lower bound on a standard probability of an effect, such as 10% of people affected.

Bioaccumulation –

An increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.

Bias –

Any effect tending to produce results that depart systematically from the true values. Two principle forms of bias in human epidemiological studies are misclassification, when there are misassignments in exposure or adverse outcome, and selection, in which subjects selected for study differ systematically from those not selected.

Bioactivation –

A metabolic process wherein an inactive chemical is converted to an active one in the body.

Bioavailability –

The state of being capable of being absorbed and available to interact with the metabolic processes of an organism. Bioavailability is typically a function of chemical properties, physical state of the material to which an organism is exposed, and the ability of the individual organism to physiologically take up the chemical.

Biomarker of Effect –

A measurable biochemical, physiological, or other alteration within an organism that, depending on magnitude, can be recognized as an established or potential health impairment or disease.

Biomarker of Exposure –

An exogenous substance, the metabolite(s) or the product of interactions between a xenobiotic agent and some target molecule or cell that is measured in a compartment within an organism.

Biologically effective dose –

The amount of the deposited or absorbed contaminant that reaches the cells or target site where an adverse effect occurs or where an interaction of that contaminant with a membrane surface occurs.


A series of chemical alterations within the body whereby a foreign substance is transformed to a more or less toxic substance.

Case-control study –

An epidemiological study in which persons are selected because they have a specific disease or other outcome (cases) and are compared to a control (referent comparison) group without the disease to evaluate whether there is a difference in their reported frequency of exposure to possible disease risk factors. Also termed a retrospective study or case referent study.

Chronic exposure –

Multiple exposures occurring over an extended

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