Accumulation and dissipation of dieldrin in mature wethers in the south-west of Western Australia

The concentrations of dieldrin in body and wool fats of wethers grazed on 6 dieldrin-contaminated sites in the south-west of Western Australia were monitored over 2.5 years. Soil and pasture concentrations of dieldrin, a legacy of previous horticultural activities at these sites, were also measured. The concentrations of dieldrin in the soils varied from about 0.2 to 1.7 m a g . The production of the pastures at all sites showed a typical Mediterranean pattern with peak production in spring. The quantity of dry matter available ranged from <1000 kg/ha during summer-autumn to 10000 kg/ha in spring. In some samples the concentration of dieldrin in the dried plant material was above the accepted limit of 0.01 m a g for fresh material, but there were decreases over spring because of the substantial increase in the amount of dry matter available. The concentrations of dieldrin in the body and wool fats of the wethers increased during the winter and peaked at the start of spring, with the highest mean concentrations (mg/kg) in 1989 of 0.09-1.10 in body fats and 0.07-0.63 in wool fats. During spring the concentrations decreased and were at relatively low levels at the start of summer, with mean concentrations (mg/kg) of 0.02-0.72 in body fats and 0.01-0.18 in wool fats. Detailed results from 2 sites are discussed: Carbunup, with poorly structured loam soil; and Donnybrook, with good loam soil. On paddocks contaminated with dieldrin, production of wool with low concentrations of dieldrin is possible. If sheep grazed on contaminated paddocks are to be slaughtered, they should be sold in late spring, when concentrations of organochlorines in body fat should be low, or they should be run on uncontaminated land for about 2 months before their sale for slaughter.