OUT: Mercury in Fish March 08, 2009

Large fish in pristine Western parks lakes susceptible to airborne contaminants, but Blue Mesa lakers OK

Anglers crowd the waters of Blue Mesa Reservoir seeking lake trout, kokanee salmon and other fish. Research indicates the fish in the reservoir have low levels of pollutants and are safe to eat.

Last week’s story about the fish consumption advisory from the Colorado Department of Public Health and Environment and the Division of Wildlife raised some questions about mercury in trout.

The advisory cautions anglers, particularly pregnant anglers and those under 6 years old, to limit the eating of certain fish because of concerns about mercury moving up through the food chain and eventually accumulating in the fish’s tissues.

The list of waters included Rifle Gap and Juniata reservoirs and focused on top-of-the-line predator fish, including large- and smallmouth bass, northern pike and walleyes.

Trout, evidently, are safe to eat, although some anglers target larger trout, such as lake trout, brown trout and brook trout, all of which are piscivorous.

Fish tend to accumulate mercury throughout their life, which is why larger (older) fish may have measurable levels of pollutants.

That means larger trout might be building up some mercury in their tissues.

The Environmental Protection Agency last year released a study saying trout taken from isolated lakes in some Western national parks had such high levels of mercury pollution they were considered unsafe for human consumption.

“We’re looking at some of the most pristine areas left in North America that are under the protection of the national parks, and we’re finding some alarming results,” said Dixon Landers, a senior scientist with the EPA’s National Health and Environmental Effects Laboratory.

The agency’s seven-year project investigated pollution in air, water, sediment, lichen, conifer needles and fish in eight “core” western parks from Alaska to California, including Rocky Mountain National Park.

Twelve other “secondary” parks were less-intensively studied.

The parks were selected partly because of their isolation, which meant the primary source of pollution would be airborne rather than local industrial or agricultural sources.

According to the study, some fish from Washington’s Olympic National Park had mercury levels exceeding 185 parts per billion, easily high enough to trigger consumption warnings.

Trout from two lakes in Rocky Mountain National Park, Mill and Lone Pine, showed elevated levels of DDT but slightly lower levels of mercury compared to trout from lakes in the Midwest and Northeast.

However, some fish from six waters in RMNP were “intersex,” sharing both male and female tissue in the reproductive organs. This, Landers said, suggests the possibility of exposure to estrogen- and hormone-mimicking chemicals, including flame retardants called polybrominated diphenyl ethers or PBDEs.

The airborne pollution comes from a variety of unidentified sources, both regional and global. Coal-fired plants in the western U.S. and from as far away as China are among the suspects, although tracing the pollution is difficult to do, said Landers.

The study, called the “Western Airborne Contaminants Assessment Project,”  said that while there are some natural sources of mercury pollution, such as wildfires and volcanic activity, up to two-thirds of the pollution comes from human activity.

Smaller trout might be safer to because they eat primarily insects and haven’t changed over to a fish diet, which cumulatively concentrates mercury and chemical pollutants.

That said, testing indicates the lake trout in Blue Mesa are safe to eat, said Division of Wildlife aquatics biologist Dan Brauch.

“We did test lake trout in Blue Mesa for mercury levels and they all were under the limits,” Brauch said. “So I don’t see any problem with the consumption of lake trout from Blue Mesa.”

If you are at all concerned, the caution here is the same. There’s no reason to stop fishing or eating some fish, just don’t eat certain fish at every meal.

Summaries of the Western Airborne Contaminants Assessment Project can be read at http://www.nature.nps.gov/air/studies/air_toxics/wacap.cfm


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