Arsenic is a toxic substance with acute as well as chronic effects. In 2001, the US arsenic drinking water limit of 50 ppb was lowered to 10 ppb (∼130 nM), the same as in the EU. An upper limit of 10 ppb, as in drinking water has an estimated
cancer risk of 1 in 500 while 1 in 10,000 is usually the highest cancer risk the US Environmental Protection Agency
(EPA) allows in tap water [1]. Assuming a linear dose–response relationship between arsenic and lung and bladder cancer the drinking water standard would have to be lowered to 0.5 ppb (7 nM) As to achieve a 1 in 10,000 risk estimate, which is difficult to detect using existing analytical methods. Furthermore, it has been demonstrated that arsenic acts as an endocrine disruptor at concentrations 20× less than the 10 ppb drinking water standard[2]. The arsenic limit has been set at this level in spite of the health risks because of measurement limitations [3].