Exposure Science Glossary of Terms -- an ISES Europe Chapter statement

The proposed glossary is intended to be broadly applicable in different areas of exposure science. The definitions given in the referenced documents were taken verbatim, as cited. If adaptations were necessary, the citation was mentioned with "based on", and the respective change explained. 

If the ISES Europe proposal is entirely based on a definition from an authoritative organization, it is referenced as such. In the case that an important term had not been defined in one of these official glossaries, definitions proposed in other publications have been taken into account (e.g. for the term “exposome”). If no reference at all was available, a definition was provided by the involved experts and the field “defined in glossary” is blank.

Proposals without a reference are definitions formulated and agreed upon by ISES Europe exposure scientists.

This excerpt is from the 'Towards further harmonization of a glossary for exposure science—an ISES Europe statement', Heinemeyer, G., Connolly, A., von Goetz, N. et al. published in the Journal of Exposure Science & Environmental Epidemiology 

Term Defined in Glossary ISES Europe Definition
Absorption barrier

US-EPA (2011)

Any exposure surface that may retard the rate of penetration of an agent into a target. Examples include the skin, respiratory tract lining, and gastrointestinal tract wall (US-EPA, 2011).

Activity pattern data US-EPA (2011) WHO/IPCS (2004, part 2) Data that characterize the habits/behaviour of the target population (WHO/IPCS, 2004, part 2).
Activity pattern   Habits/behaviour of the target population.
Acute exposure   Synonymous with Short-term exposure (see Short-term exposure).
Agent WHO/IPCS (2004; part 2),  ISO/TS 21623 (2017) A chemical, biological, or physical entity that contacts a target (WHO/IPCS 2004, part 2).  Inlcudes the terms substance, chemical, biological agent, physical agent, stressor.
Aggregte (d) exposure US-EPA (2011), ECHA (2016) Exposure to one agent from different exposure sources, via different exposure pathways and/or exposure routes.  Remark:  If all routes and sources have been considered, the aggregate exposure is equivalent to "total exposure" to a specific agent or stressor.
Background level WHO/IPCS (2004, part 2) The amount of an agent in a medium (e.g., air, water, soil, biological media) that is not attributed to the source(s) under investigation in an exposure assessment. Background level(s) can be naturally occurring and/or the result of human activities. (WHO/IPCS, 2004, part 2).  Remark:  Natural background is the concentration of an agent in a medium that occurs naturally or is not the result of human activities.
Bioaccumulation ISO/TS 21623 (2017) The increase in internal concentration of an agent in an organism due to repeated exposure and due to all routes of exposure where metabolism and excretion have not been able to cope with the repeated exposure (and absorption) over time (new definition, based on van Leeuwen & Vermeire, 2007).    Remark:  Bioconcentration often refers to the net result of uptake, distribution and elimination of a substance due to water-borne exposure of an organism. Together with bioaccumulation is may lead to biomagnification by which tissue concentrations of bioaccumulated chemicals increase as the chemical passes up to two or more trophic levels (van Leeuwen & Vermeire, 2007).
Bioavailability US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017)  The rate and extent to which an agent is systemically absorbed by an organism via all possible exposure routes and is available for metabolism or interaction with biologically significant receptors. Bioavailability involves both release from a medium (if present) and absorption by an organism.  Synonymous terms:  Systemic availability.
Biomarker of exposure US-EPA (2011), WHO/IPCS (2004, part 2), EFSA (2017), ISO/TS 21623 (2017) An indicator of the exposure of biological systems to an agent. Biomarkers of exposure refer to chemical-analytical measurements of the analyte in the biological system.  Synonymous terms:  Biological marker of exosure.
Biomonitoring EFSA (2017), IUPAC (2007) The measurement of chemical agents and/or their metabolites, or markers of subsequent health effects, in organisms and biological media such as tissues, cells or fluids (based on HBM4EU 2020 leaflet).
Chronic exposure   Synonymous with Long-term exposure (see Long-term exposure). 
Cumulative exposure

US EPA (2002)

