Day 9: Chromium
Although not all soluble forms of chromium in drinking water have been recognized as human carcinogens, the growing body of evidence in recent years has led to increasing regulation of the hard metal in all of its forms. It is widely acknowledged that chromium dust, when inhaled, is dangerous to human health, yet with a shortage of longitudinal studies to evaluate the relative risks of different chromium compounds when consumed orally, global standards for maximum allowable levels in drinking water vary: whereas WHO guidelines call for 5 parts per billion as the maximum allowable concentration, the US EPA guideline calls for 100 parts per billion.
One of the earliest uses of chromium was as a coating for metal weapons found with the Terra Cotta warriors built by the Qin dynasty. It became used in artists pigments in the 18th century, and in paints and tanning salts during the 19th century, but in the 20th century it became widely used as a plating component to make metal parts (particularly in automobiles) that when polished had a distinctive luster and shine. Today it is mostly used in the production of metal allows, however it is also used by the chemical industry.
Hexavalent Chromium, (a series of compounds that contain chromium in the +6 oxidation state) has received widespread attention as a water contaminant in recent years, primarily due to the efforts of Erin Brakovich to expose the illegal dumping of the compound in Hinkley, California, which in 1996 resulted in the largest class action lawsuit settlement in US History.