Advisory on Mercury in Fish From Several Trinity County Water Bodies - Report
OEHHA Finalizes Advisory on Mercury in Fish From Several Trinity County Water Bodies
Release No. 05- 06 October 6, 2005
Contact: Allan Hirsch (916) 324-0995
SACRAMENTO -- The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) has finalized a fish advisory concerning levels of mercury in fish from Trinity Lake (also known as Clair Engle Lake), Lewiston Lake, Carrville Pond, the Trinity River upstream of Trinity Lake, and the East Fork Trinity River, all located in northeastern Trinity County.
“Our advisory gives Trinity County residents and visitors information they need to enjoy catching and eating fish in this beautiful part of the state while minimizing their exposure to mercury that may be present in the fish,” OEHHA Director Dr. Joan Denton said. “It is especially important for women of childbearing age and children to be aware of the advisory.”
The advisory contains safe eating guidelines for consumption of fish from the above-mentioned water bodies. One set of guidelines is for women of childbearing age and children age 17 and younger, who are particularly sensitive to methylmercury, the most prevalent and toxic form of mercury in fish. A second set of guidelines is for women beyond their childbearing years and men.
The safe eating guidelines recommend consumption limits for bass and Chinook (King) salmon from Trinity Lake and rivers and creeks draining into Trinity Lake. Women of childbearing age and children age 17 and younger should limit consumption of these fish to a total of one meal a month, while women beyond childbearing years and men should limit consumption of these fish to a total of one meal a week. If none of these fish are eaten, women of childbearing age and children age 17 and younger should eat no more than one meal a week of white catfish or trout from Trinity Lake and the East Fork Trinity River.
The safe eating guidelines also identify “best choices” for people who want to eat fish frequently. Women of childbearing age and children age 17 and under may safely eat up to three meals a week of trout from Lewiston Lake, Carrville Pond, or the Trinity River upstream of Trinity Lake. Women beyond childbearing years and men may safely eat up to three meals a week of all trout or white catfish from any of the water bodies covered by the advisory. Individuals who frequently consume these fish should refrain from eating the other fish cited in the guidelines.
The guidelines incorporate the results of fish sampling conducted recently in the Trinity River watershed by the U.S. Geological Survey (USGS) and the State Water Resources Control Board. The Trinity River below Lewiston Lake is not included in the guidelines because very few fish were sampled from there. River-run salmon and steelhead from that area, like commercial or ocean-caught salmon, are usually very low in mercury and can be consumed frequently.
Mercury in fish from the upper Trinity River watershed originated from the mining of mercury and gold, the majority of which took place from the Gold Rush until approximately 1960. Miners used mercury to extract gold from mined materials and discharged the waste into rivers and streams, where mercury accumulated in the sediment. Bacteria converted the mercury to the more toxic methylmercury, which fish take in from their diet. Methylmercury can accumulate in fish to concentrations many thousands of times greater than mercury levels in the surrounding water. Mercury does not accumulate in the water itself, however, so contact with the water is safe.
Women can pass methylmercury on to their fetuses through the placenta, and to infants through breast milk. Excessive exposure to methylmercury may affect the nervous system in children, leading to subtle decreases in learning ability, language skills, attention and/or memory. These effects may occur through adolescence as the nervous system continues to develop. In adults, the most subtle symptoms associated with methylmercury toxicity are numbness or tingling sensations in the hands and feet or around the mouth. Other symptoms at higher levels of exposure could include loss of coordination and vision problems.
A fact sheet and report containing the advisory and OEHHA’s evaluation of potential health threats in the fish posed by methylmercury (the most prevalent and toxic form of mercury in fish) are available for viewing Fish Advisories.The USGS report on the sampling of fish in Trinity County is available at http://pubs.water.usgs.gov/ofr20051321.
The Office of Environmental Health Hazard Assessment is one of six entities within the California Environmental Protection Agency. OEHHA's mission is to protect and enhance public health and the environment by objective scientific evaluation of risks posed by hazardous substances.
- Mercury (Inorganic)
- Methylmercury and methylmercury compounds
