A series of USGS interactive maps have recently been published. The maps identify locations and levels of mercury contamination resulting from historical gold mining California’s Sierra Nevada.
From the USGS:
Many may not know that mercury was used by miners during the California Gold Rush to extract gold. Using a process called amalgamation miners would combine mercury with gold ore to form a gold-mercury amalgam. The mercury was then removed by heating. After the mercury had evaporated, pure gold was left behind.
However, this method had severe environmental consequences. Millions of pounds of mercury were released into rivers and other bodies of water. This caused long-lasting ecological damage, especially to wildlife. One form of mercury, called methylmercury, is especially toxic. Mercury levels in sport fish remain elevated in areas downstream of historical gold mines where amalgamation was practiced. This has led to fish-consumption advisories in these parts of California.
To better understand mercury contamination caused by historic mining, USGS scientists took samples of sediment, water, and biota, or animal life, and tested them for mercury and methylmercury.
The result of this research is set of interactive maps. The maps show what the scientists found and where they found it. The maps include: an introductory map showing the study area and its major watersheds; a map of historical placer (unconsolidated sediment) gold mines in the study area; three individual maps showing the amounts of mercury found in sediment, water, and biota (animals); a composite map showing the integrated amounts of mercury for all three sample types; and a map of remediation (or clean-up) efforts to date.
In addition to the maps themselves, there is a video on how to use the features of the maps, and a data release with the complete set of data behind the maps.
To view the maps and learn more about this science, visit: Legacy Mercury Contamination from Historical Gold Mining.
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