OCCURRENCE OF PESTICIDES IN THE YAMASKA RIVER, QUEBEC

Concentrations of pesticides in water near the mouths of the Yamaska R iver in Quebec, Canada, and five of its tributaries are reported for t he summers of 1986 and 1987. The most frequently occurring pesticides, and those at the highest concentrations, were atrazine and metolachlo r. Peak atrazine concentrations frequently exceeded the recommended Ca nadian water quality guideline of 2 mug/L for the protection of aquati c life. These peak concentrations were similar to those that had been observed a decade before. In addition, in 1986 and 1987 significant co ncentrations of metolachlor were detected in the waters. In some locat ions, the peak metolachlor concentration was greater than half its rec ommended Canadian water quality guideline of 8 mug/L for the protectio n of aquatic life, and in one location the guideline was exceeded. Als o found at much lower concentrations were some other triazine herbicid es, some degradation products of triazine herbicides, and some organop hosphorus and organochlorine insecticides. No carbamate pesticides wer e found.