Hexavalent chromium review, part 2: chemistry, occurrence and treatment

This is the second article in a two-part review of the current state of the science regarding hexavalent chromium. Part 1 discussed chromium health effects, regulations, and analysis. This review begins by discussing the chemistry of the two predominant chromium oxidation species: trivalent chromium and hexavalent chromium (Cr(VI)), including soluble and particulate forms. Although Cr(VI) is the species of concern for human health effects, both forms must be considered because they can be interconverted by a variety of oxidants and reductants. Although it is generally assumed that Cr(VI) comes from anthropogenic contamination, this review highlights many reports of it naturally occurring. This article also summarizes the limited data available on chromium occurrence in drinking water sources and finished water. Finally, a range of treatment methods and limitations associated with each is listed. Utilities should also consider potential sources and sinks of chromium within the treatment plant and distribution system. © 2012 American Water Works Association