Blood lead levels biokinetics

Preventive Measures. The intake uptake biokinetic model (lUBK) projects the impact of lead in the environment on blood lead. This model assumes conservatively high levels of intake and cannot account for chemical speciation, thus over-predictions of blood lead levels often occur. Nonetheless, because of the allegations of the impact of blood lead and neurobehavioral development, blood lead levels in children are being reduced adrninistratively to below 10 //g/dL. In order to do so, soil leads are being reduced to a level of between 500—1000 ppm where remediation is required. 

Numerous observations of non-linear relationships between PbB concentration and lead intake in humans provide further support for the existence of a saturable absorption mechanism or some other capacity limited process in the distribution of lead in humans (Pocock et al. 1983 Sherlock et al. 1984, 1986). However, in immature swine that received oral doses of lead in soil, lead dose-blood lead relationships were non-linear whereas, dose-tissue lead relationships for bone, kidney and liver were linear. The same pattern (nonlinearity for PbB and linearity for tissues) was observed in swine administered lead acetate intravenously (Casteel et al. 1997). These results suggest that the non-linearity in the lead dose-PbB relationship may derive from an effect of lead dose on some aspect of the biokinetics of lead other than absorption. Evidence from mechanistic studies for capacity-limited processes at the level of the intestinal epithelium is compelling, which would suggest that the intake-uptake relationship for lead is likely to be non-linear these studies are discussed in greater detail in Section 2.4.1. 

A second category of slope factor models employs Pb levels in some medium in combination with estimates of intakes, uptakes, and a simple biokinetic slope factor to estimate PbB levels. In a conceptual sense, the simpler slope factor approach, relating a medium Pb level like air lead to blood lead, is a variant of this second category. That is, an air Pb translating into intake and uptake quantities provides the same type of results as the earlier approach. 

In summary, both linear and nonlinear models have been applied to lead biokinetics under mainly steady-state conditions and mainly employing information from limited numbers of subjects. In many cases, depending upon the demands on the particular model, there may not be any added virtue of nonlinear over linear models, e.g., study of subjects in steady state at relatively low level of exposure. On the other hand, the various nonlinear relationships that are known to exist for external media/biological media relationships and further refined body compartments, e.g., plasma and erythrocyte pools for blood lead, require more complex approaches. The approaches of Marcus (1985c) and Chamberlain (1985) are particularly helpful in extending the use of modelling in rationalizing the various observed nonlinear relationships. 

It does not contain a probabilistic modeling component that simulates variability therefore, it is not used to predict PbB probability distributions in exposed populations. Accordingly, the current version will not predict the probability that children exposed to lead in environmental media will have PbB concentrations exceeding a health-based level of concern (e.g., 10 pg/dL). Efforts are currently underway to explore applications of stochastic modeling methodologies to investigate variability in both exposure and biokinetic variables that will yield estimates of distributions of lead concentrations in blood, bone, and other tissues. 

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