CLASSIFYING LEAD BODY BURDENS USING Z-SCORES

Twenty-nine tissues from each of 46 white males from the Cincinnati, [Ohio, USA] area were analyzed for Pb in order to characterize normal tissue values. The concentrations of Pb from the various tissues varied widely, many of them increasing or decreasing with age. A method was needed to compare the Pb concentrations among the different tissues from the same individual and to compare the body burdens of Pb from individual to individual. The z score was used for this purpose. Using overall or age-adjusted tissue means and SD, z scores for each tissue of each individual were calculated. From these were calculated overall body scores and separate scores for the individual''s bone and soft tissues. The rankings of the individuals on the basis of their overall z scores related well to the individual''s occupation, therefore providing an index of probable exposure to Pb. From the z scores for soft and hard tissue groups, an individual''s body burden could be classified into 4 exposure types: long-term low level, recent high level, past high level and long-term high level exposures. The z score also permitted the comparisons of the Pb concentrations from specific tissues to other tissues and to the overall body z scores, even though there were changes in some tissue concentrations with age. Blood concentrations correlated well with many tissues and with overall body scores.