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Arsenic Cycle
The arsenic (As) cycle covers biogeochemical processes and describes As in terms of reservoirs and fluxes through the atmosphere, lithosphere, pedosphere, hydrosphere, and biosphere. Although arsenic is naturally abundant in the Earth's crust, long-term exposure and high concentrations of arsenic can be detrimental to human health.

Arsenic Toxicity
Arsenic is a metalloid with an atomic number of 33, and its common oxidation states are +3 or +5, as arsenate(III) and arsenite(V). Arsenic is primarily found as organic arsenic compounds, inorganic arsenic compounds, and arsine gas. Arsenic toxicity is dependent on its oxidation state; As(III) is more toxic than As(V) because of its ability to bind to thiol groups on proteins and enzymes, and its slower excretion rate from the body. The World Health Organization recognizes that inorganic arsenic is extremely toxic for human and detrimental to aquatic life.

Anthropogenic Sources and Impacts
There are a variety of different arsenic sources that have and are still used by humans. Some examples include pesticides, wood preservatives, metal treatment, paint, and coal-based power plants. Anthropogenic residues and discharges by coal-based power plants, mining, and smelting can contaminate rivers, lakes, streams and soil.