Abstract
The persistence of heptachlor, triazophos, and fenvalerate in subtropical soil was studied over a 3-year period. Each insecticide was applied biweekly for 2 years to field soil and to three distinct soil types confined in wooden boxes and placed in the field. Insecticide residues in the top 15 cm soil layer were monitored from the initiation of the experiment and until 1 year after application was discontinued. Insecticide residues did not accumulate in the soil between May and October, but their concentrations increased gradually after October. High concentrations were recorded from January until April, after which they declined rapidly. No carryover of insecticide residues was noted from year to year. Precipitation and temperature appeared to influence degradation which was faster from May through October (avg precipitation 1545 mm; mean temp 28.1°C), than from November to April (avg precipitation 226 mm; mean temp 19.8°C). Soils confined in boxes had greater residue concentrations especially of heptachlor than did field soil in situ. Except for heptachlor epoxide, there was practically no movement of insecticide residues below the 0–15 cm soil layer. Application of heptachlor, triazophos and fenvalerate mixture did not result in any change in the persistence rates of individual insecticides over the rates observed when such chemicals were applied individually.
Published Version
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