Toxic remnants of gold rush will seep into San Francisco area waterways for millennia
California’s gold rush ended more than a century ago, but the contamination it caused will last thousands of years, a new analysis shows.
Some hydraulic gold mining processes use the toxic metal mercury to separate gold from gravel. In the mid-1800s, gold mining released more than a cubic kilometer of mercury-laden sediments into Northern California’s Sierra Nevada foothills. The sediments fanned out and inundated rivers that flow into the San Francisco Bay. Researchers estimate that 90 percent of the mercury is still trapped within the sediments.
To understand how flooding and erosion may trigger future releases of the poison, researchers led by Michael Bliss Singer of the University of St. Andrews in Scotland measured mercury levels in sediments at 105 locations upstream of the bay.