Residues in soil, pasture and grazing dairy cattle after the incorporation of dieldrin and heptachlor into soil before sowing

Abstract

Soil, pasture and grazing dairy cattle with calves were monitored at two locations on the North Coast of New South Wales for insecticide residues from 1972-1 975, after soil incorporation of dieldrin and heptachlor at the recommended rate of 1.1 kg/ha before sowing to control pasture weevil pests. The soil and pasture types were: Wollongbar clay loam sown with tropical legumes and grass at Wollongbar (dieldrin), and black alluvial sown with temperate legumes and grass, at Duck Creek substation, near Ballina (dieldrin and heptachlor). After the treatments, persistent residues were found in soil and pasture, and grazing stock, although residues declined over the trial period. Stock residues in many cases exceeded the 0.15 and 0.2 ¦g/g maximum residue limits recommended by the National Health and Medical Research Council for the fat of milk and meat, and similar residues were found in additional cattle introduced after fifteen months. In view of the long-term risks for grazing stock, the pre-sowing soil treatment with dieldrin and heptachlor for the control of pasture pests is no longer recommended by the New South Wales Department of Agriculture.