research FoundationGlossary]

Dose-response evaluation - quantitativeevaluation of toxicity information andcharacterization of the relationship between the

dose administered or received and theincidence of adverse health effects in theexposed population. (Source: RAGS, 1989)[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]

Dosimeter - a. Instrument to measure dose;many so-called dosimeters actually measureexposure rather than dose. [USEPA, 1992: GLfor Exposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment]; b. Aninstrument to measure dosage; many so_calleddosimeters actually measure exposure ratherthan dosage. Dosimetry is the process ortechnology of measuring and/or estimatingdosage. [USEPA, 1997a: EPA Terms ofEnvironment]

Dosimetry - a. The theory and application ofthe principles and techniques involved in themeasurement and recording of ionizingradiation doses. [USDOE, 2000: RAISGlossary]; b. Process of measuring orestimating dose. [USEPA, 1992: GL forExposure Assessment]; c. Process ofmeasuring dose. [USEPA, 1992a: DermalExposure Assessment]

Drinking water exposure - Intake of achemical into the body through the ingestionof drinking water. [OFA, 2000: OxyfuelsGlossary]

Dry weight intake rates - Intake rates that arebased on the weight of the food consumedafter the moisture content has been removed.[USEPA, 1997b: Exposure Factors Handbook]

Duration: - A measure of the length of timethe ground shaking exceeds a given thresholdof shaking, such as 5 % of the force of gravity.Also, a description of the length of timebetween the onset and the departure of anatural hazard. [PDM, 2000: DisasterTerminology]

Duration of exposure - see exposureduration

Effective dose equivalent (HE) - Thesummation of the products of the doseequivalent received by specified tissues of thebody (HT) and the appropriate weightingfactors (WT) - that is (HE = äWTHT). Itincludes the dose from radiation sourcesinternal and/or external to the body. Theeffective dose equivalent is expressed in unitsof rem (or sievert). [USDOE, 1998:Radiological Control Manual]

Effective Dose (ED10) - The dosecorresponding to a 10% increase in an adverseeffect, relative to the control response. [IRIS,1999: Glossary of IRIS Terms]

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Effective half_life - The time required for aradionuclide contained in a biological system,such as a human or an animal, to reduce itsactivity by one_half as a combined result ofradioactive decay and biological elimination.[USDOE, 2000: RAIS Glossary]

Effluent - a. Treated or untreated liquidwaste material that is discharged into theenvironment from a point source, such as awastewater treatment plant or an industrialfacility. [NCSU, 1997: WatersheddsGlossary]; b. Waste material discharged intothe environment, treated or untreated.Generally refers to water pollution. [SRA,1999: Glossary of Risk Analysis Terms]; c.Waste material discharged into theenvironment, treated or untreated. Generallyrefers to surface water pollution. [USDOE,2000: RAIS Glossary]; d. Waste materialbeing discharged into the environment, eithertreated or untreated. Effluent generally is usedto describe water discharges to theenvironment, although it can refer to stackemissions or other material flowing into theenvironment. [USEPA, 1992: GL for ExposureAssessment]; e. Wastewater__treated oruntreated__that flows out of a treatment plant,sewer, or industrial outfall. Generally refers towastes discharged into surface waters.[USEPA, 1997a: EPA Terms of Environment]

Emission - a. The release or giving out of agas, light or heat. An automobile releasesuncombusted or partially oxidizedhydrocarbon emissions from its tailpipe whenthe engine is running. Atoms in an excitedstate often emit light in order to reach a lowerenergy state. These emissions can be used todetermine the presence of the atoms in asample. [SHSU, 2000: Atmospheric ChemistryGlossary, attributed to [Journal ofEnvironmental Economics and Management25:177-195 (1993) and Science 26:1255-1257(1994)]; b. Like effluent but used in regardto air pollution. [SRA, 1999: Glossary of RiskAnalysis Terms] [USDOE, 2000: RAISGlossary]; c. Pollution discharged into theatmosphere from smokestacks, other vents,and surface areas of commercial or industrialfacilities; from residential chimneys; and frommotor vehicle, locomotive, or aircraftexhausts. [USEPA, 1997a: EPA Terms ofEnvironment]

Emissions - a. Release of pollutants into theair from a source [ODEQ, 1999: Air QualityGlossary]; b. Pollutants released into the airor waterways from industrial processes,households or transportation vehicles. Airemissions pertain to atmospheric air pollution;water emissions refer to pollutants releasedinto waterways. [RFF, 2000: Glossary of

Terms and Concepts]; c. The release of asubstance (usually a gas when referring to thesubject of climate change) into the atmosphere.[USEPA, 2000: Global Warming Glossary]

Emission rate - a. The weight of a pollutantemitted per unit of time (e.g., tons/year).[CARB, 2000: Glossary of Air PollutionTerms]; b. The amount of pollutant emittedper unit of time. [SRA, 1999: Glossary of RiskAnalysis Terms] [USDOE, 2000: RAISGlossary]

Employer tenure - The length of time aworker has been with the same employer.[USEPA, 1997b: Exposure Factors Handbook]

Endangerment assessment - A study todetermine the nature and extent ofcontamination at a site on the NationalPriorities List and the risks posed to publichealth or the environment. EPA or the stateconducts the study when a legal action is to betaken to direct potentially responsible parties toclean up a site or pay for it. An endangermentassessment supplements a remedialinvestigation. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAIS Glossary]

Environmental assessment - Anenvironmental analysis prepared pursuant tothe National Environmental Policy Act todetermine whether a federal action wouldsignificantly affect the environment and thusrequire a more detailed environmental impactstatement. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAISGlossary]

Environmental exposure - Human exposureto pollutants originating from facilityemissions. Threshold levels are not necessarilysurpassed, but low_level chronic pollutantexposure is one of the most common forms ofenvironmental exposure [USEPA, 1997a: EPATerms of Environment] [USDOE, 2000: RAISGlossary]

Environmental fate - a. Where a substanceends up after it is released into theenvironment. Environmental fate depends onmany factors, including transport (e.g., wind,runoff) and transformation processes (e.g.,degradation). [ED, 2000: EnvironmentalScorecard Glossary]; b. The destiny of achemical or biological pollutant after releaseinto the environment. Environmental fateinvolves temporal and spatial considerations oftransport, transfer, storage, and transformation.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment]; c. The destiny of a chemical orbiological pollutant after release into theenvironment. [USEPA, 1997a: EPA Terms of

Environment]

Environmental fate model - In the context ofexposure assessment, any mathematicalabstraction of a physical system used topredict the concentration of specific chemicalsas a function of space and time subject totransport, intermedia transfer, storage, anddegradation in the environment. [USEPA,1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment]

Environmental monitoring - A method ofmeasuring the amount of a pesticide present inan environmental medium. [OECD, 1997:Occupational Exposure to Pesticides]

Environmental pathway - 1. All routes oftransport by which a toxicant can travel fromits release site to human populations includingair, food chain, and water. 2.The connectedset of environmental media through which apotentially harmful substance travels fromsource to receptor. [SRA, 1999: Glossary ofRisk Analysis Terms, attributed to Stephen L.Brown] [USDOE, 2000: RAIS Glossary]

Error - a. Any discrepancy between acomputed, observed, or measured quantity andthe true, specified, or theoretically correctvalue of that quantity. (1) random error - instatistics, an error that can be predicted onlyon a statistical basis; (2) systematic error - instatistics, an error which results from somebias in the measurement process and is not dueto chance, in contrast to random error. [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]; b. (1) A false ormistaken result obtained in a study orexperiment. Several kinds of error can occur inepidemiology, for example, due to bias. (2)Random error (sampling error) is that dueto chance, when the result obtained in thesample differs from the result that would beobtained if the entire population ("universe")were studied. Two varieties of sampling errorare type I, or alpha error, and type II, or betaerror. In an experiment, if the experimentalprocedure does not in reality have any effect,an apparent difference between experimentaland control groups may nevertheless beobserved by chance, a phenomenon known astype I error. Another possibility is that thetreatment is effective but by chance thedifference is not detected on statisticalanalysis—type II error. In the theory of testinghypotheses, rejecting a null hypothesis when itis actually true is called "type I error."Accepting a null hypothesis when it isincorrect is called "type II error." (3)Systematic error is that due to factors otherthan chance, such as faulty measuringinstruments. It is further considered in bias.

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[Last, 1983: A Dictionary of Epidemiology]

Errors - Deviation between estimated valueand true value. (1) False positive: inSuperfund risk assessment, a conclusion thatcontaminant concentrations in onsite soil arehigher than background soil concentrationswhen in fact they are not; could result inunnecessary remediation; (2) False negative:a conclusion that onsite contaminantconcentrations are not higher than backgroundconcentrations when in fact they are; couldresult in failure to clean up a site when suchaction is necessary. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]

Estimated Exposure Dose (EED) - Themeasured or calculated dose to which humansare likely to be exposed considering allsources and routes of exposure. [IRIS, 1999:Glossary of IRIS Terms]

Exposed - In epidemiology, the exposed group(or simply, the exposed) is often used toconnote a group whose members have beenexposed to a supposed cause of a disease orhealth state of interest, or possess acharacteristic that is a determinant of thehealth outcome of interest. [Last, 1983: ADictionary of Epidemiology]

Exposure - a. Contact of an organism with achemical or physical agent, quantified as theamount of chemical available at the exchangeboundaries of the organism and available forabsorption. Usually calculated as the meanexposure, and some measure of maximumexposure. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist,attributed to USEPA RAGS, 1989]; b.Contact with a chemical by swallowing, bybreathing, or by direct contact (such as throughthe skin or eyes). Exposure may be short term(acute) or long term (chronic). [ATSDR, 1999:Online Glossary] [New York Department ofHealth, 1999: Glossary of EnvironmentalHealth Terms]; c. The concentration of thepollutant in the air multiplied by thepopulation exposed to that concentration overa specified time period. [CARB, 2000:Glossary of Air Pollution Terms]; d.Normally external exposure: the amount ofsubstance ingested, the amount in contact withthe skin or either the amount inhaled or theconcentration of the substance in theatmosphere (as appropriate). [EC, 1996: RiskAssessment for New Notified Subs]; e.radiobiology. A quantitative measure of x orgamma radiation at a certain place, based onits ability to produce ionisation in air. Theformer special unit of exposure was theroentgen (R). 1R = 2.58 x 10_4 C/kg. In theinternational system (SI unit), the special unit

is coulomb per kilogram. (Exposure also isfrequently used as a synonym for irradiation).[Graham, 1998: The On Line MedicalDictionary]; f. Contact made between achemical, physical, or biological agent and theouter boundary of an organism. Exposure isquantified as the amount of an agent availableat the exchange boundaries of the organism(e.g., skin, lungs, gut). [IRIS, 1999: Glossaryof IRIS Terms]; g. An event that occurswhen there is contact at a boundary between ahuman and the environment with acontaminant of a specific concentration for aninterval of time; the units of exposure areconcentration multiplied by time. [NRC, 1991:Human Exp. for Airborne Pollutants]; h.Occurs when a person comes into contact witha chemical in their environment. May involveoral ingestion, inhalation, and absorptionthrough the skin or the mucus membranes ofthe eyes, nose, or mouth. [NRDC, 1998:Trouble on the Farm]; i. A condition of oral,dermal, respiratory or ocular contact between aperson and a pesticide. [OECD, 1997:Occupational Exposure to Pesticides]; j. (1)The time integral of the concentration of atoxicant which is in the immediate vicinity ofvarious ports of entry (such as lung, GI tractand skin). (2) Qualitatively, contact between apotentially harmful agent and a receptor (e.g., ahuman or other organism) that could beaffected. [SRA, 1999: Glossary of RiskAnalysis Terms, attributed to Stephen L.Brown]; k. Similar to dose. The combinationof concentration of a substance in air and theamount of time a worker is exposed to thatconcentration gives the total exposure or dose.[University of Kentucky, 1999: Glossary ofSafety Terms]; l. Contact of an organismwith a chemical, radiological, or physicalagent. Exposure is quantified as the amount ofthe agent available at the exchange boundariesof the organism (e.g.; skin, lungs, gut) andavailable for absorption. [USDOE, 2000:RAIS Glossary]; m. Contact of a chemical,physical, or biological agent with the outerboundary of an organism. Exposure isquantified as the concentration of the agent inthe medium in contact integrated over the timeduration of that contact. [USEPA, 1992: GLfor Exposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project][USEPA, 1997b: Exposure FactorsHandbook]; n. The contact or co-occurrenceof a stressor with a receptor. [USEPA, 1997:Guidance on Cumulative Risk Assessment,Planning and Scoping] [USEPA, 1998a:Guidelines for Ecological Risk Assessment][CENR, 1999: Ecorisk in the FederalGovernment]; o. The amount of radiation orpollutant present in a given environment thatrepresents a potential health threat to livingorganisms. [USEPA, 1997a: EPA Terms of

Environment]; p. A measure of theenvironment leading to a dose. Exposure isquantified as the concentration of the agent inthe medium in contact, integrated over theduration of the contact [USEPA, 1998:Postapp. Exposure Test GL.]; q. Exposuredoes not equal poisoning, it is the dose. If yousmell ammonia you have been exposed butyou have not been poisoned with ammoniagas. [WSU, 1999: Definitions andAbbreviations of Veterinary Terms]; r.Contact between an agent and a target[Zartarian, et al., 1997: Quant. Def. of Exp. &Related Concepts]

Exposure assessment - a. Measurement orestimation of the magnitude, frequency,duration and route of exposure to a substancefor the populations of interest. [CARB, 2000:Glossary of Air Pollution Terms]; b.Identifying the ways in which chemicals mayreach individuals (e.g., by breathing);estimating how much of a chemical anindividual is likely to be exposed to; andestimating the number of individuals likely tobe exposed. [ED, 2000: EnvironmentalScorecard Glossary]; c. The qualitativeand/or quantitative evaluation of the likelyintake of biological, chemical or physicalagents via food as well as exposure from othersources if relevant. [FAO/WHO, 1997: FoodConsumption & Exp. Assessment ofChemicals]; d. An identification andevaluation of the human population exposed toa toxic agent, describing its composition andsize, as well as the type, magnitude, frequency,route and duration of exposure. [IRIS, 1999:Glossary of IRIS Terms]; e. An estimate ofthe number of people who will be exposed to achemical, along with the concentration,duration and terms of the exposure. [JHU,1999: Altweb Glossary]; f. A process thatestimates the amount of a chemical that entersor comes into contact with people. Anexposure assessment also describes the lengthof time and the nature and size of a populationexposed to a chemical. [New YorkDepartment of Health, 1999: Glossary ofEnvironmental Health Terms]; g. Theprocess of measuring or estimating theintensity, frequency, and duration of humanexposures to an agent currently present in theenvironment or of estimating hypotheticalexposure that might arise from the release ofnew chemicals into the environment. In itsmost complete form, it describes themagnitude, duration, schedule, and route ofexposures; the size, nature, and classes of thehuman populations exposed; and theuncertainties in all estimates. Exposureassessment is often used to identify feasibleprospective control options and to predict theeffects of available control technologies onexposure. [NRC 1983: Risk Assessment in the

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Federal Government]; h. Involves numeroustechniques to identify the contaminant,contaminant sources, environmental media ofexposure, transport through each medium,chemical and physical transformations, routesof entry to the body, intensity and frequency ofcontact, and spatial and temporal concentrationpatterns of the contaminant. An array oftechniques can be employed, ranging fromestimating the number of people exposed andcontaminant concentrations to sophisticatedmethodology employing contaminantmonitoring, modeling, and human biologicalmarker measurement. [NRC, 1991: HumanExp. for Airborne Pollutants]; i. The thirdstep in the assessment of risks to humans frompotentially toxic agents, in which the natureand size of the human population exposed to atoxic agent, and the magnitude and duration ofthese exposures are described. Exposureassessment can include both current andanticipated future exposures. Factors importantin exposure assessment include: (1) numbersof potentially exposed individuals, (2) route,frequency and duration of exposure, and (3)distribution of age, gender, and uniqueconditions such as pregnancy, childhood, oldage, pre-existing illnesses, and lifestyle withinthe population of interest. [OFA, 2000:Oxyfuels Glossary]; j. The process ofmeasuring or estimating the intensity,frequency, and duration of human exposures toan agent currently present in the environmentor of estimating hypothetical exposures thatmight arise from the release of new chemicalsinto the environment. [SRA, 1999: Glossaryof Risk Analysis Terms] [USDOE, 2000:RAIS Glossary]; k. The determination orestimation (qualitative or quantitative) of themagnitude, frequency, duration, and route ofexposure. [USEPA, 1992: GL for ExposureAssessment] [USEPA, 1992a: DermalExposure Assessment] [REAP, 1995:Residential Exposure Assessment Project][USEPA, 1997b: Exposure Factors Handbook][AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; l. Identifying thepathways by which toxicants may reachindividuals, estimating how much of achemical an individual is likely to be exposedto, and estimating the number likely to beexposed. [USEPA, 1997a: EPA Terms ofEnvironment]

Exposure concentration - a. Theconcentration of a chemical or other pollutantrepresenting a health threat in a givenenvironment. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAISGlossary]; b. The concentration of achemical in its transport or carrier medium atthe point of contact. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1997b:Exposure Factors Handbook]

Exposure dose reconstruction - An approachthat uses computational models and otherapproximation techniques to estimatecumulative amounts of hazardous substancesinternalized by people at presumed or actualrisk from contact with substances associatedwith hazardous waste sites. [ATSDR, 1999:Online Glossary: ATSDR-specific term]

Exposure duration - a. Toxicologically, thereare three categories describing duration ofexposure: acute (one-time), subchronic(repeated, for a fraction of a lifetime), andchronic (repeated, for nearly a lifetime).[REAP, 1995: Residential ExposureAssessment Project]; b. (1) Length of timeover which contact with the contaminant lasts;(2) Total time an individual is exposed to thechemical being evaluated. [USEPA, 1997b:Exposure Factors Handbook]

