EPA ExpoBox Terminology
This page provides definitions for terms referenced on the EPA-Expo-Box website. Definitions were obtained from multiple sources, some of which are indicated in the table below. Sources include the Exposure Factors Handbook: 2011 Edition and the 1992 Guidelines for Exposure Assessment, among others.
Links to other glossaries that define terms related to exposure and risk assessment are provided below, including the glossary developed by the International Programme on Chemical Safety (IPCS) and the Organisation for Economic Cooperation and Development (OECD). These groups joined together to "develop internationally harmonized generic and technical terms used in chemical hazard/risk assessment." IPCS and OECD sought to define both generic terms and terms related to specific technical fields. As part of this effort, the Exposure Assessment Terminology Working Group developed a glossary of exposure assessment terminology to help facilitate communication and promote consistency of language in exposure science.
- EPA’s Guidelines for Carcinogen Risk Assessment
- EPA’s Guidelines for Human Exposure Assessment
- EPA’s Integrated Risk Information System (IRIS) Glossary
- EPA’s Risk Assessment Glossary
- EPA’s Terminology Services: Terms and Acronyms
- Exposure Factors Handbook: 2011 Edition
- IPCS Risk Assessment Terminology (PDF) (122 pp, 950 K, About PDF) Exit
- USGS Toxic Substances Hydrology Program: Index of Definitions Exit
- Waste and Cleanup Risk Assessment Glossary
| Term | Definition | Location in EPA-Expo-Box |
|---|---|---|
| Additive exposure or risk | Combined exposure or risk summed, assuming each component acts as if the other were not present. (Source: U.S. EPA Framework for Cumulative Risk Assessment) | Approaches Tiers and Types: Aggregate and Cumulative |
| Aggregate exposure assessment | Aggregate exposure assessment considers combined exposures to a single stressor across multiple routes and multiple pathways. (Source: U.S. EPA Framework for Cumulative Risk Assessment) | Approaches Tiers and Types: Aggregate and Cumulative |
| Antagonistic | Exposure to multiple stressors that leads to a decreased response that is less than what would be estimated for exposure to each chemical independently. | Approaches Tiers and Types: Aggregate and Cumulative |
| Anthropogenic | Resulting from human activity. | Media: Soil and Dust, Water |
| Applied dose | Applied dose is the amount of contaminant at the absorption barrier (e.g., gastrointestinal [GI] tract, respiratory tract, skin) that can be absorbed by the body. The applied dose might be smaller than the potential dose if the contaminant is only partially bioavailable. | Routes |
| Bioaccumulation | Bioaccumulation is the uptake of a substance from an environmental medium through all routes, including food chain transfers. For example, accumulation of substances can occur through ingestion of contaminated plants or animals. | Media: Aquatic Biota |
| Bioaccumulation factor | Bioaccumulation Factor - In natural environments, a bioaccumulation factor, or BAF, is the ratio of the chemical concentration in an animal to the amount of chemical to which it is exposed through all routes, including the food chain. | Media: Aquatic Biota |
| Bioavailability | Bioavailability is a measure of how much of a contaminant is absorbed when people are exposed to that contaminant through inhalation, skin contact or food intake. | Media: Soil and Dust |
| Bioconcentration | Bioconcentration refers to direct transfers of the chemical from the surrounding environmental medium into the plant or animal (e.g., a chemical that is transferred from soil into a plant through its roots); for animals, it does not account for uptake by ingestion; for a fish, bioconcentration of a substance in the water includes direct uptake from water through its gills. | Media: Food, Aquatic Biota |
| Bioconcentration factor | A bioconcentration factor, or BCF, is the ratio of the chemical concentration in the animal (e.g., fish) or plant to the chemical concentration in the surrounding environmental media (e.g., water, soil). | Media: Aquatic Biota |
| Biodegradation | Biodegradation is the breakdown of a chemical that occurs by a biotic organism, such as bacteria. | Media: Aquatic Biota |
| Biologically effective dose | Biologically effective dose is the amount of contaminant that interacts with the internal target tissue or organ. | Routes |
| Biomagnification | Biomagnification or trophic-level transfer refers to bioaccumulated contaminants that might be transferred up the food chain. | Media: Aquatic Biota |
| Biomarker | Biomarkers are cellular, biochemical, analytical, or molecular measures obtained from biological media (e.g., tissues, cells, fluids) that can indicate exposure to a chemical. (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches: Exposure Reconstruction |
