Insecticide residues in soils on fifteen farms in southwestern Ontario, 1964–1974

Abstract

Soils on 15 farms in southwestern Ontario were sampled in 1974, as part of a long term study initiated 10 years earlier, to determine the extent to which residues of insecticides were occurring in agricultural soils through current insect control practices. Residues of organochlorine (OC) and organophosphorus (OP) insecticides were determined using gas‐liquid chromatography. DDT residues were present on all farms being highest in orchard > vegetable > tobacco > field crop soils. Residue levels of t‐DDT were generally similar to or lower than those first detected in 1964. Cyclodiene insecticide residues were present in soil on 13 of the 15 farms being highest in vegetable > tobacco > field crop > orchard soils. Residue levels in 1974 were ca. 1/2 to 3/4 those found in 1964. No significant accumulation of OP insecticides was apparent in mineral soils used for production of tobacco and other field crops. However, OP insecticide residue levels increased tenfold in vegetable soils, particularly those high in organic matter, from 1964 to 1974, and in 1974 exceeded t‐cyclodiene insecticide residue levels. The predominant OP insecticide detected in organic soils was ethion.