Environ. Sci. Technol. 2009, 43, 466–472
Nitrosamine, Dimethylnitramine, and Chloropicrin Formation during Strong Base Anion-Exchange Treatment JEROME M. KEMPER,† PAUL WESTERHOFF,‡ AARON DOTSON,‡ A N D W I L L I A M A . M I T C H * ,† Department of Chemical Engineering, Yale University, Mason Laboratory 313b, 9 Hillhouse Avenue, New Haven, Connecticut 06520, and Department of Civil and Environmental Engineering, Arizona State University, Tempe, Arizona 85287-5306
Received September 01, 2008. Revised manuscript received November 11, 2008. Accepted November 13, 2008.
Strong base anion-exchange resins represent an important option for water utilities and homeowners to address growing concerns with nitrate, arsenate, and perchlorate contamination of source waters. Most commercially available anion-exchange resins employ quaternary amine functional groups. Previous research has provided contradictory evidence regarding whether these resins serve as sources of nitrosamines, considered as highly carcinogenic nitrogenous disinfection byproducts (NDBPs), even without disinfectants. For three common varieties of commercial anion-exchange resins, we evaluated the importance of releases of nitrosamines, and two other N-DBPs (dimethylnitramine and chloropicrin), when the resins were subjected to typical column flow conditions with and without free chlorine or chloramine application upstream or downstream of the columns. In the absence of disinfectants, fresh trimethylamine- and tributylamine-based type 1 and dimethylethanolamine-based type 2 anion-exchange resins usually released 2-10 ng/L nitrosamines, likely due to shedding of manufacturing impurities, with excursions of up to 20 ng/L following regeneration. However, the lack of significant nitrosamine release in a full-scale anion-exchange treatment system after multiple regeneration cycles indicates that releases may eventually subside. Resins also shed organic precursors that might contribute to nitrosamine formation within distribution systems when chloramines are applied downstream. With free chlorine or chloramine application upstream, nitrosamine concentrations were more significant, at 20-100 ng/L for the type 1 resins and ∼400 ng/L for the type 2 resin. However, chloropicrin formation was lowest for the type 2 resin. Dimethylnitramine formation was significant with free chlorine application upstream but negligible with chloramines. Although no N-DBPs were detected in cation-exchange-based consumer point-of-use devices exposed to chlorinated or chloraminated waters, our results indicate that inclusion of anion-exchange resins in these devices, as in laboratory deionized water systems, would likely be problematic.
* Corresponding author phone: (203) 432-4386; fax: (203) 4324387; e-mail:
[email protected]. † Yale University. ‡ Arizona State University. 466
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 2, 2009
Introduction Anion-exchange resins represent an important option to address growing concerns with nitrate, arsenic, and perchlorate contamination of source waters. They are also featured in laboratory deionization devices. Although there are two common types of anion-exchange resins, both achieve a positive charge via quaternary amine functionalities. Type 1 resins utilize alkylamine groups. Although type 1 resins with trimethylamine moieties are common, type 1 resins featuring longer alkyl chains (e.g., tributylamine moieties) can be nitrate-selective (1). Type 2 resins use dialkylethanolamine moieties. Because of their reliance on amine groups, these resins may serve as precursors for nitrogenous disinfection byproducts (N-DBPs), such as nitrosamines, nitramines, and halonitromethanes (2-5). The U.S. EPA’s Integrated Risk Information System database indicates for eight nitrosamines that drinking water concentrations in the low nanogram per liter level are associated with a 10-6 lifetime cancer risk. California’s Department of Public Health has set 10 ng/L notification levels for N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine, and N-nitrosodipropylamine. The U.S. EPA has placed several nitrosamines in the Unregulated Contaminant Monitoring Rule 2 and on the Contaminant Candidate List 3. Together with NDMA, DMNA was identified as a byproduct in chlorinated pool waters (6). Halonitromethanes (e.g., chloropicrin) exhibit toxicities orders of magnitude higher than regulated DBPs (7). Results from previous research regarding the importance of nitrosamine formation from anion-exchange treatment have been contradictory. Najm and Trussell (8) soaked fresh type 1 and 2 resins in 12 000 mg/L sodium chloride for 3 h and observed up to ∼60 ng/L NDMA after placing these resins in deionized water for 4 h. NDMA concentrations were highest for the type 2 dimethylethanolamine resin and more than doubled when the deionized water contained 1 mg/L as N nitrite. These NDMA concentrations far exceed California’s 10 ng/L notification levels. However, the batch system employed may have overestimated NDMA formation, as empty bed contact times in typical plants are generally
