Mercury Rising in S.F. Bay
Is restoring wetlands bad for our health?
excerpted from from Spring 2009 issue of Terrain Magazine
by Eric Simons
for full story:
...Wetland restoration projects, probably the best thing we’ve come up with for cleaning up our bay and mitigating past errors, often make mercury levels worse. But why that is, where it’s happening, and what we can do about it, are still perplexing...
...These are the basics: Mercury gets into the environment in a number of different ways, from natural sources like volcanoes to urban sources like coal-fired power plants or stormwater runoff. In Northern California, mercury was historically used in gold mining, and many of the watersheds in the Sierra and Delta show high levels of mercury from California’s Gold Rush days. Most of the mercury used in gold mining came from mines in the New Almaden area of San Jose, where for decades it has washed down the Guadalupe River and into the southern part of the San Francisco Bay, which still has the highest mercury levels of any part of the bay.
But all this stuff in the air and water is regular ol’ mercury, and one of the odd parts of the puzzle is that regular ol’ mercury isn’t harmful to people or wildlife when it’s in the water. The damaging stuff, the kind that gets into the food chain, is a specific form of mercury called methylmercury. A confounding thing is that there isn’t necessarily a consistent relationship between the amount of mercury in the water, air, and sediment, and the amount of methylmercury in the food chain in that area. It takes a certain kind of bacteria to convert mercury into methylmercury (a process called methylation), and those bacteria are found in areas with lots of vegetation and living organisms. Which is confounding thing number two: In Northern California’s aquatic environments, those areas tend to be wetlands.
Ironically, these areas, which environmentalists have long struggled to save, can create and amplify methylmercury; in some cases restoring wetlands may resolve one eco-hazard while accidentally worsening another. Even stranger, some areas methylate more than others, which has led to delays and confusion about whether to attempt restorations...