CONTRIBUTION OF TISSUE LEAD TO BLOOD LEAD IN ADULT FEMALE SUBJECTS BASED ON STABLE LEAD-ISOTOPE METHODS

Public health and medical recommendations on prevention of lead toxici ty rely on use of blood lead concentrations to assess lead exposure an d predict onset of adverse health effects. Blood lead levels have gene rally been thought to reflect recent environmental lead exposures. How ever, tissue lead stores are accumulated over a long time period (i.e. , years). These tissue stores, primarily from bone, can be remobilized as part of both normal physiologic and pathologic processes. Although chemical analyses do not differentiate lead isotopes, mass spectromet ric determinations can differentiate the quantities of stable lead iso topes present in particular samples (e.g., lead 207, lead 206, lead 20 4, and lead 208) Selected geographic locations may have distinct isoto pic profiles. For example, on mainland Australia the Pb-206 Pb-204 rat ios reported in both environmental lead sources and blood samples are typically less than 17.0. By contrast, stable lead isotope profiles in blood samples of adult women immigrating from Eastern Europe and the former Soviet Union usually have Pb-206/Pb-204 ratios greater than 47. 5 and as high as 18.5 on entry into Australia. Longitudinal monitoring of blood samples to determine stable lead isotope profiles by mass sp ectrometry and chemical analyses of blood samples for total lead conte nt were conducted over a 300-day period. These data show that between 45% and 70% of lead in blood comes from long-term tissue lead stores. Recognition that the predominant source of lead in blood was tissue st ores rather than the contemporaneous environment should greatly modify recommendations on use of blood lead to monitor occupational or envir onmental interventions. In addition, internal biokinetics of lead, doc umented through presence of tissue lead in blood, underlie the long-te rm health risks of lead exposure. Transfer of lead to the fetus from m aternal tissue stores represents a special area of concern.