Exposure event - an incident of contact witha chemical or physical agent; can be defined bytime or by incident. (Source: RAGS, 1989)[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]

Exposure frequency - The number of times anexposure occurs in a given period; exposuremay be continuous, discontinuous but regular(e.g., once daily), or intermittent (e.g., less thandaily, with no standard quantitative definition).[REAP, 1995: Residential ExposureAssessment Project]

Exposure indicator - A characteristic of theenvironment measured to provide evidence ofthe occurrence or magnitude of a responseindicator's exposure to a chemical or biologicalstress. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAISGlossary]

Exposure level - The amount (concentration)of a chemical at the absorptive surfaces of anorganism. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAIS Glossary]

Exposure limits - Suggested or mandatoryrestrictions placed upon exposure typicallyestablished to assure that exposure below theselevels will result in no or minimal adverseeffects. [REAP, 1995: Residential ExposureAssessment Project]

Exposure medium - The contaminatedenvironmental medium to which an individualis exposed. Includes the transfer ofcontaminants from one medium to another.[USEPA, 1999: Superfund Risk AssessmentGlossary]

Exposure monitoring - To keep track of,

regulate, or control exposure (see Exposure).Frequently conducted relative to a referenceexposure limit. See Exposure Limits). [REAP,1995: Residential Exposure AssessmentProject]

Exposure pathway - a. The path a chemicalor physical agent takes from source to exposedorganism; consists of (1) source or release, (2)transport medium (possible), (3) exposurepoint, and (4) exposure route. [AIHA, 2000:Risk Assessment Principles for the IndustrialHygienist, attributed to USEPA RAGS, 1989];b. The physical course a chemical or pollutanttakes from the source to the organism exposed.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment] [REAP, 1995: ResidentialExposure Assessment Project] [USEPA,1997a: EPA Terms of Environment] [USEPA,1997b: Exposure Factors Handbook] [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]; c. The path fromsources of pollutants via, soil, water, or food toman and other species or settings. [USEPA,1997a: EPA Terms of Environment]; d. Thecourse a chemical takes from the source to theexposed individual. An exposure pathwayanalysis links the sources, locations, and typesof environmental releases with populationlocations and activity patterns to determine thesignificant pathways of human exposure.[USEPA, 1999: Superfund Risk AssessmentGlossary]

Exposure point - a. Location of potentialcontact between an organism and a chemicalor physical agent. (Source: RAGS, 1989)[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; b. An exactlocation of potential contact between a personand a chemical within an exposure medium.[USEPA, 1999: Superfund Risk AssessmentGlossary]; c. The point on a contactboundary at which contact with an agentoccurs [Zartarian, et al., 1997: Quant. Def. ofExp. & Related Concepts]

Exposure point concentration - The valuethat represents a conservative estimate of thechemical concentration available from aparticular medium or route of exposure. Seedefinitions for Medium EPC and Route EPC,which follow. Exposure Route The way achemical comes in contact with a person (e.g.,by ingestion, inhalation, dermal contact).[USEPA, 1999: Superfund Risk AssessmentGlossary]

Exposure potential - An estimate of the totaldose of a chemical received by an exposedorganism (e.g., a person) or by a population,

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not just via one pathway or medium but fromall likely pathways. [ED, 2000:Environmental Scorecard Glossary]

Exposure profile - The product ofcharacterization of exposure in the analysisphase of ecological risk assessment. Theexposure profile summarizes the magnitudeand spatial and temporal patterns of exposurefor the scenarios described in the conceptualmodel. [USEPA, 1998a: Guidelines forEcological Risk Assessment] [CENR, 1999:Ecorisk in the Federal Government]

Exposure_response relationship - a. Theconnection between the amount of a chemicaladministered and a specific toxic effect in theorganism, also called the dose_responserelationship. [JHU, 1999: Altweb Glossary];b. The relationship between exposure leveland the incidence of adverse effects. [USEPA,1997a: EPA Terms of Environment]

Exposure route - [also route, route ofexposure] a. The way an organism comesinto contact with a chemical or physical agent;ingestion, inhalation, dermal contact, etc.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist, attributed to USEPARAGS 1989]; b. The way in which a personmay contact a chemical substance. Forexample, drinking (ingestion) and bathing(skin contact) are two different routes ofexposure to contaminants that may be found inwater. [ATSDR, 1999: Online Glossary]; c.The avenue by which a chemical comes intocontact with an organism (such as a person).Possible routes include inhalation, ingestion,and dermal contact. [ED, 2000: EnvironmentalScorecard Glossary]; d. The way in which aperson may contact a chemical substance. Forexample, drinking (ingestion) and bathing(skin contact) are two different routes ofexposure to contaminants that may be found inwater. [New York Department of Health,1999: Glossary of Environmental HealthTerms]; e. The way an agent enters anorganism after contact (e.g., by ingestion,inhalation, or dermal absorption). [REAP,1995: Residential Exposure AssessmentProject]; f. The way a chemical or pollutantenters an organism after contact, e.g., byingestion, inhalation, or dermal absorption.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment] [USEPA, 1997a: EPA Terms ofEnvironment] [USEPA, 1997b: ExposureFactors Handbook]; g. The avenue by whicha chemical comes into contact with anorganism, e.g., inhalation, ingestion, dermalcontact, injection. [USEPA, 1997a: EPATerms of Environment]

Exposure scenario - a. A set of facts,

assumptions, and inferences about howexposure takes place that aids the exposureassessor in evaluating, estimating, orquantifying exposures. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project][USEPA, 1997b: Exposure FactorsHandbook]; b. A set of assumptionsconcerning how an exposure may take place,including assumptions about the exposuresetting, stressor characteristics, and activitiesthat may lead to exposure. [USEPA, 1998a:Guidelines for Ecological Risk Assessment][CENR, 1999: Ecorisk in the FederalGovernment]

Exposure time - A term used in probabilisticground shaking maps. The period of time (forexample, 50 years) that a structure or acommunity is exposed to potential earthquakeground shaking and other earthquake hazards.[PDM, 2000: Disaster Terminology]

External dose or exposure - That portion ofthe dose equivalent received from radiationsources outside the body (e.g., "externalsources"). [USDOE, 1998: RadiologicalControl Manual]

External radiation dose - The dose fromsources of radiation located outside the body.This is most often from gamma rays, thoughbeta rays can contribute to dose in the skin andother relatively superficial tissues. [USDOE,2000: RAIS Glossary]

Fault tree - a method of analyzing potentialoutcomes which starts with the final event andworks backwards, identifying all causes of theevent, the contributing factors of those causes,etc., back to the basic events. Probabilities canbe assigned to the basic events, and alikelihood thus estimated for the final event.See also event tree. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]

Fault tree analysis - A technique by whichmany events that interact to produce otherevents can be related using simple logicalrelationships permitting a methodical buildingof a structure that represents the system.[SRA, 1999: Glossary of Risk Analysis Terms]

Flux - a. The rate of continuous change, flowor movement of liquid, particles or energy. Therate of discharge of a liquid, removal of energyor particle depositing from one body toanother. [SHSU, 2000: Atmospheric ChemistryGlossary, attributed to Journal of Alloys andCompounds; 195:407 (1993) and EcologicalMonographs 58:177 (1988)]; b. Amount ofchemical absorbed across a defined surface

area of the skin per unit time (mg/em=/hr).This is equal to the dermal permeabilitycoefficient multiplied by the concentration ofthe chemical. Flux and concentration areinterdependent. [USEPA, 1992a: DermalExposure Assessment]; c. (1) A flowing orflow. (2) A substance used to help metals fusetogether. [USEPA, 1997a: EPA Terms ofEnvironment]

Food consumption - Food consumption is anestimate of per capita quantity of a food orgroup of foods eaten by a specified populationover a defined period of time. Foodconsumption is expressed in grams of food perperson per day. [FAO/WHO, 1997: FoodConsumption & Exp. Assessment ofChemicals]

Frequency distribution - see distribution

Frequency of exposure - see exposurefrequency

Fugitive emissions - a. Emissions not caughtby a capture system which are often due toequipment leaks, evaporative processes, andwindblown disturbances. [CARB, 2000:Glossary of Air Pollution Terms]; b.Emissions not caught by a capture system.[USEPA, 1997a: EPA Terms of Environment]

General population - The total of individualsinhabiting an area or making up a wholegroup. [USEPA, 1997b: Exposure FactorsHandbook]

Geographic information system (GIS) - a.A computer hardware and software systemdesigned to collect, manipulate, analyze, anddisplay spatially referenced data for solvingcomplex resource, environmental, and socialproblems. [ATSDR, 1999: Online Glossary];b. Computer programs linking featurescommonly seen on maps (such as roads, townboundaries, water bodies) with relatedinformation not usually presented on maps,such as type of road surface, population, typeof agriculture, type of vegetation, or waterquality information. A GIS is a uniqueinformation system in which individualobservations can be spatially referenced toeach other. [NCSU, 1997: WatersheddsGlossary]; c. organized collections ofcomputer hardware, software, geographic data,and personnel designed to efficiently capture,store, update, manipulate, analyze and displayall forms of geographically referencedinformation. GIS is being used by manyresearchers in the environmental field to viewa number of different indicatorssimultaneously as data layers on a geographicgrid. By associating data of all kinds withpoints on a map, GIS can illustrate patterns

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and trends that might otherwise beincomprehensive. For example, using GIS, aresearcher can map multiple health indicatorsat and around a specific toxic waste site. [RFF,2000: Glossary of Terms and Concepts]; d.A computer system designed for storing,manipulating, analyzing, and displaying datain a geographic context. See SADA .[USDOE, 2000: RAIS Glossary]

Geometric mean - a. A measure of centraltendency. Calculable only for positive values.It is calculated by taking the logarithms of thevalues, calculating their arithmetic mean, thenconverting back by taking the antilogarithm.[Last, 1983: A Dictionary of Epidemiology];b. The nth root of the product of n values.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment][USEPA, 1997b: ExposureFactors Handbook]

Half_life - a. The time in which theconcentration of a chemical in the environmentis reduced by half. [ED, 2000: EnvironmentalScorecard Glossary]; b. The time requiredfor half of a substance introduced to a livingsystem or ecosystem to be eliminated ordisintegrated by natural processes. [NCSU,1997: Watershedds Glossary]; c. the timerequired for half the amount of a substance tobe eliminated from the body or to be convertedto another substance(s). [NIAID, 1997: HIVVaccine Glossary]; d. The time required forhalf of a sample of a given radioactive isotopeto decay into another element or isotope. Thehalf-life of an isotope is inversely related to itsdecay constant. [SHSU, 2000: AtmosphericChemistry Glossary]; e. (1) The time inwhich half the atoms of a given quantity of aparticular radioactive substance disintegrate toanother nuclear form. Measured half_livesvary from millionths of a second to billions ofyears. (2) Similarly, the time in which half themolecules of a chemical substance disappearas a result of chemical or biochemicaltransformation. [SRA, 1999: Glossary of RiskAnalysis Terms, attributed to Stephen L.Brown]; f. The time in which half the atomsof a radioactive substance will havedisintegrated, leaving half the original amount.Half of the residue will disintegrate in anotherequal period of time. [USDOE, 2000: RAISGlossary]; g. (1) The time required for apollutant to lose one_half of its originalconcentration. For example, the biochemicalhalf_life of DDT in the environment is 15years. (2) The time required for half of theatoms of a radioactive element to undergoself_transmutation or decay (half_life ofradium is 1620 years). (3) The time requiredfor the elimination of half a total dose from thebody. [USEPA, 1997a: EPA Terms ofEnvironment] [cf. biological half-life]

Harmonic mean - A measure of centraltendency computed by summing thereciprocals of all the individual values anddividing the resulting sum into the number ofvalues. [Last, 1983: A Dictionary ofEpidemiology]

High-end exposure (dose) estimate - a. Aplausible estimate of individual exposure ordose for those persons at the upper end of anexposure or dose distribution, conceptuallyabove the 90th percentile, but not higher thanthe individual in the population who has thehighest exposure or dose. [USEPA, 1992: GLfor Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project]; b.An estimate of exposure, or dose level receivedanyone in a defined population that is greaterthan the 90th percentile of all individuals inthat population, but less than the exposure atthe highest percentile in that population. Ahigh end risk descriptor is an estimate of therisk level for such individuals. Note that risk isbased on a combination of exposure andsusceptibility to the stressor. [USEPA, 1997a:EPA Terms of Environment]

Household interview survey - Collection ofinformation from a (representative) sample of acivilian noninstitutionalized population, bytrained interviewers, who go to the dwellingsof the persons selected for interview. [Last,1983: A Dictionary of Epidemiology]

Household waste (domestic waste) - Solidwaste, composed of garbage and rubbish,which normally originates in a private home orapartment house. Domestic waste may containa significant amount of toxic or hazardouswaste. [USEPA, 1997a: EPA Terms ofEnvironment]

Human equivalent concentration (HEC) orhuman equivalent dose (HED) - a. Thehuman concentration (for inhalation exposure)or dose (for other routes of exposure) of anagent that is believed to induce the samemagnitude of toxic effect as the experimentalanimal species concentration or dose. Thisadjustment may incorporate toxicokineticinformation on the particular agent, ifavailable, or use a default procedure, such asassuming that daily oral doses experienced fora lifetime are proportional to body weightraised to the 0.75 power. [IRIS, 1999:Glossary of IRIS Terms]; b. [humanequivalent concentration] Exposureconcentration for humans that has beenadjusted for dosimetric differences betweenexperimental animal species and humans to beequivalent to the exposure concentrationassociated with observed effects in theexperimental animal species. If occupational

human exposures are used for extrapolation,the human equivalent concentration representsthe equivalent human exposure concentrationadjusted to a continuous basis. [USDOE,2000: RAIS Glossary]; c. [human equivalentdose] A dose that, when administered tohumans, produces an effect equal to thatproduced by a dose in animals. [REAP, 1995:Residential Exposure Assessment Project][USEPA, 1997a: EPA Terms of Environment][USDOE, 2000: RAIS Glossary]

Human exposure evaluation - a. Describingthe nature and size of the population exposedto a substance and the magnitude and durationof their exposure. The evaluation couldconcern past, current, or anticipated exposures.[USDOE, 2000: RAIS Glossary]; b.Describing the nature and size of thepopulation exposed to a substance and themagnitude and duration of their exposure.[USEPA, 1997a: EPA Terms of Environment]

Hygienic measures - those measures as toprevent diseases following a major disaster,because the infrastructure of the stricken areais non_ or malfunctioning. [PDM, 2000:Disaster Terminology; from Debacker, et al.,1999]

Incidental ingestion - Unintentional intake ofsmall amounts of agents, particularlyassociated with children’s from hand-to-mouthactivity. [REAP, 1995: Residential ExposureAssessment Project]

Indirect contact - A mode of transmission ofinfection involving fomites or vectors. Vectorsmay be mechanical (e.g., filth flies) orbiological (the disease agent under goes part ofits life cycle in the vector species). [Last,1983: A Dictionary of Epidemiology]

Indirect exposure - Often defined as anexposure involving multimedia transport ofagents from source to exposed individual.Examples include exposures to chemicalsdeposited onto soils from the air, chemicalsreleased into the ground water beneath ahazardous waste site, or consumption of fruitsor vegetables with pesticide residues. [REAP,1995: Residential Exposure AssessmentProject]

Indirect source - a. Any facility, building,structure, or installation, or combinationthereof, which generates or attracts mobilesource activity that results in emissions of anypollutant (or precursor) for which there is astate ambient air quality standard. Examples ofindirect sources include employment sites,shopping centers, sports facilities, housingdevelopments, airports, commercial andindustrial development, and parking lots and

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garages. [CARB, 2000: Glossary of AirPollution Terms]; b. Any facility orbuilding, property, road or parking area thatattracts motor vehicle traffic and, indirectly,causes pollution. [USEPA, 1997a: EPA Termsof Environment]

Infectious agent - Any organism, such as apathogenic virus, parasite, or bacterium, that iscapable of invading body tissues, multiplying,and causing disease. [USEPA, 1997a: EPATerms of Environment]

Influent - Water, wastewater, or other liquidflowing into a reservoir, basin, or treatmentplant. [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAISGlossary]

Ingestion - a. Oral intake of chemicals.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; b. Swallowing(such as eating or drinking). Chemicals can getin or on food, drink, utensils, cigarettes, orhands where they can be ingested. Afteringestion, chemicals can be absorbed into theblood and distributed throughout the body.[ATSDR, 1999: Online Glossary] [New YorkDepartment of Health, 1999: Glossary ofEnvironmental Health Terms]; c.Swallowing (such as eating or drinking).Chemicals can get into or onto food, drink,utensils, cigarettes, or hands where they canthen be ingested. [ED, 2000: EnvironmentalScorecard Glossary]; d. The intake of wateror food particles by "swallowing" them, takingthem into the body cavity or into a vacuole.Contrast with absorption. [UCMP, 1998:Glossary of Ecological Terms]; e.Swallowing. One of the ways a toxic substancecan enter the body. [University of Kentucky,1999: Glossary of Safety Terms]

Inhalable particles - All dust capable ofentering the human respiratory tract. [USEPA,1997a: EPA Terms of Environment]

Inhalation - a. Intake of chemicals throughthe respiratory system. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]; b. Breathing. Exposure mayoccur from inhaling contaminants becausethey can be deposited in the lungs, taken intothe blood, or both. [ATSDR, 1999: OnlineGlossary]; c. Breathing. Once inhaled,contaminants can be deposited in the lungs,taken into the blood, or both. [ED, 2000:Environmental Scorecard Glossary]; d. Inthe lungs, taken into the blood or both. [NewYork Department of Health, 1999: Glossary ofEnvironmental Health Terms]; e. Breathingin. The most common way for a toxicsubstance to enter the body. [University ofKentucky, 1999: Glossary of Safety Terms]

