Mercury contamination in California to last 10,000 years

Miners in some countries are still using this method, contaminating the land and water there.
Mercury damages the brain. The saying "Mad as a hatter" came from the effects of mercury on hatmakers when mercury was used in the manufacture of hats.

https://www.sciencenews.org/article/mercury-contamination-california-last-10000-years

by Jessica Shugart
3:01pm, October 28, 2013
Magazine issue: November 30, 2013

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.

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Drawing on historical flood data to predict sediment flow, the team reports October 28 in the Proceedings of the National Academy of Sciences that the mining sediments will continue to release mercury into waterways over at least the next 10,000 years. As climate change intensifies the area’s rainstorms, the researchers predict, the flood-driven discharges should become more frequent.