Technology Transfer Network - Air Toxics Web Site
Health Effects Glossary
Glossary of Health, Exposure, and Risk Assessment Terms
Absorption barrier: Any of the exchange
barriers of the body that allow differential diffusion of various substances
across a boundary. Examples of absorption barriers are the skin, lung tissue,
and gastrointestinal tract wall.
and Definitions of Acronyms
ACGIH STEL: American Conference of Governmental and Industrial Hygienists' threshold limit value short-term exposure limit; a 15-min time-weighted-average exposure which should not be exceeded at any time during a workday.
ACGIH TLV: American Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effects.
AIHA: American Industrial Hygiene Association
AIHA ERPG: American Industrial Hygiene Association's emergency response planning guidelines. ERPG 1 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed up to one hour without experiencing other than mild transient adverse health effects or perceiving a clearly defined objectionable odor; ERPG 2 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed up to one hour without experiencing or developing irreversible or other serious health effects that could impair their abilities to take protective action.
Ambient measurement: A measurement (usually of the concentration of a chemical or pollutant) taken in an ambient medium, normally with the intent of relating the measurement value to the exposure of an organism that contacts the medium.
Ambient medium: One of the basic categories of material surrounding or contacting an organism, e.g., outdoor air, indoor air, water, or soil, through which chemicals or pollutants can move and reach the organism.
ATSDR: Agency for Toxic Substances and Disease Registry
Biological medium: One of the major
categories of material within an organism, e.g., blood, adipose tissue,
or breath, through which chemicals can move, be stored, or be biologically,
physically, or chemically transformed.
Biologically effective dose: The amount of a deposited or absorbed chemical that reaches the cells or target site where an adverse effect occurs, or where that chemical interacts with a membrane surface.
Blank (blank sample): An unexposed sampling medium, or an aliquot of the reagents used in an analytical procedure, in the absence of added analyte. The measured value of a blank sample is the blank value.
Body burden: The amount of a particular chemical stored in the body at a particular time, especially a potentially toxic chemical in the body as a result of exposure. Body burdens can be the result of long-term or short-term storage, for example, the amount of a metal in bone, the amount of a lipophilic substance such as PCB in adipose tissue, or the amount of carbon monoxide (as carboxyhemoglobin) in the blood.
Bounding estimate: An estimate of exposure, dose, or risk that is higher than that incurred by the person in the population with the highest exposure, dose, or risk. Bounding estimates are useful in developing statements that exposures, doses, or risks are "not greater than" the estimated value.
California EPA: California Environmental Protection Agency
California EPA reference exposure level: A concentration at or below which adverse health effects are not likely to occur.
Data Quality Objectives (DQO): Qualitative and quantitative statements of the overall level of uncertainty that a decisionmaker is willing to accept in results or decisions derived from environmental data. DQOs provide the statistical framework for planning and managing environmental data operations consistent with the data user's needs.
Dose: The amount of a substance available for interaction with metabolic processes or biologically significant receptors after crossing the outer boundary of an organism. The potential dose is the amount ingested, inhaled, or applied to the skin. The applied dose is the amount of a substance presented to an absorption barrier and available for absorption (although not necessarily having yet crossed the outer boundary of the organism). The absorbed dose is the amount crossing a specific absorption barrier (e.g., the exchange boundaries of skin, lung, and digestive tract) through uptake processes. Internal dose is a more general term denoting the amount absorbed without respect to specific absorption barriers or exchange boundaries. The amount of the chemical available for interaction by any particular organ or cell is termed the deliverable dose for that organ or cell.
Dose rate: Dose per unit time, for example
in mg/day, sometimes also called dosage. Dose rates are often expressed
on a per-unit-bodyweight-basis, yielding units such as mg/kg/d. They are
often expressed as averages over some time period, for example a lifetime.
Dose-response curve: A graphical representation of the quantitative relationship between the administered, applied, or internal dose of a chemical or agent, and a specific biological response to that chemical or agent.
Effluent: Waste material being discharged into the environment, either treated or untreated. Effluent generally is used to describe water discharges to the environment, although it can refer to stack emissions or other material flowing into the environment.
Environmental fate model: In the context of exposure assessment, any mathematical abstraction of a physical system used to predict the concentration of specific chemicals as a function of space and time subject to transport, intermedia transfer, storage, and degradation in the environment.
Environmental medium: One of the major categories of material found in the physical environment that surrounds or contacts organisms, e.g., surface water, ground water, soil, or air, and through which chemicals or pollutants can move and reach the organisms.
Fixed-location monitoring: Sampling of an
environmental or ambient medium for pollutant concentration at one location
continuously or repeatedly over some length of time.
Geometric mean: The nth root of the product of n values.
High-end exposure (dose) estimate: A plausible 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.
High-end Risk Descriptor: A plausible estimate of the individual risk for those persons at the upper end of the risk distribution, conceptually above the 90th percentile but not higher than the individual in the population with the highest risk. Note that persons in the high end of the risk distribution have high risk due to high exposure, high susceptibility, or other reasons, and, therefore, persons in the high end of the exposure or dose distribution are not necessarily the same individuals as those in the high end of the risk distribution.
