This article has been reviewed and approved by the following Topic Editor: M. N. Rashed (other articles)
Arsenic is an element that is widely distributed in the Earth's crust. Elemental arsenic is ordinarily a steel grey, metal-like material that occurs naturally. However, arsenic is usually found in the environment combined with such other elements as oxygen, chlorine, and sulfur. Arsenic combined with these elements is called inorganic arsenic. Arsenic combined with carbon and hydrogen is referred to as organic arsenic. Understanding the difference between inorganic and organic arsenic is important because some of the organic forms are less harmful than the inorganic forms.