Organochlorine Insecticides and Industrial Pollutants in the Milk Supply of the Southern Region of Ontario, Canada

Abstract

A province-wide survey conducted between 1967 and 1969 revealed that milk produced in the Southern region had the highest residues of organochlorine insecticides in Ontario. It was in this region where 90% of the organochlorine insecticides purchased in the province were applied. In 1969–70 restrictions were placed on DDT and the cyclodiene insecticides. Disappearance of these organochlorine insecticides from milk were studied in surveys conducted in 1970–71 and 1973. The mean ∑DDT levels declined from 0.20 ppm in 1967 to 0.05 ppm in 1973, whereas the mean dieldrin residues declined from 0.044 ppm to 0.015 ppm in the same period. These data include counties where there had been only small reductions in the use of DDT and where milk residues remained unchanged until further restrictions were effected in 1971. Residues of lindane and heptachlor epoxide were virtually absent from milk fat. Chlordane, endosulfan, methoxychlor and endrin were absent from all samples in spite of increasing quantities being used of the first two insecticides. Residues of polychlorinated biphenyls appeared slightly higher in the 1973 survey than in the 1970–71 survey. Hexachlorobenzene was present at very low levels in the 1973 survey.