Inhalation exposure - Intake of a chemical orsubstance (e.g., dust) into the body through thelungs. [OFA, 2000: Oxyfuels Glossary]

Inhaled dose - The amount of an inhaledsubstance that is available for interaction withmetabolic processes or biologically significantreceptors after crossing the outer boundary ofan organism. [USEPA, 1997b: ExposureFactors Handbook]

Insensible fluid loss - Insensible routes offluid loss are those that are not readilyobserved and include the loss of fluid throughthe respiratory tract during respiration and lossof fluid by sweating. Dogs and cats sweatminimally through their foot pads so mostinsensible losses are through the respiratorytract. The fluid lost during breathing is close topure water and does not contain many solutes(a hypotonic loss). The basal loss of waterthrough breathing is about: 10_15 ml/lb/day.High environmental temperatures, fever andactivity result in increased insensible losses.[WSU, 1999: Definitions and Abbreviations ofVeterinary Terms]

Insensible water loss - Evaporative waterlosses that occur during breast feeding.Corrections are made to account for insensiblewater loss when estimating breast milk intakeusing the test weighing method. [USEPA,1997b: Exposure Factors Handbook]

Inspirable fraction - That fraction of airborneparticulate capable of entering the respiratorytract via the nose and the mouth, so providing asource of absorption into the body, either fromdirect inhalation or from subsequent oralingestion. [OECD, 1997: OccupationalExposure to Pesticides]

Instantaneous point exposure - Contactbetween an agent and a target at a single pointon a contact boundary at a single instant intime; the joint occurrence of two events: 1)point i of the target is located at (xi,yi, zi), and2) an agent of concentration Ci, the exposureconcentration, is present at location (xi,yi,zi);measured as a concentration [Zartarian, et al.,1997: Quant. Def. of Exp. & RelatedConcepts]

Instantaneous rate - In a short time interval(e.g a week), the number of events (e.g. birthsin the UK) taking place during the interval isapproximately proportional to the length of theinterval. The constant of proportionality is therate at which these events occur. Thisargument becomes more and more exact as thelength of the time interval becomes shorter andshorter. When the time interval has shrunk toan instant, the rate has become an

`instantaneous rate'. A bad term; just call it arate. [Swinton, 1999: A Dictionary ofEpidemiology]

Intake - a. A measure of exposure expressedas mass of substance in contact with theexchange boundary per unit body weight perunit time, i.e., mg/kg-day. (1) acute: intakeaveraged over a period less than two weeks;(2) chronic (daily) - intake averaged over along period of time (seven years to lifetime);(3) subchronic - intake averaged over a periodfrom two weeks to seven years. [AIHA, 2000:Risk Assessment Principles for the IndustrialHygienist, attributed to USEPA RAGS, 1989];b. The amount of contact with a mediumcontaining an agent. Used for estimating dosereceived from a particular medium. [REAP,1995: Residential Exposure AssessmentProject]; c. The process by which asubstance crosses the outer boundary of anorganism without passing an absorptionbarrier, e.g., through ingestion or inhalation.(See also potential dose) [USEPA, 1992: GLfor Exposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [USEPA,1997b: Exposure Factors Handbook]

Intake dose - Dose resulting from the agentcrossing the contact boundary withoutsubsequently diffusing through a resistingboundary layer [Zartarian, et al., 1997: Quant.Def. of Exp. & Related Concepts]

Intake rate - Rate of inhalation, ingestion, anddermal contact depending on the route ofexposure. For ingestion, the intake rate issimply the amount of food containing thecontaminant of interest that an individualingests during some specific time period (unitsof mass/time). For inhalation, the intake rate isthe rate at which contaminated air is inhaled.Factors that affect dermal exposure are theamount of material that comes into contactwith the skin, and the rate at which thecontaminant is absorbed. [USEPA, 1997b:Exposure Factors Handbook]

Integrated exposure assessment -Cumulative summation (over time) of themagnitude of exposure to a toxic chemical inall media. [USEPA, 1997a: EPA Terms ofEnvironment]

Intensity - a. seismology. (1) A measure of thepower or force (magnitude) of the event inrelation to the time over which the eventoccurs and the area over or in which it occurs(Dorland 843). (2) A numerical index denotedby Roman numerals from I to XII describingthe physical effects of an earthquake at aspecific location on the earth's surface, man, oron structures built by man. These values aredetermined subjectively by individuals

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performing postearthquake investigations todetermine the nature and spatial extent of thedamage distribution. There are no instrumentalreadings. The most commonly used scalesthroughout the world are Modified MercalliIntensity (MMI), developed in the 1930's andnamed for the Italian author, and the MSKscale, developed in the 1960's and denoted bythe first initial of the last name of twoscientists of the former Soviet Union and onescientist of the former Czechoslavakia whocreated the scale. Intensity VI denotes thethreshold for potential ground failure such asliquefaction. Intensity VII denotes thethreshold for architectural damage. IntensityVIII denotes the threshold for structuraldamage. Intensity IX denotes intense structuraldamage. Intensities X to XII denote variouslevels of destruction up to total destruction.The MMI and MSK scales are essentiallyequivalent for intensities VII to X. Anearthquake has many intensities, but only onemagnitude. (3) [seismic intensity] The degreeof shaking or of vibrations, signifying theintensity of an earthquake as measurednumerically on the Mercalli scale. [PDM,2000: Disaster Terminology]; b.parasitology. (1) (Traditional) The meanparasite burden within all the infectedmembers of the host population. Also calledmean abundance. (2) (Newer) The meanparasite burden within both infected anduninfected hosts. It is important to indicatewhich usage is adopted, since they givedifferent statistics, unless the prevalence is100%. Macroparasites, and infections likemalaria, are usually measured in terms ofintensity. [Swinton, 1999: A Dictionary ofEpidemiology]; c. exposure assessment.Amount of energy-form agent per area[Zartarian, et al., 1997: Quant. Def. of Exp. &Related Concepts]

Internal dose - a. Refers to the amount of theenvironmental contaminant absorbed in bodytissue or interacting with an organ's membranesurface. [NRC, 1991: Human Exp. forAirborne Pollutants]; b. That portion of thedose equivalent received from radioactivematerial taken into the body (e.g., "internalsources"). [USDOE, 1998: RadiologicalControl Manual] c. The amount of asubstance penetrating across the absorptionbarriers (the exchange boundaries) of anorganism, via either physical or biologicalprocesses. For the purpose of theseGuidelines, this term is synonymous withabsorbed dose. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project][USEPA, 1997b: Exposure FactorsHandbook]; d. In exposure assessment, theamount of a substance penetrating the

absorption barriers (e.g., skin,, lung tissue,gastrointestinal tract) of an organism througheither physical or biological processes. (See:absorbed dose) [USEPA, 1997a: EPA Termsof Environment]; e. The amount of pesticideabsorbed through the exchange boundaries ofthe body (equivalent to the absorbed dose).[USEPA, 1998: Postapp. Exposure Test GL.][cf. absorbed dose]

Internal exposure - Amount of the substancewhich is bioavailable. [EC, 1996: RiskAssessment for New Notified Subs]

Internal radiation dose - The dose to organsof the body from radioactive materials insidethe body. It may consist of any combination ofalpha, beta, and gamma radiation. [USDOE,2000: RAIS Glossary]

Lifetime - a. Covering the life span of anorganism (generally considered 70 years forhumans). [USEPA, 1995: Benchmark Dose];b. [atmospheric lifetime] The lifetime of agreenhouse gas refers to the approximateamount of time it would take for theanthropogenic increment to an atmosphericpollutant concentration to return to its naturallevel (assuming emissions cease) as a result ofeither being converted to another chemicalcompound or being taken out of theatmosphere via a sink. This time depends onthe pollutant's sources and sinks as well as itsreactivity. The lifetime of a pollutant is oftenconsidered in conjunction with the mixing ofpollutants in the atmosphere; a long lifetimewill allow the pollutant to mix throughout theatmosphere. Average lifetimes can vary fromabout a week (sulfate aerosols) to more than acentury (CFCs, carbon dioxide). [USEPA,2000: Global Warming Glossary]

Lifetime average daily dose (LADD) - a.Total dose received over a lifetime multipliedby fraction of lifetime during which exposureoccurs, expressed in mg/kg body weight/day.Ordinarily used for assessing cancer risk.[REAP, 1995: Residential ExposureAssessment Project]; b. Figure forestimating excess lifetime cancer risk.[USEPA, 1997a: EPA Terms of Environment];c. Dose rate averaged over a lifetime. TheLADD is used for compounds withcarcinogenic or chronic effects. The LADD isusually expressed in terms of mg/kg-day orother mass/mass-time units. [USEPA, 1997b:Exposure Factors Handbook]; d. Dose that isaveraged over an individual’s lifetime takinginto account the frequency, duration, andintensity of exposure events. LADDs areusually expressed in units of mg/kg/day.[USEPA, 1998: Postapp. Exposure Test GL.]Lifetime dose - Total occupational exposureover a worker's lifetime, including external and

committed internal dose. [USDOE, 1998:Radiological Control Manual]

Lifetime exposure - Total amount ofexposure to a substance that a human wouldreceive in a lifetime (usually assumed to be 70years). [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAISGlossary]

Limit of detection (LOD) - a. The lowestconcentration of a substance that can reliablymeasured. [CARB, 2000: Glossary of AirPollution Terms]; b. [limit ofdetermination] The LOD is the lowestconcentration of a pesticide residue orcontaminant that can be identified andquantitatively measured in a specified food,agricultural commodity, or animal feed withan acceptable degree of certainty by aregulatory method of analysis. The LOD isconsidered synonymous with the limit ofquantitation/quantification. [FAO/WHO, 1997:Food Consumption & Exp. Assessment ofChemicals]; c. The level at which a pesticidecan be detected but not quantified for a givenanalytical procedure. [OECD, 1997:Occupational Exposure to Pesticides]; d.[also, method detection limit (MDL)] Theminimum concentration of an analyte that, in agiven matrix and with a specific method, has a99% probability of being identified,qualitatively or quantitatively measured, andreported to be greater than zero. [USEPA,1992: GL for Exposure Assessment]; e. Theminimum concentration of a substance beinganalyzed test that has a 99 percent probabilityof being identified. [USEPA, 1997a: EPATerms of Environment]; f. LOD is the pointat which "a measured value becomes...largerthan the uncertainty associated with it"(Taylor, 1987). The LOD can be defined in anumber of ways, such as the backgroundresponse plus three times the standarddeviation of the lowest measurableconcentration, three times the signal-to-noiseratio of baseline noise, three times the standarddeviation of the lowest measurableconcentration, etc. [USEPA, 1998: Postapp.Exposure Test GL.]

Limit of quantification (LOQ) - a. Thesmallest amount of the pesticide that can bequantified by the analytical method. [OECD,1997: Occupational Exposure to Pesticides];b. LOQ is the point at which "measurementsbecome quantitatively meaningful" (Taylor,1987). It is the lowest pesticide residue thatcan be accurately quantitated in a reproduciblefashion. The LOQ can be defined in a numberof ways, such as the background response plusten times the standard deviation of the lowestmeasurable concentration, ten times the signal-to-noise ratio of the baseline noise, ten times

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the standard deviation of the lowestmeasurable concentration, etc. In practice, theLOQ is the lowest fortification level thatshows adequate recovery during the methodvalidation process. [USEPA, 1998: Postapp.Exposure Test GL.]

Linear dose response - A pattern offrequency or severity of biological responsethat varies proportionately with the amount ofdose of an agent. [IRIS, 1999: Glossary ofIRIS Terms]

Linear model - A statistical model of adependent variable y as a function of a factor,x: y = a + bx + E, where E represents randomvariation. [Last, 1983: A Dictionary ofEpidemiology]

Log_normal distribution - If a variable Y issuch that X = log Y is normally distributed, itis said to have log_normal distribution. This isa skew distribution. [Last, 1983: A Dictionaryof Epidemiology]

Lowest acceptable daily dose - The largestquantity of a chemical that will not cause atoxic effect, as determined by animal studies.[USEPA, 1997a: EPA Terms of Environment]

Margin of Exposure (MOE) - a. The LED10

or other point of departure divided by theactual or projected environmental exposure ofinterest. [IRIS, 1999: Glossary of IRISTerms]; b. The ratio of the NO(A)EL orNOEL to an estimated dose/exposure level.[REAP, 1995: Residential ExposureAssessment Project]; c. The ratio of theno_observed adverse_effect_level to theestimated exposure dose. [USEPA, 1997a:EPA Terms of Environment]; d. Representsthe ratio of a no observable adverse effectlevel (NOAEL) to an estimated dose/exposurelevel. [USEPA, 1998: Postapp. Exposure TestGL.]

Mathematical model - a. A representation ofa system, process, or relationship inmathematical form in which equations areused to simulate the behavior of the system orprocess under study. The model usuallyconsists of two parts: the mathematicalstructure itself, e.g., Newton's inverse squarelaw or Gauss's "normal" law, and the particularconstants or parameters associated with them,such as Newton's gravitational constant or theGaussian standard deviation. A mathematicalmodel is deterministic if the relations betweenthe variables involved take on values notallowing for any play of chance. A model issaid to be statistical, stochastic, or random, ifrandom variation is allowed to enter thepicture. [Last, 1983: A Dictionary of

Epidemiology]; b. A formal framework toconvey ideas about the components of ahost_parasite interaction. Construction requiresthree major types of information: (a) a clearunderstanding of the interaction within theindividual host between the infectious agentand the host, (b) the mode and rate oftransmission between individuals, and (c) hostpopulation characteristics such as demographyand behaviour. Mathematical models can aidexploration of the behaviour of the systemunder various conditions from which todetermine the dominant factors generatingobserved patterns and phenomena. They alsoaid data collection and interpretation andparameter estimation, and provide tools foridentifying possible approaches to control andfor assessing the potential impact of differentintervention measures. [Swinton, 1999: ADictionary of Epidemiology]

Maximally exposed individual (MEI) -[sometimes, most exposed individual] a. Thesingle individual with the highest exposure in agiven population (also, maximum exposedindividual). This term has historically beendefined various ways, including as definedhere and also synonymously with worst case orbounding estimate. Assessors are cautioned tolook for contextual definitions whenencountering this term in the literature.[USEPA, 1992: GL for Exposure Assessment];b. The single individual with the highestexposure in a given population. [USEPA,1992a: Dermal Exposure Assessment] [REAP,1995: Residential Exposure AssessmentProject] [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist,attributed to USEPA, 1992a]; c. The personwith the highest exposure in a givenpopulation. [USEPA, 1997a: EPA Terms ofEnvironment]

Maximum exposure limit (MEL) - Themaximum permitted concentration of achemical to which a worker may be exposedover an extended period of time. Typically,MELs are quoted in ppm for an 8_hourreference period, though shorter periods maybe quoted for some materials. MELs are, inmany countries, enforceable by law. A list ofchemicals for which MELs are defined in theUK is held athttp://physchem.ox.ac.uk/MSDS/mels.html[Oxford University, 2000 - Chemical SafetyInformation Glossary]Maximum exposure range - a. Asemiquantitative term referring to the extremeuppermost portion of the distribution ofexposures. For consistency, this term (and thedose or risk analogues) should refer to theportion of the individual exposure distributionthat conceptually falls above about the 98th

percentile of the distribution, but is not higher

than the individual with the highest exposure.[USEPA, 1992: GL for Exposure Assessment];b. Estimate of exposure or dose levelreceived by an individual in a definedpopulation that is greater than the 98thpercentile dose for all individuals in thatpopulation, but less than the exposure levelreceived by the person receiving the highestexposure level. [USEPA, 1997a: EPA Termsof Environment]

Mean - see arithmetic mean, geometricmean, harmonic mean

Mean, arithmetic - see arithmetic mean

Mean, geometric - see geometric mean

Mean, harmonic - see harmonic mean

Measure of exposure - a. A measurablestressor characteristic that is used to helpquantify exposure. [CENR, 1999: Ecorisk inthe Federal Government]; b. A measurablecharacteristic of a stressor (such as the specificamount of mercury in a body of water) used tohelp quantify the exposure of an ecologicalentity or individual organism. [USEPA,1997a: EPA Terms of Environment]; c. Ameasure of stressor existence and movement inthe environment and its contact or co-occurrence with the assessment endpoint.[USEPA, 1998a: Guidelines for EcologicalRisk Assessment]

Measurement - The procedure of applying astandard scale to a variable or to a set ofvalues. [Last, 1983: A Dictionary ofEpidemiology]

Measurement, problems with terminology -There is uncertainty about the terms used todescribe the properties of measurement:accuracy, precision, validity, reliability,repeatability, and reproducibility. Accuracyand precision are often used synonymously,validity is defined variously, and reliability,repeatability, and reproducibility arefrequently used interchangeably. Etymologiesare helpful in making a case for preferredusages, but they are not always decisive.Accuracy is from the Latin cure, care, andwhile this may be of interest to those in thehealth field, it does not illuminate the originsof the standard definition, that is, "conformingto a standard or a true value" (OLD). Accuracyis distinguished from precision in this way: Ameasurement or statement can reflect orrepresent a true value without detail. Atemperature reading of 98.6°F is accurate, butit is not precise if a more refined thermometerregisters a temperature of 98.637°F. Precision,(from Latin praecidere, cut short) is thequality of being sharply defined through exact

