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    The Gold Rush's Legacy… Once Gold, Now Mercury in Abundance

    Posted by Jason Davis on Oct 28, 2014 3:26:31 PM

    The following is Part I of a multi-part series of posts about Mercury



    A recent series of articles in the The Tribune, a newspaper covering San Luis Obispo, Calif. and surrounding communities, highlighted the legacy of California’s mountain of gold and the environmental hazard leftover from the intense mining of the era. The articles reminded me of a 2013 report1 in USA Today about the findings of high levels of mercury in sites along the California’s Yuba River. While mercury emissions and environmental contamination is not a new topic, I was surprised to learn that the origins of the mercury were traced to the immense piles of Gold Rush-era mining debris in the river valley.  As one subject is often interwoven with another, I eventually found myself digging up mining practices of 1848, sifting through fact sheets explaining mercury’s various forms and health effects, and finally examining statistics and perspectives on how researchers are addressing mercury contamination today.

    The result was an interesting journey.  These various topics spanning geography and time are the individual components of a greater mercury contamination issue in our world today.  The glue that binds this discussion together is an understanding of the various forms of mercury, their varied risks, and their ability to change from one form to another.  Equally important is the mercury source, method of dispersion, and the means of human and wildlife exposure. More than just a story of blatant pollution, this is a story of mankind and the useful and dangerous element we know as mercury.

    Part I

    “All that glitters is not gold,” so the saying goes.  California’s Sierra Nevada mountain range, a picturesque, pale granite sculpture that rises on the eastern California border was formed 4 million years through ecology and geology and heavily mined during California’s 1848 Gold Rush.2 Pondering the beauty of this natural monument, we also now find ourselves obligated to understanding the effects of the ecologically destructive mining practices used 160 years ago.  The legacy of those golden days is not only the gold that has bedazzled civilization since ancient times and defined a period of American history; rather it is the environmental threat of mercury-laden mining deposits that may threaten human health for thousands of years. 

    Mercury Use in the California Gold Rush


    The California Gold Rush was an exhilarating race to monetize on newly discovered gold deposits that enticed nearly 300,000 people to seek their fortunes amid the rugged landscape. The urgency of exhausting the range of its golden egg, with little to no understanding of the environmental effects of large-scale mining practices, took priority over other concerns.  These factors, combined with an absence of property rights, advancements in large-scale mining, immense financial backing, and the common conception that America contained a limitless expanse of land, led to unprecedented environmental destruction.3 Today, the reality of mercury contamination of soil, water, and fish looms in stark contrast to the romantic image of the grizzled 19th century gold miner, an apparition of America’s westward expansion and a long-standing symbol of American aspirations and ingenuity.

    Upon the initial discovery of gold, less invasive techniques (such as panning) were employed, but quickly gave way to new technologies based on mining and ore separation; techniques dating back to the Romans.4 These techniques were capable of obtaining more gold from new geological sources, but were more openly destructive to the landscape, employing high-pressure water cannons to blast gravel deposits from entire hillsides. The gold rich gravel slurry was then washed into sluices for processing.  The small particles of gold (gold fines) were separated from the other slurry components by adding hundreds of pounds of mercury to the mix. The mercury would bind the gold into a mercury-gold amalgam, whose higher density caused it to sink to the bottom of the sluices. Sand and gravel would pass over and out the sluice, leaving the amalgam.5 Once separated, the mercury-gold amalgam was heated, boiling off the mercury and leaving the extracted gold.6

    While some of the mercury was recovered and reused, large quantities contaminated the environment, by washing out the end of sluice, leaking out of the sluices into the soil and bedrock below, and some wantonly disposed.  From the 1860s through the early 1900s, hundreds of hydraulic placer gold mines were operated in California, especially in the northern Sierra Nevada. The total amount of mercury lost to the environment from placer mining operations throughout California has been estimated at 10 million lbs., of which an estimated 80 to 90 percent was in the Sierra Nevada7.

    150 years and possibly 10,000 more

    Fast forward to today in the Sierra Nevada’s Yuba Fan, an enormous refuse pile of mining debris in the valley of California’s Yuba River, and in close vicinity to several abandoned gold mines. Researchers, lead by Michael Singer, a geomorphologist at the University of St. Andrews in Scotland and the University of California, Santa Barbara, have surveyed 105 sites along the Yuba river, as well as two other rivers nearby. Their research has concluded that, “there are massive amounts of mercury-sediment making its way to the lowlands.” The Yuba River eventually makes its way to the San Francisco Bay delta, a network of bays and rivers that connects with the Pacific Ocean.

    While Singer’s team did not investigate the mercury’s migration all the way to the bay delta, Duke University’s Gretchen Gehrke, a geochemist asserts there is “plenty of evidence that mercury from mining does reach the Bay.” 

    Concern is heightened by climactic trends leaning toward ongoing flooding that can carry the mercury down river.  Floods in 1986, 1997, and 2006, have historically shown to wash mercury downstream according to estimates by Singer and his team.  Reports by scientists during the recent Proceedings of the National Academy of Sciences, speculate that mercury may continue to contaminate the river valley below the fan for more than 10,000 years.1

    When speaking of contamination, especially an element like mercury that has a long period of environmental contamination, dwarfing our own very short lifespan, the past and the present easily lose their distance. The decisions of the past are very easily the concerns of today, and the decisions of today the possible concerns of the future.  It is very easy to look at this historic snapshot in light of the findings of current research and trace the causes and effects with the convenience of hindsight.  We lay blame based on our current knowledge of mercury risks very comfortably, but what does that mean for our current mercury emission decisions.  In the forthcoming blog posts, we will continue to examine mercury and move toward a more circumspect historic understanding of it, not just as an issue of the past, nor a current issue, but in a perspective of historic emissions leading up to today, and what it means for the future.

    Teledyne Leeman Labs Mercury analyzers are used to test soil and water for mercury contamination.  For more information on these analyzers, visit http://www.teledyneleemanlabs.com/products/mercury/index.asp 

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    Information in this blog was derived from the following sources.  Information maybe be edited in content and length.  For further information, please refer to the source document and/or website.

    1. Watson, Traci. Mercury from Gold Rush leaves toxic legacy in West. USA Today [Online] October 28, 2013.http://www.usatoday.com/story/news/nation/2013/10/28/mercury-gold-rush-california/3191565/ (accessed November 08, 2013).
    2. Wikipedia. http://en.wikipedia.org/wiki/Sierra_Nevada_(U.S.) (accessed November 08, 2013)
    3. Wikipedia.  http://en.wikipedia.org/wiki/California_gold_rush (accessed November 08, 2013)
    4. Wikipedia.  http://en.wikipedia.org/wiki/Gold_extraction (accessed November 08, 2013)
    5. Alpers, Charles N; Hunerlach, Michael P; May, Jason T; Hothem, Roger L.  Mercury Contamination from Historical Gold Mining in California; Publications - Fact Sheet 2005-3014 Version 1.1; November 2005. U.S. Geological Survey.; http://pubs.usgs.gov/fs/2005/3014/ (accessed online November 08, 2013).
    6. Wikipedia.  http://en.wikipedia.org/wiki/Amalgam_(chemistry)#Use_in_mining (accessed November 08, 2013)
    7. Churchill, R.K., 2000, Contributions of mercury to California's environment from mercury and gold mining activities; Insights from the historical record, in Extended abstracts for the U.S. EPA sponsored meeting, Assessing and Managing Mercury from Historic and Current Mining Activities, November 28-30, 2000, San Francisco, Calif., p. 33-36 and S35-S48


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