Arsenic (As) is a naturally occurring element that has been used in a variety of applications—in pesticides, as wood preservatives, and as a treatment for syphilis. Throughout history, arsenic was the most often used poison. Some historians believe that Nero used arsenic to poison Claudius in 54 C.E. Arsenic has also been the poison of choice in murder mysteries due to its easy availability in rat poison and insecticides.

In its elemental form, arsenic is a steel gray metal-like material. Combined with carbon and hydrogen, it forms organic arsenic compounds. When combined with oxygen, chloride, and sulfur, it forms inorganic arsenic compounds. Organic arsenic is generally less toxic than inorganic arsenic. Chromated copper arsenate (CCA), a pesticidal compound, has been widely used as a wood preservative. In February 2002 industry announced a voluntary decision to remove arsenic-treated lumber products (play structures, picnic tables, deck wood, etc.) from the...