Mercury is present in the environment as a result of both natural processes and human activities. Natural sources of mercury include volcanoes, hot springs, and natural mercury deposits. Sources related to human activities include coal combustion, waste incineration, certain industrial activities and some mining activities. California environmental mercury issues relate to historical mining operations  in two ways. The first is to mercury mining activity that occurred between 1846 and 1981, during which time about 100 million kilograms of mercury were produced within the state. The second is to historic gold mining activities that took place between 1848 and the first part of the 20th century, which depended upon gold recovery processes using mercury. Significant quantities of mercury were lost to the environment during both of these activities.

Mercury is a human neurotoxin with developing fetuses and small children being at greatest risk. The principal route of human exposure is through consumption of mercury contaminated fish. Mercury occurs in various forms and compounds in the environment, some of which are not bioavailable. When mercury enters an aquatic environment, by erosion, atmospheric deposition or as the result of human activity, it may encounter conditions that cause its conversion methyl mercury. Methyl mercury is readily taken up by aquatic organisms and tends to concentrate as it moves up the food chain. This process is referred to as biomagnification and can result in high mercury concentrations in predatory fish such as striped bass and sharks, and in fish eating birds and mammals.

Cinnabar specimen

Cinnabar - New Almaden district, Santa Clara County, California. Cinnabar is a mercury sulfide with the chemical formula HgS. It was the main ore of mercury at many California mercury mines. It is characterized by its bright red color. Mercury was recovered by heating the cinnabar and collecting and cooling the mercury vapors that were produced. Click on image for larger view.

 The California Geological Survey (CGS) participanted along with other state and federal government agency and university research groups in the three year CALFED research project titled “An Assessment of Ecological and Human Health Impacts of Mercury in the Bay Delta Watershed”.  This research project was completed in 2003.

In this research project, CGS was responsible for Task 5C1, Assessment of the Feasibility of Remediation of Mercury Mine Sources in the Cache Creek Watershed.  The CGS study investigated mine sites in the Sulphur Creek mining district within the Cache Creek watershed.  It identified the mine site materials present at each site and estimated their volumes and mercury contents, and estimated offsite mercury transport.  The study also estimated regional mercury background concentrations and contributions from background and other non-mine site mercury sources to the Cache Creek watershed mercury loads.  The CGS Task 5C1 final report and appendix pdf files can be viewed and downloaded at:  
CGS Task 5C1 Report
CGS Task 5C1 Appendix Files

All of the final reports for this CALFED mercury research project can be viewed and downloaded at: