Abstract
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.
Highlights
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 describes the second of two proposed approaches that regulatory toxicologists may use to analyze risks and associated uncertainties for noncancer effects of HAPs with limited toxicological databases
The first approach treats HAPs as random draws from reference sets of putatively analogous chemicals that have been studied in the past
Summary
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). The variability among previously studied chemicals is used to create distributions that represent each of the concerns that are addressed by traditional “uncertainty factors” in the derivation of reference concentrations (RfCs) [2, 3] This approach builds on previous work by adding the ability incorporate the expected implications for risks of a user-specified incidence of effects from interacting background processes, as recommended in a recent report by the National Research Council [4] (2008). This paper describes another approach toward risk assessments for HAPs, based on a growing set of human biomarkers of early effect that allow assessors to “move upstream” from ultimate endpoints of concern [5]. Differences in traditional cardiovascular risk factors (e.g., blood pressure, serum cholesterol) and some
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