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Mercury Found In County Reservoirs

Published on: 6/27/2018 10:46 AM


SANTA CLARA COUNTY - State and local health officials are advising anglers to limit their intake of fish caught from Anderson and Stevens Creek reservoirs following testing showing elevated levels of mercury and PCBs in fish at both reservoirs.

The contaminants are not detected in the reservoirs' water, but are present in smaller organisms consumed by fish. Eating too many of the fish, according to health officials' warnings, could endanger human health."In Santa Clara County, we regularly conduct water-quality testing in all of the reservoirs, looking for contaminants like these," said Walt Wadlow, Water Utility Enterprise COO for the Santa Clara Valley Water District."Although mercury is found in sediment and in fish, it has never been detected in our drinking water resources."

According to a study released today by regional water regulators, some fish sampled from Anderson and Stevens Creek reservoirs-as well as from eight other reservoirs in the Bay Area-exceeded human health guidelines for methylmercury, an organic form of mercury, and for polychlorinated biphenyls, or PCBs, a group of industrial chemicals.

In response, the Santa Clara County Public Health Department is distributing interim fish-consumption guidelines for Anderson and Stevens Creek reservoirs in cooperation with the state Office of Environmental Health Hazard Assessment.

The multilingual advisories recommend that women of childbearing age and children under the age of 18 eliminate largemouth bass from their diets, and limit themselves to one meal a week of carp, black crappie and/or channel catfish.Older women and men are advised to limit their intake of largemouth bass and/or channel catfish to no more than once a month, and to limit carp and/or black crappie meals to four or less per month.

The findings-contained in a San Francisco Regional Water Quality Control Board report of a study conducted under the Surface Water Ambient Monitoring Program, or SWAMP-sampled fish caught in Del Valle and Shadow Cliffs reservoir, and Lake Chabot in Alameda ​County; San Pablo and Lafayette reservoirs in Contra Costa County; Soulajule, Nicasio and Bon Tempe reservoirs in Marin County, and the two Santa Clara County reservoirs.

In Anderson Reservoir, east of Morgan Hill, and Stevens Creek Reservoir, above Cupertino, largemouth bass contained the highest concentrations of mercury while carp and channel catfish showed the highest levels of PCB contamination.

For the past few years, the Santa Clara Valley Water District has been working with the San Francisco Bay Regional Water Quality Control Board to identify and measure sources of mercury, calculate how much mercury "load" the system can absorb and still meet water-quality standards, and to determine what controls can be put in place to meet the standards.

The partnership included a $1 million study to help reduce mercury contamination in affected areas of the Guadalupe Watershed, which stretches from the Santa Cruz mountains to San Francisco Bay.

Mercury is a metal found in rock and soil, and is washed into lakes and reservoirs during storms, particularly in areas where mercury mining occurred. Mercury is also discharged into the air when fossil fuels and industrial waste are burned, falling back to earth in rain.

The source of mercury in Anderson and Stevens Creek reservoirs appears to be atmospheric and naturally occurring, based on local geologic formations.

Once mercury enters water, much of it settles to the bottom of reservoirs where bacteria in the mud or sand convert it to the organic form of methlymercury. Once in the reservoirs or the bay, it moves up through the food chain.

Mercury in high concentrations is a threat to human health, affecting the brain and nervous system. The principal danger lies in eating too much fish caught from the reservoirs and San Francisco Bay, although there are no documented cases of mercury poisoning from eating California sport fish.

The other contaminant found in local fish, PCBs, are a group of more than 200 industrial chemicals that can cause a wide variety of adverse health effects. Although PCB manufacturing ended in 1977, the chemicals remain in the environment for years.

Like mercury, PCBs can accumulate in fish.​

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