Arsenic is widely distributed throughout the Earth’s crust, most often as arsenic sulfide
or as metal arsenates and arsenides. Arsenicals are used commercially and industrially,
primarily as alloying agents in the manufacture of transistors, lasers and semiconductors.
Arsenic is introduced into drinking-water sources primarily through the
dissolution of naturally occurring minerals and ores. Except for individuals who are
occupationally exposed to arsenic, the most important route of exposure is through
the oral intake of food and beverages. There are a number of regions where arsenic
may be present in drinking-water sources, particularly groundwater, at elevated
concentrations. Arsenic in drinking-water is a significant cause of health effects in
some areas, and arsenic is considered to be a high-priority substance for screening in
drinking-water sources. Concentrations are often highly dependent on the depth to
which the well is sunk.