Exchange of Mirex between Lake Ontario and its Tributaries
The 1974 discovery of mirex in Lake Ontario fish by Kaiser (1974) triggered a period of intensive study on the substance within the lake ecosystem. Two Lake Ontario tributaries were identified as sources of mirex. The Niagara River is the major source of mirex (366 kg) to Lake Ontario, while the Oswego River discharge (224 kg) has been attributed to the Armstrong Cork Company in Volney, NY (Holdrinet et al. 1978). Hooker Chemical and Plastics Corporation manufactured and processed mirex at its Niagara Falls, NY. plant from 1957 - 1976 (Task Force on Mirex [TFM] 1977). Peak discharge to the lake occurred in the 1960's and subsequently declined (Durham and Oliver 1983) as follows; 200 kg/yr from 1960 to 1962, 13.3 kg/yr in 1979 and 8 kg/yr in the period 1979 - 1981 (Warry and Chan 1981, Kuntz and Warry 1983, Halfon 1987). A single discharge (~1961) into the watershed of the Oswego River (Holdrinet et al. 1978) continues to supply mirex to the lake ecosystem (Scrudato and DelPrete 1983). Total mirex loading to Lake Ontario has been estimated at 688 kg (Holdrinet et al. 1978) of which half has been incorporated into the sediments (Pickett and Dossett 1979). Continuing losses from dump sites will augment existing mirex levels in Lake Ontario (Warry and Chan 1981, Scrudato and DelPrete 1982, Kuntz and Warry 1983, Halfon 1987). Mirex bioaccumulates at all trophic levels in aquatic systems (TFM 1977). During the period of intensive monitoring from 1975 to 1981 (TFM 1977, Armstrong and Sloan 1980, Insalaco 1980, Norstrom et &· 1978) revealed detectable levels (usually > 5 ppb) of mirex in fish. The top predators (e.g. salmonines) contained the highest concentrations of mirex which often exceeded the U.S. Food and Drug Administration's action level of 0.1 ppm. This knowledge prompted government agencies on both sides of the U.S.- Canadian border to issue health advisories on eating fish from Lake Ontario. A high correlation between mirex levels and organic content of the sediments exists (Scrudato and DelPrete 1983). Availability of mirex to Lake Ontario biota ranges from 200 - 600 years before the contamination is buried by clean sediments (Halfon 1981, cited in Scrudato and DelPrete 1982). Since mirex is considered one of the most stable compounds ever evaluated (Metcalf et al. 1973), it could recycle within the lake ecosystem for many years via resuspension, uptake and bioaccumulation in the foodweb and sedimentation. Another potential mechanism of recycling, not generally considered, is the spawning migration of mirex laden fish. I report here an estimate of the amount of mirex available for recycling back to the Lake Ontario ecosystem by spawning migrations and on the contamination of resident fish in tributaries.
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