Hexavalent Chromium refers to chemical compounds that contain the element Chromium in the +6 oxidation state that when inhaled, is recognized as a human carcinogen. This chemical is banned by the RoHS directive of 2011.
Hexavalent chromium (chromium(VI), Cr(VI), chromium 6) is the chromium in any chemical compound that contains the element in the +6 oxidation state (thus hexavalent). Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate. Approximately 136,000 tonnes of hexavalent chromium were produced in 1985. Thus hexavalent chromium is key to all materials made from chromium.
Additional hexavalent chromium compounds are chromium trioxide and various salts of chromate and dichromate, among others. Hexavalent chromium is used in textile dyes, wood preservation, anti-corrosion products, chromate conversion coatings, and a variety of niche uses. Industrial uses of hexavalent chromium compounds include chromate pigments in dyes, paints, inks, and plastics; chromates added as anticorrosive agents to paints, primers, and other surface coatings; and chromic acid electroplated onto metal parts to provide a decorative or protective coating. Hexavalent chromium can be formed when performing "hot work" such as welding on stainless steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state. Hexavalent chromium can also be found in drinking water and public water systems.
All hexavalent chromium compounds are toxic (due to their oxidizing power) as well as carcinogenic (IARC Group 1), especially if airborne and inhaled where they cause lung cancer. Also positive associations have been observed between exposure to chromium (VI) compounds and cancer of the nose and nasal sinuses. Workers in many occupations are exposed to hexavalent chromium. Problematic exposure is known to occur among workers who handle chromate-containing products and those who grind and/ or weld stainless steel. Workers who are exposed to hexavalent chromium are at increased risk of developing lung cancer, asthma, or damage to the nasal epithelia and skin. Within the European Union, the use of hexavalent chromium in electronic equipment is largely prohibited by the Restriction of Hazardous Substances Directive.