Environ. Sci. Technol. 2010, 44, 794–799
Comparative Analysis of Halonitromethane and Trihalomethane Formation and Speciation in Drinking Water: The Effects of Disinfectants, pH, Bromide, and Nitrite J I A H U , † H O C H E O L S O N G , * ,‡ A N D T A N J U K A R A N F I L * ,† Department of Environmental Engineering and Earth Sciences, Clemson University, Anderson, South Carolina 29625, and Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Korea
Received August 31, 2009. Revised manuscript received November 16, 2009. Accepted November 20, 2009.
A bench-scale study was performed to investigate formation and speciation of halonitromethanes (HNMs) in raw and treated waters obtained from a drinking water treatment plant. HNM speciesweremeasuredafterchlorination,ozonation-chlorination, chloramination, and ozonation-chloramination, and compared with trihalomethanes (THMs). Pre-ozonation before chlorination resulted in enhanced HNM formation, producing trihalogenated HNMs as major species. Formation of THMs showed very a different formation pattern from HNM formation such that it was much higher in the raw than the treated water, and decreased after pre-ozonation. These findings indicated that precursors and formation pathways for HNMs and THMs are not the same. Increases in pH and bromide concentrations increased HNM and THM formation during ozonation-chlorination and THM formation during chlorination. The bromide effect shifted the formation of HNMs and THMs toward brominated species, with its impact being greater in the treated than raw water. On the other hand, there was no pH or bromide effect on HNM formation during chlorination. The presence of nitrite increased HNM formation under both chlorination and ozonation-chlorination conditions, but it had no influence on THM formation. HNM formation during ozonation-chloramination remained about 1 µg/L level even at the highest bromide and nitrite concentrations. Monochloramination alone did not form any measurable HNMs. The results indicated that the use of chloramine can be an effective way to minimize HNM formation at typical drinking water treatment conditions.
Introduction In a nationwide occurrence study funded by the United States Environmental Protection Agency (USEPA) during 2000-2002, 12 utilities treating waters with high total organic carbon (TOC) and bromide, and employing advanced treatment, * Address correspondence to either author. H.S. Phone: 82-42868-3373; fax: 82-42-868-3414; e-mail:
[email protected]; T.K. Phone: 1-864-656-1005; fax: 1-864-656-0672: e-mail:
[email protected]. † Clemson University. ‡ Korea Institute of Geoscience and Mineral Resources. 794
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were selected and monitored for occurrence of various disinfection byproduct (DBPs) including approximately 50 unregulated DBPs deemed to cause the highest potential human health risks (i.e., high-priority DBPs) (1, 2). These high-priority DBPs included halonitromethanes (HNMs), iodinated trihalomethanes (I-THMs), haloacetonitriles, haloketones, haloacetaldehydes, haloacetamides, and analogues of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)furanone (MX). Among these DBPs, HNM species (i.e., chloro(CNM), dichloro- (DCNM), trichloro- (TCNM), bromo(BNM), dibromo- (DBNM), tribromo- (TBNM), bromochloro(BCNM), bromodichloro- (BDCNM), and dibromochloronitromethane (DBCNM)) received special attention because of their potential high toxicity and occurrence in finished waters at some treatment facilities. The toxicology studies on emerging DBPs conducted in recent years showed HNMs to be one of the most cytotoxic and genotoxic classes among the unregulated DBPs. For example, DBNM was reported to be 82.6 times more cytotoxic and 67.2 times more genotoxic than dibromoacetic acid (3, 4). Therefore, the adverse effects of HNMs can be more severe than the regulated haloacetic acids (HAAs) even at low levels in finished drinking waters. Furthermore, it was reported that brominated HNMs were found to be more toxic than their chlorinated analogues, with dibromonitromethane being the most cyto- and genotoxic (4). The high degree of cyto- and genotoxicity of HNMs was attributed to the greater intrinsic reactivity conferred by the nitro group. The presence of HNMs in drinking water was first realized in the late 1970s and 1980s (5-10). Bromine-substituted trihalogenated HNMs were found in a bench-scale chlorination study with mass spectrometric identification (9). TBNM (bromopicrin) was detected in a pilot-plant study after ozone treatment (11). In later studies, other HNM species (including brominated HNMs and mono- or dihalogenated HNMs) were identified by gas chromatography/mass spectrometry in waters treated with ozone-chlorine and chlorine alone (2, 11-13). During the data collection for the Information Collection Rule (ICR) in the late 1990s, utilities only monitored for TCNM in treated surface and groundwaters. TCNM concentrations were very low, and the difference between treated surface and groundwaters were negligible (i.e., 1.1 µg/L versus
