Along with the caddis flies, nymphs and minnows they eat, fish native to Western river systems are ingesting a toxic metal: mercury.
The dangerous element turned up in virtually every fish sampled in a joint study by OSU and the U.S. Environmental Protection Agency. The contaminant’s ubiquity — present in 600 rivers, streams and creeks across 12 states — surprised the researchers.
"Mercury is everywhere," says Professor Alan Herlihy of OSU’s Department of Fisheries and Wildlife and an author of the study, published in Environmental Science and Technology. "It is in fish throughout the western United States."
Only a few fish had alarmingly high levels of mercury, which causes neurological damage in humans and other animals. Most likely, these fish lived near a "point source" — a mine, gravel pit or dump site loaded with mercury. Fish that eat other fish — species such as bass, walleye and northern pike — showed much higher concentrations than insect–eaters like trout.
Mercury enters atmospheric and aquatic systems when fossil fuels are burned. Forest fires, too, can contribute mercury vapors to the environment.