Mercury Found in Fish of Southwest Alaska
Nutritional experts recently recommended that people in a certain area limit their diet of fish because the fish contained a surprising amount of mercury. That area wasn't the industrial zone of a big city; it was southwest Alaska.
As part of a study, subsistence fishermen who live in the lower Yukon-Kuskokwim Delta gave scientists 66 fish to be tested for traces of mercury. Several chemists, among them Larry Duffy of the University of Alaska Fairbanks Department of Chemistry and Biochemistry, discovered that 16 of the fish contained mercury above the "level of concern" established by the Environmental Protection Agency. Scientists sampled a gram of tissue from whitefish, grayling, burbot, pike, and sheefish for concentrations of mercury. Pike most often exceeded the EPA standard, a fact that says something about the pathway of mercury in Alaska waters.
Algae and plankton ingest the chemical from the air or from minerals in the water. Small fish eat the plankton and algae, accumulate the mercury in muscle cells, and pass the chemical to bigger fish when eaten. The northern pike, a predator near the top of the freshwater food chain, eats fish, frogs and sometimes even small birds. In doing so, the pike gets a dose of whatever is inside its meals.
Mercury, a metal with such a low melting point that it's a liquid at room temperature, binds to sulfur atoms in living cells and destroys important enzymes, such as those that control nerve cells. Mercury has been linked to birth defects and is especially dangerous to children and pregnant women. The levels of mercury in Yukon-Kuskokwim pike are high enough that nutritional experts recommend people don't eat large pike-which accumulate more mercury than smaller fish-every day.
Where's the mercury coming from? According to Duffy, the mercury could leach into the water from a natural source, the mineral cinnabar. Air currents might transport mercury north, or mercury might hitch a ride in the cells of migrating salmon or birds. Of these scenarios, Duffy thinks the leaching of mercury from cinnabar deposits is the most plausible. In addition to fish, Duffy and others at UAF have checked a variety of bird feathers and mammal hair, both of which accumulate mercury. They've found that animals such as moose, musk ox, and ptarmigan show very low levels of mercury, while sea birds, river otters, people, and other species that eat fish show the highest levels.
