Pesticide Residues in Onions and Carrots Grown on Organic Soils, Ontario 1975 to 1980

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Abstract
Between 1975 and 1980, six farm surveys and five field experiments were conducted on onions, Allium cepa L., and carrots, Daucas carota L., grown on organic soils in the Holland and Keswick Marshes. In three main studies, pesticide residues were determined in: onions treated at planting time to control the onion maggot, Hylemya antique (Meigen); onions treated in windrow to control the flies of the onion maggot; and carrots, in rotation with onions, for residues of insecticides persisting from uses in onions. Because of maggot resistance and heavy dependence on ethion in 1975, 38% of onion samples in an eight-farm survey contained ethion residues above the 100-μg/kg negligible level found in the Food and Drug Act and Regulations of Canada. In 1978, with less dependence on ethion, onions from another eight-farm survey had residues below 100 μg/kg, and only 3% contained ethion above 100 μg/kg. In field experiments conducted in 1978 and 1979, none of the seven insecticides tested gave residues above 100 μg/kg in dry onions, with the exception of the highest application rates of ethion (4.5 kg/ha). When drying onions lying in windrows were treated with parathion and diazinon, residues declined below the permitted tolerances at first sampling 3 and 7 days later respectively. In experiments in 1979, residues of cypermelhrin, permethrin, and parathion decreased below 100 μg/kg in 7, 1, and 3 days, respectively, when applied to drying onions in the windrow. In 1980, initial residues on onions treated in the windrow were below 100 μg/ha. Residues remaining in the soil from insecticides used on onions in 1975, 1976, and 1977 resulted in residues below 100 μg/kg in carrots grown and harvested the following seasons, respectively.

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