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article imageMercury contamination to last 10,000 years in SF

By Tim Sandle     Nov 2, 2013 in Environment
San Francisco - Alarming figures suggest that that toxic remnants of the infamous gold rush will seep into San Francisco area waterways for millennia.
California’s gold rush ended more than a century ago, but the mercury contamination that resulted from gold mining will last thousands of years, according to new analysis.
In the mid-1800s, NBC News recounts, gold mining released more than a cubic kilometer of mercury-laden sediments into Northern California’s Sierra Nevada foothills. This was due to most hydraulic gold mining processes of the era using the toxic metal mercury to separate gold from gravel. It has been estimated that between 3 million and 8 million pounds of mercury entered the environment from the hundreds of hydraulic gold mines that were operated in the Sierra before a court order banned the downstream deposition of mining debris in the region.
Over time the sediments fanned out and seeped into the rivers that flow into the San Francisco Bay. Researchers estimate that 90 percent of the mercury is still trapped within the sediments.
The researchers also predict that the mining sediments will continue to release mercury into waterways over at least the next 10,000 years. Furthermore, as climate change intensifies the area’s rainstorms, then the flood-driven discharges could become even more frequent.
The analysis was undertaken at the University of St. Andrews in Scotland. The findings have been published in the journal Proceedings of the National Academy of Sciences. The paper is titled "Enduring legacy of a toxic fan via episodic redistribution of California gold mining debris."
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