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detail. A faulty measurement may beexpressed precisely, but may not be accurate.Measurements should be both accurate andprecise, but the two terms are not synonymous.In Kendall and Buckland's Dictionary ofStatistical Terms, precision is defined as "aquality associated with a class ofmeasurements and refers to the way in whichrepeated observations conform to themselves."Standard, as well as epidemiologic definitionsare not in agreement with this statistical usage.Consistency or reliability describes theproperty of measurements or results thatconform to themselves. Reliability (Latinreligare, to bind) is defined by the OED as aquality that is sound and dependable. Itsepidemiologic usage is similar; a result ormeasurement is said to be reliable when it isstable, i.e., when repetition of an experimentor measurement gives the same results. Theterms "repeatability" and "reproducibility" aresynonymous (the OED defines each in termsof the other), but they do not refer to a qualityof measurement, rather only to the action ofperforming something more than once. Thus, away of discovering whether or not ameasurement is reliable is to repeat orreproduce it. The terms "repeatability" and"reproducibility," formed from their respectiveverbs, are used inaccurately when they aresubstituted for "reliability," a noun that refersto the measuring procedure rather than theattribute being measured. However, incommon usage, both repeatability andreproducibility refer to the capacity of ameasuring procedure to produce the sameresult on each occasion in a series ofprocedures conducted under identicalconditions. Validity is used correctly when itagrees with the standard definition given bythe QED: "sound and sufficient." If, in theepidemiologic sense, a test measures what itpurports to measure (it is sufficient) then thetest is said to be valid. [Last, 1983: ADictionary of Epidemiology]

Measures of central tendency - A generalterm for several characteristics of thedistribution of a set of values or measurementsaround a value or values at or near the middleof the set. The principal measures of centraltendency are the mean (average), median, andmode.[Last, 1983: A Dictionary ofEpidemiology]

Median - a. The middle value in a populationdistribution, above and below which lie anequal number of individual values; midpoint.[CARB, 2000: Glossary of Air PollutionTerms]; b. A measure of central tendency.The simplest division of a set of measurementsis into two parts—the lower and the upperhalf. The point on the scale that divides thegroup in this way is called the "median." [Last,

1983: A Dictionary of Epidemiology]; c. Themidpoint value obtained by ranking all valuesfrom highest to lowest and choosing the valuein the middle. The median divides a populationinto two equal halves. [NIAID, 1997: HIVVaccine Glossary]

Medium (pl. media) - a. Any one of the basiccategories of material surrounding orcontacting an organism (e.g., outdoor air.indoor air, water, soil, sediments) throughwhich chemicals or pollutants can move andreach the organism. [USEPA, 1992a: DermalExposure Assessment]; b. The environmentalsubstance (e.g, air, water, soil) originallycontaminated. [USEPA, 1999: Superfund RiskAssessment Glossary]

Medium intake rate - the rate at which thecarrier medium crosses the contact boundary[Zartarian, et al., 1997: Quant. Def. of Exp. &Related Concepts]

MEL - see maximum exposure limit

Microenvironment - A three_dimensionalspace with a volume in which contaminantconcentration is spatially uniform during somespecific interval. [NRC, 1991: Human Exp. forAirborne Pollutants]

Microenvironments - a. Well-definedsurroundings such as the home, office,automobile, kitchen, store, etc. that can betreated as homogeneous (or well characterized)in the concentrations of a chemical or otheragent. [USEPA, 1992: GL for ExposureAssessment] [REAP, 1995: ResidentialExposure Assessment Project]; b.Well_defined areas such as the home, office,automobile, kitchen, store, etc. that can betreated as homogeneous (or well characterized)in the concentrations of a chemical or otheragent. [USEPA, 1992a: Dermal ExposureAssessment]; c. Well_defined surroundingssuch as the home, office, or kitchen that can betreated as uniform in terms of stressorconcentration. [USEPA, 1997a: EPA Terms ofEnvironment]

Microenvironment method - a. A methodused in predictive exposure assessments toestimate exposures by sequentially assessingexposure for a series of areas(microenvironments) that can be approximatedby constant or well-characterizedconcentrations of a chemical or other agent.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment]; b. A method for sequentiallyassessing exposure for a series ofmicroenvironments that can be approximatedby constant concentrations of a stressor.[USEPA, 1997a: EPA Terms of Environment]

Mobile source - a. A source of air pollution,such as automobiles, motorcycles, trucks,off_road vehicles, boats, and airplanes.[CARB, 2000: Glossary of Air PollutionTerms]; b. A moving object that releasesregulated air pollutants, e.g. cars, trucks,buses, planes, trains, motorcycles, andgas_powered lawn mowers. [ODEQ, 1999: AirQuality Glossary]; c. A moving producer ofair pollution, mainly forms of transportation _cars, motorcycles, planes. [SRA, 1999:Glossary of Risk Analysis Terms]; d. Anynon_stationary source of air pollution such ascars, trucks, motorcycles, buses, airplanes, andlocomotives. [USEPA, 1997a: EPA Terms ofEnvironment] [Cf. stationary source]

Mobility - The ability of a chemical elementor a pollutant to move into and through theenvironment (e.g., the mobilization of anelement from a water column to sediment)[SRA, 1999: Glossary of Risk AnalysisTerms] [USDOE, 2000: RAIS Glossary]

Mode - a. One of the measures of centraltendency. The most frequently occurring valuein a set of observations. [Last, 1983: ADictionary of Epidemiology]; b. The valuein the data set that occurs most frequently.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment] [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]

Model - a. A mathematical function withparameters that can be adjusted so the functionclosely describes a set of empirical data. Amechanistic model usually reflects observed orhypothesized biological or physicalmechanisms, and has model parameters withreal world interpretation. In contrast, statisticalor empirical models selected for particularnumerical properties are fitted to data; modelparameters may or may not have real worldinterpretation. When data quality is otherwiseequivalent, extrapolation from mechanisticmodels (e.g., biologically based dose_responsemodels) often carries higher confidence thanextrapolation using empirical models (e.g.,logistic model). [IRIS, 1999: Glossary of IRISTerms]; b. A representation or simulation ofan actual situation. This may be either (1) amathematical representation of characteristicsof a situation that can be used to examineconsequences of various actions, or (2) arepresentation of a country’s situation throughan "average region" with characteristicsresembling those of the whole country. Inepidemiology the use of models began with aneffort to predict the onset and course ofepidemics. In the second report of theRegistrar_General of England and Wales(1840), William Farr developed the beginnings

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of a predictive model for communicabledisease epidemics. He had recognizedregularities in the smallpox epidemics of the1830s. By calculating frequency curves forthese past outbreaks, he estimated the deaths tobe expected. [Last, 1983: A Dictionary ofEpidemiology]; c. A mathematicalrepresentation of a natural system intended tomimic the behavior of the real system,allowing description of empirical data andpredictions about untested states of the system.[USEPA, 1995: Benchmark Dose]

Modeling - Use of mathematical equations tosimulate and predict real events and processes.[REAP, 1995: Residential ExposureAssessment Project]

Moderator variable - (Syn: qualifier variable)In a study of a possible causal factor and anoutcome, a moderator variable is a thirdvariable exhibiting statistical interaction byvirtue of its being antecedent or intermediatein the causal process under stiffly. If it isantecedent, it is termed a conditionalmoderator variable or effect modifier; if it isintermediate, it is a contingent moderatorvariable. [Last, 1983: A Dictionary ofEpidemiology]

Monte Carlo simulation - A technique thatcan provide a probability function of estimatedexposure using distributed values of exposurefactors in an exposure scenario. The MonteCarlo simulation involves assigning a jointprobability distribution to the input variables(i.e., exposure factors) of an exposurescenario. Next, a large number of independentsamples from the assigned joint distributionare taken and the corresponding outputscalculated. This is accomplished by repeatedcomputer runs (i.e., >=1,000 iterations) usingrandom numbers to assign values to theexposure factors. The simulated outputrepresents a sample from the true outputdistribution. Methods of statistical inferenceare used to estimate, from the exposure outputsample, some parameters of the exposuredistribution, such as percentiles, mean,variance, and confidence intervals. The MonteCarlo simulation can also be used to test theeffect that an input parameter has on the outputdistribution. [REAP, 1995: ResidentialExposure Assessment Project]

Monte Carlo technique - A repeated randomsampling from the distribution of values foreach of the parameters in a generic (exposureor dose) equation to derive an estimate of thedistribution of (exposures or doses in) thepopulation. [USEPA, 1992: GL for ExposureAssessment] [USEPA, 1992a: DermalExposure Assessment] [USEPA, 1997b:Exposure Factors Handbook] [IRIS, 1999:

Glossary of IRIS Terms] [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]

Multimedia exposure - Exposure to a toxicsubstance from multiple pathways such as air,water, soil, food, and breast milk. [CARB,2000: Glossary of Air Pollution Terms]

National estimated daily intake (NEDI) -The NEDI is a prediction of the daily intake ofa pesticide residue which is based on the mostrealistic estimate of residue levels in food andthe best available data on food consumptionfor a specific population. The residue levelsmay be estimated based on median residuesfrom supervised trials and allowing forresidues in edible portion of a commodity. Theresidue includes the parent, metabolites anddegradation products considered to betoxicologically significant. Changes in residuesresulting from processing and cooking may beincluded. The proportion of the commoditytreated or imported may be used to correctresidue estimates. When adequate informationis available, monitoring and surveillance dataor total diet studies may also be used. Whenappropriate, exposure to residues from otherknown uses are assessed. The NEDI iscalculated in milligrams of the residue perperson and expressed as a percent of the ADI.[FAO/WHO, 1997: Food Consumption & Exp.Assessment of Chemicals]

Natural sources - Non_manmade emissionsources, including biological and geologicalsources, wildfires, and windblown dust.[CARB, 2000: Glossary of Air PollutionTerms]

Negative dose - the amount of agent exiting atarget over a specified time interval. (cf:“positive dose”) [Zartarian, et al., 1997: Quant.Def. of Exp. & Related Concepts]

Non_linear dose response - A pattern offrequency or severity of biological responsethat does not vary proportionately with theamount of dose of an agent. When mode ofaction information indicates that responsesmay not follow a linear pattern below the doserange of the observed data, non_linear methodsfor determining risk at low dose may bejustified. [IRIS, 1999: Glossary of IRISTerms]

Nonpoint source - a. A diffuse pollutionsource that is not recognized to have a singlepoint of origin. [CARB, 2000: Glossary of AirPollution Terms]; b. A contributing factor towater pollution that cannot be traced to aspecific spot; like agricultural fertilizer runoff,sediment from construction. [SRA, 1999:Glossary of Risk Analysis Terms] [USDOE,

2000: RAIS Glossary]; c. A diffusepollution source (i.e., without a single point oforigin or not introduced into a receivingstream from a specific outlet). The pollutantsare generally carried off the land by stormwater. Common non_point sources areagriculture, forestry, urban, mining,construction, dams, channels, land disposal,saltwater intrusion, and city streets. [USEPA,1997a: EPA Terms of Environment]

Nonpoint source controls - General phraseused to refer to all methods employed tocontrol or reduce nonpoint source pollution.[NCSU, 1997: Watershedds Glossary]

Normal distribution - (Syn: Gaussiandistribution) The continuous frequencydistribution of infinite range represented by theequation: f(x) = (1/[2BF2]1/2) e-(x-:)2/2F2, where xis the abscissa,f(x) is the ordinate, : is themean, and F the standard deviation. Theproperties of a normal distribution include thefollowing: (1) It is a continuous, symmetricaldistribution; both tails extend to infinity; (2)the arithmetic mean, mode, and median areidentical; and (3) its shape is completelydetermined by the mean and standarddeviation. [Last, 1983: A Dictionary ofEpidemiology]

Occupational exposure limit (OEL) - A(generally legally_enforcable) limit on theamount or concentration of a chemical towhich workers may be exposed. [OxfordUniversity, 2000 - Chemical SafetyInformation Glossary]

Occupational tenure - The cumulativenumber of years a person worked in his or hercurrent occupation, regardless of number ofemployers, interruptions in employment, ortime spent in other occupations. [USEPA,1997b: Exposure Factors Handbook]

Passive dosimetry - A method of measuringthe amount of pesticide coming into contactwith an individual. [OECD, 1997:Occupational Exposure to Pesticides]

Pathway - see exposure pathway

Per capita intake rate - The average quantityof food consumed per person in a populationcomposed of both individuals who ate the foodduring a specified time period and those thatdid not. [USEPA, 1997b: Exposure FactorsHandbook]

Percutaneous Absorption - The process bywhich pesticides pass through the skin barrierand enter systemic circulation; normallyexpressed as flux (mass per unit skin surfacearea per unit time), but may also be expressed

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as a percent (fraction of amount deposited onskin (exposure) reaching systemic circulationtimes 100) per unit time. [USEPA, 1998:Postapp. Exposure Test GL.]

Permissible dose - The dose of a chemicalthat may be received by an individual withoutthe expectation of a significantly harmfulresult. [USEPA, 1997a: EPA Terms ofEnvironment]

Permissible exposure limit (PEL) -[sometimes, permissible exposure level] a.An occupational health standard to safeguardemployees against dangerous chemicals orcontaminants in the workplace. [Last, 1983: ADictionary of Epidemiology]; b. The legallimit for occupational exposure to airborneconcentrations of several hundred agents.Established by OSHA (U.S. OccupationalSafety and Health Administration). [REAP,1995: Residential Exposure AssessmentProject]; c. OSHA's number that tells theconcentration of a chemical in air that aworker may breathe for a given period of time,without experiencing adverse effects, (seeTLV). [University of Kentucky, 1999:Glossary of Safety Terms]

Persistence - a. In Scorecard, persistencegenerally refers to environmental persistence:the length of time a chemical stays in theenvironment, once introduced. Persistentchemicals do not break down easily in theenvironment. [ED, 2000: EnvironmentalScorecard Glossary]; b. The quality ofremaining for a long period of time (such as inthe environment or the body). Persistentchemicals (such as DDT and PCBs) are noteasily broken down. [New York Departmentof Health, 1999: Glossary of EnvironmentalHealth Terms]; c. Refers to the length oftime a compound stays in the environment,once introduced. A compound may persist forless than a second or indefinitely. [USEPA,1997a: EPA Terms of Environment] [CARB,2000: Glossary of Air Pollution Terms]

Person_time - A unit of measurementcombining persons and time, used asdenominator in instantaneous incidence rates.It is the sum of individual units of time that thepersons in the study population have beenexposed to the condition of interest. A variantis person_distance, e.g., as in passenger_miles.The most frequently used person_time isperson_years. With this approach, each subjectcontributes only as many years of observationto the population at risk as he is actuallyobserved; if he leaves after one year, hecontributes one person_year; if after ten, tenperson_years. The method can be used tomeasure incidence over extended and variabletiffs periods. [Last, 1983: A Dictionary of

Epidemiology]

Person_year - The sum of the number of yearseach person in the study population is at risk; ametric used to aggregate the total population atrisk assuming that 10 people at risk for oneyear is equivalent to 1 person at risk for 10years. [SRA, 1999: Glossary of Risk AnalysisTerms] [USDOE, 2000: RAIS Glossary]Personal air samples - Air samples takenwith a pump that is directly attached to theworker with the collecting filter and cassetteplaced in the worker's breathing zone (requiredunder OSHA asbestos standards and EPAworker protection rule). [USEPA, 1997a: EPATerms of Environment]

Personal exposure monitor - A device wornon or near the contact boundary that measuresconcentration [Zartarian, et al., 1997: Quant.Def. of Exp. & Related Concepts]

Personal measurement _ A measurementcollected from an individual's immediateenvironment using active or passive devices tocollect the samples. [USEPA, 1992a: DermalExposure Assessment]

Pharmacodynamics- Broadly, this is thescience concerned with the study of the way inwhich xenobiotics exert their effects on livingorganisms. Such a study aims to define thefundamental physicochemical processes whichlead to the biological effect observed. [Duffus,2000: Univ. Edinburgh Med School On-lineChemical Safety Glossary] [Cf.toxicodynamics]

Pharmacokinetic model - A model that canbe used to predict the time course ofabsorption, distribution, metabolism, andexcretion of a foreign substance in anorganisms body (e.g., pesticide). [USEPA,1998: Postapp. Exposure Test GL.]

