EVALUATION OF BLOOD AND TISSUE LEAD AS ESTIMATORS OF EXPOSURE IN SHEEP

From 1992 to 1994, samples of whole blood, liver, kidney, muscle and b one were collected at slaughter from 70 lambs which had grazed on a re -vegetated tailings pond of a lead/zinc mine for periods ranging from 49 to 168 days, together with similar samples from 24 unexposed contro l lambs. Concentrations of Pb in blood, liver, kidney and bone in the exposed lambs were significantly higher than those in the controls in each of the 3 years although tissue levels in all cases remained below 2 mg/kg wet weight, the maximum permitted for human consumption under current Irish legislation. While blood Pb levels generally showed a g ood correlation with those in liver, kidney and bone, a greater degree of overlap between exposed and control lambs for blood values compare d to tissue values reduced the sensitivity and specificity of blood Pb as an indicator of Pb exposure. The Pb content of liver, kidney and b one provided better discrimination of animals exposed to the tailings and this suggests that these tests are more suitable for inclusion in environmental monitoring programmes.