Pesticides in Ontario drinking water - 1985

In 1984 the herbicide alachlor was detected in several municipal and private drinking water supplies. On the basis of the toxicity data available, Health and Welfare Canada set an interim maximum acceptable concentration (IMAC) of 5 ?g/L. As a consequence a program was established in 1985 to sample numerous municipal waterworks, private wells and some ambient locations for alachlor. The pesticide analyses were done by the Ministry of the Environment (MOE) and the Ontario Ministry of Agriculture and Food (OMAF). Alachlor was the priority compound and every effort was made to expedite the availability of these results. The analysis by gas chromatography/mass spectrometry (GC/MS) did reveal other pesticides. The MOE laboratory, analysing samples almost exclusively from municipal waterworks, was reporting results on alachlor and some other pesticides throughout the sampling period. Most of these results were included in the document entitled "Alachlor Monitoring of Ontario Drinking Water May-November 1985" (the Alachlor Report)1. The OMAF Laboratory, which analysed samples from private wells, ambient waters and two municipal locations, was able to quickly provide results on alachlor but due to insufficient staff the reporting on other pesticides was left until later. High results for these other pesticides were transmitted qualitatively to the regions but it was not until the middle of December 1985 that a complete data set was available. The data set was subsequently tabulated and corrected, and forms the basis of the present report.