Pharmacokinetics - a. This is the sciencewhich describes quantitatively the uptake ofdrugs by the body, their biotransformation,their distribution, metabolism, and eliminationfrom the body. Both total amounts and tissueand organ concentrations are considered."Toxicokinetics" is essentially the same termapplied to xenobiotics other than drugs.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary]; b. Theprocesses of absorption, distribution,metabolism and excretion of a drug or vaccine.[NIAID, 1997: HIV Vaccine Glossary]; c.The study of the absorption, distribution,metabolism and excretion of a substance in anyliving system. [OECD, 1997: OccupationalExposure to Pesticides]; d. The processes bywhich a chemical is handled, and transportedwithin the body, including how it is absorbed

into the body, how it is distributed in the bodytissues, how it is transformed in the body tometabolites and other breakdown compounds,and how it is excreted. [OFA, 2000: OxyfuelsGlossary]; e. The study of the time course ofabsorption, distribution, metabolism, andexcretion of a foreign substance (e.g., a drugor pollutant) in an organism's body. [USEPA,1992: GL for Exposure Assessment] [USEPA,1992a: Dermal Exposure Assessment] [REAP,1995: Residential Exposure AssessmentProject]; f. The field of study concerned withdefining, through measurement or modeling,the absorption, distribution, metabolism, andexcretion of drugs or chemicals in a biologicalsystem as a function of time. [USEPA, 1995:Benchmark Dose]; g. The study of the waythat drugs move through the body after theyare swallowed or injected. [USEPA, 1997a:EPA Terms of Environment] [Cf.toxicokinetics]

Physiologically Based Pharmacokinetic(PBPK) Model - a. Physiologically basedcompartmental model used to characterizepharmacokinetic behavior of a chemical.Available data on blood flow rates, andmetabolic and other processes which thechemical undergoes within each compartmentare used to construct a mass_balanceframework for the PBPK model. [IRIS, 1999:Glossary of IRIS Terms]; b. For dermalexposure testing, use of models to estimate thedermal permeability constant and amountsabsorbed by the best_fit method based onblood concentration_time profile data or bymonitoring the appearance and amounts ofmetabolites in postexposure urine samples orby measuring the concentration of parentcompound in the expired air. [USEPA, 1992a:Dermal Exposure Assessment]

Pica - Deliberate ingestion of non-nutritivesubstances such as soil. [USEPA, 1997b:Exposure Factors Handbook]

Plume - a. An area of chemicals in aparticular medium, such as air or groundwater,moving away from its source in a long band orcolumn. A plume can be a column of smokefrom a chimney or chemicals moving withgroundwater. [ATSDR, 1999: OnlineGlossary]; b. A visible or measurabledischarge of a contaminant from a given pointof origin that can be measured according to theRingelmann scale. [CARB, 2000: Glossary ofAir Pollution Terms]; c. An area ofchemicals moving away from its source in along band or column. A plume, for example,can be a column of smoke from a chimney orchemicals moving with groundwater. [NewYork Department of Health, 1999: Glossary ofEnvironmental Health Terms]; d. A plume isa visible smoke-like structure, which may

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contain pollutants emitted from an exhaust orsmoke stack and released into the atmosphere.This elongated band of smoke has changingcharacteristics that vary with its localenvironmental conditions. These conditionsmay include the physical and chemical natureof the pollutant, weather conditions anddownwind topography. [SHSU, 2000:Atmospheric Chemistry Glossary, attributed toWorld Press Review 41:24 (1994); Journal ofApplied Meteorology 33:996-1016 (1994);and Air Quality by Thad Godish, pages 58-64(1985)]; e. (1) The cloud of steam or smokethat comes from a chimney stack and blowsdownwind. (2) The contaminated portion ofgroundwater that moves past a source ofpollution. [SRA, 1999: Glossary of RiskAnalysis Terms, attributed to Stephen L.Brown]; f. (1) A visible or measurabledischarge of a contaminant from a given pointof origin. Can be visible or thermal in water,or visible in the air as, for example, a plume ofsmoke. (2) The area of radiation leaking froma damaged reactor. 3. Area downwind withinwhich a release could be dangerous for thoseexposed to leaking fumes. [USEPA, 1997a:EPA Terms of Environment] [USDOE, 2000:RAIS Glossary]

Point estimate - a single numerical valueresulting from calculation(s). [AIHA, 2000:Risk Assessment Principles for the IndustrialHygienist]

Point-of-contact exposure - Exposureexpressed as the product of the concentrationof an agent in the medium of exposure and theduration and surface area of contact with thebody surface (e.g. mg/cm2-hours). Someagents do not need to be absorbed into thebody but rather produce toxicity directly at thepoint of contact (e.g., the skin, mouth, GI tract,nose, bronchial tubes, or lungs). In such casesthe absorbed dose is not the relevant measureof exposure; rather it is the amount of toxicagents coming directly into contact with thebody surface. [REAP, 1995: ResidentialExposure Assessment Project]

Point-of-contact measurement of exposure -a. An approach to quantifying exposure bytaking measurements of concentration overtime at or near the point of contact between thechemical and an organism while the exposureis taking place. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [REAP, 1995:Residential Exposure Assessment Project]; b.Estimating exposure by measuringconcentrations over time (while the exposureis taking place) at or near the place where it isoccurring. [USEPA, 1997a: EPA Terms ofEnvironment]Point source - a. Any confined and discrete

conveyance from which pollutants are or maybe discharged. These include pipes, ditches,channels, tunnels, conduits, wells, containers,and concentrated animal feeding operations.[NCSU, 1997: Watershedds Glossary]; b. Asingle isolated stationary source of pollution.[SRA, 1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary]; c. Astationary location or fixed facility from whichpollutants are discharged; any singleidentifiable source of pollution; e.g., a pipe,ditch, ship, ore pit, factory smokestack.[USEPA, 1997a: EPA Terms of Environment]

Population - a. (1) All the inhabitants of agiven country or area considered together; thenumber of inhabitants of a given country orarea. (2) sampling. The whole collection ofunits from which a sample may be drawn; notnecessarily a population of persons; the unitsmay be institutions, records, or events. Thesample is intended to give results that arerepresentative of the whole population. [Last,1983: A Dictionary of Epidemiology]; b. Agroup of interbreeding organisms occupying aparticular space; the number of humans orother living creatures in a designated area.[USEPA, 1997a: EPA Terms of Environment];c. An aggregate of individuals of a specieswithin a specified location in space and time.[USEPA, 1998a: Guidelines for EcologicalRisk Assessment]; d. A group of individualswith common ancestry that are much morelikely to mate with one another than withindividuals from another such group. [WRI,1992: Biodiversity Glossary of Terms]

Population based - Pertaining to a generalpopulation defined by geopolitical boundaries;this population is the denominator and/or thesampling frame. [Last, 1983: A Dictionary ofEpidemiology]

Population dose (population exposure) - Thesummation of individual radiation dosesreceived by all those exposed to the source orevent being considered. [SRA, 1999: Glossaryof Risk Analysis Terms] [USDOE, 2000:RAIS Glossary]

Positive dose - The amount of agent entering atarget over a specified time interval (cf:“negative dose”) [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Potential dermal exposure - The total amountof pesticide coming into contact with theprotective clothing, work clothing and exposedskin. [OECD, 1997: Occupational Exposure toPesticides]

Potential dose - a. An exposure valuemultiplied by a contact rate (e.g., rates ofinhalation, ingestion, or absorption through the

skin) and assumes total absorption of thecontaminant. [NRC, 1991: Human Exp. forAirborne Pollutants]; b. The amount of achemical contained in material ingested, airbreathed, or bulk material applied to the skin.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment] [REAP, 1995: ResidentialExposure Assessment Project] [USEPA,1997b: Exposure Factors Handbook]; c. Theamount of a compound contained in materialswallowed, breathed, or applied to the skin.Potentially Responsible Party (PRP): Anyindividual or company__including owners,operators, transporters orgenerators__potentially responsible for, orcontributing to a spill or other contaminationat a Superfund site. Whenever possible,through administrative and legal actions, EPArequires PRPs to clean up hazardous sites theyhave contaminated. [USEPA, 1997a: EPATerms of Environment]; d. The amount ofchemical that could be inhaled withoutwearing a respirator, or which could bedeposited on the skin without wearingclothing. Potential dose is typically expressedas a mass per unit body weight per unit time(i.e., mg/kg/day). [USEPA, 1998: Postapp.Exposure Test GL.]

Potentially exposed - The condition wherevalid information, usually analyticalenvironmental data, indicates the presence ofcontaminant(s) of a public health concern inone or more environmental media contactinghumans (i.e., air, drinking water, soil, foodchain, surface water), and there is evidencethat some of those persons have an identifiedroute(s) of exposure (i.e., drinkingcontaminated water, breathing contaminatedair, having contact with contaminated soil, oreating contaminated food). [ATSDR, 1999:Online Glossary: ATSDR-specific term]

Precision - a. Quality of being exactly orsharply defined or stated. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]; b. (1) The quality of beingsharply defined or stated. One measure ofprecision id the number of distinguishablealternatives from which a measurement wanselected, sometimes indicated by the numberof significant digits in the measurement.Another measure of precision is the standarderror of measurement, the standard deviationof a series of replicate determinations of thesame quantity. See also measurement,problems with terminology. (2) In statistics,precision is defined as the inverse of thevariance of a measurement or estimate. [Last,1983: A Dictionary of Epidemiology]; c. Ameasure of how consistently the result isdetermined by repeated determinations withoutreference to any "true" value. [SRA, 1999:

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Glossary of Risk Analysis Terms]; d. Ameasure of the reproducibility of a measuredvalue under a given set of conditions.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1997b: Exposure Factors Handbook][Cf. accuracy]

Probabilistic analysis - Calculation andexpression of health risks using multiple riskdescriptors to provide the likelihood of variousrisk levels. Probabilistic risk resultsapproximate a full range of possible outcomesand the likelihood of each, which often ispresented as a frequency distribution graph,thus allowing uncertainty or variability to beexpressed quantitatively. [USEPA, 1999:Superfund Risk Assessment Glossary]

Probabilistic uncertainty analysis -Technique that assigns a probability densityfunction to each input parameter, thenrandomly selects values from each of thedistributions and inserts them into theexposure equation. Repeated calculationsproduce a distribution of predicted valuesreflecting the combined impact of variabilityin each input to the calculation. Monte Carlo isa common type of probabilistic uncertaintyanalysis. [USEPA, 1997b: Exposure FactorsHandbook]

Probability - a. A basic concept that may beconsidered undefinable, expressing "degree ofbelief." Alternatively, it is the limit of therelative frequency of an event in a sequence ofn random trials as n approaches infinity:(Number of occurrences of the event) / n.[Last, 1983: A Dictionary of Epidemiology];b. A probability assignment is a numericalencoding of the relative state of knowledge.[SRA, 1999: Glossary of Risk AnalysisTerms]; c. The chance that a particular eventwill occur given the population of all possibleevents. See definition for risk. [USDOE,2000: RAIS Glossary]

Probability density function (PDF) -Probability density functions are particularlyuseful in describing the relative likelihood thata variable will have different particular valuesof x. The probability that a variable will havea value within a small interval around x can beapproximated by multiplying f(x) (i.e., thevalue of y at x in a PDF plot) by the width ofthe interval. [Note: the original has a samplePDF plot that is not reproduced here.][USEPA, 1998a: Guidelines for EcologicalRisk Assessment]

Probability sample - see random sample

Probable error - The magnitude of errorwhich is estimated to have been made indetermination of results. [SRA, 1999:

Glossary of Risk Analysis Terms] [USDOE,2000: RAIS Glossary]Protective clothing - Clothing provided topersonnel to minimize the potential for skin,personal and company issued clothingcontamination. Also referred to as"anticontamination clothing," "anti-Cs" and"PCs." [USDOE, 1998: Radiological ControlManual]

Qualitative data - Observations orinformation characterized by measurement ona categorical scale, i.e., a dichotomous ornominal scale, or, if the categories are ordered,an ordinal scale. Examples are sex, hair color,death or survival, and nationality. [Last, 1983:A Dictionary of Epidemiology]

Random error - Indefiniteness of result due tofinite precision of experiment. Measure offluctuation in result upon repeatedexperimentation. [SRA, 1999: Glossary ofRisk Analysis Terms]

Random sample - a. A sample that is arrivedat by selecting sample units such that eachpossible unit has a fixed and determinateprobability of selection. [Last, 1983: ADictionary of Epidemiology]; b. A sampleselected from a statistical population such thateach individual has an equal probability ofbeing selected. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1997b:Exposure Factors Handbook]

Range - The difference between the largestand smallest values in a measurement data set.[USEPA, 1992: GL for Exposure Assessment][REAP, 1995: Residential ExposureAssessment Project] [USEPA, 1997b:Exposure Factors Handbook]

Reasonable maximum exposure (RME) - a.Used in conservative exposure assessmentcalculations; based not on worst-case scenario,but on 90% or 95% upper confidence limits oninput parameters. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist]; b. The maximum exposurereasonably expected to occur in a population.[USEPA, 1997a: EPA Terms of Environment][USDOE, 2000: RAIS Glossary]

Reasonable worst case - a. Reasonableunfavourable but not unrealistic situation:covering normal use patterns, including caseswhere populations are exposed to the samesubstance in more than one scenario, e.g.consumers or workers may use severalproducts containing the same substance. Thereasonable worst case prediction should alsoconsider upper estimates of the extreme useand reasonably foreseeable misuse. [EC, 1996:Risk Assessment for New Notified Subs]; b.

The lower portion of the "high end" of theexposure, dose, or risk distribution. Thereasonable worst case conceptually should betargeted at or above the 90th percentile in thedistribution, but below the 98th percentile.[REAP, 1995: Residential ExposureAssessment Project]; c. A semiquantitativeterm referring to the lower portion of the highend of the exposure, dose, or risk distribution.The reasonable worst case has historicallybeen loosely defined, including synonymouslywith maximum exposure or worst case, andassessors are cautioned to look for contextualdefinitions when encountering this term in theliterature. As a semiquantitative term, it issometimes useful to refer to individualexposures, doses, or risks that, while in thehigh end of the distribution, are not in theextreme tail. For consistency, it should referto a range that can conceptually be describedas above the 90th percentile in the distribution,but below about the 98th percentile. (comparemaximum exposure range, worst case).[USEPA, 1992: GL for Exposure Assessment];d. An estimate of the individual dose,exposure, or risk level received by anindividual in a defined population that isgreater than the 90th percentile but less thanthat received by anyone in the 98th percentilein the same population. Reasonably AvailableControl Technology (RACT): Controltechnology that is reasonably available, andboth technologically and economicallyfeasible. Usually applied to existing sources innonattainment areas; in most cases is lessstringent than new source performancestandards. Reasonably Available ControlMeasures (RACM): A broadly defined termreferring to technological and other measuresfor pollution control. [USEPA, 1997a: EPATerms of Environment]

Receptor - a. molecular biology. A moleculeon the surface of a cell that serves as arecognition or binding site for antigens,antibodies or other cellular or immunologiccomponents. [NIAID, 1997: HIV VaccineGlossary]; b. ecology. A plant, animal,community of organisms, or ecosystem that isexposed to stressors in the environment.[SETAC, 1997: Ecological Risk AssessmentTechnical Issue Paper]; c. ecology. The(ecological) entity which is exposed to thestressor. [USEPA, 1997: Guidance onCumulative Risk Assessment, Planning andScoping] [USEPA, 1997a: EPA Terms ofEnvironment] [USEPA, 1998a: Guidelines forEcological Risk Assessment] [CENR, 1999:Ecorisk in the Federal Government]

Receptor population - The exposedindividual relative to the exposure pathwayconsidered. [USEPA, 1999: Superfund RiskAssessment Glossary]

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Recommended Exposure Limit (REL) - An8_ or 10_hour time_weighted average (TWA)or ceiling (C) exposure concentrationrecommended by NIOSH that is based on anevaluation of the health effects data. NIOSHDefinition [OSHA, 2000: On-lineOSHA/NIOSH Glossary of RespiratoryProtective Terms]

Reconstructed source - Facility in whichcomponents are replaced to such an extent thatthe fixed capital cost of the new componentsexceeds 50 percent of the capital cost ofconstructing a comparable brand_new facility.New_source performance standards may beapplied to sources reconstructed after theproposal of the standard if it is technologicallyand economically feasible to meet thestandards. [USEPA, 1997a: EPA Terms ofEnvironment]

Reconstruction of dose - a. An approach toquantifying exposure from internal dose,which is in turn reconstructed after exposurehas occurred, from evidence within anorganism such as chemical levels in tissues orfluids or from evidence of other biomarkers ofexposure. [USEPA, 1992: GL for ExposureAssessment] [USEPA, 1992a: DermalExposure Assessment] [REAP, 1995:Residential Exposure Assessment Project]; b.Estimating exposure after it has occurred byusing evidence within an organism such aschemical levels in tissue or fluids. [USEPA,1997a: EPA Terms of Environment]

Reentry dose level (RDL) - Dose level atwhich reentry into an area previously treatedwith a chemical can occur with negligibledeleterious effects caused by exposure to thechemical because the biological mode ofaction threshold for that chemical has not beenmet (mg/kg/day). [USEPA, 1998: Postapp.Exposure Test GL.]

