Using Biomonitoring Equivalents to interpret human biomonitoring data in a public health risk context

Increasingly sensitive analytical tools allow measurement of trace concentrations of chemicals in human biological media in persons from the general population. Such data are being generated by biomonitoring programs conducted by the US Centers for Disease Control and other researchers. However, few screening tools are available for interpretation of such data in a health risk assessment context. This review describes the concept and implementation of Biomonitoring Equivalents (BEs), estimates of the concentration of a chemical or metabolite in a biological medium that is consistent with an existing exposure guidance value such as a tolerable daily intake or reference dose. The BE approach integrates available pharmacokinetic data to convert an existing exposure guidance value into an equivalent concentration in a biological medium. Key concepts regarding the derivation and communication of BE values resulting from an expert workshop held in 2007 are summarized. BE derivations for four case study chemicals (toluene, 2,4-dichlorophenoxyacetic acid, cadmium and acrylamide) are presented, and the interpretation of biomonitoring data for these chemicals is presented using the BE values. These case studies demonstrate that a range of pharmacokinetic data and approaches can be used to derive BE values; fully developed physiologically based pharmacokinetic models, while useful, are not required. The resulting screening level evaluation can be used to classify these compounds into relative categories of low, medium and high priority for risk assessment follow-up. Future challenges related to the derivation and use of BE values as tools in risk management are discussed.