Quicksilver in Silver Creek: mercury contamination in fish
By KATHLEEN L. TURNER<br><i>The Wood River Journal</i>
The problem of the increasing pool of atmospheric mercury, once more commonly known as quicksilver, has moved from global to local. Fish tissues taken from the pristine waters in Silver Creek have demonstrated levels of mercury contamination that create cause for concern by biologists and toxicologists.	
Twenty brown trout taken from Silver Creek at two locations in June of 2007 revealed methylmercury levels ranging from 0.17 to 1.91 micrograms per gram of tissue, or parts per million, according to analysis by the USGS mercury lab in Middleton, WI. The overall average number of 0.48 parts per million from the fish tested will likely result in the Department of Health and Welfare issuing a fish consumption advisory for the Blaine County waterway. Generally, the rule is the bigger and older the fish, the heavier the contamination, due to biomagnification up the food chain.   
According to Dorene E. MacCoy, a Biologist with the U.S. Geological Survey Water Resources Division in Boise, ten fish were caught below the visitor center of the preserve and 10 at the USGS Silver Creek flow gage near Picabo with assistance of from Fish and Game and The Nature Conservancy biologists. The above numbers are raw data that will be reviewed by the Idaho Department of Health and Welfare from which any advisories concerning consumption of such fish will be issued.
Jim Vannoy of the Idaho Department of Health said analysis and the possible resulting advisories are expected to be published by mid-December. Currently, Idaho fish consumption advisories are in effect on fish taken from  Lake Coeur d&#039;Alene, Brownlee Reservoir, CJ Strike Main Reservoir, Salmon Falls Creek Reservoir, East Mill Creek, Lake Lowell, American Falls, Jordan Creek, Priest Lake and Lake Pend Orielle. To review the advisories and the population that should limit fish intake, and what types of fish have been sampled that exhibit unsafe levels of mercury, go to  www.healthandwelfare.idaho.gov and click on Idaho&#039;s fish consumption advisory map.
Idaho State Health Toxicologist Kai Elgethun confirmed that brown trout are more aggressive predators of fish than other Idaho trout, which can contribute to increased levels of contamination. MacCoy said that August, 2006 samples of rainbow trout taken from the Big Wood River near Stanton Crossing exhibited only 0.05 micrograms of mercury per gram of fish tissue, below the established risk rate. 
           Elgethun said that the EPA reference dose (RfD) is 0.1 microgram of mercury per kg of a person&#039;s body weight per day, with advisories set on levels above 0.3 micrograms per kg of body weight per day. The EPA RfD is defined as the amount of mercury a person, including sensitive subpopulations, can be exposed to on a daily basis over a lifetime without appreciable risk of effects.  Not used to weighing or surveying your meals? A good rule of thumb is provided on the EPA website as well as the Idaho Health and Welfare fish advisory page listed above.  
Elgethun emphasized that there is no danger to anglers from wading in the water. Additionally, much of Silver Creek is designated a catch and release area as well, but, according to Silver Creek Preserve&#039;s Dayna Gross, there are areas outside of the preserve where fish are caught for the purpose of nutrition rather than sport. Anglers who intend to eat their catch are advised to limit consumption in accordance with established guidelines.  
Vannoy noted that Silver Creek brown trout, by comparison, while they may pose a risk to certain groups, are smack in the middle of the pack as far as contamination levels detected in Idaho waterways statewide.
Clyde Lay with the Idaho Department of Environmental Quality in Twin Falls has been studying Salmon Falls Creek and other Idaho fish populations for contamination. 
&#8220;It doesn&#039;t really surprise me,&#8221; Lay said, that Silver Creek browns are showing up with elevated levels of methylmercury, a result of a combination of slower moving water, bigger fish and positioning upwind of manmade or anthropogenic, as well as natural sources, of mercury contamination such as cement plants, coal-fired power plants, mining activity, fires and rock and mineral degradation.  
Lay noted that while some mercury in the environment is natural, Nevada mines, Oregon cement manufacturers and Utah coal plants contribute to the mercury deposited in Idaho rivers, lakes and waterways. Wind, rain, snow and weather of all types can move the contamination around the globe, hopping from place to place as the mercury cycle changes the contaminant from the elemental form to the organic, methylated form, to vapor form. 
 A major contributor (to airborne mercury within Idaho), Lay said, is the P4 phosphate plant in Pocatello. The EPA toxic release inventory for the state of Idaho listed them as the number one contributor of mercury to the environment in 2006. To review possible sources go to the EPA Web site and locate the Toxic Release Inventory for the state of Idaho and surrounding states. 
Lay said there is good news in that the EPA will soon be able to use information from the predictive REMSAD, or Regional Modeling System for Aerosols and Deposition, process that can offer predictive models that look at wind patterns and velocities to determine sources more accurately. 
Lay said scientists and biologists are collecting fish tissue samples from 48 other water bodies around the state to see where efforts should be focused.