Mercury contamination in California waterways

Mercury contamination in California waterways poses a threat to both the environment and human health. This naturally occurring heavy metal may be released into the environment from natural geological sources, but most commonly occurs from anthropogenic mining operations. This metal poses a threat not only for its effects on organisms, but also for difficulty of removal from waterways and the trouble in efficiently detecting it. The roots of mercury poisoning in waterways began with the historic mining of gold within California's streambed and hillsides; since the California Gold Rush, mercury has been used for gold extraction for its ability as a catalyze with the precious metal. due to the process of extraction and washing, mercury used would either be burned away as a hazardous vapor, or washed away into waterflows, resulting in widespread contamination of river and lake sediments. Mercury continues to be released today through anthropogenic sources, though state and federal agencies work to manage and ban these practices and to mitigate its effect on the environmental and on people. Many water bodies in the state of California bear fish consumption advisories due to mercury content.

Historical start of mercury pollution in California

Historically the Gold rush represents the beginning of mercury pollution in California's waterways, as well as a plethora of water related issues. The California Gold Rush can be traced to James Marshall's January 24, 1848 discovery of gold on John Sutter's property. Marshall was a carpenter who helped construct the Sutter saw mill for Sutter, and the night before the iconic gold discovery Marshall diverted water from the American River through the lumber mill he was constructing tailrace to wash away loose gravel and dirt. The next morning (January 24, 1848) he discovered metallic flecks where the river water was flowing through the saw mill. He thought it was gold immediately, but didn't pursue it until the Sutter sawmill was completed. By the time of the following spring Marshall's gold discovery, the largest Gold Rush in American history began. In this short year the non-Native American population raised from 14,000 to 100,000. The population increased again to 250,000 by the year of 1892. While gold was initially easily extracted from the river soil and gravel by scooping and silling, the bottom trawler method was also developed to extract more gold at once. As the amount of miners and rate of mining increased, easily collected placer gold became scarcer, and new mining techniques were developed to extract gold more efficiently from rivers and the harder to reach lode gold. One of the main, and also most destructive methods was that of hydraulic mining. This involved the redirecting of water from the river into a narrow channel, into a large canvas hose, and iron nozzle. Then these water cannons, which were called monitors, would shoot a very high pressure stream that would break apart hillsides. The water, slurry, and debris, mostly gravel would flow over large sluices and drainage tunnels. One of the most useful tools for increasing gold collection was the use of mercury, which prompted the mass use and mining of mercury in response.

Use of mercury in gold mining Historically, mercury, also called "quicksilver," was used during the mining process of gold. During hydraulic mining, as the water, slurry, and debris flowed over the sluices and drainage tunnels, the particles were mixed with liquid mercury. The mercury was used to attract the gold and sometimes silver from the mining ore for extraction. The most common use of mercury for gold and silver extraction was a process called mercury amalgamation. During this process, the miner mixes mercury with mining silt or ore and the mercury then sticks to the gold, thus separating from the ore and silt and forming one solid piece of mercury–gold amalgam. Additional separation from the silt and ore is done by washing away the ore with water until only the amalgam is left. The next step of the process involves separating the gold from the now useless mercury. To do so, miners heat up the mercury-gold amalgam to a high temperature to vaporize the mercury, leaving only the gold. The vaporization of mercury requires a temperature of at least 357 °C. In addition to the mercury-gold amalgam, some residue mercury is also still present in the silt and ore that was washed away, sometimes referred to as mine tailings. When these mine tailings are disposed of during the washing process, large amounts of the remaining mercury often pollutes and infiltrates the local ecosystems and especially waterways around and down steam from the mining sites. There was a loss of 10-30% of the mercury used during the extraction process, per season, which resulted in highly contaminated sediments at and down stream from mining sites. The highest mercury contamination levels are present and can be sourced back to the Placer area in California. Much of the mercury for mining was produced from deposits on the West side of California's central valley by the coast range, and it is estimated that 220,000,000 lb of mercury was procured from these deposits between 1850 and 1981.

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