Environ. Sci. Technol. 2006, 40, 3609-3616
Occurrence and Removal of Chloro-s-Triazines in Water Treatment Plants H . J I A N G , † C . A D A M S , * ,† N . G R A Z I A N O , ‡ A. ROBERSON,§ M. MCGUIRE,⊥ AND D. KHIARI| University of Missouri-Rolla, 220 Butler Carlton Hall, Rolla, Missouri 65409, Malcolm Pirnie, 1855 Blake Street, Suite 101, Denver, Colorado 80202, American Water Works Association, 1401 New York Avenue, Northwest #640, Washington, D.C., 20005, Malcolm Pirnie, 1919 Santa Monica Boulevard, Santa Monica, California 90404, and American Water Works Association Research Foundation, 6666 West Quincy Avenue, Denver, Colorado 80235
Atrazine, simazine, and propazine and their major chlorinated degradates (deethylatrazine, deisopropylatrazine, and didealkylatrazine) are considered as a group to be endocrine-disrupting chemicals by the U.S. Environmental Protection Agency. On this basis, regulatory action levels are currently under consideration for the total chloros-triazine (TCT) levels in drinking waters. To assess the concentrations of each of these species in drinking water and their treatability in conventional water treatment, a comprehensive, full-scale study was conducted that included frequent monitoring at 33 and 47 water utilities during 2003 and 2004, respectively. Approximately 900 paired raw and treated water samples were analyzed using a gas chromatography/mass spectrometry method with preconcentration using a mixed-mode, solid-phase extraction that allowed quantitation of each species including didealkylatrazine. The results showed that atrazine concentrations were generally well within the 3 µg/L maximum contaminant level (MCL) and that simazine and propazine concentrations were generally negligible. Ninetyfifth-percentile values for the ratio of TCT/atrazine were 4.8 and 4.7, respectively. Effectiveness of conventional treatment technologies, including carbon, was observed to vary significantly. Concerns that didealkyatrazine concentrations may be high and significantly elevate the TCT appear to be unfounded. In general, the results suggest that potential treatment requirements for TCT are not likely to be any more difficult for utilities to meet than the current requirements for atrazine.
Introduction An estimated 34 000-36 000 tons of the herbicide atrazine (ATZ) are used to control weeds in crops including corn, soybeans, and sugarcane each year (1). Simazine (SIM) is * Corresponding author phone: (573)341-4041; fax: (573)341-7217; e-mail:
[email protected]. † University of Missouri-Rolla. ‡ Malcolm Pirnie, Denver, CO. § American Water Works Association. ⊥ Malcolm Pirnie, Santa Monica, CA. | American Water Works Association Research Foundation. 10.1021/es052038n CCC: $33.50 Published on Web 05/05/2006
2006 American Chemical Society
another common triazine herbicide used for protecting crops, including grapes. Propazine is no longer sold in the United States, but remaining stocks are still used occasionally under older labeling protocols. The maximum contaminant levels (MCL) for ATZ and SIM are 3 and 2 µg/L, respectively, as set by the U.S. Environmental Protection Agency (USEPA) (2). These MCLs are based on running annual averages of quarterly finished (treated) samples. While ATZ is classified by the USEPA as “not a likely human carcinogen”, there are concerns about ATZ regarding its potentially adverse developmental and reproductive effects (2). Triazine herbicides biodegrade in the environment to various degradates (3, 4). Dealkylation of ATZ, SIM, and PROP results in deethylatrazine (DEA) and/ or deisopropylatrazine (DIA). Further, dealkylation results in didealkylatrazine (DDA), also known as diaminochloros-triazine (or DACT). While other dechlorinated degradates are formed (e.g., hydroxyatrazine), it is the chlorinated parent and degradates (i.e., ATZ, SIM, PROP, DEA, DIA, and DDA) that have been implicated by the USEPA as exhibiting the potential for disrupting the endocrine systems of mammals, including humans (2). The sum of these six chloro-s-triazines may be denoted as the total chloro-s-triazines (TCT). Specific endocrine-disruption effects cited by the USEPA are attenuation of the luteinizing hormone serge, altered pregnancy maintenance, effects on pubertal development, and alteration of the estrous cycle. While many studies have examined ATZ and the other parent herbicide concentrations, few studies have addressed the occurrence and removal of the combined compounds comprising the TCT. One reason for this is that the degradates are infrequently monitored by standard GC methods due to analytical difficulties (especially with DDA). To estimate the impact of potential regulations based on TCT, it is critical that specific questions are answered with respect to occurrence and control. Control. Treatment technologies for control of synthetic organic chemicals (SOCs), such as TCT, in drinking water can be organized into broad groups: partitioning processes that separate or