Traces of mercury and PCBs are widespread in sport fish in California's urban coastal waters, a survey released last week by the state water board found.
But 19% of the urban coastline sampled by researchers harbored fish with mercury in such high concentrations that they shouldn't be eaten by young women and children. Fourteen percent of locations had similarly elevated levels of PCBs.
The findings, part of a two-year inquiry that is the largest statewide survey of contaminants in sport fish along the California coast, examined more than 2,000 fish from three dozen species gathered in 2009 from waters near Los Angeles, San Francisco and San Diego.
Researchers said the study highlights the health problem of lingering mercury, a poisonous metal that is found in fish globally, and of PCBs, toxic chemicals the United States banned in the 1970s. Both substances continue to pose a risk to people who eat fish caught along the California coast because they can lead to nervous system damage and developmental problems in children and can cause cancer, liver damage and reproductive harm.
"Unfortunately, we're not seeing many areas that are totally clean," said Jay Davis, a senior scientist for the San Francisco Estuary Institute and lead author of the study. But a catalog of where and in what fish the substances abound should help anglers make better choices, he said. "With good information, people can reduce their exposure significantly."
Sharks had some of the highest levels of mercury because of their unusual tendency to accumulate contaminants in their flesh, researchers said. The most elevated concentrations of mercury and PCBs were found in San Francisco Bay and San Diego Bay.
As for which species is the safest: Southern California anglers can rest easy catching and eating chub mackerel because it had the lowest levels of contamination in the survey.
The survey results were used in part to help craft new fish consumption guidelines issued earlier this week for anglers in San Francisco Bay, the first update there by state health officials in 17 years. The advisory identifies shiner perch and other surf perches as unsafe to eat in any quantity and warns young women and children not to eat white sturgeon, striped bass and sharks caught in the bay.
The buildup of metals and other chemicals in fish is such a problem along the Southern California coast that health officials two years ago expanded the number of fish species on the "do not eat" list from one to five because of high levels of PCBs, mercury and the banned pesticide DDT.
Next year the state is expected to release the next portion of the survey: data on fish collected from the less populated central and north coasts. After that, researchers will show test results from fish in rivers and streams.