Department of Water Resources
A daily compilation for DWR personnel of significant news articles and comment
November 6, 2007
1. Top Item
Surprise on Delta fish; Mercury levels modest in south section
Sacramento
By Matt Weiser, staff writer
It's safe for pregnant women to eat catfish, crappie, carp and bluegill caught in the south Delta. But other fish from other places?
That depends.
These are some of the initial findings from the largest study ever conducted of mercury contamination in fish from the Bay-Delta watershed, a vast region of rivers and lakes that covers 40 percent of
The $4.5 million study, led by the San Francisco Estuary Institute, sampled more than 2,000 fish from 22 species at 69 popular fishing spots. The goal was to help understand how far the toxic legacy of the state's mining history spread throughout the watershed and wildlife.
Mercury is a naturally occurring element. But it was broadcast in a most unnatural way by decades of intensive mining that began with the Gold Rush.
Fortune hunters used mercury to separate gold from raw ore during hard-rock and placer mining. Mercury was mined on its own for this purpose.
The state produced an estimated 230 million pounds of mercury between 1846 and 1981, about 88 percent of the nation's total. About 75 million pounds was released to the environment, and mercury continues to wash into lakes and streams from old mining sites because of natural erosion and runoff.
Fish accumulate mercury in their tissue when they feed on bugs and plants. People accumulate mercury in their flesh when they eat the fish.
At low levels, this mercury is harmless. But too much can cause birth defects in children and nervous system disorders in adults.
The surprising news, according to the study, is that fish in the southern Sacramento-San Joaquin Delta are not carting around as much mercury as researchers expected. This has allowed state health officials to loosen the consumption guidelines for certain fish species caught in the estuary.
"This is actually some good news that this popular fishing area actually has pretty low concentrations," said Jay Davis, a senior scientist at the institute and lead author of the study.
The Delta long was thought to be a major concentrating point for mercury, a logical conclusion because the entire watershed drains through the estuary.
As a result, the California Office of Health Hazard Assessment for years had a blanket advisory in place warning children and pregnant women not to eat more than one serving per month of Delta fish, no matter the species.
But the new study prompted the state to revise its consumption guidelines for the south Delta, defined as areas south of the
The new guidelines say children and pregnant women can eat up to four servings per week of bluegill, catfish, clams or crayfish, and up to two servings per week of crappie, carp, sucker, or largemouth, smallmouth or spotted bass. Women beyond childbearing years and adult men can eat even more of these species.
"We want to encourage people to eat fish that's low in mercury so they get the benefits without the drawbacks of mercury exposure," said Allan Hirsch, chief deputy director of the health agency, a partner in the study, which was funded by the CalFed Bay-Delta Authority.
The bad news is that nearly one-fourth of all the fish sampled in the watershed had "high" or "very high" levels of mercury in their tissues. Largemouth bass and
Effects vary throughout the watershed. For instance, researchers found more mercury in the
Laura Leonelli, executive director of the
"Mercury contamination is not obvious. People look at the fish, and they can't see anything wrong, so it's hard to persuade people that there's a problem," said Leonelli. "People have to hear it a lot to be able to absorb the information and realize the health effects of it."
New guidelines have not been developed yet for the north Delta and
http://www.sacbee.com/101/story/473841.html
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