Reference Concentration (RfC) - a. Anestimate, derived by the U.S. EPA with anuncertainty spanning perhaps an order ofmagnitude) of a daily exposure to the humanpopulation, (including sensitive subgroups)that is likely to be without appreciable risk ofdeleterious effects during a lifetime ofexposure. The RfC is derived from a no orlowest observed adverse effect level fromhuman or animal exposures, to whichuncertainty or "safety" factors are applied.[CARB, 2000: Glossary of Air PollutionTerms]; b. An estimate of the dailyinhalation dose, expressed in terms of anambient concentration, that can be taken dailyover a lifetime without appreciable risk. [ED,2000: Environmental Scorecard Glossary]; c.An estimate (with uncertainty spanning

perhaps an order of magnitude) of a continuousinhalation exposure to the human population(including sensitive subgroups) that is likely tobe without an appreciable risk of deleteriouseffects during a lifetime. It can be derived froma NOAEL, LOAEL, or benchmarkconcentration, with uncertainty factorsgenerally applied to reflect limitations of thedata used. Generally used in EPA's noncancerhealth assessments. [IRIS, 1999: Glossary ofIRIS Terms]; d. An estimate (withuncertainty spanning perhaps an order ofmagnitude) of a continuous inhalationexposure to the human population (includingsensitive subgroups) that is likely to be withoutan appreciable risk of deleterious noncancereffects during a lifetime. [USEPA, 1995:Benchmark Dose] [USDOE, 2000: RAISGlossary]

Reference Dose (RfD) - a. EPA toxicityvalue for evaluating noncarcinogenic effectsresulting from exposures at Superfund sites; anestimate (with uncertainty spanning an order ofmagnitude or greater) of daily exposure levelfor humans, including sensitivesubpopulations, that is likely to be without anappreciable risk or deleterious effects during alifetime.(1) chronic RfD: applicable for timeperiods of seven years to lifetime; (2)developmental RfD: likely to be withoutappreciable risk of developmental effects,applicable to a single exposure event; (3)subchronic RfD: applicable for time periodsof two weeks to seven years. (Source: RAGS,1989) [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]; b. Anestimate delivered by the U.S. EPA (withuncertainty spanning perhaps an order ofmagnitude) of the daily exposure to the humanpopulation, (including sensitivesubpopulations) that is likely to be withoutdeleterious effects during a lifetime. The RfDis reported in units of mg of substance/kg bodyweight/day for oral exposures. [CARB, 2000:Glossary of Air Pollution Terms]; c. Anestimate of the daily ingestion dose, expressedin terms of amount per unit of body weight,that can be taken daily over a lifetime withoutappreciable risk. [ED, 2000: EnvironmentalScorecard Glossary]; d. An estimate (withuncertainty spanning perhaps an order ofmagnitude) of a daily oral exposure to thehuman population (including sensitivesubgroups) that is likely to be without anappreciable risk of deleterious effects during alifetime. It can be derived from a NOAEL,LOAEL, or benchmark dose, with uncertaintyfactors generally applied to reflect limitationsof the data used. Generally used in EPA'snoncancer health assessments. [IRIS, 1999:Glossary of IRIS Terms]; e. A dose of apesticide that the U.S. EPA considers safe forregular daily consumption by humans without

adverse health effects. Generated by taking theNOAEL from animal studies and addinguncertainty factors to account for differencesbetween animals and humans, andsusceptibility within the human population.[NRDC, 1998: Trouble on the Farm]; f.Toxicity value for evaluating noncarcinogenic(systemic) effects of daily exposure tocontaminant levels without appreciabledeleterious effects during a lifetime. See ourtoxicity values. [USDOE, 2000: RAISGlossary]; g. An estimate (with uncertaintyspanning perhaps an order of magnitude) of adaily exposure to the human population(including sensitive subgroups) that is likely tobe without appreciable risk of deleteriousnoncancer effects during a lifetime. [USEPA,1995: Benchmark Dose]

Reference Exposure Level (REL) - A termused in risk assessment. It is the concentrationat or below which no adverse health effects areanticipated for a specified exposure period.[CARB, 2000: Glossary of Air PollutionTerms]

Representative sample - a. The term"representative" as it is commonly used isundefined in the statistical or mathematicalsense; it means simply that the sampleresembles the population in some way. Theuse of probability sampling will not ensurethat any single sample will be "representative"of the population in all possible respects. If,for example, it is found that the sample agedistribution is quite different from that of thepopulation, it is possible to make correctionsfor the known differences. A common fallacylies in the unwarranted assumption that, if thesample resembles the population closely onthose factors that have been checked, it is"totally representative" and that no differenceexists between the sample and the universe orreference population. Kendall and Buckland(1971) comment as follows: "In the widestsense, a sample which is representative of apopulation. Some confusion arises accordingto whether 'representative' is regarded asmeaning 'selected by some process whichgives all samples an equal chance of appearingto represent the population'; or, alternatively,whether it means 'typical in respect of certaincharacteristics, however chosen’. On thewhole, it seems best to confine the word'representative' to samples which turn out to beso, however chosen, rather than apply it tothose chosen with the object of beingrepresentative." [Last, 1983: A Dictionary ofEpidemiology]; b. A sample that closelyapproximates both the concentration ofactivity and the physical and chemicalproperties of material (e.g., particle size andsolubility in case of air sampling of the aerosolto which workers may be exposed). [USDOE,

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1998: Radiological Control Manual]; c. Aportion of material or water that is as nearlyidentical in content and consistency as possibleto that in the larger body of material or waterbeing sampled. [USEPA, 1997a: EPA Termsof Environment]Representativeness - The degree to which asample is, or samples are, characteristic of thewhole medium, exposure, or dose for whichthe samples are being used to make inferences.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1997b: Exposure Factors Handbook]

Respirable particle - Particle of the size (<5.0:m) most likely to be deposited in thepulmonary portion of the respiratory tract.[SRA, 1999: Glossary of Risk AnalysisTerms]Respiration - The process by which animalsuse up stored foods (by combustion withoxygen) to produce energy. [USEPA, 2000:Global Warming Glossary]

Response rate - The number of completed orreturned survey instruments (questionnaires,interviews, etc.) divided by the total number ofpersons who would have been surveyed if allhad participated. Usually expressed as apercentage. Nonresponse can have severalcauses, e.g., death, removal out of the surveycommunity, and refusal. [Last, 1983: ADictionary of Epidemiology]

Risk_specific dose - The dose associated witha specified risk level. [USEPA, 1997a: EPATerms of Environment] [USDOE, 2000: RAISGlossary]

Route - see exposure route

Route of administration - The way a drug isadministered to an animal; i.e. orally,intramuscularly, intravenously. [WSU, 1999:Definitions and Abbreviations of VeterinaryTerms]

Route of entry - Means by which a chemicalenters the body: ingestion, inhalation, dermalabsorption, or injection. [AIHA, 2000: RiskAssessment Principles for the IndustrialHygienist] [Cf. exposure route]

Route of exposure - see exposure route

Sample - a. A selected subset of a population.A sample may be random or nonrandom andmay be representative or nonrepresentative.Several types of sample can be distinguished,including the following: Cluster sample: Eachunit selected is a group of persons (all personsin a city block, a family, etc.) rather than anindividual. Grab sample (Syn: sample ofconvenience): These ill_defined terms describesamples selected by easily employed but

basically nonprobabilistic methods."Man_inthe_street" surveys and a survey ofblood pressure among volunteers who drop inat an examination booth are in this category. Itis improper to generalize from the results of asurvey based upon such a sample for there isno way of knowing what sorts of bias mayhave been operating. Probability (random)sample: All individuals have a known chanceof selection. They may all have an equalchance of being selected, or, if a stratifiedsampling method is used, the rate at whichindividuals from several subsets are sampledcan be varied so as to produce greaterrepresentation of some classes than of others.A probability sample is created by assigning anidentity (label, number) to all individuals in the"universe" population, e.g., by arranging themin alphabetical order and numbering insequence, or simply assigning a number toeach, or by grouping according to area ofresidence and numbering the groups. The nextstep is to select individuals (or groups) forstudy by a procedure such as use of a table ofrandom numbers (or comparable procedure) toensure that the chance of selection is known.Simple random sample: In this elementary kindof sample each person has an equal chance ofbeing selected out of the entire population. Oneway of carrying out thil procedure is to assigneach person a number, starting with 1, 2, 3, andso on. The l numbers are selected at random,preferably from a table of random numbers,until the desired sample size is attained.Stratified random sample: This involvesdividing the population into distinc subgroupsaccording to some important characteristic,such as age or socioeconomi status, andselecting a random sample out of eachsubgroup. If the proportion o the sample drawnfrom each of the subgroups, or strata, is thesame as the propor tion of the total populationcontained in each stratum (e.g., age group40_59 con stitutes 20% of the population, and20~o of the sample comes from this age strasum), then all strata will be fairly representedwith regard to numbers of person in thesample. Systematic sample: The procedure ofselecting according to some simple, systematrule, such as all persons whose names beginwith specified alphabetical letters, bar oncertain dates or located at specified points on amaster list. A systematic sampl may lead toerrors that invalidate generalizations. [Last,1983: A Dictionary of Epidemiology]; b. Asmall part of something designed to show thenature or quality of the whole. Exposure-related measurements are usually samples ofenvironmental or ambient media, exposures ofa small subset of a population for a short time,or biological samples, all for the purpose ofinferring the nature and quality of parametersimportant to evaluating exposure. [USEPA,1992: GL for Exposure Assessment] [USEPA,

1997b: Exposure Factors Handbook]

Scenario evaluation - An approach toquantifying exposure by measurement orestimation of both the amount of a substancecontacted, and the frequency/duration ofcontact, and subsequently linking thesetogether to estimate exposure or dose.[USEPA, 1992: GL for Exposure Assessment][USEPA, 1992a: Dermal ExposureAssessment] [REAP, 1995: ResidentialExposure Assessment Project]Scenario timeframe - The time period(current and/or future) being considered for theexposure pathway. [USEPA, 1999: SuperfundRisk Assessment Glossary]

Sensitivity - a. The degree to which a systemwill respond to a change in climaticconditions. [RFF, 2000: Glossary of Termsand Concepts]; b. The ability of a test towork on people you know have the infection.More precisely TP/(TP+FN), where TP is thenumber of true positives and FN is the numberof false negatives [Swinton, 1999: ADictionary of Epidemiology]

Sensitivity analysis - a. In uncertaintyanalysis, comparison of risk estimates basedon the means and upper bounds of theprobability distributions of the input variables.[AIHA, 2000: Risk Assessment Principles forthe Industrial Hygienist]; b. A technique thattests the sensitivity of an output variable to thepossible variation in the input variables of agiven model. The purpose of sensitivityanalysis is to quantify the influence of inputvariables on the output variable and developbounds on the model output. The sensitivityof the output variable of a given mathematicalmodel depends on the nature of themathematical relationship of the model (andplausible values of its input variables). For agiven model, the sensitivity of the outputvariable with respect to each input variable iscomputed, and the sensitivities of all inputvariables are compared. When computing thesensitivity with respect to a given inputvariable, all other input variables are heldfixed at their nominal vales. Sensitivity can becalculated for a point estimate of an inputvariable or over a range of an input variable.Varying several input parameters at the sametime will often highlight interaction effects inthe model which are not obvious during "oneat a time" variation. [REAP, 1995: ResidentialExposure Assessment Project]; c. Process ofchanging one variable while leaving the othersconstant to determine its effect on the output.This procedure fixes each uncertain quantity atits credible lower and upper bounds (holdingall others at their nominal values, such asmedians) and computes the results of eachcombination of values. The results help to

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identify the variables that have the greatesteffect on exposure estimates and help focusfurther information gathering efforts. [USEPA,1997b: Exposure Factors Handbook]

Sensitivity and specificity (of a screeningtest) - Sensitivity is the proportion of trulydiseased persons in the screened populationwho are identified as diseased by the screeningtest. Sensitivity is a measure of the probabilityof correctly diagnosing a case, or theprobability that any given case will beidentified by the test (Syn: true positive rate).Specificity is the proportion of trulynondiseased persons who are so identified bythe screening test. It is a measure of theprobability of correctly identifying anondiseased person with a screening test (Syn:true negative rate). [Last, 1983: A Dictionaryof Epidemiology]

Short Term Exposure Limit (STEL)- a.According to American Conference ofGovernmental Hygienists, this is the timeweighted average (TWA) airborneconcentration to which workers may beexposed for periods up to 15 minutes, with nomore than 4 such excursions per day and atleast 60 minutes between them. [Duffus, 2000:Univ. Edinburgh Med School On-lineChemical Safety Glossary]; b. Themaximum permissible concentration of amaterial, generally expressed in ppm in air, fora defined short period of time (typically 5minutes). These values, which may differ fromcountry to country, are often backed up byregulation and therefore may be legallyenforceable. [Oxford University, 2000 -Chemical Safety Information Glossary] ; c.Represented as STEL or TLVSTEL, this is themaximum concentration to which workers canbe exposed for a short period of time (15minutes) for only four times throughout theday with at least one hour between exposures.Also the daily TLVTWA must not beexceeded. [University of Kentucky, 1999:Glossary of Safety Terms] [also see timeweighted average]

Short_Term Exposure - Multiple orcontinuous exposure to an agent for a shortperiod of time, usually one week. [IRIS,1999: Glossary of IRIS Terms]

Skew distribution - An older and lessrecommended term for an asymmetricalfrequency distribution. If a unimodaldistribution has a longer tail extending towardlower values of the variate, it is said to havenegative skewness; in the contrary case,positive skewness. [Last, 1983: A Dictionaryof Epidemiology]

Skin Adherence - The property of a material

which causes it to be retained on the surface ofthe epidermis (adheres to the skin). [USEPA,1992a: Dermal Exposure Assessment]

Sorption - a. A general term covering theprocesses of adsorption, absorption,desorption, ion exchange, ion exclusion, ionretardation, chemisorption, and dialysis. (1)adsorption: surface retention of solid, liquid,or gas molecules, atoms, or ions by a solid orliquid; (2) absorption: penetration ofsubstances into the bulk of the solid or liquid;(3) desorption: process of removing a sorbedsubstance by the reverse of adsorption orabsorption. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]; b. Aclass of processes by which one material istaken up by another. Absorption is refers to theprocess of the penetration of one material intoanother; adsorption to the action of onematerial being collected on another's surface.[SHSU, 2000: Atmospheric ChemistryGlossary, attributed to Crutzen, Paul J. andGraedel, T.E. Atmospheric Change: An EarthSystem Perspective, p. 435]; c. The action ofsoaking up or attracting substances; processused in many pollution control systems.[USEPA, 1997a: EPA Terms of Environment]

Source - a. Any place or object from whichair pollutants are released. Sources that arefixed in space are stationary sources andsources that move are mobile sources. [CARB,2000: Glossary of Air Pollution Terms][ODEQ, 1999: Air Quality Glossary]; b. Theactivity or entity from which an agent isreleased for potential human exposure. [REAP,1995: Residential Exposure AssessmentProject]; c. A place where pollutants areemitted, for example a chimney stack. [SRA,1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary]; d. Anentity or action that releases to theenvironment or imposes on the environmentchemical, biological, or physical stressor orstressors. [USEPA, 1997: Guidance onCumulative Risk Assessment, Planning andScoping] [USEPA, 1998a: Guidelines forEcological Risk Assessment] [CENR, 1999:Ecorisk in the Federal Government]

Source term - a. As applied to chemicalstressors, the type, magnitude, and patterns ofchemical(s) released. [USEPA, 1998a:Guidelines for Ecological Risk Assessment];b. The release rate of hazardous agent from afacility or activity. [SRA, 1999: Glossary ofRisk Analysis Terms] [USDOE, 2000: RAISGlossary]

Spatially-averaged boundary exposure - thespatially-integrated exposure divided by thecontact boundary area [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Spatially-averaged exposure - The spatially-integrated exposure divided by the volume ofthe contact zone [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]

Spatially-integrated exposure - The amountof agent present in the contact zone [Zartarian,et al., 1997: Quant. Def. of Exp. & RelatedConcepts]Standard deviation - a. A measure ofdispersion or variation. It is the most widelyused measure of dispersion of a frequencydistribution. It is equal to the positive squareroot of the VARIANCE. The mean tells wherethe values for a group are centered. Thestandard deviation is a summary of howwidely dispersed the values are around thiscenter. [Last, 1983: A Dictionary ofEpidemiology]; b. A measure of dispersionor variation, usually taken as the square root ofthe variance. [SRA, 1999: Glossary of RiskAnalysis Terms] [USDOE, 2000: RAISGlossary]

Standard error - The standard deviation of anestimate. [Last, 1983: A Dictionary ofEpidemiology]

Stationary source - a. A non_mobile sourcesuch as a power plant, refinery, ormanufacturing facility which emits airpollutants. [CARB, 2000: Glossary of AirPollution Terms]; b. A fixed source ofregulated air pollutants (e.g. industrialfacility). See also source; mobile sources.[ODEQ, 1999: Air Quality Glossary]; c. Apollution location that is fixed rather thanmoving. [SRA, 1999: Glossary of RiskAnalysis Terms]; d. A fixed_site producerof pollution, mainly power plants and otherfacilities using industrial combustionprocesses. (See: point source.) [USEPA,1997a: EPA Terms of Environment] [Cf.mobile source]

Statistical power - The probability that onecan detect an effect if there really is one.[FACS, 2000: Epidemiology for Journalists]

Statistical significance - a. The probabilityof obtaining a result as extreme or moreextreme as that observed even if the nullhypothesis is true. [FACS, 2000:Epidemiology for Journalists]; b. Theprobability that a result likely to be due tochance alone. By convention, a differencebetween two groups is usually consideredstatistically significant if chance could explainit only 5% of the time or less. Study designconsiderations may influence the a priorichoice of a different statistical significancelevel. [IRIS, 1999: Glossary of IRIS Terms];c. Statistical methods allow an estimate to be

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made of the probability of the observed orgreater degree of association betweenindependent and dependent variables under thenull hypothesis. From this estimate, in asample of given size, the statistical"significance" of a result can be stated.Usually the level of statistical significance isstated by the P value. [Last, 1983: ADictionary of Epidemiology]; d. theprobability that an event or difference occurredas the result of the intervention (vaccine)rather than by chance alone. This probability isdetermined by using statistical tests to evaluatecollected data. Guidelines for definingsignificance are chosen before data collectionbegins. [NIAID, 1997: HIV VaccineGlossary]; e. The statistical significancedetermined by using appropriate standardtechniques of statistical analysis with resultsinterpreted at the stated confidence level andbased on data relating species which arepresent in sufficient numbers at control areasto permit a valid statistical comparison withthe areas being tested. [SRA, 1999: Glossaryof Risk Analysis Terms] [USDOE, 2000:RAIS Glossary]; f. An inference that theprobability is low that the observed differencein quantities being measured could be due tovariability in the data rather than an actualdifference in the quantities themselves. Theinference that an observed difference isstatistically significant is typically based on atest to reject one hypothesis and acceptanother. [USEPA, 1992: GL for ExposureAssessment]

Statistically significant effect - In statisticalanalysis of data, a health effect that exhibitsdifferences between a study population and acontrol group that are unlikely to have arisenby chance alone. [USEPA, 1995: BenchmarkDose]

Steady state exposure - Exposure to anenvironmental pollutant whose concentrationremains constant for a period of time. [SRA,1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary]

STEL - see short term exposure limit

Stochastic - This is the adjective applied toany phenomenon obeying the laws ofprobability. [Duffus, 2000: Univ. EdinburghMed School On-line Chemical SafetyGlossary]

Stochastic model - A mathematical modelwhich takes into consideration the presence ofsome randomness in one or more of itsparameters or variables. The predictions of themodel therefore do not give a single pointestimate but a probability distribution ofpossible estimates. Contrast with deterministic.

