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 α- and γ-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.