Abstract
Studies on the distribution of lead (Pb) at exposure levels that produce blood Pb levels similar to those considered a potential concern ( 10-14 mug/dl) are seriously lacking in the scientific literature. Because the manifestations of toxic effects of Pb vary depending on concentration and site of action, delineation of patterns of accumulation of Pb in tissues that may serve as sites of action at low levels of exposure may provide critical clues in elucidating the toxic effects of Pb. Also of importance is the contention that blood Pb levels may not adequately represent the potential for tissue-specific toxicity, particularly at low levels of exposure. This study was designed to examine the temporal pattern of Pb accumulation in blood and in various soft tissues during subchronic oral exposure to 5 or 50 ppm Pb. Sixty-three Long-Evans male rats (21 days old) were randomly divided into three groups and were provided 0 (50 ppm sodium acetate), 5, or 50 ppm Pb acetate in drinking water for 90 days. Rats from the three groups were sacrificed at 2-week intervals, and lead concentrations in the blood and seven soft tissues were determined with an atomic absorption spectrophotom eter. While there were no significant blood Pb elevations following 5 ppm Pb exposure, the kidney and the brain showed significant Pb accumulation relative to the respective controls. In the 50-ppm Pb-exposed group, all tissues except testis and liver showed significantly greater Pb accumulation (p < .05)than the controls. However, in theprostate, spleen, liver, and testis, there were no significant differences between the 50-ppm and the 5-ppm exposure groups. Although there were time-dependent variations over the 90-day period, the order of m agnitude (ng/g wet tissue) of Pb accumulation in the Pb-treated groups was as follows: kidney > brain > spleen > prostate > heart > testis and liver. These results show that at 5 ppm Pb exposure, brain and kidney accumulate Pb significantly, confirming that at these exposure levels, blood Pb is not a good index of tissue burden.