| Biomonitoring | Biomonitoring involves analyzing tissues (including blood and hair), body fluids, excreta, or exhaled air to determine contaminant or biomarker concentrations. (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches: Exposure Reconstruction |
| Biota-sediment accumulation factor (BSAF) | A biota sediment accumulation factor, or BSAF, is an empirical partitioning ratio relating concentration in sediment to the concentration in an aquatic organism, including benthic organisms and higher trophic level fish. | Media: Aquatic Biota |
| Biotransfer factor (BTF) | BTF is an empirical ratio relating the chemical concentration in biota, such as produce, livestock, or animal products (such as eggs), to the amount of chemical to which the plant or animal is exposed in soil or feed (or other media). | Media: Food |
| Biotransformation | Biotransformation refers to the alteration of a contaminant in the body. | Media: Food |
| Bounding estimate | An estimate of exposure, dose, or risk that is higher or lower than that incurred by the person with the highest or lowest exposure, dose, or risk in the population being assessed. Bounding estimates are useful in developing statements that exposures, doses, or risks are "not greater than" or "less than" the estimated value, because assumptions are used which define the likely bounding conditions. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Approaches Tiers and Types: Deterministic and Probabilistic |
| Central tendency exposure | A measure of the middle or the center of an exposure distribution. The mean is the most commonly used measure of central tendency. | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Consumer-only intake rate | The average quantity of food consumed per person in a population composed only of individuals who ate the food item of interest during a specified period. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Approaches |
| Cumulative exposure assessment | Cumulative exposure assessment generally evaluates combined exposure to multiple stressors via multiple exposure pathways. (Source: U.S. EPA Framework for Cumulative Risk Assessment) | Tiers and Types: Aggregate and Cumulative |
| Deterministic exposure assessments | Deterministic exposure assessments use point estimates (or, single values) to quantify the amount of exposure that is likely to occur for potential receptors. They produce an exposure estimate that is also a point estimate. | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Direct measurement | Direct measurement or point-of-contact measurement "evaluates an exposure as it occurs, by using direct methods to measure the chemical concentrations at the interface between the person and the environment as a function of time, resulting in an exposure profile." (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches |
| Dose | Dose is the amount of a substance available for interactions with metabolic processes or biologically significant receptors after crossing the outer boundary of an organism. | Routes |
| Exposure factors | Exposure factors are factors related to human behavior and characteristics that help determine an individual's exposure to a chemical. | Approaches |
| Exposure or risk descriptor | Exposure or risk descriptor is an estimate for a specific point on the exposure distribution (e.g., mean, median, 95th percentile, maximum) for individual or population exposures. | Approaches: Scenario Evaluation |
| Exposure reconstruction | Exposure reconstruction (reverse dosimetry) relies on biomarker measurements and intake and uptake predictions to estimate dose levels (Source: U.S. EPA Biomonitoring—An Exposure Science Tool for Exposure and Risk Assessment) | |
| Exposure route | An exposure route is the way that a contaminant enters an individual or population after contact. (Source: IPCS Risk Assessment Terminology (PDF) (122 pp, 950 K, About PDF) Exit) | Routes |
| Exposure scenario | Exposure scenario is a set of facts, assumptions, and inferences about how exposure takes place that aids the exposure assessor in evaluating or quantifying exposure. | Routes Media |
| Exposure setting | Exposure setting is the physical setting where an exposure of interest occurs and is defined by the boundaries of the analysis and the scope and geographic scale of the assessment. | Approaches: Scenario Evaluation |
| Forward dosimetry | Uses animal pharmacokinetic models to convert the administered dose-response relationship from toxicology studies to a target site dose-response relationship that can be used to evaluate human biomonitoring results (Sources: NRC, 2006; U.S. EPA Biomonitoring—An Exposure Science Tool for Exposure and Risk Assessment) | Approaches |
| General population | General population is the total of individuals inhabiting an area or making up a whole group. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Lifestages and Populations |
