Coastal Post Online
MARIN COUNTY'S NEWS
MONTHLY - FREE PRESS
(415)868-1600 -
(415)868-0502(fax) - P.O. Box 31, Bolinas, CA, 94924
November, 2004
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OEHHA Advisory On Fish In Tomales Bay
SACRAMENTO -- The California Environmental
Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA)
has finalized a fish advisory concerning elevated levels of mercury in fish in Tomales Bay in Marin County.
"With the exception of sharks, fish caught in Tomales Bay can be part of a healthy, balanced diet. But the public-and particularly women of
childbearing age and children-should monitor and limit their fish consumption
to avoid excessive exposure to mercury," OEHHA Director Dr. Joan Denton
said.
A fact sheet and a report containing the advisory and OEHHA's evaluations of
potential health threats in the fish posed by methylmercury (the most prevalent
and toxic form of mercury in fish) are available for viewing and downloading on
OEHHA's Web site at www.oehha.ca.gov.
The advisory contains guidelines for consumption of fish and shellfish from Tomales Bay. One set of guidelines is for women of childbearing age and children age 17
and younger, who are particularly sensitive to methylmercury. A second set of
guidelines is for women beyond their childbearing years and men.
The advisory recommends that women of childbearing age and children age 17
and younger refrain from eating all sharks (including brown smoothhound sharks,
Pacific angel sharks and leopard sharks), while limiting consumption to one
meal a month of bat rays; or one meal a week of California halibut, redtail
surfperch, pile surfperch, shiner surfperch or red rock crab; or three meals a
week of jacksmelt.
Women beyond childbearing years and adult men should limit consumption to
one meal a month of brown smoothhound sharks or leopard sharks; or one meal a
week of Pacific angel sharks or bat rays; or three meals a week of California halibut, redtail surfperch, pile surfperch or red rock crab. Jacksmelt and
shiner surfperch can be eaten daily provided that no other fish are eaten.
The advisory does not apply to commercial oysters, clams and mussels from Tomales Bay, as elevated levels of mercury have not been found in commercially grown
shellfish in the area.
A principal source of mercury in Tomales Bay is believed to be the Gambonini
mercury mine, which operated from 1968 to 1972 about six miles upstream from
Tomales Bay. Water-quality studies have suggested that mercury-containing
drainage from the mine entered Walker Creek, which flows into Tomales Bay. Remediation work at the mine has focused on reducing runoff from the mine into Walker Creek. The overall prevalence of naturally occurring mercury in the California
Coast Ranges may also be contributing to mercury in Tomales Bay. Mercury from coal-burning power plants, medical waste incineration and volcanic emissions
may also enter the environment and migrate to the bay.
After entering rivers, streams, and estuaries, mercury accumulates in the
sediment. Bacteria convert the inorganic 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.
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.
The new advisory contains the same consumption guidelines as an earlier
draft advisory that OEHHA released for public review and comment in May 2004.
The draft advisory replaced an interim advisory issued in December 2000 by
Marin County Department of Health and Human Services, in cooperation with
OEHHA. The county advisory was based on fish and shellfish samples taken in
1999 by the San Francisco Bay Regional Water Quality Control Board. Samples
taken since the county advisory have provided additional information on mercury
levels in Tomales Bay fish and shellfish.
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.