Study Finds Widespread Mercury Concentrations In Western Fish

In a study of more than 600 rivers and streams in the western United States, researchers at Oregon State University (OSU) and EPA found widespread mercury concentrations in fish, according to a Jan. 23 announcement by the university.

Though few of the more than 2,700 fish analyzed in the study contained alarmingly high levels of mercury, the prevalence of the element throughout 12 western states caught the researchers by surprise, they said.

"Mercury is everywhere," said Alan Herlihy, a research associate professor with OSU's Department of Fisheries and Wildlife and one of the authors of the study. "It was literally in every fish we sampled, which suggests an atmospheric source. There also tended to be a noticeable difference between 'piscivores,' or fish-eating fish, and non-piscivores such as salmonids."

The researchers found that mercury levels were much higher in the larger fish-eating species, including bass, walleye, northern pike and pikeminnow. These piscivores are not as widespread throughout western river systems as salmonids, such as rainbow and cutthroat trout, which had lower levels of mercury.

The authors of the study said the risk for humans who may occasionally eat fish from the streams is fairly low. The researchers compare the mercury levels in most of the larger piscivorous fish they analyzed to that found in cans of store-bought tuna. Consumption of those products in moderation is considered safe, though infants, young children, pregnant women and persons who eat a lot of fish have higher risk levels than the general population.

Less clear is the impact of that mercury on fish-eating birds and mammals, said Robert Hughes, also an author on the paper and an OSU fisheries and wildlife research associate professor.

"If I were a mink or an otter, I'd be concerned," Hughes said. "Those guys are loading up on fish containing mercury, and we don't really know at what levels they may be affected. In birds, the effects of mercury contamination are neurological or behavioral -- and often subtle. They may not clean their young, or they may leave eggs unattended in their nests.

"We simply haven't done enough studies to know all of the impacts, especially on fish-eating animals," Hughes added.

The study, based on data collected from EPA's Environmental Monitoring and Assessment Program, encompassed nearly 188,000 miles of perennial streams and rivers in the western United States. The selection of the more than 600 creek and river sample sites was done randomly to address regional questions about the prevalence of mercury contamination among fish in western rivers; not to do a stream-by-stream analysis of the impact.

Mercury entering the water via the atmosphere has a variety of natural and human-made sources, the researchers said, including coal power plants from as far away as China, the burning of heavy oils and other fossil fuels, and even forest fires.

In the survey, the researchers did find 13 fish from eight different sites that had very high mercury concentrations -- levels of 1.0 microgram or higher -- likely indicating a point source. These high levels could be caused by nearby mines, dump sites or gravel pits, they added.

"There are mercury 'hotspots' out there," Hughes said, "but they are not common in the West. What we found, though, is that mercury is in fish throughout the western United States, and at higher levels in piscivores than in salmonids."

Alan Herlihy: http://oregonstate.edu/Dept/pnw-erc/personnel/herlihy.htm

OSU Department of Fisheries and Wildlife: http://fw.oregonstate.edu/index.htm

This article originally appeared in the 01/01/2007 issue of Environmental Protection.

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