Subchronic Lead Feeding Study in Male Rats

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This study was done to establish baseline information on the bioavailability of low levels of different species of lead by oral feeding in young rats and to compare this with lead-contaminated soils of similar dosage. These results can be used to help establish low-level risk assessments for lead exposure in children. Lead acetate was used in this study as a point of reference because it was considered to be 100% bioavailable. The required amounts of either lead acetate or lead nitrate were added to the control soil of 135 mg/kg lead to match the targeted test soil lead concentrations of 375, 750, 1500, and 3000 mg/kg lead. This lead-contaminated soil was mixed 5% (soil/diet) by weight with a semipurified lab chow diet, which resulted in final dietary lead concentrations of 6.75, 18.75, 37.5, 75, and 150 μg Pb/g diet. Results from this study indicated that (1) the dietary lead concentrations used did not result in any overt signs of lead toxicity (i.e., no significant effect on body weight gain, food consumption, or fecal output), (2) there were significant dose-dependent increases in fecal lead concentration and total fecal lead output, although there were no significant differences among study groups, (3) there was a time-dependent decrease in net whole-body lead uptake from a total group average of 65% at week 1 down to ∼40% by week 5, and (4) there were no significant differences in terminal blood lead levels among study groups. Results from this study demonstrated a significant dose-dependent increase in tissue lead concentrations (μg Pb per g tissue weight) for bone, kidney, and liver for all study groups. There were no significant differences between the lead acetate and the test soil study groups at any lead dosages; however, there was a significantly increased lead incorporation into the bones from the lead nitrate study group. In summary, these results demonstrate that rats metabolize and handle lead of relatively small particle size from different soils and from different sources in a similar manner, although the use of lead acetate as the standard for 100% bioavailability might need to be reevaluated.

James B. Heneghan—Retired.