Arsenic (As) is a ubiquitous element with atomic number 33. It was first documented by Albertus Magnus in 1250. It can be found in many oxidative forms (-3, 0, +3, +5) and is released through various natural and anthropogenic activities. Humans may get exposed to arsenic through food, water and air. Exposure may also occur through skin contact with soil or water that contains arsenic; but exposure through groundwater contamination is more serious and has become the major concern throughout the world. According to recent reports over 150 millions of people are exposed to chronic arsenic poisoning by groundwater throughout the world. Owing to its extreme toxicity EPA (Environmental Protection Act, US) has ranked the arsenic as number one in a list of drinking water contaminants and has set the arsenic standard for drinking water at .010 parts per million (10 parts per billion).
Early exposure leads to change in skin Pigmentation and development of keratosis at chronic level. Chronic arsenic poisoning also produces various systemic manifestations over and above skin lesions viz. chronic lung disease, chronic obstructive pulmonary disease, liver disease, peripheral vascular disease, hypertension, heart disease, diabetes mellitus, non-pitting edema of feet/hands, weakness and anemia. Cancer of skin, lung and urinary bladder are also associated with chronic arsenic toxicity.
References: Chronic arsenic toxicity & human health , D.N. Guha Mazumder, 2008
Wikipedia, US-EPA, NRDC.