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 somewhat by surprise.
"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.
Results of the study were published earlier this month in the journal Environmental Science and Technology.
The researchers say the risk for humans who may occasionally eat fish from the streams is fairly low and they 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," Hughes said, "I'd be concerned. Those guys are loading up on fish conta
Source:Oregon State University