We might distinguish demographicstochasticity which arises from the discretenessof individuals and individual events such asbirth, and environmental stochasticity arisingfrom more_or_less unpredictable interactionswith the outside world. [Swinton, 1999: ADictionary of Epidemiology]

Stressor - Any physical, chemical, orbiological entity that can induce an adverseresponse. [SETAC, 1997: Ecological RiskAssessment Technical Issue Paper] [USEPA,1997: Guidance on Cumulative RiskAssessment, Planning and Scoping] [USEPA,1997a: EPA Terms of Environment] [USEPA,1998a: Guidelines for Ecological RiskAssessment] [CENR, 1999: Ecorisk in theFederal Government] [Note: Some of thedefinitions above also say that “stressor” issynonymous with “agent.” Although this isgenerally true, the term “stressor” also includesthe connotation that the adverse response canbe the result of a lack of something – such as ahabitat – which would also be called a“stressor.” The term “agent” does not havethis connotation, and is only used to denote acausative entity which actually physicallyexists as part of the environment.]

Subchronic Exposure - a. Exposure to asubstance spanning approximately 10% of thelifetime of an organism. [IRIS, 1999: Glossaryof IRIS Terms]; b. An exposure ofintermediate duration between acute andchronic. [REAP, 1995: Residential ExposureAssessment Project]; c. Exposure to asubstance spanning no more thanapproximately 10 percent of the lifetime of anorganism. [USEPA, 1995: Benchmark Dose];d. Multiple or continuous exposures lastingfor approximately ten percent of anexperimental species lifetime, usually over athree_month period. [USEPA, 1997a: EPATerms of Environment]

Synergism - [also, synergy] a. When theadverse effect or risk from two or morechemicals interacting with each other is greaterthan what it would be if each chemical wasacting separately. [ED, 2000: EnvironmentalScorecard Glossary]; b. The definition ofsynergism in epidemiology is somewhatcontroversial. We offer two definitions, thefirst a common dictionary definition, thesecond a more specific definition encounteredin bioassay. (1) A situation in which thecombined effect of two or more factors isgreater than the sum of their solitary effects.(2) Two factors act synergistically if there arepersons who will get the disease when exposedto both factors but not when exposed to eitheralone. Antagonism, the opposite of synergism,exists if there are persons who will get thedisease when exposed to one of the factors

alone, but not when exposed to both. Note thatunder these definitions, two factors may actsynergistically in some persons andantagonistically in others. [Last, 1983: ADictionary of Epidemiology]; c. Aninteraction between two substances that resultsin a greater effect than both of the substancescould have had acting independently. [SRA,1999: Glossary of Risk Analysis Terms][USDOE, 2000: RAIS Glossary] [USEPA,1997a: EPA Terms of Environment]

Synergistic effect - a. A synergistic effect isthe any effect of two chemicals acting togetherwhich is greater than the simple sum of theireffects when acting alone: such chemicals aresaid to show synergism. [Duffus, 2000: Univ.Edinburgh Med School On-line ChemicalSafety Glossary]; b. Joint effects of two ormore agents, such as drugs that increase eachother's effectiveness when taken together.[SRA, 1999: Glossary of Risk AnalysisTerms] [USDOE, 2000: RAIS Glossary]

Systematic error - A reproducible inaccuracyintroduced by faulty equipment, calibration, ortechnique. [SRA, 1999: Glossary of RiskAnalysis Terms] [Cf. bias]

Systemic dose - The dose of agent within thebody (i.e., not localized at the point ofcontact). Thus skin irritation cause by contactwith an agent is not a systemic effect, but liverdamage due to absorption of the agent throughthe skin is. [REAP, 1995: ResidentialExposure Assessment Project]

Target - A physical, biological, or ecologicalobject exposed to an agent [Zartarian, et al.,1997: Quant. Def. of Exp. & RelatedConcepts]

Target organ - a. The biological organ(s)most adversely effected by exposure to achemical substance. [IRIS, 1999: Glossary ofIRIS Terms]; b. An organ (such as the liveror kidney) that is specifically affected by atoxic chemical. [New York Department ofHealth, 1999: Glossary of EnvironmentalHealth Terms]

Target organ dose - The target organ dose isthe amount of a potentially toxic substancereaching the organ chiefly affected by thatsubstance. [Duffus, 2000: Univ. EdinburghMed School On-line Chemical SafetyGlossary]

Target population - 1. The collection ofindividuals, items, measurements, etc., aboutwhich we want to make inferences. The termis sometimes used to indicate the populationfrom which a sample is drawn and sometimesto denote any "reference" population about

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which inferences are required. 2. The group ofpersons for whom an intervention is planned.[Last, 1983: A Dictionary of Epidemiology]

Temporally-averaged exposure - Thetemporally-integrated exposure divided by theduration of the time period [Zartarian, et al.,1997: Quant. Def. of Exp. & RelatedConcepts]

Temporally-integrated exposure - Theintegral of instantaneous point exposure valuesover a time period [Zartarian, et al., 1997:Quant. Def. of Exp. & Related Concepts]Theoretical maximum daily intake (TMDI)- The TMDI is a prediction of the maximumdaily intake of a pesticide residue, assumingthat residues are present at the MRLs and thataverage daily consumption of foods per personis represented by regional diets. The TMDI iscalculated for the various GEMS/Foodregional diets in milligrams of residue perperson and is expressed as a percent of theADI. [FAO/WHO, 1997: Food Consumption& Exp. Assessment of Chemicals]

Threshold limit value (TLV) - a. Themaximum permissible concentration of amaterial, generally expressed in parts permillion in air for some defined period of time(often 8 hours). These values, which maydiffer from country to country, are oftenbacked up by regulation and therefore may belegally enforceable. [Oxford University, 2000- Chemical Safety Information Glossary]; b.The TLV_C (ceiling exposure limit) is anexposure limit which should not be exceededunder any circumstances. [Oxford University,2000 - Chemical Safety Information Glossary]

Time profile - A continuous record ofinstantaneous values (e.g., exposure, dose, ormedium intake rate) over a time period[Zartarian, et al., 1997: Quant. Def. of Exp. &Related Concepts]

Time weighted average concentration(TWA) - a. This is a regulatory value definingthe concentration of a substance to which aperson is exposed in ambient air, averagedover a period, usually 8 hours. For a personexposed to 0.1 mg m_3 for 6 hours and 0.2 mgm_3 for 2 hours, the 8 hour TWA is (0.1 x 6 +0.2 x 2) / 8 which equals 0.125 mg m_3.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary]; b. Theaverage value of a parameter (such asconcentration of an agent in air) that variesover time. [REAP, 1995: Residential ExposureAssessment Project]; c. The average time,over a given work period (e.g., 8 hour workday), of a person's exposure to a chemical oran agent. The average is determined bysampling for the contaminant throughout the

time period. Represented as TLV_TWA.[University of Kentucky, 1999: Glossary ofSafety Terms]

Time-activity Pattern - Information onactivities in which various individuals engage,length of time spent performing variousactivities, locations in which individuals spendtime, and length of time spent by individualswithin various environments. [REAP, 1995:Residential Exposure Assessment Project]

TLV or TLV-C - see threshold limit value

Tolerable Daily Intake (TDI) - TDIs areapplied to chemical contaminants in food anddrinking water. The presence of contaminantsis unwanted and they have no useful function,differing from additives and residues wherethere is or was deliberate use resulting in theirpresence. TDIs are calculated on the basis oflaboratory toxicity data with the application ofuncertainty factors. A TDI is thus an estimateof the amount of a substance (contaminant) infood or drinking water that can be ingesteddaily over a lifetime without appreciable healthrisk. [Duffus, 2000: Univ. Edinburgh MedSchool On-line Chemical Safety Glossary]

Total effective dose equivalent (TEDE) - Thesum of the effective dose equivalent (forexternal exposures) and the committedeffective dose equivalent (for internalexposures). Deep dose equivalent to the wholebody may be used as effective dose equivalentfor external exposures. [USDOE, 1998:Radiological Control Manual]

Total fluid intake - Consumption of all typesof fluids including tap water, milk, soft drinks,alcoholic beverages, and water intrinsic topurchased foods. [USEPA, 1997b: ExposureFactors Handbook]

Total human exposure - Accounts for allexposures a person has to a specificcontaminant, regardless of environmentalmedium or route of entry (inhalation,ingestion, and dermal absorption). Sometimestotal exposure is used incorrectly to refer toexposure to all pollutants in an environment.Total exposure to more than one pollutantshould be stated explicitly as such. [NRC,1991: Human Exp. for Airborne Pollutants]

Toxicodynamics - a. Alterations in abiological system resulting from exposure tochemicals. [JHU, 1999: Altweb Glossary]; b.See pharmacodynamics. [Duffus, 2000: Univ.Edinburgh Med School On-line ChemicalSafety Glossary] [Note: The terms“toxicodynamics” and “pharmacodynamics”describe the same processes;“pharmacodynamics” was derived in reference

to drugs or other substances used fortreatment, while “toxicodynamics” has morerecently been used to refer to non-pharmaceutical toxic substances such asenvironmental pollutants.] [Cf.pharmacodynamics]

Toxicokinetics - a. The absorption,distribution, metabolism, storage, andexcretion of chemicals. [JHU, 1999: AltwebGlossary]; b. See pharmacokinetics.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary] [Note:The terms “toxicokinetics” and“pharmacokinetics” describe the sameprocesses; “pharmacokinetics” was derived inreference to drugs or other substances used fortreatment, while “toxicokinetics” has morerecently been used to refer to non-pharmaceutical toxic substances such asenvironmental pollutants.] [Cf.pharmacokinetics]

Transport - a. The movement of chemicalswithin one environmental compartment, orfrom one compartment to another. [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]; b. The movement of asoil particle, nutrient, or pesticide from itsoriginal position. This movement may occur inwater or air currents. Nutrients and pesticidescan be attached to soil particles or dissolved inwater as they move. [NCSU, 1997:Watershedds Glossary]

Uncertainty - a. The deviation in predictedvalues from the actual values; may result fromlack of data or variability in the data. [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]; b. A lack ofconfidence in the prediction of a riskassessment that may result from naturalvariability in natural processes, imperfect or incomplete knowledge, or errors in conductingan assessment. [SETAC, 1997: EcologicalRisk Assessment Technical Issue Paper][CENR, 1999: Ecorisk in the FederalGovernment]; c. In the conduct of riskassessment (hazard identification,dose_response assessment, exposureassessment, risk characterization) the need tomake assumptions or best judgments in theabsence of precise scientific data createsuncertainties. These uncertainties, expressedqualitatively and sometimes quantitatively,attempt to define the usefulness of a particularevaluation in making a decision based on theavailable data. [USEPA, 1995: BenchmarkDose]; d. Uncertainty represents a lack ofknowledge about factors affecting exposure orrisk and can lead to inaccurate or biasedestimates of exposure. The types ofuncertainty include: scenario uncertainty,parameter uncertainty, and model uncertainty.

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[USEPA, 1997b: Exposure Factors Handbook]

Uncertainty analysis - a. A process in whichthe sources of uncertainty in an estimate areidentified, and an estimate made of themagnitude and direction of the resulting error.(1) qualitative: utilizes descriptive methods;(2) semi-quantitative: uses simplemathematical techniques such as sensitivityanalysis; (3) quantitative: uses complexmathematical techniques such as Monte Carloanalysis. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]; b. Adetailed examination of the systematic andrandom errors of a measurement or estimate;an analytical process to provide informationregarding the uncertainty. [SRA, 1999:Glossary of Risk Analysis Terms] [USDOE,2000: RAIS Glossary]

Uncertainty factor (UF) - [sometimes alsocalled safety factor or modifying factor] a.Used in converting NOAELs / LOAELs toRfDs and generally equal 10; account for (1)intraspecies variation, (2) interspeciesvariation, (3) use of a RfD based on a differenttime period, or (4) use of a LOAEL rather thana NOAEL to develop a RfD. [AIHA, 2000:Risk Assessment Principles for the IndustrialHygienist]; b. This term may be used ineither of two ways depending upon the context(i) Mathematical expression of uncertaintyapplied to data that are used to protectpopulations from hazards which cannot beassessed with high precision. (ii) With regardto food additives and contaminants, a factorapplied to the no_observed effect level toderive acceptable daily intake (ADI) (theno_observed_effect level is divided by thesafety factor to calculate the ADI). The valueof the safety factor depends on the nature ofthe toxic effect, the size and type of thepopulation to be protected, and the quality ofthe toxicological information available.[Duffus, 2000: Univ. Edinburgh Med SchoolOn-line Chemical Safety Glossary]; c. Oneof several, generally 10_fold factors, used inoperationally deriving the RfD and RfC fromexperimental data. UFs are intended to accountfor (1) the variation in sensitivity among themembers of the human population, i.e.,interhuman or intraspecies variability; (2) theuncertainty in extrapolating animal data tohumans, i.e., interspecies variability; (3) theuncertainty in extrapolating from data obtainedin a study with less_than_lifetime exposure tolifetime exposure, i.e., extrapolating fromsubchronic to chronic exposure; (4) theuncertainty in extrapolating from a LOAELrather than from a NOAEL; and (5) theuncertainty associated with extrapolation fromanimal data when the data base is incomplete.[IRIS, 1999: Glossary of IRIS Terms]; d.Factors used to adjust for multiple sources of

uncertainty encountered in using experimentalanimal data for predicting effects on humans,such as intraspecies variation, interspeciesvariation, synergism, and different route ofexposure (i.e. oral versus inhalation). [REAP,1995: Residential Exposure AssessmentProject]; e. One of several, generally 10_foldfactors used in operationally deriving thereference dose (RfD) from experimental data.UFs are intended to account for (1) thevariation in sensitivity among members of thehuman population; (2) the uncertainty inextrapolating animal data to the case ofhumans; (3) the uncertainty in extrapolatingfrom data obtained in a study that is ofless_than_lifetime exposure; and (4) theuncertainty in using LOAEL data rather thanNOAEL data. [USEPA, 1995: BenchmarkDose] [USEPA, 1997a: EPA Terms ofEnvironment] [USDOE, 2000: RAIS Glossary]

Upper bound - An plausible upper limit to thetrue value of a quantity. This is usually not atrue statistical confidence limit. [IRIS, 1999:Glossary of IRIS Terms]

Uptake - The process by which a substancecrosses an absorption barrier and is absorbedinto the body. [USEPA, 1992: GL forExposure Assessment] [USEPA, 1992a:Dermal Exposure Assessment] [USEPA,1997b: Exposure Factors Handbook]

Variability - a. A source of uncertainty in riskassessment, due to the fact that manyparameters are best described not as pointvalues but as probability distributions. [AIHA,2000: Risk Assessment Principles for theIndustrial Hygienist]; b. Variability arisesfrom true heterogeneity across people, placesor time, and can affect the precision ofexposure estimates and the degree to whichthey can be generalized. The types ofvariability include: spatial variability,temporal variability, and inter-individualvariability. [USEPA, 1997b: Exposure FactorsHandbook]

Variable - a. Any quantity that varies. Anyattribute, phenomenon, or event that can havedifferent values. [Last, 1983: A Dictionary ofEpidemiology]; b. A water qualityconstituent (for example, total phosphoruspollutant concentration) or other measuredfactors (such as streamflow, rainfall). [NCSU,1997: Watershedds Glossary]

Variance - a. statistics. A measure of thevariation shown by a set of observations,defined by the sum of the squares of deviationsfrom the mean, divided by the number ofdegrees of freedom in the set of observations.[Last, 1983: A Dictionary of Epidemiology];b. law. Permission granted for a limited time

(under stated conditions) for a person orcompany to operate outside the limitsprescribed in a regulation. [CARB, 2000:Glossary of Air Pollution Terms]; c. law.Government permission for a delay orexception in the application of a given law,ordinance, or regulation. [USEPA, 1997a:EPA Terms of Environment] [USDOE, 2000:RAIS Glossary]

Wet deposition - The removal of atmosphericparticles to the earth's surface by rain or snow.[SRA, 1999: Glossary of Risk AnalysisTerms]

Whole body dose - The sum of the annualdeep dose equivalent for external exposuresand the committed effective dose equivalentfor internal exposures. [USDOE, 1998:Radiological Control Manual]Whole body - For the purposes of externalexposure, head, trunk (including male gonads),arms above and including the elbow, or legsabove and including the knee. [USDOE,1998: Radiological Control Manual]Worst case - A semiquantitative termreferring to the maximum possible exposure,dose, or risk, that can conceivably occur,whether or not this exposure, dose, or riskactually occurs or is observed in a specificpopulation. Historically, this term has beenloosely defined in an ad hoc way in theliterature, so assessors are cautioned to lookfor contextual definitions when encounteringthis term. It should refer to a hypotheticalsituation in which everything that canplausibly happen to maximize exposure, dose,or risk does in fact happen. This worst casemay occur (or even be observed) in a givenpopulation, but since it is usually a veryunlikely set of circumstances, in most cases, aworst-case estimate will be somewhat higherthan occurs in a specific population. As inother fields, the worst-case scenario is a usefuldevice when low probability events may resultin a catastrophe that must be avoided even atgreat cost, but in most health risk assessments,a worst-case scenario is essentially a type ofbounding estimate. [USEPA, 1992: GL forExposure Assessment] [REAP, 1995:Residential Exposure Assessment Project]

Worst-case scenario - a method of conductingan exposure assessment in which the mostconservative value of each input parameter isselected. See also reasonable maximumexposure. [AIHA, 2000: Risk AssessmentPrinciples for the Industrial Hygienist]

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REFERENCES

AIHA (2000). Risk Assessment Principles for the Industrial Hygienist (Authors: Michael Jayjock, Jerry Lynch, Deborah Nelson) AmericanIndustrial Hygiene Association. American Industrial Hygiene Association Press, Fairfax, VA.

