TRACE-METAL ACCUMULATIONS IN TISSUES OF GOATS FED SILAGE PRODUCED ON SEWAGE SLUDGE-AMENDED SOIL

Studies were conducted to document the impact of sewage sludge-fertilized corn (Zea mays) on the feed and food chain under controlled experimental conditions that eliminated any direct ingestion of sewage sludge by animals. Accumulations of trace metals were measured in various tissues of dairy goats (Capra hircus) consuming corn silage that contained up to 5.3 mg Cd/kg and 113 mg Zn/kg for 3 consecutive yr. The Cd concentrations in goat livers increased as the amount of silage-borne Cd increased and reached a high concentration of 2.94 mg/kg. Kidney Cd concentrations were .apprx. 10-fold greater than those observed in liver, ranging from 3 mg/kg for animals fed control corn silage to 22 mg/kg for those consuming silage grown on soil amended with the highest rate of sewage sludge. This concentration was an order of magnitude less than the critical level suggested for induction of renal dysfunction. Kidney Zn ranged from 76.6-91.8 mg/kg with animals fed control silage having less Zn than animals fed sludge-fertilized corn silage. Concentrations of Zn in livers did not differ among treatments. Cu concentrations in livers and kidneys were significantly lower (.apprx. 2 mg/kg) in animals receiving sludge-fertilized silage than in animals fed control silage. The reduced Cu absorption may have been caused by a Cd and/or Zn metabolic interference. The elemental concentrations of 12 other metals and minerals in goat liver and kidney were not affected by treatment. Similarly, elemental concentrations in heart and muscle were not affected by treatment.