Biomarkers of Exposure Categories

Chemical –The most specific exposure biomarker is direct measurement of the chemical of interest in the body. Typically, measurement of the chemical is made in an accessible biological matrix (e.g., blood, urine). While some pesticides can be directly measured in the body, it is generally more common to measure metabolites of pesticides.

Metabolite – Many chemicals are rapidly metabolized or difficult to measure. In these cases, a more stable breakdown product (metabolite) of the chemical may be measured to estimate exposure to the chemical. When a metabolite may derive from a number of different chemicals (as in the 3-PBA example above), additional information is needed to resolve to which chemical the person was exposed.

Endogenous surrogate – In some cases, a chemical or class of chemicals may result in an endogenous response (response within the body) that is highly characteristic of that chemical or class. Measures of that response can be used as a surrogate in lieu of direct measurement of the chemical or metabolite concentration when sufficient additional information is available. Since there are many factors that can influence endogenous responses, this type of exposure biomarker is accompanied by many uncertainties that should be identified and discussed.

(from www.epa.gov)

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