concentrate SOCs, such as physisorption on activated carbon or other sorbents (5-8), membrane separation (9), ion exchange, and air stripping. Transformation processes can chemically modify the parents, such as oxidation with disinfectants such as chlorine (10, 11), chlorine dioxide, ozone (12-14), and peroxide, direct or indirect photolysis with UV, catalyzed oxidation, advanced oxidation with hydroxyl-radical-mediated reactions, or biofiltration (15, 16). Transformation processes have the advantage of generally having no residual stream. However, because SOCs are rarely mineralized (i.e., completely converted to inorganic species) by drinking water treatment, byproducts are formed from the parent compounds that may also have toxicity or adverse properties. For example, atrazine is converted during ozonation to various oxidation byproducts, including DEA, DIA, and DDA, as well as dechlorinated hydroxylated byproducts such as hydroxyatrazine (CAS 2163-68-0), deethylhydroxyatrazine, and deisopropylhydroxyatrazine. The most common adsorbent used in drinking water treatment is activated carbon, which can be applied as powdered activated carbon (PAC) or granular activated carbon (GAC). PAC is most commonly applied to the front end of a drinking water treatment plant and comes to partial equilibrium with SOCs in the water before being removed by rapid sand filters after several hours. When GAC is used in a drinking water treatment plant it is usually in a GACVOL. 40, NO. 11, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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capped rapid sand filter or in a postfiltration GAC contactor. GAC has the advantage of achieving higher capacities than PAC, based on contact dynamics. PAC has the advantage of being able to have increased or decreased dosages depending on treatment needs and objectives and in response to variations in influent water quality or pesticide concentrations. Purpose. The purpose of this study was to determine the occurrence and removal of TCT (and its individual constituents) in raw (source) and finished (treated) drinking waters at full-scale drinking water treatment plants in the United States. This paper reports results that utilized a new gas chromatography/mass spectrometry (GC/MS) method with dual-cartridge solid-phase extraction that provided low detection levels for all six TCT compounds, including DDA. A key question of interest in this study was to what extent does DDA contribute to the TCT and how well is the TCT (including DEA, DIA, and DDA) removed by conventional treatment processes. Both absolute concentrations as well as ratios of degradate-to-ATZ or TCT-to-ATZ were analyzed.
Site Selection and Sampling Samples were collected over a 2-year period from water utilities in regions of the United States where atrazine is commonly used. Specifically, water samples were collected from seven USGS hydrologic watersheds, designated Hydrologic Unit Code (HUC) 2, 3, 4, 5, 7, 8, 10, 11, and 12 representing the Mid-Atlantic, South Atlantic Gulf, Great Lakes, Ohio, Upper Mississippi, Lower Mississippi, Missouri, Arkansas-White-Red, and Texas-Gulf watersheds, respectively. In 2003, approximately 6000 samples were collected from 38 water sources at 33 water utilities. Surface water sources were utilized by 92% of these water utilities. PAC was used by 76% of the participating utilities, primarily for the control of taste and odor (though sometimes for control of pesticides). In 2004, approximately 4000 samples were collected at 47 utilities. A majority of the utilities were surface water sources, and 77% utilized PAC. In both years, the utilities represented a broad variety of plants with respect to treatment strategies, population, and water source. Service populations ranged from fewer than 500 to more than 1 million people with approximately one-half of the utilities serving a population of 10 000-50 000 people. In all cases, paired raw and finished water samples were taken (as grab samples) at each plant at approximately the same time using 250-mL amber glass bottles with Teflonlined caps. No allowance was made to hydraulically couple the raw and finished samples by allowing one plant residence time between samples. All samples were analyzed for ATZ concentrations by enzyme-linked immunoassay (ELISA) using the EPAapproved Beacon test kit in 2003 and the Abraxis test kit in 2004 by McGuire Environmental Consultant staff in Colorado. The results of the ELISA testing are reported elsewhere (17, 18). Ten percent of all samples were randomly selected and shipped to the Environmental Research Center (ERC) at the University of MissourisRolla (UMR). There they were analyzed by gas chromatography/mass spectrometry (GC/ MS) using a method that determines both parent chloros-triazines and their primary chlorinated degradates. The GC/MS-based results concerning raw and treated waters for both parent and degradate chloro-s-triazines are presented in this paper.
