However, human activities can contribute to arsenic levels in drinking water. Past use or disposal of pesticides containing arsenic, mining operations, and manufacturing all displace arsenic from its original location and make it available to work its way into groundwater or to run-off into surface water, which seeps down to the water table. The effects of arsenic on health depend both on the form of arsenic, and on the amount of the exposure and how long the exposure lasts. Organic arsenic is generally not toxic. Arsenic in soil, rock, and water is usually inorganic.
Inorganic arsenic is toxic.
A single dose of inorganic arsenic can be fatal. Consumed over a longer period, much lower amounts of arsenic can also be harmful. Studies have also linked long-term exposure to arsenic in drinking water to increased cancer of the bladder, lungs, kidney, nasal passages, liver, and prostate. This standard is currently pending further federal review. EPA standards apply to public water supplies.