Predicting blood lead concentrations from lead in environmental media

Policy statements providing health and environmental criteria for blood lea d (PbB) often give recommendations on an acceptable distribution oi PbB con centrations Such statements may recommend distributions of PbB concentratio ns including an upper range (e.g., maximum and/or 90th percentile values) a nd central tendency (e.g., mean and/or 50th percentile) of the PbB distribu tion. Two major, and fundamentally dissimilar, methods to predict the distr ibution of PbB are currently in use: statistical analyses of epidemiologic data, and application of biokinetic models to environmental lead measuremen ts to predict PbB. Although biokinetic models may include a parameter to pr edict contribution oi lead from bone (PbBone), contemporary data based on c hemical analyses of pediatric bone samples are rare. Dramatic decreases in environmental lead exposures over the past 15 years make questionable use o f earlier data on PbBone concentrations to estimate a contribution of lead from bone; often used by physiologic modelers to predict PbB. X-ray fluores cent techniques estimating PbBone typically have an instrument-based quanti tation limit that is too high for use with many young children. While these quantitation limits have improved during the late 1990s, PbBone estimates using an epidemiologic approach to describing these limits for general popu lations of children may generate values lower than the instrument's quantit ation limit. Additional problems that occur ii predicting PbB from environm ental lead by biokinetic modeling include a) uncertainty regarding the frac tional lead absorption by young children; b) questions of bioavailabilty of specific environmental sources of lead; and c) variability in fractional a bsorption values over a range of exposures. Additional sources of variabili ty in lead exposures that affect predictions of PbB from models include dif ferences in the prevalence oi such child behaviors as intensity of hand-to- mouth activity and pica. In contrast with these sources oi uncertainty and variability affecting physiologic modeling of PbB distributions, epidemiolo gic data reporting PbB values obtained by chemical analyses of blood sample s avoid these problems but raise other issues about the validity of the rep resentation of the subsample for the overall population of concern. Stare a nd local health department screening programs and/or medical evaluation of individual children provide PbB data that contribute to databases describin g the impact of environmental sources on PbB. Overall, application of epide miologic models involves fewer uncertainties and more readily reflects vari ability in PbB than does current stare-of-the-art biokinetic modeling.