Mercury and Weed Killer Contaminate Wyoming's Fish & Frogs

by Steve Jones

If you moved to Wyoming, as I did, to be close to superlative landscapes and abundant wildlife and to get away from the pollution inundating much of the rest of the United States, this news may disturb you. There are problems cropping up in Wyoming. In our fish. In our frogs. But the sources of contamination may be far, far away.

Mercury in Big Horn Reservoir Walleye

In the Big Horn Reservoir, also known as the Yellowtail Reservoir, north of Greybull, walleye are showing up with high levels of mercury. Walleye are flesh eaters, so they are eating other fish, and the mercury in those fish is accumulating in the flesh of walleye.

According to the Wyoming Game and Fish Department, the level of mercury in walleye is .6 parts per billion. This is considered too high for human consumption. (Because we humans live for many years, mercury accumulates in us too.)

So even though the Wyoming Department of Health hasn't told you about this yet (which is rather strange, since the state of Montana has had a fish advisory on walleye in the Big Horn Reservoir for some time), avoid eating walleye if you catch them in that reservoir.

No studies have been done to determine the source of this mercury pollution. But mercury is a rather common air pollutant from coal-fired power plants, such as the JE Corette Power Plant, located near Billings, Montana, approximately 40 miles north of the reservoir. Mercury is also used commonly in thermometers. People who casually toss away their mercury thermometers may not know the damage they are doing to our environment.

Frog Mutations in the North Platte

Meanwhile, Wyoming's frogs are having their own problems. Dr. Tyrone Hayes of the University of California at Berkeley has studied leopard frogs, one of the most common frog species in North America. Looking for the effects of atrazine (a commonly-used weed killer) on these frogs in laboratory studies, he had already found that frogs exposed to even very low levels of atrazine had an increased rate of hermaphroditism. In other words, male frogs were becoming "feminized." This means that female egg cells were appearing in the gonads of male frogs.

What Dr. Hayes discovered in Wyoming was particularly scary. In leopard frogs taken from the North Platte River, he found a 92% rate of hermaphroditism, due, he suspects, to a level of atrazine in the water of only .2 parts per billion. This was the highest rate for feminized frogs, by far, of any of the sites he studied.

Here's the rub: there is no obvious evidence that atrazine is being used anywhere near the site where these leopard frogs were located. So where is the contamination coming from? As with the mercury in the walleye in the Big Horn Reservoir, it appears that atrazine is coming from outside Wyoming.

We don't know if atrazine is either the sole or even a contributing cause of the hermaphroditic frogs in the North Platte River, and the source of this weed killer is not readily apparent. It could be coming from some distance away Ñ upstream in Colorado, perhaps, or even from airborne sources that are still further away. But using this common weed killer may be doing more environmental damage than we realize.

John Muir said it simply, and perhaps best, more than 90 years ago: "When we try to pick out anything by itself, we find it hitched to everything else in the Universe."

The North American Reporting Center for Amphibian Malformations has been established at the US Geological Survey's Northern Prairie Science Center in Jamestown, ND. For more information on amphibian malformations see the center's website at www.npwrc.usgs.gov/narcam.

The center is also asking the public to report sightings of deformed frogs. Access their website to submit information if you see a deformed frog. Alternatively, call 1-800-238-9801.