Lindane residues on pasture and in the fat of sheep grazing pasture treated with lindane prills

Abstract

Sheep pasture was topdressed with lindane (20%) prills at the rate of 2 lb active ingredient per acre. Residues in the fat of sheep grazed for seven-10 days initially on the pasture after withholding periods of nil, nine, 17, and 27 days were 4.0, 1.8, 0.7, and 0.4 p.p.m. lindane respectively (mean values for four sheep). When these sheep were transferred to untreated pasture, lindane was eliminated rapidly from their fat, all sheep having less than 0.5 p.p.m. lindane at one month and less than 0.1 p.p.m. lindane at two months after their last exposure to the insecticide. Subsequently, pasture that grew again on the topdressed area was close-grazed by sheep during the periods 17–21, 33–39, and 53–57 weeks after lindane topdressing. Lindane residues in sheep fat after these grazing periods were 0.9, 0.4, and 0.3 p.p.m. respectively (mean values for eight sheep). Evidence indicates that this continuing low-level contamination of sheep fat was caused by lindane contained both in the topsoil and in plant surface waxes. Approximately half of the lindane applied was recovered in the topsoil 10 months later. These results are discussed in relation to the concept and evaluation of withholding periods for stock.