| Geophagy | A form of soil ingestion involving the intentional ingestion of earths, usually associated with cultural practices. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Media: Soil and Dust |
| Half-life | Time required for one-half of the original mass of the chemical to be degraded, transformed, or destroyed in a particular medium. | Approaches: Exposure Reconstruction Media: Aquatic Biota |
| Henry’s law constant (KH) | Ratio of vapor pressure to water solubility; provides an index of partitioning for a compound between atmospheric and aqueous phases. | Media: Air, Aquatic Biota Chemical Classes: Organics |
| High-end exposure | High-end exposure is an estimate of individual exposure or dose for those persons at the upper end of an exposure or dose distribution, conceptually above the 90th percentile, but not higher than the individual in the population who has the highest exposure or dose. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Internal dose | Internal dose is the amount of contaminant that gets past the exchange boundary (e.g., GI tract, lung) and into the blood, or the amount of the contaminant that can interact with organs and tissues to cause biological effects. | Routes |
| Lifestage | Lifestages are temporal stages of life that have distinct anatomical, physiological, and behavioral or functional characteristics that contribute to potential differences in vulnerability to environmental exposures. (Source: U.S. EPA Framework for Assessing Health Risk of Environmental Exposures to Children) | Lifestages and Populations |
| Lipophilicity | Ability of a chemical to dissolve in fats, oils, and lipids. | Media: Aquatic Biota |
| Maximum exposure | Maximum exposure is a semiquantitative term referring to the uppermost portion of the exposure range (above the 98th percentile). (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Mechanism of toxicity | The specific biochemical interactions and processes initiated by a stressor that lead to an adverse outcome. | Approaches: Scenario Evaluation |
| Mode of action | Mode of action is generally considered to be the sequence of major biochemical events that lead to an adverse response. | Approaches Tiers and Types: Aggregate and Cumulative |
| Molecular diffusivity | Molecular diffusivity represents the propensity of a chemical to move through a medium, and is a function of the chemical (primarily molecular weight) and the medium (e.g., temperature, atmospheric pressure, water density). | Media: Air |
| Monte Carlo simulation | A Monte Carlo simulation is a technique for characterizing the uncertainty and variability in exposure (or risk) estimates by repeatedly sampling the probability distributions of the exposure (or risk) equation inputs and using these inputs to calculate a range of exposure (or risk) values. (Source: U.S. EPA Risk Assessment Guidance for Superfund (RAGS) Volume III - Part A) | Approaches: Scenario Evaluation Tiers and Types: Deterministic and Probabilistic |
| Nanomaterials (engineered) | Engineered nanomaterials include a wide range of compounds that are intentionally manufactured in a research or commercial setting. They are designed to exhibit specific properties and maintain uniform structures, so that they can be used in a wide range of advanced applications. | Chemical Classes: Nanomaterials |
| Nanoscale materials (nanomaterials) | Nanomaterials exhibit unique properties that can be defined by their small size, ≤ 100 nanometers in at least one dimension. | Chemical Classes: Nanomaterials |
| Nonchemical stressor | Biological, radiological, and other physical stressors; socioeconomic stressors; and lifestyle conditions that might contribute to differences in exposure and adverse health outcomes. | Approaches Tiers and Types: Aggregate and Cumulative |
| Occupational mobility | An indicator of the frequency at which workers change from one occupation to another. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Lifestages and Populations: Occupational Worker |
| Octanol-air partition coefficient (log value) | Ratio of a chemical that has reached equilibrium in adjacent fractions of octanol and air. This ratio is used frequently to estimate how an organic chemical will partition in the environment (e.g., between gaseous and particulate fractions in the atmosphere, between soil organic matter and air) as well as how it will behave with respect to human respiratory tissues. A compound with a high octanol-air partition coefficient is more likely to bioaccumulate in human respiratory tissues, particularly is the log octanol-water partition coefficient moderate. | Chemical Classes: Organics |
| Octanol/air partition coefficient (Koa) | Koa describes partitioning between air and aerosol particles, air and foliage, and air and soil and is an indicator of chemical mobility in the atmosphere; higher values of Koa indicate a tendency to sorb onto solid surfaces—vegetation, soils, aerosol particles, etc. | Media: Air |
