Insecticides in tile drainage effluent

Drainage effluent from systems located on irrigated land in the San Joaquin Valley of California was analyzed for insecticide residues. Only relatively small quantities of chlorinated hydrocarbon residues were found in tile drainage effluent, but higher concentrations were found in effluent from open drains where both surface and subsurface drainage waters were collected. Traces of residue were found in the irrigation water applied to tile drained farms. When the concentration factor is considered, i.e., depth of irrigation water applied/depth of drainage water removed, on a unit baas, the total quantity of insecticide residue in tile drainage effluent does not exceed and is generally less than the total quantity of residue applied in the irrigation water. Tailwater, or surface runoff, contained from 7 to 12 times as much residue as the applied water when DDT was applied to the land and as much as 85 times more residue than the irrigation water when Lindane was applied to the land. Relatively large concentrations of residue were found in the surface soil of the area studied, even where no pesticides had been applied directly to the soil. (Key words: Drainage; groundwater; insecticides; quality of water)