Accumulation of potentially toxic metals in the liver tissue of sheep grazed on sewage sludge-treated pastures

Concentrations of potentially toxic metals (PTMs) in the livers of pregnant, mature ewes and their 110 day foetuses, and in 6-month old lambs born to other ewes, were determined. The animals had been reared on pastures fertilized for 5 years with either sewage sludge ( treated; T) or conventional inorganic fertilizer ( control; C). The effects of treatment on patterns of accumulation of PTMs differed with stage of development and with individual PTM. In the liver of lambs, concentrations of Pb were elevated in T compared with C liver ( P < 0.01), while Cu and Zn were lower ( P < 0.001) in T than C liver. By contrast, in ewe liver, Cu concentrations were lower in T than C liver ( P < 0.05), as in lambs, but there were no other treatment differences in PTM concentration. Ewe and lamb tissue data were not directly comparable because they were exposed to different diets but mean concentrations of Cd, Ni and Pb were approximately two-to four-fold higher in ewe than lamb liver while mean Cu concentrations were approximately five-fold lower, suggesting that more prolonged exposure to PTMs may have enhanced treatment differences in tissue PTM concentrations. Mean foetal PTM concentrations were not significantly affected by treatment. It is concluded that the repeated application of sludge to pasture is associated with altered, but not necessarily increased, rates of accumulation of PTMs in liver tissue, that rates of accumulation depend on the individual PTM measured and that they are probably influenced by duration and route of exposure and source of nutrient. Limited observations suggested that there was little effect of year, and associated variation in climatic conditions and herbage growth, on PTM accumulation.