Hexavalent Chromium (aka Chrome-6 or Cr-6) is a known human carcinogen when inhaled; there has been considerable debate in recent years regarding its toxicity if ingested.
Cr-6 has been used in the past as an anti-microbial on cooling towers. Chromium compounds are also used 1) in the fabrication of alloys; 2) in the preparation of alloy steels to enhance corrosion and heat resistance; 3) in the fabrication of plated products for decoration or increased wear resistance; 4) in the production of non-ferrous alloys to impart special qualities to the alloys; 5) in the production and processing of insoluble salts; 6) as chemical intermediates (e.e., in the textile industry in the dyeing, silk treating, printing, and moth proofing wool); 7) in the leather industry in tanning; 8) in photographic fixing baths; 9) as catalysts for halogenation, alkylation, and catalytic cracking of hydrocarbons; and, 10) as fuel additives and propellant additives. Old plating and other industrial operations have also yielded Cr-6 as a byproduct. As a result of these activities, Cr-6 (among other chromium compounds) can be found in groundwater, and thus has appeared in drinking water supplies.
Because of its presence, California has been evaluating Cr-6 in terms of evaluating its toxicology and determining whether to set a drinking water standard for Cr-6. Currently chromium compounds are regulated in drinking water under the general catchall category of "total chrome" (MCL, 50 ppb). As the initial step in the MCL process, California's Office of Environmental Health Hazard Assessment (OEHHA) has been been charged with assessing Cr-6, and if toxicity is found to set a Public Health Goal (PHG), the predecessor step to establishing an MCL.
OEHHA's proposed standard, released Friday, would set the limit at .02 parts per billion, which is expected to cause a "negligible risk" for people drinking 2 liters of water over a 70-year lifetime. The goal was lowered from the 2009 proposal of .06 parts per billion after input from scientists pointing out the increased effects on infants. Samples taken by the State during the past decade have shown chromium-6 levels into the 50s- and 60s-parts per billion at peak sites in southern California. In San Jose, which is supplied by three water districts, chromium-6 levels generally hover between one and 11 parts per billion, still higher than the proposed goal; much of this impact derives from the past operations of plating and so-called high-tech businesses.
The next step will be for the California Department of Public Health to determine a MCL. As part of this process, CDPH will consider to what extent it is economically feasible to meet the PHG, and if not, then what level of compliance can be reasonably achieved.
More information on OEHHA's evaluation can be found at http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Chromium6.aspx.