Mercury found in Tomales Bay fish
By Gregory Foley
Marin health officials this week recommended that consumption of Tomales Bay sportfish be limited or altogether stopped after seven types of common finfish showed elevated levels of mercury.
The county health department – following the advice of the state Office of Environmental Health Hazard Assessment – recommended that people avoid leopard sharks or brown smoothhound sharks taken from the bay. Shiner and redtail surfperch should be consumed no more than once a week, California halibut and Pacific angel sharks no more than twice a month, and bat rays only once a month.
County health officer Dr. Fred Schwartz said the high concentrations of methylmercury – a highly toxic form of mercury that has subtle but damaging effects on the nervous system – found in the fish pose a particular threat to children and pregnant women.
Pregnant women & children
"Women who are pregnant or may become pregnant within a year, nursing mothers, and children under age six should take special care to follow these guidelines," Schwartz said. "These are conservative but prudent recommendations. Testing will continue, and the [state] will formalize the advisory, but we want to be sure to get the word out now."
The county also recommended that individuals who eat the limit of one species in a one-month period should not eat any of the other affected species in the same period. In addition, individuals who regularly eat the fish covered in the advisory should also limit consumption of commercially-harvested sharks and swordfish, which tend to also carry elevated levels of mercury.
The testing of the Tomales Bay fish was done in 1999 as part of the state’s Coastal Fish Contamination Program, which is being conducted by several agencies including the state Water Resources Control Board and the Department of Fish and Game.
Jacksmelt okay
A total of eight species of sportfish were tested, with only jacksmelt found not to contain dangerously high levels of methylmercury.
Limited testing of commercially-grown crabs, oysters, and clams from Tomales Bay showed that the shellfish do not have significant levels of mercury and are safe to eat. Simultaneous tests for polychlorinated biphenyls (PCBs) and pesticides found no hazardous levels of those chemicals.
While the testing did not seek out the sources of the mercury, at least some of the metal is believed to have been carried downstream into the bay from the now defunct and recently cleaned-up mercury mine at the Gambonini Ranch.
The mine, which lies six miles upstream along Walker Creek, was operated as an open-pit mercury mine in the 1960s and early 1970s by Buttes Gas and Oil. The Environmental Protection Agency in 1999 estimated that in the previous 20 years as much as 170 pounds of mercury had eroded from old tailings and flowed into the bay via Walker Creek.
Probably from mines
Wil Bruhns, a senior engineer for the San Francisco Bay Regional Water Quality Control Board, said that while a small percentage of mercury found in regional waterways comes from the natural breakdown of minerals in the landscape, roughly 90 percent of the quicksilver detected in San Francisco Bay was determined to have come from mining operations.
As for Tomales Bay, Bruhns said, "We as an agency have investigated all the mines in the region, and most were not a problem. But we still need to determine how much mercury is in Walker Creek and if it is a significant reservoir... It’s certainly expected that the mercury level in the bay will drop off now that the Gambonini site is capped."
Several mercury mines operated in West Marin at various times in the past, the mineral first coming into great demand in California because of its usefulness in extracting gold from ore.
County health department and state Fish and Game staff will post flyers explaining the consumption guidelines at fishing supply stores, boat launches, and several access points around Tomales Bay, Schwartz said.