ATSDR (1999). “Glossary of Terms”. Agency for Toxic Substances and Disease Registry, Atlanta, GA. (On-line; last update December 21,1999) http://www.atsdr.cdc.gov/glossary.html (Downloaded May 4, 2000)

CARB (2000). “Glossary of Air Pollution Terms.” California Air Resources Board, Sacramento, CA. (On-line; Last update March 3, 2000)http://arbis.arb.ca.gov/html/gloss.htm (Downloaded May 5, 2000).

CENR (1999). “Ecological Risk Assessment in the Federal Government.” Committee on Environment and Natural Resources, National Scienceand Technology Council, Washington, DC. CENR/5-99/001 Available on-line at http://www.epa.gov/ncea/cenrecog.htm (Downloaded May 8,2000)

Dark, Graham (1998). “The On Line Medical Dictionary.” CancerWEB, Academic Medical Publishing, UK. (On-line: Last update November 27,1998) http://www.graylab.ac.uk/omd/ (Downloaded May 5, 2000)

Debacker M; Domres B; de Boer J (1999). Glossary of new concepts in disaster medicine: A supplement to Gunn's, Multilingual Dictionary ofDisaster Medicine. Prehospital and Disaster Medicine 14(3):146_149 [cited from PDM (2000)]

Duffus, John H. (2000). “Some Terms used in Toxicology, Chemical Safety and Allied Subjects.” Department of Community Health Sciences,University of Edinburgh Medical School, Edinburgh, Scotland. (On-line; last update April 28, 2000.)http://www.med.ed.ac.uk/HEW/tox/glossall.html (Downloaded May 8, 2000) Note: This same glossary appears at other web sites such as theHeriot-Watt University, Edinburgh.

EC (1996). “Technical Guidance Document in Support of Commission Directive 93/67/EEC on Risk Assessment for New Notified Substancesand Commission Regulation (EC) No 1488/94 on Risk Assessment for Existing Substances, Part 1"

ED (2000). “Scorecard Glossary.” Environmental Scorecard, Environmental Defense [Formerly Environmental Defense Fund], New York, NY(On-line: Last update unknown) http://www.scorecard.org/about/glossary.tcl (Downloaded May 10, 2000)

EDVCB (2000). “Environmental Economics Glossary.” Environmental Damage Valuation and Cost Benefit Website, Long Beach, NY. (On-line:Last update January 20, 2000) http://www.damagevaluation.com/glossary.htm (Downloaded May 10, 2000)

FACS (2000). “Epidemiology for Journalists: Glossary of Epidemiological Terms.” Foundation for American Communications, Pasadena, CA.(On-line: Last update unknown) http://www.facsnet.org/report_tools/guides_primers/epidemiology/glossary.html (Downloaded May 5, 2000)

FAO/WHO (1997). “Food consumption and exposure assessment of chemicals, Report of a FAO/WHO Consultation.” Geneva, Switzerland 10-14 February 1997 WHO/FSF/FOS/97.5

Gunn, Sisvan William (1990). Multilingual Dictionary of Disaster Medicine, Kluwer Academic Publishers. [cited from PDM (2000)]

IRIS (1999). “Glossary of IRIS Terms, October, 1999.” Integrated Risk Information System, U.S. Environmental Protection Agency, Office ofResearch and Development. (On-line: Last revised January 19, 2000) http:/www.epa.gov/iris/gloss8.htm (Downloaded May 8, 2000). Note: Thisglossary contains definitions of terms used frequently in IRIS. It is intended to assist users in understanding terms utilized by the U.S. EPA inhazard and dose_response assessments. These definitions are not all_encompassing, but are useful "working definitions". It is assumed that theuser has some familiarity with risk assessment and health science.

JHU (1999). “Altweb Glossary.” Center for Alternatives to Animal Testing, John Hopkins University, Baltimore, MD (On-line: Last updateMarch 8, 2000) http://altweb.jhsph.edu/general/glossary.htm (Downloaded May 10, 2000). Note: Altweb is a collaborative effort funded by theAlternatives Research & Development Foundation, the Doerenkamp _ Zbinden Foundation, the Humane Society of the United States, the Officefor Laboratory Animal Welfare at the National Institutes of Health, and the Procter & Gamble Company. It is being developed by the Center forAlternatives to Animal Testing at Johns Hopkins University, in collaboration with the Altweb Project Team, to serve academic, industrial andgovernment scientists, educators, the media, and the general public.

Last, John M. [Ed.] (1983). A Dictionary of Epidemiology. International Epidemiological Association, Inc. Oxford University Press, New York.ISBN 0-19-503257-8.

NCSU (1997). “Watershedds Glossary.” Watershedds (WATER, Soil, and Hydro_ Environmental Decision Support System), NCSU WaterQuality Group, North Carolina State University, Raleigh, NC. (On-line: Last update October 15, 1997)http://h2osparc.wq.ncsu.edu/info/glossary.html (Downloaded May 10, 2000)

NRC (1983). Risk Assessment in the Federal Government: Managing the Process. National Research Council, National Academy Press,

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Washington, DC ISBN: 0-309-03349-7. Pages 3-4, from text.

NRC (1989). Improving Risk Communication. National Research Council, National Academy Press, Washington, DC ISBN: 0-309-03943-6.Pages 321-322, “Key Terms and Distinctions.”

NRC (1991). Human Exposure Assessment for Airborne Pollutants. National Research Council, National Academy Press, Washington, DC.ISBN: 0-309-04284-4.

NRC (1996). Understanding Risk: Informing Decisions in a Democratic Society. National Research Council, National Academy of Sciences,National Academy Press, Washington, DC. ISBN: 0-309-05396-X.

NIAID (1997). “HIV Vaccine Glossary.” National Institute of Allergy and Infectious Diseases, National Institutes of Health. (On-line: June,1997) http://www.niaid.nih.gov/factsheets/GLOSSARY.htm (Downloaded May 5, 2000) Selected entries were used.

New York Department of Health (1999). “Glossary of Environmental Health Terms.” New York State Department of Health, Center forEnvironmental Health, Education Unit. Troy, NY. (On-line: Last update November 1, 1999)http://www.health.state.ny.us/nysdoh/consumer/environ/toxglos.htm (Downloaded May 5, 2000). Note: This glossary is intended to help peoplebecome familiar with the terms they are likely to see in government reports, engineering studies and health literature.

NIEHS (1999). “Environmental Genome Project Glossary.” National Institutes of Environmental Health Sciences, National Institutes of Health,Research Triangle Park, NC. (On-line: Last update November 8, 1999) http://www.niehs.nih.gov/envgenom/glossary.htm#glossary (DownloadedMay 4, 2000) Selected entries used.

NRDC (1998). “Trouble on the Farm: Growing Up with Pesticides in Agricultural Communities.” Natural Resources Defense Council, NewYork, NY, October, 1998. (On-line) http://www.nrdc.org/health/kids/farm/glos.asp (Downloaded May 10, 2000)

ODEQ (1999). “Air Quality Glossary.” Oregon Department of Environmental Quality, Portland, OR. (On-line: Last update October 11, 1999)http://www.teleport.com/~hanrahan/glossary.htm (Downloaded May 10, 2000)

OECD (1997). “Series on Testing and Assessment No. 9: Guidance Document for the Conduct of Occupational Exposure to Pesticides DuringAgricultural Application” Organisation for Economic Co-Operation and Development, Paris. OCDE/GD(97)148

OECES (1998). “Glossary of Terms.” Online Ethics Center for Engineering and Science. (On-line only: Last update September 5, 1998)http://www.onlineethics.org/gloss/ (Downloaded May 10, 2000) Note: The Online Ethics Center for Engineering and Science’s mission is toprovide engineers, scientists, and science and engineering students with resources useful for understanding and addressing ethically significantproblems that arise in their work, and to serve those who are promoting learning and advancing understanding of responsible practice inengineering and science. The Ethics Center will occasionally sponsor conferences located in physical space, such as the 1999 InternationalConference on Ethics in Engineering and Computer Science. In other respects, the Ethics Center has no physical locale. It exists in "cyberspace"and provides materials exclusively by posting them on line.

OFA (2000). “Glossary of Technical Terms and Acronyms.” Oxygenated Fuels Association, Arlington, VA (On-line: Last update January 14,2000) http://www.ofa.net/glossary.htm (Downloaded May 10, 2000)

OSHA (2000). On-line Glossary of Respiratory Protective Terms (OSHA/NIOSH). Occupational Health and Safety Administration, U.S.Department of Labor, Washington, DC. http://www.osha_slc.gov/SLTC/respiratory_advisor/oshafiles/glossary.html (Downloaded May 5, 2000)

Oxford University (2000). “Chemical Safety Information _ Glossary” The Physical and Theoretical Chemistry Laboratory, Oxford University,England. (On-line; last update April 28, 2000)http://physchem.ox.ac.uk/MSDS/glossary.html (Downloaded May 5, 2000.)

PDM (2000). “Disaster Terminology.” From Health Disaster Management: Guidelines for Evaluation and Research in the Utstein Style, TaskForce on Quality Control of Disaster Management, Prehospital and Disaster Medicine (On-line: Last update May 10, 2000)http://pdm.medicine.wisc.edu/vocab.htm (Downloaded May 10, 2000) Note: Includes terms from Debacker M; Domres B; de Boer J (1999).Glossary of new concepts in disaster medicine: A supplement to Gunn's, Multilingual Dictionary of Disaster Medicine. Prehospital and DisasterMedicine 14(3):146_149 [Debacker, et al., 1999], and Gunn, Sisvan William (1990). Multilingual Dictionary of Disaster Medicine, KluwerAcademic Publishers, Boston. [Gunn, 1990]

REAP (1995). Residential Exposure Assessment Project. A joint project of the Society for Risk Analysis, International Society of ExposureAnalysis, and the U.S. Environmental Protection Agency, with support from the Chemical Manufacturers Association and Procter & Gamble.Washington, DC. (to be published, 2000)

RERF (1999). “Radiation Effects Research Foundation Glossary.” Radiation Effects Research Foundation, Hiroshima, Japan. (On-line: Lastupdate August 18, 1999) http://www.rerf.or.jp/eigo/glossary/gloshmpg.htm (Downloaded May 4, 2000) Selected definitions used. Note: RERF isa cooperative Japan_United States research organization. RERF conducts research and studies__for peaceful purposes__on the effects of

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radiation exposure on humans with a view toward contributing to the maintenance of the health and welfare of atomic_bomb survivors and to theenhancement of the health of all people.

RFF (2000). “Glossary of Terms and Concepts.” Resources for the Future, Washington, DC (On-line: Last update March 1, 2000)http://www.rff.org/glossary.htm (Downloaded May 10, 2000) Note: Resources for the Future is a nonprofit and nonpartisan organization based inthe nation's capital that conducts independent research __ rooted primarily in economics and other social sciences __ on environmental andnatural resource issues.

SETAC (1997). “Ecological Risk Assessment Technical Issue Paper” Society of Environmental Toxicology and Chemistry, Pensacola, FL, USA

SHSU (2000). “Atmospheric Chemistry Glossary, 2000 Version.” Sam Houston State University, Huntsville, TX. (On-line: Last updated Spring,2000) http://www.shsu.edu/~chemistry/Glossary/glos.html (Downloaded May 10, 2000)

SRA (1999). “Glossary of Risk Analysis Terms.” Society for Risk Analysis, McLean, VA.(On-line: Last update July 15, 1999) http://www.sra.org/glossary.htm (Downloaded May 10, 2000)

Stanford University (1998). “Glossary from Stanford Radiation Manual.” Stanford University, Palo Alto, CA. (On-line: Last update August 27,1998) http://www.stanford.edu/dept/EHS/rad/manual/appendices/glossary.htm (Downloaded May 5, 2000). Note: Not used in this combinedglossary, since (a) it was copyrighted, and (b) the terms were either specific to Stanford or were redundant with USDOE (1998).

Swinton, Jonathan (1999). “A Dictionary of Epidemiology.” University of Cambridge, Cambridge, UK. (On-line: Last update: November 12,1999) http://www.kings.cam.ac.uk/~js229/glossary.html (Downloaded May 4, 2000) Selected entries included. Note from the author (JonathanSwinton): Dictionary definitions are always prone to dispute; the guiding principle here is to record the usages of groups in Oxford, Cambridge,and Warwick. Thus I've included some terms from immunology and what we call classical epidemiology, but the chief perspective here is that ofecological epidemiology. Many terms, such as distribution, are discussed only from this specialist perspective. I'd be pleased to hear yoursuggestions, as long as you bear this in mind.

UCMP (1998). “UCMP Glossary of Natural History Terms, Vol. 5: Ecological Terms) University of California Museum of Paleontology,University of California, Berkeley, CA. (On-line: Last update September 30, 1998) http://www.ucmp.berkeley.edu/glossary/gloss5ecol.html(Downloaded May 10, 2000)

University of Kentucky (1999). “Glossary of Terms.” Hazard Communication Program, Occupational Health and Safety, Environmental Healthand Safety Division, University of Kentucky, Lexington, KY. (On-line: Last update June 15, 1999)http://www.uky.edu/FiscalAffairs/Environmental/ohs/glos.html (Downloaded May 5, 2000)

USDOE (1998). “Radiological Control Manual.” U.S. Department of Energy, Oak Ridge, TN. (Available on-line: Last modified September 11,1998.) http://tis.eh.doe.gov/docs/rcm/gloss.html (Downloaded May 5, 2000)

USDOE (2000). “Risk Assessment Information System (RAIS) Glossary: A Glossary of Useful Terms Found in Risk Assessment, EMBAM,Health Physics, and Waste Management Reports.” Environmental Restoration/Waste Management Risk Assessment Program, Oak RidgeOperations Office, United States Department of Energy, Oak Ridge, TN (On-line: Last update unknown) http://risk.lsd.ornl.gov/rap_hp.shtml(Downloaded May 10, 2000)

USEPA (1992). “Guidelines for Exposure Assessment.” U.S. Environmental Protection Agency, Washington, DC. EPA/600/Z-92/001.

USEPA (1992a). “Dermal Exposure Assessment: Principles and Applications.” U.S. Environmental Protection Agency, Exposure AssessmentGroup, Washington, DC. EPA/600/8-91/011B Available on-line at http://www.epa.gov/ncea/dermal.htm (Downloaded May 8, 2000)

US EPA (1995). “The Use of the Benchmark Dose Approach in Health Risk Assessment.” Risk Assessment Forum, U.S. EnvironmentalProtection Agency, Washington, DC. EPA/630/R-94/007.

USEPA (1997) “Guidance on Cumulative Risk Assessment. Part 1. Planning and Scoping.” Washington, DC: Science Policy Council, U.S.Environmental Protection Agency. Memo dated July 3, 1997. (Available on-line at: http://www.epa.gov/ORD/spc/2cumrisk.htm)

USEPA (1997a). “EPA Terms of Environment.” U.S. Environmental Protection Agency, Office of Communications, Education, and PublicAffairs, Washington, DC. (On-line: Last update May 13, 1998) http://www.epa.gov/OCEPAterms/ (Downloaded May 5, 2000) Note: "Terms OfEnvironment" defines in non_technical language the more commonly used environmental terms appearing in EPA publications, news releases,and other Agency documents available to the general public, students, the media, and Agency employees. The definitions do not constitute theAgency's official use of terms and phrases for regulatory purposes, and nothing in this document should be construed to alter or supplant anyother federal document. Official terminology may be found in the laws and related regulations as published in such sources as the CongressionalRecord, Federal Register, and elsewhere. The terms selected for inclusion are derived from previously published lists, internal glossariesproduced by various programs and specific suggestions made by personnel in many Agency offices. The chemicals and pesticides selected forinclusion are limited to those most frequently referred to in Agency publications or that are the subject of major regulatory or program activities.

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USEPA (1997b). “Exposure Factors Handbook.” U.S. Environmental Protection Agency, National Center for Environmental Assessment,Washington, DC. EPA/600/P-95/002F Available on-line at http://www.epa.gov/ORD/WebPubs/exposure/glossary.pdf (Downloaded May 8,2000)

USEPA (1998). “Occupational and Residential Exposure Test Guidelines; Group B _ Postapplication Exposure Montoring Test Guidelines.” U.S.EPA Series 875 (Version 5.4, Feb 10, 1998). U.S. Environmental Protection Agency, Washington, DC. draft

USEPA (1998a). “Guidelines for Ecological Risk Assessment.” U.S. Environmental Protection Agency, Risk Assessment Forum, Washington,DC. EPA/630/R-95/002F (Available on-line at http://www.epa.gov/ncea/ecorsk.htm)

USEPA (1999). “Superfund Risk Assessment Glossary.” U.S. Environmental Protection Agency, Office of Emergency Response andRemediation, Washington, DC. (On-Line: Last update March 30, 1999) http://www.epa.gov/oerrpage/superfund/programs/risk/glossary.htm(Downloaded May 5, 2000)

USEPA (2000). “Global Warming Glossary.” U.S. Environmental Protection Agency, Washington, DC. (On-line: Last update January 14, 2000)http://www.epa.gov/globalwarming/glossary.html (Downloaded May 10, 2000)

WRI (1992). “Biodiversity Glossary of Terms.” World Resources Institute, Washington, DC. (On-line: Last update unknown)http://www.wri.org/biodiv/gbs_glos.html (Downloaded May 10, 2000)

WSU (1999). “Definitions and Abbreviations of Veterinary Terms.” Washington State University, Pullman, WA. (On-line: Last updateDecember 9, 1999) Available at http://www.vetmed.wsu.edu/glossary/ (Downloaded May 5, 2000) Only a few of the terms have been included.

Zartarian, V.G., Ott, W.R., Duan, N. (1997) A Quantitative Definition of Exposure and Related Concepts. J. Expos. Anal. Environ. Epidem.,7(4): 411-438


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