Arsenic is a naturally occurring element. Its poisonous properties were known to the ancients. Arsenic is highly persistent in the environment and thus can remain long after use. Products containing arsenic included wood preservatives, pesticides, and alloys used in certain batteries and electronic components.
U.S. EPA's Integrated Risk Information System states that arsenic is a human carcinogen. The National Institutes of Health has determined that arsenic and inorganic arsenic compounds are known to be human carcinogens. The International Agency for Research on Cancer has determined that "There is sufficient evidence in humans for the carcinogenicity of mixed exposure to inorganic arsenic compounds, including arsenic trioxide, arsenite, and arsenate. Inorganic arsenic compounds, including arsenic trioxide, arsenite, and arsenate, cause cancer of the lung, urinary bladder, and skin. Also, a positive association has been observed between exposure to arsenic and inorganic arsenic compounds and cancer of the kidney, liver, and prostate." (IARC, page 85).