absorbable in mammalian gastrointestinal tracts (Casteel et al. 1996a-d, 1997a,b, 1998a-e). Studies generally are consistent in demonstrating that a nonnegligible fraction of lead in soil can be absorbed but that the efficiency of absorption depends on multiple factors including chemical speciation of lead, other dietary components, and particle size of soil ingested. Typically paint-derived lead is relatively available for absorption, whereas lead associated with sulfide minerals is relatively unavailable.
Under the environmental health paradigm, preventing injury is the first choice (see Box 6-1). As discussed in Chapter 5, the primary threat presented by lead relates to its ability to cause developmental deficits in children. Although chelation therapy can be applied to reduce body burdens of lead, available information suggests that chelation is not effective in restoring neurological function (Rogan et al. 2001). Hence a “monitor and react” strategy, even if conducted well, cannot prevent injury. The primary prevention strategy (Campbell and Osterhoudt 2000; Rosen and Mushak 2001) is widely recognized as the only truly effective method for eliminating pediatric lead poisoning; this requires a degree of predictive capability for both risk assessment and risk management.
The U.S. Environmental Protection Agency (EPA) has adopted a strategy that entails modeling lead exposure rather than biomonitoring as the first line of defense. Existing epidemiological evidence for health effects of lead exposure is anchored to BLLs rather than to dose rates. The relationship between dose and blood level is complicated by the fact that lead is stored in bone. This entails a greater level of modeling sophistication than the standard risk assessment guidance for Superfund (RAGS) paradigm.
A primary difference between lead risk assessment and cancer and noncancer risk assessment for other chemicals or compounds is that BLLs can be readily measured in individuals and used to “ground-truth” risk calculations. BLLs provide an integrated picture of lead exposure over the preceding months to years, depending on age and other characteristics of
BOX 6-1 Preventing Lead Exposure
Children with access to lead-contaminated soils are likely to be exposed to that lead. To establish levels of lead contamination that would not be expected to present unacceptable or unavoidable risk, it is necessary to define the relationship between magnitude of exposure and level of soil contamination.
Children exposed to lead who develop elevated blood lead levels (BLLs) may have already been irreversibly damaged by the time they have been identified in screening programs. A primary prevention strategy requires the predictive capability of models for exposure risk assessment and management activities.