In-use Pesticide Concentrations in Surface Waters of the Laurentian Great Lakes, 1994–2000

Pesticides are heavily used in agricultural production in the Great Lakes basin. Large-volume surface water samples were collected between 1994 and 2000 from Lakes Ontario, Erie, Huron (including Georgian Bay), and Superior and analyzed for neutral and phenoxy-acid herbicides, and organophosphorus insecticides. Thirty-nine pesticides from these three pesticide classes, including analytes and some metabolites, were measured. Six pesticides—barban, diallate-2, triallate, phorate, phosmet, and disulfoton—were not detected. Atrazine, metolachlor, simazine, and 2,4-D were detected in greater than 50% of the samples. The highest maximum concentrations were observed for atrazine (1,039 ng/L), metolachlor (736 ng/L), and D-simazine (281 ng/L). No pesticide concentrations exceeded water quality guidelines/criteria for the protection of aquatic life and drinking water. In general, an increasing concentration gradient from north to south was observed with Superior < Huron < Ontario < Erie. The spatial and seasonal variability of selected pesticides are discussed in relation to their use and application.