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INTRODUCTION

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Biologic monitoring or biomonitoring is the measurement of a chemical, its metabolite, or a biochemical effect in a biologic specimen for the purpose of assessing exposure. The term biomonitoring may be used for measuring chemicals in nonhuman organisms, forensic medicine, and drug development; in this chapter it refers to human exposure monitoring. Biomonitoring is an important tool to identify the nature and amount of chemicals in the body resulting from occupational and environmental exposures. Biologic monitoring has evolved from a research tool to an essential component of exposure assessment. Although biomonitoring has been used to monitor workers for decades, it is increasingly being applied to nonoccupational settings.

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While classical exposure assessment relies on the measurement of chemicals in the external environment to estimate the dose of a chemical, biomonitoring provides a more direct measure of the internal dose. Traditionally, dose estimation is accomplished with environmental monitoring, the measurement of the ambient (external) exposure using chemical samples taken from the air, water, hard surface, or other media (eg, food) in the workplace or community. Environmental monitoring provides information about exposure only from the specific external source measured. Conversely, biologic monitoring provides a measure of the quantity of a chemical absorbed from all sources and routes of exposure (eg, dermal absorption, inhalation, and/or ­ingestion) and does not distinguish the source of exposure or whether exposure occurred at the workplace, at home, or in other settings.

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Environmental measurements do not reflect the amount of a chemical that gets into the body and may not correlate well with the biomonitored level for several reasons. The primary route of exposure may not be the environmental medium measured; for example, air measurements will not accurately indicate uptake if dermal absorption is a more significant exposure route. Moreover, individual differences in work practices, activity levels, genetics, demographic ­characteristics (eg, age, gender, and ethnicity), and physical factors, (eg, amount of body fat) impact the absorption, ­distribution, metabolism, and excretion of a chemical.

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The decision to conduct biomonitoring is complex and based on multiple factors. Multidisciplinary collaboration involving toxicologists, epidemiologists, chemists, health educators, and clinicians is required for proper program implementation and interpretation of results. Basic considerations include the availability of appropriate biologic markers, the ability to collect relevant samples, availability of a qualified laboratory, and resources to appropriately plan and conduct all phases of a program.

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BIOLOGIC MARKERS

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Biologic markers or biomarkers are indicators of biochemical, genetic, molecular, immunologic, or physiologic signals of events in biologic systems. The ideal biomarker is sensitive, specific, biologically relevant, practical, inexpensive, and available. Seldom does a biomarker meet all these criteria; most represent a compromise. With respect to chemicals, biomarkers are defined as follows:

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Biomarkers of exposure are chemicals, their metabolites, or a reaction product between a chemical and a target molecule (eg, dialkylphosphate metabolites of organophosphate pesticides or hemoglobin adducts from ethylene ...

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