Insecticide Residues in Water, Sediment, and Fish of the Drainage System of the Holland Marsh, Ontario, Canada, 1972–751

Abstract

Insecticide residues in the drainage system of the Holland Marsh in southern Ontario were studied from 1972– 75 inclusive. Concentrations of insecticides in water were combined with pumping data to calculate amounts (g/wk) transferred from the marsh drainage system into the Schomberg River and Lake Simcoe. Residues of organochlorine (OC) and organophosphorus (OP) insecticides were present in the drainage system during the 4-yr period. The rate of insecticide transfer was highest in spring during maximum runoff. OC insecticides, chiefly DDT and its metabolites, predominated during this time. Dieldrin and endrin also were detected. OP insecticides, including diazinon and parathion, predominated in the water during summer and fall. Concentrations of OC and OP insecticides in the Schomberg River downstream were 3.5 × higher than those found upstream of the marsh. Total amounts of OP insecticides transferred from the marsh to the river system over the 4-yr period were ca. 7/10 those of the OC insecticides. Insecticide residues were present in bed material of the drainage system at ppb (pp10°) levels and comprised mainly DDT and its metabolites (especially TDE). Other insecticide residues present in sediments were ethion > dieldrin > diazinon. DDT residues in some species of fish from the drainage canal exceeded 5 ppm, while diazinon and ethion were present at < 0.1 ppm. DDT residues in fish from Lake Simcoe were < 0.25 ppm and no OP insecticides were present, indicating that insecticides transferred from the Holland Marsh to the Schomberg River are not currently causing significant contamination of the lake.