Persistence in earthworms and potential hazards to birds of soil applied DDT, dieldrin and heptachlor.
DDT, dieldrin and heptachlor were applied to separate plots in a hay field at 0.6, 2.2 or 9.0 kg/ha. For 11 yr thereafter, soil and earthworms were analysed for residues. The average ratios of residues in earthworms (dry weight) to residues in soil (dry weight) were: total DDT, 5; dieldrin, 8; heptachlor epoxide, 10. The average time for the initial residues in soil to be reduced by 50% were: total DDT, 3.2 yr; dieldrin, 5.1 yr; heptachlor epoxide, 3.2 yr. The corresponding times for residues in earthworms were: total DDT, 3.2 yr; dieldrin, 2.6 yr; heptachlor epoxide, 3.0 yr. DDE was most persistent, and in plots treated at 9.0 kg/ha its concentration remained constant at about 0.4 ppm in soil and about 7 ppm in earthworms. When applied at 9.0 kg/ha, DDT accumulated in earthworms to concentrations (32 ppm) which are hazardous to some sensitive bird species. When heptachlor was applied at 2.2 or 9.0 kg/ha, heptachlor epoxide in earthworms reached concentrations (8 ppm) potentially hazardous to woodcock. Dieldrin remained at potentially hazardous concentrations (8 ppm) for 3 yr in plots treated with 2.2 kg/ha and for 11 yr in plots treated with 9.0 kg/ha.