<P> Because of the high toxicity of mercury, both the mining of cinnabar and refining for mercury are hazardous and historic causes of mercury poisoning . In China, prison labor was used by a private mining company as recently as the 1950s to develop new cinnabar mines . Thousands of prisoners were used by the Luo Xi mining company to establish new tunnels . Worker health in functioning mines is at high risk . </P> <P> The European Union directive calling for compact fluorescent bulbs to be made mandatory by 2012 has encouraged China to re-open cinnabar mines to obtain the mercury required for CFL bulb manufacture . Environmental dangers have been a concern, particularly in the southern cities of Foshan and Guangzhou, and in Guizhou province in the southwest . </P> <P> Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines . Water run - off from such sites is a recognized source of ecological damage . Former mercury mines may be suited for constructive re-use . For example, in 1976 Santa Clara County, California purchased the historic Almaden Quicksilver Mine and created a county park on the site, after conducting extensive safety and environmental analysis of the property . </P> <P> Mercury exists in two main oxidation states, I and II . </P>

When was mercury added to the periodic table