Estimating Human Exposure: Improving Accuracy with Chemical Markers

Exposure to chemicals, natural as well as anthropogenic, occurs in the human environment. In the absence of chemical-specific data for the wide variety of exposure scenarios, federal agencies have adopted two approaches to estimating exposures. The first is to set chemical standards for exposures, usually through a single route. These standards are set based on risk assessment principles and economic feasibility. When there are standards, measurement of environmental chemical concentrations can be used to prevent unacceptable levels of exposure. The second approach is to estimate external exposure (typically route-specific) and/or an absorbed dose using a series of assumptions regarding translation of chemical concentrations from one part of the environment to another, human activity patterns, and chemical absorption through various routes into the body. These assumptions have been converted into algorithms that can be used to estimate a human exposure and dosage, typically expressed on body weight basis. These algorithms, designed to avoid underestimations of human exposure, have, in some instances, been incorporated into computer models. Chemical markers, measured either as the parent compound or as metabolites in human populations with known exposure to the parent compound, can be applied to improve the accuracy of these estimates of exposure.