By Brian Bienkowski, Great Lakes Echo
A long-banned pesticide remains in the Great Lakes environment but is on the decline, scientists say.
Toxaphene was a heavily used pesticide in the U.S. until people realized how toxic it was in 1982, the year it was banned in the Great Lakes region and most other places. It was banned nationally by 1990. Toxaphene mostly came to the Great Lakes on winds from the South where it was used heavily in agriculture.
The pesticide breaks down slowly and accumulates in the fatty tissues of fish and other wildlife, so it’s remained in the Great Lakes long afterwards.
However, slowly but surely, the contaminants are going away.
Purging the pollutants
Researchers examined toxaphene in the Great Lakes and found that between the mid-1970s and the mid-90s, concentrations in fish decreased rapidly. Since the mid-90s decreases have been slower, but the downward trend continues. The study is in press at the Journal of Great Lakes Research.
Researchers analyzed lake trout from every lake except Erie, where they used walleye, to determine toxaphene levels. Concentrations were highest in Lake Superior and lowest in Lake Erie.
The chart below shows toxaphene concentrations (in nanograms) in whole fish in 1977 (1980 for Lake Ontario) and the 2009 levels. (Data: Toxaphene trends in the Great Lakes fish)
Bigger, deeper, colder
Lake Superior has always had the highest concentrations.
“Lake Superior is bigger and colder, so when toxaphene came to the Great Lakes through the air, it was attracted to the lake,” said Thomas Holsen, professor of civil and environmental engineering at Clarkston University and co-author of the study.
While its size gives toxaphene a larger target, the cold water doesn’t release the chemicals as gases very quickly.
Holsen said toxaphene “cycles around the globe” so now that the Great Lakes are purging the chemicals, they’re heading elsewhere.
“In the Great Lakes, the out arrow is bigger than the in arrow right now,” Holsen said.
But since the chemicals are world travelers, those arrows can change direction quickly. AsEcho reported, after the official ban in 1990, the lake’s toxaphene levels continued to rise for a few years.
But, even in the biggest, coldest and deepest lake, the overall trend has been positive. From 1990 to 2009, toxaphene levels in Lake Superior’s lake trout have decreased approximately 86 percent.
There are no legal uses of toxaphene in the world, according to Holsen. Eventually, the chemicals will break down.
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