No abstract

Thirty-four years of data from the Great Lakes Fish Monitoring Program (GLFMP) show significant changes in the behavior of most contaminants in lake trout over time consistent with changes in contaminant inputs following regulation and remediation. Polybrominated diphenyl ethers (PBDEs) show positive apparent first-order rate constants falling to near zero. Dieldrin shows relatively unchanging half-lives of around 10 years except in Lake Superior (approximately 25 years). Mirex, consistently detected only in Lake Ontario fish, shows a slow decrease until the 1990s, when remediation of a source site occurred, after which half-lives are 2-3 years. Half-lives of oxychlordane, polychlorinated biphenyls (PCBs), and dichloro-diphenyl-trichlorethane (DDT) and its metabolites were typically 3-6 years until the mid 1980s; since then, the newest data confirm half-lives are usually around 15-30 years. For PCBs, an increasing half-life is found in other media as well. Changes in food web structure, fishery dynamics, and climate undoubtedly affect concentrations but cannot explain observed long-term trends across several media. Concentrations of legacy contaminants in the Great Lakes are likely to continue to decline only slowly and pose a health concern for decades without identifying and containing remaining sources.

We report here on the concentrations of toxaphene, a complex mixture of hexa- to decachlorinated norbornanes and norbornenes, in Great Lakes' lake trout and smelt sampled in 1982 and 1992. Lake trout from Lakes Superior, Michigan, and Huron had higher lipid-normalized toxaphene concentrations than the smelt, while in Lakes Ontario and Erie both trophic levels had about the same concentrations. Concentrations in both species declined between 1982 and 1992, with the exception of Lake Superior, where there was no significant difference. Except for the Lake Superior samples, these trends were expected because toxaphene was banned in the United States in 1982. The fact that the Lake Superior samples did not show lower concentrations over time suggests that there may be some lake-specific source that is continuing to load toxaphene into Lake Superior or that toxaphene is not being removed from Lake Superior as quickly as the other Great Lakes.

No abstract

Toxaphene is a complex mixture of at least 600 hexa- to decachlorinated bornanes and bornenes, which was used as an insecticide in the United States from the late 1950s to the mid-1980s. A previous study in our laboratory showed that the levels of toxaphene in lake trout collected in 1982 and 1992 from Lake Superior had remained about the same but that the concentrations in lake trout from the other Great Lakes had decreased during this same time period. These observations in Lake Superior trout were counter-intuitive given that toxaphene had been banned in 1982. We have reinvestigated this issue using more samples from both Lake Superior and northern Lake Michigan and using an improved analytical method. The level of toxaphene was constant in all of the trout samples from Lake Superior during the period 1977−1992, while the level decreased by a factor of 1.4−5 in trout from the other Great Lakes. These results suggest that the toxaphene concentrations in very large and very cold lakes (such as Lake Superior) decrease much more slowly than they do in relatively small and warm lakes (such as Lake Ontario).