DDT AND LINDANE . NEW ASPECTS OF STOCK RESIDUES DERIVED FROM A FARM ENVIRONMENT

DDT priUs, lindane prills, and DDT “wet” mix superphosphate dust were applied to short, dry pasture at the rate of 2 lb active ingredient per acre. Treatments were carried out in mid-Canterbury in winter and were followed by several months of low rainfall and minimal pasture growth. The treated areas were grazed continuously by sheep for periods of 1 month after withholding periods of 2, 6, and 12 weeks. Analyses of soil, pasture, and omental fat, sampled before the trials, established baseline levels of background contamination by insecticides, and subsequent analyses indicated the effects of the various treatments and grazing schedules. The fat of the experimental flock contained relatively high background residues of DDT and metabolites (predominantly DDE), which persisted ihroughout the series of trials. Evidence indicated that this contamination was derived from DDT that had persisted in the topsoil after topdressing with DDT in previous years. Exposure of sheep to the areas newly treated with DDT or lindane resulted in an increase in the levels of DDT/DDD or lindane respectively in the fat, these levels decreasing again to approximately the pre-trial background values when the sheep were returned to run-off areas. Lindane accumulated in sheep fat at a higher rate than DDT, but was eliminated more rapidly when exposure to lindane ceased. There were increases in lindane (and total DDT) in the fat of sheep grazed on the insecticide-treated areas for periods of 4 to 6 weeks beginning at 16, 26, and 52 weeks after topdressing. The only source of this continuing contamination was insecticide contained in topsoil. The amount of topsoil ingested by the sheep varied inversely with pasture length, and soil intakes on short pasture were approximately 100 g soil/kg dry matter of feed consumed under dry winter conditions. Sheep fed on short pasture supplemented with grain ingested more topsoil than sheep fed hay on bared ground. Off-flavour was detected in hot roast meat from sheep that had been exposed to lindane-treated pasture in one out of three experiments, but there appeared to be no correlation between off-flavour in meat and lindane content of body fat. © 1969 Taylor & Francis Group, LLC. All rights reserved.