A problem in evaluating the hazard represented by an environ mental toxicant is that exposures can occur via multiple media such as water, land, and air. Lead is one of the toxicants of con cern that has been associated with adverse effects on heme me tabolism, serum vitamin D levels, and the mental and physical development of infants and children exposed at very low envi ronmental levels. Effects of lead on development are particularly disturbing in that the consequences of early delays or deficits in physical or mental development may have long-term conse quences over the lifetime of affected individuals.
Experimental and epidemiologic studies have indicated that blood lead levels in the range of 10-15 μg/dl, or possibly lower, are likely to produce subclinical toxicity. Since a discernible threshold has not been demonstrated, it is prudent to preclude development of a Reference Dose (RfD) for lead. As an alter nate, the U. S. Environmental Protection Agency (U. S. EPA) has developed the uptake/biokinetic lead model that provides a means for evaluating the relative contribution of various media to establishing blood lead levels in children. This approach will allow for the identification of site- and situation-specific abate ment strategies based on projected blood lead levels in vulnera ble human populations exposed to lead in air, diet, water, soil/ dust, and paint; thus making it possible to evaluate regulatory decisions concerning each medium on blood levels and potential health effects.
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