Mercury that exists in a stable state in the Earth’s crust is referred to as “geologic” mercury. The active mercury cycle begins when mercury is released from this stable form to the environment through natural processes or human interven- tion. There are four principal pathways releasing mercury to the environment. First is through natural processes; for example, mercury that was once in the Earth’s crust could be released through a volcanic eruption or other geological activity. Second is the release of mercury that is incidental to some other activity; for example, the natural mercury found in coal is released when the coal is burned in a power plant to produce electricity. The third way.
