Suitability of thin-layer chromatography, gas chromatography and bioassay for the determination of aldrin, dieldrin and DDT residues in different soils without cleanup
Chiba, M; Yule, WN; Morley, HV
HAPAB The suitability of thin-layer chromatography ( TLC ), gas chromatography ( GLC ) and insect bioassay was compared for the determination of aldrin, dieldrin and DDT residues in different soils without cleanup. Samples of Matilda sandy loam, muck and Rideau clay, each with a known history of organochloride insecticide trretment, were air-dried at room temperature and screened through a 10-mesh sieve before extraction. The extract solvents, all distilled and checked for impurities before use, were acetonitrile, acetonitrile and acetone ( 1: 1 v/v ). Postextraction procedures were those of Chiba and Morley ( 1968 ). TLC was carried out using 5% acetone in n-hexane ( 1: 9 v/v ) and methanol and methylene chloride ( 1: 1 v/v ). Postextraction procedures were those of Chiba and Morley ( 1968 ). TLC was carried out using 5% acetone in n-hexane and then observed under ultraviolet ( UV ) light; the plate was sprayed with ammonical silver nitrate as the chromogenic reagent. An Aeorgraph Hi-Fi Model 600 ( iwth an electron- capture device ) with column, injection and detector temperatures of 173, 164 and 173 C, respectively ) was used for GLC. The operating parameters are given. Solvent extracts of soils were assayed with Drosophila using the dry-film technique of Yale ( 1965 ) and the direct bioassay method of Edwards et al. ( 1957 ). When the ewuivalent of 2 g sandy loam or clay soil was spotted, the lower limits of detectability for p,p'-DDE, p,p'-DDT, aldrin and dieldrin were 0.1, 0.2, 0.5 and 1.0 mmg, respectively, indicating that TLC screening of these pesticides can be done without cleanup. With muck, however, screening cannot be achieved with these conditions because of coextractives. GLC analyses detected higher concentrations of residues without background interference. VQlues as high as 0.82, 0.72 and 0.68 ppm of aldrin, dieldrin and DDT ( o,p'- and p,p'-DDT ) respectively were found in Matilda sandy loam. Concentrations as high as 0.61, 0.79, 0.43 and 8.27 ppm of aldirn, dieldrin, p,p'-DDE and DDT, respectively. were found in muck treated with aldrin and DDT. Rideau clay with no pesticide treatment, contained as high as 0.1, 0.12 and 0.21 ppm of aldrin, DDE and DDT, respectively. These high concentr ations required most soil extracts to be diluted 10 to 25 times to approximate the levels of the standards. If dilution of the soil samples had not been required for GLC, cleanup would have been necessary. In general, the results obtained by TLC and bioassay suggested that assay of extracts without cleanup was impracticable or at least inaccurate. The best hope for quantitative analysis appears to be for dry-film bioassay in which cleanup of the extracts and separation and identification of the toxic residues has been effected. TLC would appear to be the most pormising approach for this purpose. ANALYSIS 70/12/00, 598 1970