Heavy Metals and Persistent Organics Content in Cattle Exposed to Sewage Sludge

Cattle grazing a sewage sludge disposal site were examined to determine whether, and to what extent, contamination of tissues had occurred as a result of exposure to sewage sludge. The heavy metal and persistent organics content of kidney, liver, muscle, and bone tissues from cattle grazing a sewage sludge disposal site were compared with tissues of cattle from a nearby control ranch. Tissues were analyzed for As, Cd, Cu, Hg, Mo, Ni, Pb, Se, Zn, and 22 persistent organics. The sludge-exposed cattle had an average kidney-Cd content of 16 mg/kg (dry weight), which was significantly higher than the 4 mg/kg found in the control herd, but was not above a range that would be expected from older range cattle. There were no other tissue differences between the two groups with respect to Cd. The average liver-Cu concentration (4.6 mg/kg) of the sludge-exposed cattle was significantly lower than that of the controls (19 mg/kg); however, both groups of animals displayed liver-Cu concentrations that were considerably lower than levels previously considered normal. Mean kidney-Hg and liver-Se concentrations were significantly higher in the control cattle than in the sludge-exposed cows. Kidney-Zn concentrations of the sludge-exposed cattle were significantly higher than those of the controls, but the magnitude of the differences was small. Differences between the two groups of animals in relation to Hg and Se were small, and it is doubtful that any real biological significance can be assigned to these differences. Fat was the only tissue that contained detectable levels of 22 persistent organics. The only significant difference observed was alpha-BHC (hexachlorocylohexane, alpha); the control herd averaged 30 µg/kg (wet weight), whereas the sludge-exposed cattle averaged 10 µg/kg.