Total or aggregate exposures (or doses) for multiple chemicals or stressors evaluated together.  Synonymous with Combined exposure, mixture exposure.  Remarks:  Broadly discussed in WHO/IPCS (2009) and Meek et al. (2011). Cumulated exposure may vary from a small number to mixtures of a broad variety of agents.  Cumulative exposure is generally understood for substances having similar actions. Within (occupational) epidemiology, cumulative exposure is generally and frequently to describe chronic exposure (exposure level > year).
Dose US-EPA (2011) WHO/IPCS (2004, part 2) OECD (2003) EFSA (2017), ISO/TS 21623 (2017) The amount of an agent that enters a target due to total exposure over a certain time-period. Dose can refer to the amount of chemical taken in by the entire target organism or the amount taken in by specific target cells within the target organism. In the case of absorption, the dose is an absorbed dose/uptake dose (see uptake); otherwise, it is an intake dose. (Adopted from US-EPA, 2011; WHO-IPCS, 2004 part 2,).
Emission ISO/TS 21623 (2017) Release of an agent from an exposure source, including discharges into the wider environment (van Leeuwen and Vermeire, 2007).  Synonymous term:  Release.
Exposome   The totality of a person's exposure from conception to death (based on Wild, 2005).  Remark:  This term is not mentioned in any of the reference documents mentioned previously.  However, it is an emerging, important term that should be considered in a list on exposure terminology. The proposed definition is a condensation of wording in Wild, 2005 ("At its most complete, the exposome encompasses life-course environmental exposures (including lifestyle factors), from the prenatal period onwards.")
Exposure US-EPA (2011), WHO/IPCS (2004, part 2), OECD (2003), EFSA (2017), ISO/TS 21623 (2017) Contact between an agent and a target. Exposure is measured as the concentration or amount of a particular agent that reaches a target organism, system or (sub) population in a specific exposure frequency for a defined exposure duration (OECD, 2003; WHO/IPCS, 2004 part 1).  Remarks:  In WHO/IPCS (2008), exposure is characterized by the three elements "exposure scenario", "exposure model", and "exposure parameters".
Exposure assessment OECD, 2003; WHO/IPCS, 2004 part 1; US-EPA, 2011 WHO/IPCS, 2004 part 2; ECHA (2013, 2016, 2016a), EFSA (2012, 2017), ISO/TS 21623 (2017) The process of estimating or measuring the magnitude,  frequency, and duration of exposure to an agent, along with the number and characteristics of the population exposed. (US-EPA, 2011).
Exposure duration US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017) A single event during which there is continuous contact between an agent and a target. The event is normally of a short duration (less than 24 hours).  Remarks:  The attribute "continuous contact" in this context means that there is no interruption of the exposure.
Exposure event US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017) A single event during which there is continuous contact between an agent and a target. The event is normally of a short duration (less than 24 hours).  Remarks:  The attribute "continuous contact" in this context means that there is no interruption of the exposure.
Exposure factor US-EPA (2011), ISO/TS 21623 (2017) Exposure factors are exposure parameters related to human behaviour and characteristics that help determine an individual's exposure to an agent (US-EPA, 2011).
Exposure frequency US-EPA (2011), WHO/IPCS (2004, part 2) The number of exposure events in an exposure duration (US-EPA; 2011; WHO/IPCS 2004 part 2).
Exposure model WHO/IPCS (2004, part 2) A conceptual or mathematical representation of one or more exposure processes. WHO/IPCS (2004, part 2).
Exposure parameter   All (model) data that are necessary to calculate exposure, including exposure factor and agent concentrations.  Remarks:  In WHO/IPCS (2008), the term "exposure parameter" is mentioned as one of the three elements of exposure, namely exposure scenario,  exposure model and exposure parameter.  The ISO/TS 21623 (2017) term refers to temperature differences and cannot be applied for exposure assessment.
Exposure pathway US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017)

The course an agent takes from the exposure source to the target (WHO/IPCS 2004, part 2).

