Arsenic is one of the most important environmental agents in causing chronic human disease. Elevated levels of arsenic drinking water may affect >100 million people around the world .A wide variety of adverse health effects, most seriously, cancers of bladder, lung, urinary tract, and skin, have been attributed to chronic exposure to arsenic . However, the biochemical mechanisms responsible for these effects caused by arsenic remain unclear ,but may be mediated by the binding of trivalent arsenicals to thiol groups in proteins, thereby changing the conformation of these proteins and inhibiting their functions. If some of the affected proteins are responsible for cellular repair of DNA damage, for example, the inhibition of these proteins could lead to carcinogenesis.