Materials and Methods Chemicals. HPLC-grade methanol was obtained from Fisher Scientific (Fair Lawn, NJ). All other chemicals (including ammonium acetate, ammonium hydroxide, methylene chlo3610
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ride, and acetone) were at least reagent grade and also obtained from Fisher Scientific. One hundred fifty milligram Oasis MCX solid-phase extraction (SPE) cartridges were obtained from Water (Milford, MA), and 500-mg ENVI-carb graphite carbon cartridges were obtained from Supelco (Bellefonte, PA). Chloro-s-triazine standards for ATZ (CAS 1912-24-9), SIM (CAS 122-34-9), PROP (CAS 139-40-2), DEA (CAS 6190-65-4), DIA (CAS 1007-28-9), DDA (CAS 3397-62-4), and terbuthylazine (TBUT; CAS 5915-41-3) were purchased from Supelco. Deuterated standardssATZ-d5, DEA-d6, SIM-d5, and DIAd5swere obtained from EQ Laboratories (Atlanta, GA). Sample Preparation and Analysis. Analysis of the chloros-triazines utilized a two-cartridge solid-phase extraction (SPE) method for sample concentration, followed by GC/MS in selected ion monitoring (SIM) mode. The method and its validation are described in detail elsewhere (19). SPE utilized an Oasis MCX cartridge, followed by an ENVI-Carb graphite cartridge in a series using a VisiPrep 24-port manifold (Supelco; Bellefonte, PA) and a drop rate of 1 drop per second. Samples were analyzed using an Agilent 6893 series GC with a 5973 mass-selective detector (MSD) and a 7673 sample autoloader (Agilent, Palo Alto, CA). Analyte separation of a 2-µL sample injection was achieved using a HP-5MS capillary column (Agilent, 30-m × 0.25-mm i.d., 0.25-µm film thickness) with helium as the carrier gas, a 225 °C injection temperature, a 84 kPa inlet pressure, and 54 mL/min total gas flow. A temperature ramp consisted of 100 °C ramped to 280 °C at varied rates (19). At least one blank and one check standard sample were analyzed at the beginning and end of each sample set. Approximately 10% of the samples were analyzed in replicate. Sample mass recoveries and spike recovery samples were determined for each sample set, as described elsewhere (Jiang et al., 2005). For all analytes, the standard curves were linear (R2 > 0.99) and recoveries were good (72-104% in DI water and 90-112% in surface water). Deuterated triazine compounds were used as internal standards. Method detection limits in surface water for ATZ, SIM, PROP, DEA, DIA, and DDA were 0.02, 0.01, 0.02, 0.01, 0.01, and 0.01 µg/L, respectively, with recoveries in surface water of 94%, 104%, 103%, 110%, 108%, and 102%, respectively (19). Data were organized, regressed, and queried using Microsoft Access database software. Other statistical analyses were conducted using Statistica (version 5.0, Statsoft, Tulsa, OK). Box-and-whisker plots were generated using Statistica and are presented in this paper. The box represents the 5thand 95th-percentile values, and the symbol within the box represents the 50th-percentile (or median). The whiskers on the plots represent the maximum and minimum values.
