Minimal Concentrations of Aldrin, Dieldrin, and Heptachlor in Soil for Control of White-Fringed Beetles as Determined by Parallel Gas Chromatographic and Biological Assays

Abstract

The minimal concentrations of aldrin, dieldrin, and heptachlor in Norfolk fine sandy loam required for control of a white-fringed beetle, Graphognathus leucoloma fecundus Buchanan, were sought to provide a sound basis for field treatments. Soil samples were treated with 7 concentrations (0.02–0.40 lb/3-in. acre) of each toxicant and bioassayed in the field with newly hatched larvae for periods of 87–93 days. These tests were paralleled by electron capture gas chromatographic analyses of similar samples, which provided information concerning the initial concentrations of the insecticides and their residues and degradation products during the bioassays, initial uniformity, and vertical distribution of the insecticides in the soil during the bioassays. Results from the bioassays were related to the chemical data to provide initial minimal LC100 values for aldrin (97 ppb), dieldrin (56 ppb), and heptachlor (ca. 46 ppb). Heptachlor was degraded to 1-hydroxychlordene (4,5,6,7,8,8-hexachloro-3a,4,7,7a-tetrahydro-4,7-methanoinden-1-ol) in the insecticidal dust used for the soil treatment but further degradation after its addition to the soil was not detected. About half the heptachlor was lost during the bioassay, 1-hydroxychlordene diminished rapidly, and gamma chlordane (impurity in technical heptachlor) was more persistent than heptachlor. Small quantities of heptachlor epoxide were detected during the latter part of the bioassay. Dieldrin was very persistent, while aldrin residues diminished markedly with the formation of appreciable quantities of dieldrin. Vertical distribution of the insecticides varied widely, but the top layers of soil generally contained a lower concentration than the center or bottom layers. Gas chromatographic procedure and a chromatogram of a soil extract known to be free of chlorinated insecticides also are presented.