Appendix A Glossary of Selected Terms and Definitions Some scientific and environmental terminologies that are commonly found to be pertinent to the evaluation of environmental contamination and chemical exposure problems are provided below. Absorption Generally used to refer to the uptake of a chemical by a cell or an organism following exposure through the skin, lungs, and/or gastrointestinal tract. Systemic absorption—refers to the flow of chemicals into the bloodstream. In general, chemicals can be absorbed through the skin into the bloodstream, and then transported to other organs; chemicals can also be absorbed into the bloodstream after breathing or oral intake. Absorption barrier Any of the exchange barriers of the human body that allow differential diffusion of various substances across a boundary—i.e., any expo- sure surface that may retard the rate of penetration of an agent into a target organism; examples of absorption barriers are the skin, the respiratory tract lining (or lung tissue), and the gastrointestinal tract wall. Absorption fraction Refers to the percent or fraction of a chemical in contact with an organism that becomes absorbed into the receptor—i.e., the relative amount of a substance at the exchange barrier that actually penetrates into the body of an organism. Typically, this is reported as the unitless fraction of the applied dose or as the percent absorbed—e.g., relative amount of a substance on the skin that penetrates through the epidermis into the body. Acceptable daily intake (ADI) An estimate of the maximum amount of a chemi- cal/agent, expressed on a body mass basis (viz., in mg/kg body weight/day), to which a potential receptor (or individuals in a [sub]population) can be exposed to on a daily basis over an extended period of time (usually a lifetime) without suffering a deleterious effect, or without anticipating an adverse effect. Acceptable risk A risk level generally deemed by society to be acceptable or tolerable. This is commonly considered as a risk management term—with the acceptability of the risk being dependent on: available scientific data; social, © Springer Science+Business Media B.V. 2017 435 K. Asante-Duah, Public Health Risk Assessment for Human Exposure to Chemicals, Environmental Pollution 27, DOI 10.1007/978-94-024-1039-6 436 Appendix A Glossary of Selected Terms and Definitions economic, and political factors; and the perceived benefits arising from exposure to an agent/stressor/chemical. Action level (AL) The limit of a chemical in selected media of concern above which there are potential adverse health and/or environmental effects. On the whole, this represents the environmental chemical concentration above which some correc- tive action (e.g., monitoring or remedial action) is typically required by regulation. Acute Of short-term duration—i.e., occurring over a short time, usually a few minutes or hours. Acute exposure—refers to a single large exposure or dose to a chemical, generally occurring over a short period (usually lasting <24 to 96 hours), in relation to the lifespan of the exposed organism. In general, this would typically address contact between an agent and a target occurring over a relatively short period of time—usually less than a day. An acute exposure can result in short-term or long-term health effects. Acute effect—generally takes place a short time (up to 1 year) after exposure. Acute toxicity—refers to the development of symptoms of poisoning or the occurrence of adverse health effects after exposure to a single dose or multiple doses of a chemical within a short period of time. It represents the sudden onset of adverse health effects that are of short duration—generally resulting in cellular changes that are reversible. Additivity (of chemical effects) A pharmacologic or toxicologic interaction in which the combined effect of two or more chemicals is approximately equal to the sum of the effect of each chemical acting alone. Administered dose The mass of substance administered to an organism, and that is in contact with an exchange boundary (e.g., gastrointestinal tract) per unit body weight per unit time (e.g., mg/kg-day). It actually is a measure of exposure only—since it does not account for absorption. [See also, applied dose.] Adsorption The removal of contaminants from a fluid stream via a mechanism of concentrating the constituents onto a solid material. It consists of the physical process of attracting and holding molecules of other chemical substances on the surface of a solid, usually by the formation of chemical bonds. A substance is considered adsorbed if the concentration in the boundary region of a solid (e.g., soil) particle is greater than in the interior of the contiguous phase. Adverse effect A biochemical change, functional impairment, or pathologic lesion that affects the performance of the whole organism, or reduces an organism’s ability to respond to a future environmental challenge. It is often exhibited by a change in the morphology, physiology, growth, development, reproduction, or life span of an organism, system, or (sub)population that