Residues of organochlorine pesticides in Alabama soils

A survey was made of 36 Alabama agricultural soils to assess residues of formerly used organochlorine pesticides. Compounds determined comprised alpha- and gamma-hexachlorocyclohexane, heptachlor, heptachlor-exo-epoxide, trans- and cis-chlordane, trans-nonachlor, dieldrin, toxaphene, DDT and DDE. Concentrations varied by several orders of magnitude among farms and appeared to be log-normally distributed. Highest concentrations (ng g(-1) dry soil, arithmetic means) were found for toxaphene (285+/-390) and DDTs (p,p'-DDE, 22.7 +/- 21.4; p,p'-DDT, 24.6 +/- 30.5; o,p'-DDT, 4.00 +/- 5.86; p,p'-DDD, 2.40 +/- 2.41) which were once heavily used in the southern USA. Pesticide residues were not proportional to soil organic carbon content indicating that residue concentrations were a reflection of pesticide application history and dissipation rates rather than air-soil equilibrium Mean ratios of DDT/DDE in six regions of the state ranged from 0.39 to 1.5, and compound ratios for chlordanes and toxaphene were different from those in the technical mixtures. (C) 1999 Elsevier Science Ltd. All rights reserved.