Environ. Sci. Technol. 2008, 42, 3341–3348
Occurrence of Halogenated Furanones in U.S. Drinking Waters G R E T C H E N D . O N S T A D , †,§ H O W A R D S . W E I N B E R G , * ,† A N D STUART W. KRASNER‡ Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7431, and Metropolitan Water District of Southern California, 700 Moreno Ave., La Verne, California 91750-3399
Received June 8, 2007. Revised manuscript received November 25, 2007. Accepted December 3, 2007.
Chlorinated and brominated forms of MX (3-chloro-4(dichloromethyl)-5-hydroxy-2(5H)-furanone) were detected in the disinfected waters of six pairs of U.S. drinking water treatment plants, with MX as high as ∼310 ng/L in finished water. The strength of this study is in its comparison between pairs of plants that drew water from the same or similar watersheds and treated the raw source water with two contrasting disinfection and/or treatment schemes. As expected, the brominated MXanalogues were produced in greater abundance than MX from raw source waters with high bromide concentrations. Disinfection of waters with free chlorine produced more MXanalogues than disinfection with monochloramine. Use of chloramines as the residual disinfectant appeared to stabilize MXanalogues once they were formed. Pretreatment with ozone and biologically active granular activated carbon minimized MXanalogue formation upon subsequent chlorination or chloramination, either because MX precursors were altered by ozone, removed by granular activated carbon, or degraded by biological filtration. Pretreatment with chlorine dioxide did not minimize MX-analogue formation. In plant effluent samples, MX and chloroform were positively correlated (molar R2 ) 0.7, N ) 6). Similar formation patterns of MX-analogues, trihalomethanes, and haloacetic acids in these water treatment plants suggest that the three classes of disinfection byproduct follow a common formation mechanism from natural organic matter and chlorine.
Introduction Halogenated furanones are a class of highly mutagenic compounds formed from the reaction of chlorine with natural organic matter (NOM) and bromide (1). Among them, MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) and its analogues (Figure 1) represent 11–71% of the mutagenicity in chlorinated drinking waters (2) and have been detected in drinking waters across Finland, the United Kingdom, Australia, Canada, Spain, China, and Japan in the range of 0.1-90 ng/L (2–7). MX was detected in Russian drinking * Corresponding author phone: (919) 966-3859; fax: (919) 9667911; e-mail:
[email protected]. † University of North Carolina at Chapel Hill. ‡ Metropolitan Water District of Southern California. § Current address: University of Washington, Department of Environmental & Occupational Health Sciences, Box 357234, Seattle, WA 98195-7234. 10.1021/es071374w CCC: $40.75
Published on Web 03/22/2008
2008 American Chemical Society
waters at an average of 160 ng/L (8). There is a paucity of occurrence data on these compounds in U.S. drinking waters but, when found, plant effluent and distribution system samples showed levels typically in the range 2–80 ng/L (9, 10). Concentrations and speciation of MX-analogues are dependent upon source water quality and treatment technologies. MX has been detected primarily in waters treated with free chlorine and less so with the use of chlorine dioxide (ClO2) or chloramines. In Finland, MX concentrations of plant effluent samples were compared before and after changing treatment strategies to determine MX formation and removal conditions (11). MX formation by chlorination was minimized by switching sources from surface water to artificially recharged groundwater, therefore reducing the concentration of NOM and its MX precursors. When chlorine was replaced by ClO2 as the predisinfectant, no reduction in MX formation was observed in the chlorinated effluent, suggesting that ClO2 reaction with NOM did not prevent subsequent formation of MX by terminal chlorination. When prechlorination was replaced by ozonation and terminal disinfection used chloramines, the level of MX was radically diminished. Formation of MX also depends on the ratio of chlorine dose to total organic carbon (TOC) and the overall chlorine consumption. The surface waters examined in Finland averaged 7.3 mg/L TOC, which was reduced 60% by coagulation (to ∼2.9 mg/L TOC). Postdisinfection of these waters with 1 mg/L Cl2, a Cl2/TOC ratio of 0.3:1 by weight, generated MX concentrations below 50 ng/L (2). Granular activated carbon (GAC) adsorption effectively filters mutagenicity from drinking water (12). MX adsorbs completely onto clean GAC, but 40% less effectively on preloaded carbon (after 10 weeks of operation) (7). Compared to trihalomethanes (THMs), which are regulated disinfection byproducts (DBPs) in the U.S., MX adsorbs better to GAC, implying that THMs would break through a GAC filter and be detected in the filter effluent prior to MX breakthrough. When there is no residual chlorine across the filter, “biological filtration” may take place and microbial communities on the filter media could assist in the removal of MX and other DBP precursors. To provide more data on the formation, control, and stability of MX and other halogenated furanones in U.S. drinking waters, this class of DBPs was included in a survey of U.S. drinking waters targeting regulated and unregulated DBPs (13). MX and its analogues in Figure 1 were selected as high-priority DBPs (along with ∼50 other DBPs) according to their carcinogenic potential using a mechanism-based structure–activity relationship analysis (14). An analytical method, validated by ion trap mass spectrometry, was developed for the detection of MX and 12 analogues in this survey, using liquid–liquid extraction, derivatization, and gas chromatography (GC) with microelectron capture detection (µECD), which used relatively small sample volumes and allowed for processing of large numbers of samples (15). Krasner et al. (13) presented an overview of the U.S. survey data for several classes of DBPs, including halogenated furanones, briefly highlighting the treatment conditions which minimized or maximized their occurrence. This paper expands upon the summary (13) offering specific insights into the formation, occurrence, and control of a number of halogenated furanones in U.S. drinking water treatment plants and their persistence in water distributed to consumers.
