Mercury Found in All Fish Tested in the West
By Richard L. Hill
The Oregonian
Wednesday 24 January 2007
Dietary limits - The extent of the neurotoxin surprises Oregon scientists, who suspect the air is the source.
A sweeping study by Oregon scientists has found mercury-contaminated fish throughout the West.
In the most widespread survey of mercury in the nation's streams, four Corvallis researchers with the U.S. Environmental Protection Agency and Oregon State University sampled more than 2,700 fish in Oregon, Washington and 10 other Western states. They found detectable - and in some cases, high - amounts of mercury in every fish sampled from 626 randomly selected rivers and streams that flow nearly 190,000 miles.
Although they found only a few fish with high enough mercury levels that could pose a risk to people who eat them frequently, the scientists suggested that consumers - especially pregnant women and young children - follow federal guidelines that limit intake of fish known to contain mercury. They, as well as federal officials, recommend calling state and county agencies for any advisories issued on locally caught fish.
The study found that the highest mercury concentrations were primarily in larger fish-eating species called "piscivores," comprising northern pike, bass, walleye and pikeminnow. The levels in more than half of the piscivore samples were similar to those found in cans of albacore or "white" tuna, for which federal officials already urge dietary limits. The EPA and the U.S. Food and Drug Administration recommend pregnant women eat no more than one 6-ounce can of albacore tuna each week.
Levels in trout and other salmonid species had far lower levels of mercury.
To the scientists, the findings signal more surprise than alarm.
"We found a relatively low concentration of mercury across a broad expanse," said Spencer Peterson, a research ecologist with the EPA in Corvallis. "I think the beneficial effects of eating fish outweigh the hazard potential."
But mercury levels varied by site and fish species. Nearly all fish contain trace amounts of mercury - in a form called methylmercury - that can accumulate over time in the flesh of long-lived fish such as piscivores.
Salmon Not Tested
The scientists did not test salmon - which spend time in the ocean as well as inland rivers - to avoid taking fish from protected populations of threatened or endangered species. The researchers speculate that mercury in salmon would be similar to the low levels found in trout.
Mercury is a neurotoxin. If consumed at high levels, it can impair the neurological systems of people and wildlife, especially in the infant and younger years. Mercury is emitted by natural sources such as volcanoes and geothermal springs - making it a "background" element - but also by coal-burning power plants, waste incinerators, forest fires and cement kilns.
Peterson and his colleagues, who report their findings this month in the journal Environmental Science & Technology, say most of the contamination appears to be from the movement of mercury in the atmosphere.
"When we look at the entire West at these hundreds of sites, we're not seeing a lot of really high point-source signals," said Alan Herlihy, an OSU aquatic ecologist. "The mercury was at low levels everywhere, which means to me there's some sort of uniform source, and atmospheric deposition is something that would fit that."
Other Exclusions
The survey did not examine local sources that might be involved in contamination. It also did not look at whether mercury has been increasing or decreasing in the streams.
"I was surprised that the mercury was everywhere and in measurable amounts," said Robert Hughes, an aquatic ecologist at OSU. "I'm concerned about fish-eating mammals and birds - mink, otter, heron and osprey - that depend on these fish, but I don't know how much they may be affected."
The EPA has set a threshold of concern for human health at 0.3 micrograms of mercury per gram - or .3 parts per million - of fish tissue. The survey found that only 2.3 percent of the streams had large - 5 inches or longer - trout and other salmonids with mercury levels at or above that level. The salmonids were found in 41 percent of the stream network.
However, large piscivores measuring 5 inches or more were found in only 10 percent of the streams, but more than half were at or exceeded the 0.3 level.
Sampling in '02, '04
In their sampling between 2000 and 2004, the researchers found only 13 fish from eight sites that had a high mercury concentration of 1 part per million or more.
Herlihy said two of those sites were in the Willamette River, one near Creswell and the other south of Corvallis. The fish were northern pikeminnow or largemouth bass.
"Our goal was to get a 'snapshot' of the extent and level of mercury contamination in streams across a wide area," Herlihy said. "That hasn't been done before. What we need to do now is do this on a regular basis, say every five years."
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