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 [Cr(VI)]. Part 1 covered chromium health effects, regulations, and analysis. This review begins by discussing the chemistry of the two predominant chromium species: trivalent chromium [Cr(III)] and Cr(VI), including soluble and particulate forms. Although it is generally assumed that Cr(VI) comes from anthropogenic contamination, this review highlights many reports of naturally occurring Cr(VI). This article also summarizes the limited data available on chromium occurrence in drinking water sources and finished water. Finally, a range of treatment methods is listed, as are limitations associated with each. Utilities should also consider potential sources and sinks of chromium within the treatment plant and distribution system.