Intermediate Effect Biomarkers--Alternatives to Direct Concentration- Response Data for Regulatory Benefits Analyses

Perceived needs for extensive chemical-specific toxicological information have impeded efforts to assess risks and evaluate likely public health protection benefits of possible standards for hazardous air pollutants (HAPs). This paper discusses opportunities to use effects of HAPs on early effect biomarkers, such as birth weights, to predict likely changes in rare quantal effects of concern that would be relevant for the quantification of likely regulatory benefits from exposure reductions. In the birth weight example, even modest exposures to common air pollutants can be seen as producing a kind of tax on the limited resources available to the fetus to grow and develop. In contrast to teratogenic effects, dose response relationships for fetal growth restriction in animals are often nearly linear, suggesting that the developing fetus may not generally have untapped "functional reserve capacity" that is expected to buffer the effects of modest exposures to toxicants in the traditional toxicological paradigm. Given this mechanistic perspective, supported in part by parallel dose response relationships between reported cigarette smoking and both birth weight and infant mortality, restriction on fetal growth can be associated with changes in quantal end effects of concern that are more difficult to assess directly in epidemiological studies.