The arsenic (As) cycle is the biogeochemical cycle of natural and anthropogenic exchanges of arsenic with the environment. The cycle is of interest because arsenic is detrimental to human health. The World Health Organization recognizes that inorganic arsenic is extremely toxic for humans (U.S. EPA maximum of 10 ppb in water) and detrimental to aquatic life. Arsenic toxicity can harm nearly every organ system within the human body, as well as causing lung and skin cancer.
Arsenic's largest reservoir on Earth is the lithosphere. Earth's crust contains more than 200 mineral types containing As, including many sulfide minerals. Arsenic is found in only a few ore deposits, especially containing arsenopyrite (FeAsS) and tennantite. Sedimentary rocks bearing coal and shale may also contain high As. Major fluxes of As from the lithosphere to the atmosphere are volcanic emissions.
Freshwater and groundwaters commonly contain <1 ppb of As. The concentration of As is pH dependent; acidic conditions mobilize As at pH <5. Oxic seawater contains As(III) as arsenate (average of 1.7 ppb). Major sinks include sedimentation and subduction.
Arsenic is a component of a few man-made materials: pesticides, wood preservatives, metal treatment, paint. It is also emitted from coal-based power plants. Some As is emitted from steel and glass production, and forest and grassland burning.
In the atmosphere, As is mainly present in particulates such as dust, with a residence time of 7 to 10 days.
The toxicity of As is well known.