Residues in cattle grazed on land contaminated with heptachlor.

Abstract

Heptachlor epoxide residues exceeding the maximum residue limit of 0.2 mg/kg have been found in fat of cattle grazed on land previously treated with heptachlor prior to planting potatoes or maize. To determine the residues accumulated in cattle exposed to contaminated land and the rate of decline on removal from the contamination, steers were grazed on a former potato paddock which had been treated the 2 previous years with heptachlor at 1.1 kg/ha. Soil residues in the paddock varied from a total of 0.42 mg/kg heptachlor and its epoxide at the beginning of the trial to 0.31 mg/kg after 16 months. Residues in the soil decreased only slightly down to a depth of 300 mm. Pasture residues were less than 0.02 mg/kg (wet basis). Heptachlor epoxide residues in the body fat of the steers increased during 19 months of exposure and reached a maximum of 0.72 mg/kg. In 4 steers removed after 14 weeks exposure, the heptachlor epoxide concentrations continued to increase from a mean of 0.24 mg/kg to a mean of 0.34 mg/kg after a further 4 weeks. Concentrations then fell progressively with a half life of 11 weeks in the body fat. There was an apparent relationship between pasture length and body fat residue, with residues increasing as pasture length decreased. The results of the experiments preclude the option of grazing cattle on pasture grown on soil treated with heptachlor for any extended period of time. It is possible that if short pastures and soft soil are avoided, and if cattle are not exposed to contaminated land for any more than 1 week in each month, then residues would remain below the maximum residue limit of 0.2mg/kg heptachlor.