Exposure route US-EPA (2011) WHO/IPCS (2004, part 2), ISO/TS 21623 (2017)  The means through which an agent enters a target organism after contact (e.g. by ingestion, inhalation, or dermal absorption) (US-EPA 2011), WHO/IPCS 2004, part 2).  Synonymous term:  Route of exposure.
Exposure Scenario US-EPA (2011), WHO/IPCS (2004, part 2), OECD (2003), ECHA (2013, 2016, 2016a), ISO/TS 21623 (2017) A combination of facts, assumptions, and inferences that define a discrete situation where potential exposures may occur. These may include the exposure source, the exposed target population, and the time frame of exposure, microenvironment, and activities. Scenarios are often created to aid exposure assessors in estimating exposure (WHO/IPCS, 2004).  Remarks:  In regulatory risk assessments, a range of exposure scenarios is often investigated (e.g. realistic as well as worst-case scenarios, meaning an average as well as an extreme exposure situation). In the European Chemicals Regulation (REACH), the Exposure scenario is defined by regulation (European Union, 2006).
Exposure Science   Exposure science studies the contact between stressors and receptors and the associated exposure sources, exposure pathways and processes potentially leading to impacts on human health and the natural and built environment. Stressors primarily refer to chemical, biological, and physical agents, and receptors range from molecules, cells, and organs to humans and other organisms. (based om Fandtke et al., 8).
Exposure Source US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017)  The origin of an agent entering an exposure pathway for the purposes of an exposure assessment (based on WHO/IPCS; 2004, part2).  Synonymous term:  Source of exposure.  
External exposure   Exposure of an organism at an exposure barrier before it is taken up by an organism.  Synonymous term:  External dose. 
Internal dose US-EPA (2011) The amount of an agent that enters the organ system by crossing an absorption barrier (US-EPA, 2011).  Synonymous term:  Absorbed dose.  
Intake US-EPA (2011) WHO/IPCS (2004, part 2)

The process by which a substance crosses the outer boundary of an organism without passing an absorption barrier (e.g., through ingestion or inhalation) (US-EPA, 2011).

Intake fraction   Fraction of chemical mass emitted into the environment that eventually passes into an individual or a population through intake (i.e., inhalation or ingestion) or dermal absorption. (based on Bennet et al., 2002).
Long-term exposure US-EPA (2011), WHO/IPCS (2004, part 2, EFSA (2017) Continuous exposure, or multiple exposures, occurring over an extended period of time or a significant fraction of the organism's lifetime (US-EPA 2011).  Synonymous term:  Chronic exposure. Remarks:  In human toxicology, chronic exposure corresponds to chronic toxicity, which is defined as the effects observed following repeated exposure by the oral, dermal, or inhalation route for more than approximately 10% of the life span in humans (more than approximately 90 days to 2 years in typically used laboratory animal species) and in environmental toxicology as the effects observed following multiple exposures occurring over an extended period of time or over a significant fraction of an organism's lifetime. Chronic exposures can be understood as a special case of "long-term exposure".
Monitoring ISO/TS 21623 (2017)  Measuring one or more agents/stressors in environmental media or in body fluids or tissues (derived from the definition of biomonitoring).  Remarks:  Many different types of monitoring exist: risk monitoring, biomonitoring, exposure monitoring, and human biomonitoring, environmental monitoring, monitoring at the workplace (e.g. personal air sampling). Definitions exist in terms of the particular types of monitoring and should be evaluated.
Reference Dose (RfD) US-EPA (2011), WHO/IPCS (2004, part 1), ISO/TS 21623 (2017)

An estimate of the daily dose of an agent for a human population that is likely to be without deleterious effect even if continued exposure occurs over a lifetime (OECD, 2003).  In the case of inhalation exposure, the reference "dose" is a reference concentration.

