Suspected in Minnesota Fish Kill
(Beyond Pesticides, August 5, 2005) In late June, an estimated 100,000 to 300,000 black crappie fish (Pomoxis nigromaculatus) died suddenly in Clear Lake in Waseca County, Minnesota. Water samples show the presence of permethrin, the pesticide that had been used two days prior for mosquito control.
During the fish kill, the Minnesota Department of Natural Resources (DNR) and the Minnesota Department of Agriculture took water and fish samples to pinpoint the cause. Upon analysis, officials say permethrin was found in two of three water samples.
Permethrin was not detected in the fish samples. The problem officials face in conclusively determining permethrin as the cause of the fish kill lies in the nature of the pesticide's toxicity. Permethrin's acute toxicity can be difficult to detect due to its relatively short half-life and ability to be quickly flushed out of an organism's system.
DNR pathologist Joe Marcino told a local paper that the analysis turned up no evidence of other possible causes of death for the fish. "Damage as observed is consistent with the effect of a chemical toxin,'' Marcino said.
Permethrin had been sprayed in the surrounding area on June 19th and 20th -- approximately two days before the fish kill was discovered. The pesticide apparently contaminated the lake as runoff from a subsequent rainstorm.
According to Waseca County Historical Files, Clear Lake has a history of ecological problems and has undergone several restoration efforts. However, the June fish kill is said to be one of the area's largest.
Permethrin is a synthetic pyrethroid that is highly toxic to fish, aquatic animals, and bees. Permethrin is a suspected endocrine disruptor, immunotoxin, and neurotoxin. It is also thought to have reproductive effects, and is a possible human carcinogen.
State officials say they will determine whether any state or federal pesticide laws were violated, but despite the die-off, local officials say people can still fish on the lake.
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