Experimental Section Study Sites and Sampling. Six pairs of drinking water treatment plants were chosen, each pair treating the same VOL. 42, NO. 9, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Structures of halogenated furanones (MX-analogues) measured in this survey (not shown: ox-MX). or similar water source with two different treatment and/or disinfection schemes, so that the impact of these treatment/ disinfection processes on DBP formation using the same or similar DBP precursor materials could be evaluated. In addition, plants were picked that were in different geographical regions of the U.S. defined by the Environmental Protection Agency (EPA) (16). The identities of the 12 water treatment plants in the study are represented by a plant number (1–12) and their EPA region number (3–7 and 9: Supporting Information Table S1). All of the plants treated surface water supplies except for two plants (7 and 8) which treated a colored groundwater. Grab samples were collected for halogenated furanone analysis in warm- and/or cold-water seasons (warm > 20 °C > cold). The technologies used at the plants included coagulation, lime softening, membrane softening, biological filtration, and oxidation/disinfection by chlorine, ozone, permanganate, chlorine dioxide, or chloramines (Supporting Information Table S1). Most of the plants that used biological filtration employed GAC in their filters. In addition, some plants added powdered activated carbon (PAC). An effort was made to select plants treating waters that were high in TOC and/or bromide to enable the detection of priority DBPs. This study was not an occurrence survey per se, rather it was a targeted survey of waters with “challenged” conditions. The raw water TOC concentrations ranged from 3.0 to 12.6 mg/L, and the bromide concentrations varied from 0.05 to 0.33 mg/L (Supporting Information Table S2). Samples were taken at a number of locations in each plant and in the corresponding distribution system. For most of the plants, samples were taken before and after oxidant/ disinfectant additions, before and after filtration (FI and FE), at the plant effluent (PE), and at average and maximum distribution system (DS) residence times (range 24–168 h). An illustration of treatment regime and sampling points is presented in Supporting Information Figure S1 for plants 5 and 6 and Supporting Information Figure S2 for plant 8. The processes for all plants are summarized in Supporting Information Table S1. Some of the plants used chlorine dioxide as a disinfectant/oxidant (plants 6, 11, 12), one used permanganate (plant 12), and some used ozone (plants 1, 5, 7); most used chloramines in the plant or distribution system and some used biologically active filter media including GAC (plants 1, 3, 5, 10). Plant 4 used free chlorine as a primary and secondary (terminal) disinfectant. Oxidant/disinfectant doses are given in Supporting Information Table S2. Samples for halogenated furanone analysis were collected headspace free in 250 mL amber bottles fitted with Teflonsealed caps, quenched of residual free chlorine with ammonium sulfate (no acidification prior to storage), stored on ice in a cooler, shipped overnight to the University of North Carolina (UNC), stored at 4 °C in the dark, and extracted within 48 h of receipt. Field blanks filled with laboratorygrade water were included in the coolers sent out for sample 3342
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collection. An extra 1 L sample was collected from each plant effluent to allow for a matrix spike sample. One 4 L sample was collected from the finished water of plant 6 for concentration and confirmation of halogenated furanone detection by GC-ion trap MS/MS (see Supporting Information Figure S3). Materials. The halogenated furanone standard mucochloric acid (MCA) was obtained from Sigma-Aldrich (St. Louis, MO). MX, reduced MX (red-MX), and oxidized MX (ox-MX) (17, 18) were synthesized at UNC at Chapel Hill. The brominated MX species (BMX1, BMX2, and BMX3) (19) were synthesized at ICER, Spain. The open forms of these compounds (MCAopen, MBAopen, ZMX, EMX, BEMX1, BEMX2, BEMX3) were detected in the standards following derivatization with boron-trifluoride methanol. High purity control standards, extraction solvents, and reagents were obtained from Supelco (Bellefonte, PA), Sigma-Aldrich, and EM Science (Gibbstown, NJ). Safety. Due to the mutagenic properties of these chemicals they must be handled in a laminar flow hood to prevent human exposure and dermal contact prevented by the use of double gloves. Cleaning of labware that has contact with these chemicals must take place within a confined and protected hood with waste disposal following the defined protocols established by local health and safety jurisdictions. Analysis. Routine analysis of 13 halogenated furanones (MX, MCA, BMX1, BMX2, BMX3, and their open forms, full names listed in Supporting Information Table S3) in the collected samples was conducted using liquid–liquid extraction (LLE) of acidified 250 mL samples with methyl t-butyl ether, derivatization with boron trifluoride in methanol, final extraction with hexane, and detection on a µ-ECD of an HP 6890 GC-µECD (Agilent, Palo Alto, CA) (15). Samples for redMX analysis did not require acidification prior to LLE, derivatization, nor extraction with hexane prior to analysis by GC-µECD (see Supporting Information for full details). The THMs listed in Supporting Information Table S3 were analyzed using a modification of EPA Method 551.1, whereas the haloacetic acids (HAAs) were analyzed using EPA Method 552.2, both within 14 days of sample collection (20).
Results and Discussion The levels of individual halogenated furanones (Figure 1) measured in this study ranged from below the reporting limits of 20–40 ng/L to above 1000 ng/L (1.0 µg/L), which is much higher than previously reported in drinking waters (2, 5). The analysis of halogenated furanones is reported for the 12 drinking water treatment plants surveyed in this study in Tables 1 and 2, and Figures 2–4. Most plants were surveyed on two different occasions to capture seasonal differences, but because the early part of the survey was conducted while method development was continuing, not all 13 species of the halogenated furanones were measured for all plants on
TABLE 1. Removal of DBPs and TOC by GAC (Bio)filtration in Cold Water Seasona plant sample MX MCA ring MCA open THM4 DXAAs TXAAs HAA9 TOC (mg/L)
3
4
FI (µg/L)
FE (µg/L)
0.03 0.53b 0.11 30 25 21 47 2.9