| Octanol-water partition coefficient (log value) | Ratio of a chemical that has reached equilibrium in adjacent fractions of octanol and water. This ratio is used frequently to estimate how an organic chemical will partition in the environment (e.g., between dissolved and sorbed fractions in surface water) as well as how it will behave in with respect to human tissues. A compound with a high octanol-water partition coefficient is more likely to bioaccumulate in human tissues, especially fatty tissues. | Chemical Classes: Organics |
| Octanol/water partition coefficient (Kow) | Partitioning of organic chemicals between octanol (a nonaqueous, nonpolar solvent and reasonable surrogate for lipids, fat) and water. | Media: Aquatic Biota |
| Organic carbon/water partition coefficient (Koc) | Ratio of chemical sorbed to organic carbon (component of suspended particles and sediment) to the chemical concentration dissolved in the surrounding water. | Media: Aquatic Biota |
| Per capita intake rate | The average quantity of food consumed per person in a population composed of both individuals who ate the food during a specified time period and those that did not. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Approaches |
| Persistent, bioaccumulative, and toxic (PBT contaminants) | PBTs are chemicals (organic or inorganic) that are persistent in the environment, bioaccumulate in food chains, and are toxic. | Media: Aquatic Biota Chemical Classes: Organics, Inorganics and Fibers |
| Pesticide | A pesticide is any chemical used to prevent, destroy, repel, or mitigate pests. | Chemical Classes: Pesticides |
| Physiologically based pharmacokinetic (PBPK) model | Physiologically based PK (PBPK) models are complex, multi-compartment models that account for an organism’s physiology and the chemical properties of the contaminant. | Approaches: Exposure Reconstruction |
| Pica | Pica behavior is the repeated eating of nonnutritive substances, whereas soil-pica is a form of soil ingestion that is characterized by the recurrent ingestion of unusually high amounts of soil (i.e., on the order of 1,000–5,000 milligrams per day or more). (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Media: Soil and Dust |
| Point estimate | Single value used for input variable (e.g., concentration); usually the mean, median, or a high percentile of all observed values. | Approaches Tiers and Types: Screening-Level and Refined |
| Point-of-contact measurement | Direct measurement or point-of-contact exposure measurement "evaluates an exposure as it occurs, by using direct methods to measure the chemical concentrations at the interface between the person and the environment as a function of time, resulting in an exposure profile." (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches: Direct Measurement |
| Population mobility | Population mobility is an indicator of the frequency at which individuals move from one residential location to another. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Lifestages and Populations: Residential Consumer |
| Potential dose | Potential dose is the amount of contaminant ingested, inhaled, or applied to skin, not all of which is actually absorbed. | Routes |
| Probabilistic approach | A probabilistic approach uses distributions of data from which multiple points are used as inputs to the exposure equation. This approach provides a distribution of potential exposure values. | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Probability distribution | Probability distributions describe the range of values that certain variables might take within a population and estimate the relative likelihood (probability) that any of those values might occur in the given population. (Source: U.S. EPA Risk Assessment Guidance for Superfund (RAGS) Volume III - Part A) | Approaches: Scenario Evaluation Tiers and Types: Deterministic and Probabilistic |
| Problem formulation | Problem formulation is the process by which the assessor, in conjunction with risk managers and often various stakeholders, determines the purpose, scope, level of detail, and approach of an assessment. | Approaches: Scenario Evaluation |
| Reasonable maximum exposure | The highest exposure reasonably likely to occur, generally assumed to be in the range of the 90th and 99.9th percentiles. (Source: U.S. EPA Risk Assessment Guidance for Superfund (RAGS) Volume III - Part A) | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Reasonable worst-case exposure | Semiquantitative term referring to the lower part of the high-end exposure range, which is above the 90th percentile, but below the 98th percentile. (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Reverse dosimetry | Uses human pharmacokinetic models to convert biomarker measurements to dose levels that are comparable to an RfD or other dose-based toxicity value (Sources: NRC, 2006; U.S. EPA Biomonitoring—An Exposure Science Tool for Exposure and Risk Assessment) | Approaches: Scenario Evaluation, Dose Reconstruction |
