The mercury cycle is a biogeochemical cycle influenced by natural and anthropogenic processes that transform mercury through multiple chemical forms and environments.
Mercury is present in the Earth's crust and in various forms on the Earth's surface. It can be elemental, inorganic, or organic.[1] Mercury exists in three oxidation states: 0 (elemental mercury), I (mercurous mercury), and II (mercuric mercury).
Mercury emissions to the atmosphere can be primary sources, which release mercury from the lithosphere, or secondary sources, which exchange mercury between surface reservoirs.[2] Annually, over 5000 metric tons of mercury is released to the atmosphere by primary emissions and secondary re-emissions.[3]