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
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 the health of those who ingest too many.
According to a study released this week 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 methlymercury, 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 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, north of Cupertino, largemouth bass contained the highest concentrations of mercury while carp and channel catfish showed the highest levels of PCB contamination.
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 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.
A full copy of the draft SWAMP report is available at www.swrcb.ca.gov/rwqcb2. A copy of interim fish consumption advisories for Anderson and Stevens Creel reservoirs are available at www.oehha.ca.gov/fish/so_cal/bayareares.html.