| Scenario evaluation (indirect assessment) | An approach to quantifying exposure by measurement or estimation of both the amount of a substance contacted, and the frequency/duration of contact, and subsequently linking these together to estimate exposure or dose. (Source: U.S. EPA Guidelines for Exposure Assessment) | Approaches |
| Sensitive receptor | Receptor (e.g., child, adult, worker) expected to have highest level of risk or exposure. | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Sensitivity | Differences in toxic response resulting from toxicodynamics differences and/or toxicokinetics differences. These differences can arise due to numerous biological factors such as lifestage (windows of enhanced sensitivity), genetic polymorphisms, gender, disease status, nutritional status, etc. (Source: U.S. EPA Risk Assessment Glossary) | Approaches Tiers and Types Lifestages and Populations |
| Sensitivity analysis | Sensitivity analysis is used to determine which parameters and exposures have the most impact on an exposure estimate. | Approaches: Scenario Evaluation Tiers and Types: Screening-Level and Refined, Deterministic and Probabilistic |
| Solid/water distribution ratio (Kd) | Ratio of the sorbed concentration (to suspended particles in water, sediment) to the concentration of the chemical dissolved in the aqueous solution. | Media: Aquatic Biota |
| Solubility in water (mg/L) | Measure of a substance’s partitioning between dissolved and insoluble phases. Depends on the solute (e.g., water, alcohol) and other substances dissolved in the solute. | Chemical Classes: Organics |
| Stressor | A stressor is any biological, chemical, or physical entity that can cause or induce an adverse response in a human or ecological receptor. | Approaches: Scenario Evaluation |
| Susceptibility | Differences in risk resulting from variation in both toxicity response (sensitivity) and exposure (as a result of gender, lifestage, and behavior). (Source: U.S. EPA Risk Assessment Glossary) | Approaches Tiers and Types Lifestages and Populations |
| Synergistic | Exposure to multiple stressors that leads to an increased response that exceeds what would be estimated for exposure to each chemical independently. | Approaches Tiers and Types: Aggregate and Cumulative |
| Tiers and Types | Exposure scenarios can be developed to support different tiers and types of exposure assessments. Individual “tiers” correspond to iteratively more complex, and typically data-intensive, steps in the assessment. At each stage of a tiered exposure assessment, investigators evaluate whether the assessment results are sufficient to support the risk management decisions. The type of assessment might refer to whether the assessment is considering aggregate or cumulative exposures or whether is at the individual or population level. | Approaches: Scenario Evaluation |
| Transformation | Transformation in the environment refers to a change in a chemical or physical state. | Approaches: Scenario Evaluation Media |
| Transport | Transport in the environment refers to movement within a medium or between media. | Approaches: Scenario Evaluation Media |
| Uncertainty | Uncertainty refers to a lack of data or an incomplete understanding of the context of the risk assessment decision. It can be either qualitative or quantitative. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Approaches Tiers and Types: Screening-Level and Refined |
| Vapor pressure | Vapor pressure is a measure of a substance’s volatility, or its propensity to partition to the vapor (gaseous) phase from its condensed phase (i.e., solid or liquid). | Chemical Classes: Organics Media: Air, Aquatic Biota |
| Variability | Variability refers to the inherent heterogeneity or diversity of data in an assessment. It is "a quantitative description of the range or spread of a set of values", and is often expressed through statistical metrics such as variance, standard deviation, and interquartile ranges that reflect the variability of the data. (Source: U.S. EPA Exposure Factors Handbook: 2011 Edition) | Approaches Tiers and Types: Screening-Level and Refined |
| Vulnerability | Differences in risk resulting from the combination of both intrinsic differences in susceptibility and extrinsic social stress factors such as low socioeconomic status, crime and violence, lack of community resources, crowding, access to health care, education, poverty, segregation, geography, etc. (Source: U.S. EPA Risk Assessment Glossary) | Approaches Tiers and Types Lifestages and Populations |
| Water solubility | Measure of the maximum amount of a chemical that will dissolve in pure water. | Media: Aquatic Biota |