Heavy Metal Retention in Tissues of Cattle Fed High Cadmium Sewage Sludge

A diet containing 11.5% (dry matter basis) of a moderately high Cd sewage sludge was fed to six Hereford steers for 106 days to simulate a high sludge intake from sludge-amended soils. At a mean live weight of 460 kg, the steers were slaughtered and liver, kidney, bone, muscle, lung, brain and spleen tissues were collected for heavy metal determinations; tissues were also collected at this time from six control steers fed the same diet with no sludge. The sludge-fed cattle consumed an average of 8.95 kg of diet dry matter/day and gained 1.13 kg/day. This feed intake was slightly higher, but the gain lower than that of control cattle. All gains were equal to those expected from intake of non-sludge diet components. This indicated that the sludge had approximately zero energy value and was acting as a dietary diluent. The sludge metal content (ppm, dry basis) was: Cd, 98; Hg, 18; Pb, 466; Cu, 1,733, and Zn, 1,733. Addition of sludge increased metal contents of the feedlot diet to 30 to 100 times that of the control. Retention of heavy metals in the total animal from sludge ingestion averaged .09%, .06% and .3% for Cd, Hg and Pb; no retention was noted from Cu and Zn. These low fractional retentions increased tissue Cd, Hg and Pb concentrations of liver and kidney tissues by five to 20-fold. Estimates of levels that would enter the human diet from average beef tissue consumption if all feedlot steers were fed sludge are presented for Cd, Hg and Pb. The data indicate that cattle are a moderately effective screen against the entry of these potentially toxic metals into the human diet.