During October 1983, 36-L water samples were collected at 14 stations in Lake Ontario and analyzed for a range (23) of organochlorine contaminants: chlorobenzenes, pesticides and their by-products, and polychlorinated biphenyls (PCBs). Fifteen of the 23 compounds analyzed were ubiquitous in distribution and, of the remaining eight compounds, toxaphene, mirex, photomirex and dichloro· benzenes were undetected. A station located east of Hamilton Harbour was ranked highest in total PCBs (3.1 ng· L -1 ), oxychlordane (0.263 ng · L -1 ) and heptachlor epoxide (0.375 ng· L -1), and ranged second highest in total DDT (tDDT). The highest concentrations for a-BHC (8.08 ng· L -1 ), a-chlordane and r·chlordane (0.046 and 0.062 ng· L -1, respectively) were recorded at a station situated just west of Toronto Harbour. Most of the chlorobenzenes were highest offshore of Eighteen Mile Creek; sampling, however, was insufficient to demonstrate that the observed levels were the result of the Niagara River plume. While pesticide levels did not exceed current criteria established by the Great Lakes Water Quality Agreement and the United States Environmental Protection Agency, concentrations of lindane, dieldrin, endrin, and tDDT were within one order of magnitude of these criteria
