The potential promulgation of a national maximum contaminant level (MCL) for hexavalent chromium (Cr[VI]) and the continued loss of consumer confidence caused by news reports about chromium (Cr) in drinking water increases the urgency for understanding how Cr behaves in treatment plants and distribution systems. Some utilities have reported Cr in their treated water when no Cr was detected in their source water, while other utilities have reported a loss of Cr through their treatment plant, even though Cr removal is not a treatment objective. Cr levels have also been observed to alternatively increase, decrease, or remain the same in distribution systems. Moreover, the behavior of trivalent chromium (Cr[III]) and Cr(VI) species needs to be understood since they possess different toxicities and readily inter-convert in the presence of oxidant and reductants. Fundamentally, Cr's often unexpected behavior is a product of its complex aqueous chemistry, involving sorption/desorption, precipitation/dissolution, and oxidation/reduction reactions.
his webcast presented results from the project Sources, Chemistry, Fate, and Transport of Chromium in Drinking Water Treatment Plants and Distribution Systems
(4497). Topics included:
The kinetics of Cr(III) oxidation in the presence of common drinking water treatment oxidants measured by oxidation studies
Cr concentration and speciation profiles observed by sampling of treatment plants
Potential sources of Cr, including treatment chemicals and leaching from stainless steel piping
The degree that Cr concentrations and speciation changes in distribution systems under the influence of residual disinfectants as observed by sampling, pipe loop studies, and analysis of the third unregulated contaminants monitoring rule (UCMR3) database
he webcast emphasized that there are several potential sources of Cr in treatment plants, the importance of particulate Cr(III) in controlling the fate of Cr in treatment plants, and the variable behavior of Cr under the influence of residual disinfectants in distribution systems.