results in an impair- ment of functional capacity, an impairment of the capacity to compensate for additional stress, or an increase in susceptibility to other influences. Aerosol A suspension of liquid or solid particles in air. Agent (or Stressor) A chemical, biological, or physical entity that contacts a target material or organism. Aliphatic compounds Organic compounds in which the carbon atoms exist as either straight or branched chains; examples include pentane, hexane, and octane. Ambient Pertaining to surrounding conditions or area. Ambient medium—one of the basic categories of material surrounding or contacting an organism (e.g., Appendix A Glossary of Selected Terms and Definitions 437 outdoor air, indoor air, water, or soil) through which chemicals or pollutants can move and reach the organism. Analyte A chemical component of a sample that is to be investigated or measured; for example, if the analyte of interest in an environmental sample is mercury, then the laboratory testing or analysis will determine the likely amount of mercury in the sample. The analytical method defines the sample preparation and instrumentation procedures or steps that must be performed to estimate the quantity of analyte in a given sample. Antagonism (or, antagonistic chemical effect) A pharmacologic or toxicologic interaction in which the combined effect of two chemicals is less than the sum of the effect of each chemical acting alone. This phenomenon is the result of interference or inhibition of the effects of one chemical substance by the action of other chemicals—and reflects the general counteracting effect of one chem- ical on another, thus diminishing their additive effects. Anthropogenic Caused or influenced by human activities or actions. Applied dose The amount of a substance in contact with the primary absorption boundaries of an organism (e.g., skin, lung, gastrointestinal tract), and that is available for absorption. This actually is a measure of exposure only—since it does not take absorption into account. [See also, administered dose.] Arithmetic mean (also, average) A statistical measure of central tendency for data from a normal distribution—defined, for a set of n values, as the sum of the values divided by n, as follows: Xn Xi ¼ i¼1 Xm n Aromatic compounds Organic compounds that contain carbon molecular ring structures (i.e., a benzene ring); examples include benzene, toluene, ethylben- zene, xylenes (BTEX). Attenuation Any decrease in the amount or concentration of a pollutant in an environmental matrix as it moves in time and space. It represents the reduction or removal of contaminant constituents by a combination of physical, chemical, and/or biological factors acting upon the contaminated ‘parent’ media. Attributable risk (also, incremental risk) The difference between risk of exhibiting a certain adverse effect in the presence of a toxic substance in comparison with that risk to be expected in the absence of the substance. [See also, excess lifetime risk.] Average concentration A mathematical average of chemical concentration (s) from more than one sample—typically represented by the ‘arithmetic mean’ or the ‘geometric mean’ for environmental samples. Average daily dose (ADD) The average dose calculated for the duration of recep- tor exposure, defined by: ½Â½ ðÞ¼= chemical concentration contact rate ADD mg kg-day ½body weight This is used to estimate risks for chronic non-carcinogenic effects of environ- mental chemicals. 438 Appendix A Glossary of Selected Terms and Definitions Averaging time The time period over which a function (e.g., human exposure concentration of a chemical) is measured—yielding a time-weighted value. Background (threshold) level The normal, or typical, average ambient environ- mental concentration of a chemical constituent. It represents the amount of an agent in a medium (e.g., air, water, soil) that is not attributed to the source (s) under investigation in an exposure assessment. Overall, two types of back- ground levels may exist for chemical substances—namely, naturally-occurring concentrations and elevated anthropogenic levels resulting from non-site-related human activities. Anthropogenic background levels—refer to concentrations of chemicals that are present in the environment due to human-made, non-site sources (e.g., lead depositions from automobile exhaust and ‘neighboring’ industry). Naturally occurring background levels—refer to ambient concentra- tions of chemicals that are present in the environment and yet have not been influenced by human activities (e.g., natural formations of aluminum, arsenic, and manganese). Benchmark concentration (BMC) A statistical lower confidence limit on the concentration that produces a predetermined change in response rate of an adverse effect (called the ‘benchmark response’ or BMR) compared to back- ground. It is represented by the concentration calculated to be associated with a given incidence (e.g., 5% or 10% incidence) of effect estimated from all toxicity data on that effect within that study; in actuality, BMCL is the statistical lower confidence limit of the BMC.