Risk assessment US-EPA (2011), WHO/IPCS (2004, part 1), EFSA (2017)), ISO/TS 21623 (2017)  A process intended to calculate or estimate the risk for a specified target organism, system, or (sub)population, including the identification of related uncertainties, following exposure to a particular agent, taking into account the inherent characteristics of the agent of concern as well as the characteristics of the specific target system.  The risk assessment process includes the following steps: hazard identification, problem formulation), hazard characterization (related term: Dose–response assessment), exposure assessment, and risk characterization. Risk assessment is the first component in a risk analysis process ((US-EPA, 2011).  Remarks:  Risk assessment may also include the assessment of statistical correlations between an analyte level (exposure biomarker) and an effect level (effect biomarker or apical effect).
Risk characterization US-EPA (2011), WHO/IPCS (2004, part 2), EFSA (2017), ISO/TS 21623 (2017)  The qualitative and, wherever possible, quantitative determination, including related uncertainties, of the probability of occurrence of known and potential adverse effects of an agent in a given organism, system, or (sub) population, under defined exposure conditions.  Risk characterization is the fourth step in the risk assessment process (WHO/IPCS, 2004).
Risk management WHO/IPCS (2004, part 1), EFSA (2017), ISO/TS 21623 (2017) Decision-making process involving considerations of political, social, economic, and technical factors with relevant risk assessment information relating to a hazard so as to develop, analyze, and compare regulatory and non-regulatory options and to select and implement appropriate response option(s) to that hazard.  Risk management comprises three elements: risk evaluation; emission and exposure control; and risk monitoring (OECD, 2003).  Remarks:  Risk management is primarily supported by exposure assessment, which delivers the essential information needed for risk reduction.
Sensitivity analysis US-EPA (2011), ISO/TS 21623 (2017) Process of changing one variable of a quantitative analysis while keeping the others constant to determine its effect on the output. Generally, this procedure varies each uncertain quantity between its credible lower and upper bounds (holding all others at their nominal values, such as medians) and computes the results of each combination of values. The results help to identify the variables that have the greatest effect on exposure estimates and help focus further information-gathering efforts (US-EPA, 2011).
Short term exposure US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017) A single exposure to a toxic agent/stressor which may result in severe biological harm or death. Short-term exposures are usually characterized as lasting no longer than a day, as compared to longer, continuing exposure over a period of time (according to the definition of 'acute exposure' in US-EPA, 2011).  Synonymous term:  Acute exposure.  Remarks:  Acute exposure corresponds to the acute (severe) effects observed following a single exposure or an exposure of a duration of less than a day. In ecotoxicology, the term short-term toxicity or acute toxicity is used for the effects observed after an exposure that is short in relation to the lifespan of an organism. Acute exposure can be understood as a special case of "Short-term exposure."
Stressor WHO/IPCS (2004, part 2), EFSA (2017) Any entity, stimulus, or condition that can modulate normal functions of an organism or ecosystem or induce an adverse response (e.g., an agent, lack of food, drought) (WHO/IPCS, 2004, part 2).  Remarks:  Stressors primarily refer to adverse effects from chemical, biological, and physical agents, which induce the adverse effects, and receptors range from molecules, cells, and organs to humans and other organisms and ecosystems (Fantke et al., 2020).
Target US-EPA (2011), WHO/IPCS (2004, part 2), ISO/TS 21623 (2017)  Any biological entity that receives an exposure or a dose (e.g., a human, a human population, or a human organ, cell or receptor) (WHO/IPCS 2004, part 2)
Target population EFSA (2017) Group or subgroup of human or environmental populations defined by a particular physiological status (species, age-range and gender, disease status). Because of their particular physiological status, pregnant and lactating women are specific target populations.
Total exposure

US-EPA (2011)

The sum of exposure originating from all exposure sources in any consumer products, workplace exposures and via the environment to a particular agent (in accordance with the US-EPA (2011) definition of total food exposure).  Remarks:  Total exposure may refer to the total of "Aggregate (d) exposure" or of “Cumulative exposure ”.

Toxicokinetics US-EPA (2011), EFSA (2017), ISO/TS 21623 (2017) The entry into, the distribution through and the metabolism and excretion of an agent through an organism as a function of dose and time.  Synonymous term:  Pharmacokinetics
Uptake US-EPA (2011), ISO/TS 21623 (2017) The process by which an agent crosses an absorption barrier and is absorbed into the body (US-EPA, 2011).  Synonymous term:  Absorption
Uncertainty US-EPA (2011), WHO/IPCS (2004, part 1), EFSA (2017), ISO/TS 21623 (2017) Lack of knowledge that can lead to inaccurate or biased estimates of exposure. Can refer to exposure scenario, exposure parameter, and exposure model.
Variability US-EPA (2011),  EFSA (2017), ISO/TS 21623 (2017) True heterogeneity across locations, time, or individuals in a human or environmental population. Variability can affect the precision and accuracy of exposure estimates and the degree to which they can be generalized.