Gold Rush’s poisonous legacy: Mercury lingering for 10,000 years

Sediments like these along the Yuba River in northern California can be eroded by large floods, unleashing mercury pollution into the water.



"This is a big deal because at the moment, there's quite a bit of mercury contamination that's in the ecosystems of the (San Francisco) Bay and Sacramento Delta," Singer told LiveScience.

Going up the food chain


As larger animals eat smaller ones and are, in turn, eaten by even bigger creatures, mercury accumulates and increases in concentration. For this reason, predatory fish such as bass and salmon in the bay have been found to have high levels of mercury, Singer said.

This amount of mercury pollution is "already significant, and what the authors show is that it's going to get worse," said Manny Gabet, a geologist at San Jose State University who wasn't involved in the study. [World's 10 Most Polluted Places]

Toxic legacy
Gold-rush miners sought gold by eroding entire hillsides with high-pressure water cannons, contrary to popular conceptions of panning for gold, Gabet told LiveScience. The sediment was then run through "sluice boxes," where mercury was added to bind to gold. But large quantities of the heavy metal made its way into sediment downstream. This destructive mining filled valleys with sediments that caused flooding in California's Central Valley, and in 1884, the federal government shut down much of this gold-mining activity, Singer said.



"Unfortunately, gravity is on the side of future contamination," as floods will eventually move mercury-tainted soils downward in California and elsewhere, Singer said.