LC50 (Lethal Concentration50): A calculated concentration of a chemical in air to which exposure for a specific length of time is expected to cause death in 50% of a defined experimental animal population.
Limit of Detection (LOD) (or Method Detection
Limit [MDL]): The minimum concentration of an analyte that, in a given
matrix and with a specific method, has a 99% probability of being identified,
qualitatively or quantitatively measured, and reported to be greater than
LOAEL (lowest-observed-adverse-effect level): The lowest dose of a chemical in a study or group of studies that produce statistically or biologically significant increases in frequency or severity of adverse effects between the exposed population and its appropriate control.
Maximally exposed individual (MEI): The single individual with the highest exposure in a given population (also, maximum exposed individual). This term has historically been defined in various ways, including as defined here and also synonymously with worst case or bounding estimate.
Maximum exposure range: A semiquantitative term referring to the extreme uppermost portion of the distribution of exposures. For consistency, this term should refer to the portion of the individual exposure distribution that conceptually falls above the 98th percentile of the distribution but is not higher than the individual with the highest exposure.
Microenvironment method: A method used in predictive exposure assessments to estimate exposures by sequentially assessing exposure for a series of areas (microenvironment) that can be approximated by constant or well-characterized concentrations of a chemical or other agent.
Monte Carlo technique: A repeated random sampling from the distribution of values for each of the parameters in a generic (exposure or dose) equation to derive an estimate of the distribution of (exposures or doses in) the population.
NIOSH IDLH--NIOSH's immediately dangerous to life and health; NIOSH concentration representing the maximum level of a pollutant from which an individual could escape within 30 minutes without escape-impairing symptoms or irreversible health effects.
NIOSH REL--NIOSH's recommended exposure limit; NIOSH-recommended exposure limit for an 8- or 10-h time-weighted-average exposure and/or ceiling.
NIOSH STEL--NIOSH's recommended short-term exposure limit; a 15-minute TWA exposure which should not be exceeded at any time during a workday.
NOAEL (no-observed-adverse-effect level): That dose of chemical at which there are no statistically or biologically significant increases in frequency or severity of adverse effects seen between the exposed population and its appropriate control. Effects may be produced at this dose, but they are not considered to be adverse.
OSHA PEL: Occupational Safety and Health Administration's permissible exposure limit expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effect averaged over a normal 8-h workday or a 40-h workweek.
Point-of-contact measurement of exposure: An approach to quantifying exposure by taking measurements of concentration over time at or near the point of contct between the chemical and an organism while the exposure is taking place.
Quality assurance (QA): An integrated system of activities involving planning, quality control, quality assessment, reporting and quality improvement to ensure that a product or service meets defined standards of quality with a stated level of confidence.
Quality control (QC): The overall system of technical activities whose purpose is to measure and control the quality of a product or service so that it meets the needs of its users. The aim is to provide quality that is satisfactory, adequate, dependable, and economical.
Reasonable worst case: A semiquantitative term referring to the lower portion of the high end of the exposure, dose, or risk distribution. The reasonable worst case has historically been loosely defined, including synonymously with maximum exposure or worst case. As a semiquantitative term, it is sometimes useful to refer to individual exposures, doses, or risks that, while in the high end of the distribution, are not in the extreme tail. For consistency, it should refer to a range that can conceptually be described as above the 90th percentile in the distribution, but below about the 98th percentile.
Reconstruction of dose: An approach to quantifying exposure from internal dose, which is in turn reconstructed after exposure has occurred, from evidence within an organism such as chemical levels in tissues or fluids or from evidence of other biomarkers of exposure.
RfC (inhalation reference concentration): An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure of a chemical to the human population through inhalation (including sensitive subpopulations), that is likely to be without risk of deleterious noncancer effects during a lifetime.
RfD (oral reference dose): An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure of a chemical to the human population (including sensitive subpopulations) that is likely to be without risk of deleterious noncancer effects during a lifetime.
Sample: A small part of something designed to show the nature or quality of the whole. Exposure-related measurements are usually samples of environmental or ambient media, exposures of a small subset of a population for a short time, or biological samples, all for the purpose of inferring the nature and quality or parameters important to evaluating exposure.
Scenario evaluation: 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 characterization measurements: Measurements made to characterize the rate of release of agents into the environment from a source of emission such as an incinerator, landfill, industrial or municipal facility, consumer product, etc.
Statistical control: The process by which the variability of measurements or of data outputs of a system is controlled to the extent necessary to produce stable and reproducible results. To say that measurements are under statistical control means that there is statistical evidence that the critical variables in the measurement process are being controlled to such an extent that the system yields data that are reproducible within well-defined limits.
Statistical significance: An inference that the probability is low that the observed difference in quantities being measured could be due to variability in the data rather than an actual difference in the quantities themselves. The inference that an observed difference is statistically significant is typically based on a test to reject one hypothesis and accept another.
Worst case: A semiquantitative term referring to the maximum possible exposure, dose, or risk, that can conceivably occur, whether or not this exposure, dose, or risk actually occurs in a specific population.