Results and Discussion Concentration Overview. For both raw and finished water samples, Table 1 presents parent, degradate, and TCT concentration statistics (e.g., mean, confidence intervals, and percentiles) for GW-only systems and for combined SW and MIX (SW + GW) systems. Over the 2-year study period, ATZ concentrations in raw water ranged from undetected to a maximum 84 µg/L (Table 1). This high value was confirmed and caused by a storm event after ATZ application in a sugarcane-growing region. Each of ATZ’s primary chlorinated degradatessDEA, DIA, and DDAswere detected with maximum concentrations of 2.76, 1.50, and 0.98 µg/L, respectively (Table 1). Both SIM and PROP were detected with maximum concentrations of 11.95 and 1.20 µg/L, respectively. In finished waters, ATZ concentrations ranged from undetected to a maximum of 5.70 µg/L. This maximum value corresponded to the same plant and sampling time as the maximum raw water sample. All three degradates were detected in at least some finished drinking waters with
TABLE 1. Raw and Finished Water Chloro-s-triazine and Total Chloro-s-triazine (TCT) Concentrations in Surface Water (means were used for calculations for replicate samples) concentration (µg/L)
ratio of concentration
source
ATZ
DEA
DIA
DDA
SIM
PROP
TCT
DEA/ATZ
DIA/ATZ
DDA/ATZ
TCT/ATZ
n (no. of sample)a mean min 5th % 25th % 50th % (median) 75th % 95th % max n (no. of sample)a 50th % (median) max
SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX GW only GW only GW only
373 1.11 0.00 0.03 0.14 0.32 0.81 3.50 84.0 15 0.07 0.66
373 0.21 0.00 0.00 0.05 0.10 0.23 0.92 2.76 15 0.00 0.60
373 0.12 0.00 0.00 0.00 0.04 0.14 0.46 1.50 15 0.00 0.30
raw water 373 373 0.05 0.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.04 0.07 0.25 0.24 0.98 12.0 15 15 0.00 0.00 0.26 0.26
373 0.01 0.00 0.00 0.00 0.00 0.00 0.05 1.20 15 0.00 0.00
373 1.63 0.00 0.05 0.31 0.65 1.38 4.64 89.6 15 0.07 1.64
359 0.42 0.00 0.00 0.15 0.26 0.50 1.27 4.56 9 0.73 2.11
359 0.27 0.00 0.00 0.00 0.06 0.28 1.12 11.0 9 0.00 0.45
359 0.19 0.00 0.00 0.00 0.00 0.10 1.29 3.25 9 0.00 3.25
359 2.17 1.00 1.09 1.32 1.61 2.48 4.77 17.7 9 2.48 5.75
n (no. of sample)a mean min 5th % 25th % 50th % (median) 75th % 95th % max n (no .of sample)a 50th % (median) max
SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX SW and MIX GW only GW only GW only
356 0.45 0.00 0.00 0.09 0.20 0.48 1.74 5.70 13 0.05 0.11
356 0.12 0.00 0.00 0.03 0.07 0.14 0.46 1.32 13 0.04 0.19
356 0.04 0.00 0.00 0.00 0.00 0.07 0.20 0.76 13 0.00 0.12
finished water 356 356 0.05 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.03 0.05 0.29 0.14 0.89 0.48 13 13 0.00 0.00 0.36 0.03
356 0.01 0.00 0.00 0.00 0.00 0.00 0.03 0.10 13 0.00 0.01
356 0.73 0.00 0.02 0.19 0.41 0.90 2.58 7.68 13 0.16 0.71
326 0.40 0.00 0.00 0.15 0.27 0.53 1.00 8.0 9 1.11 1.90
326 0.17 0.00 0.00 0.00 0.00 0.13 0.77 6.0 9 0.00 0.64
326 0.35 0.00 0.00 0.00 0.00 0.11 1.76 14.0 9 0.00 3.33
326 2.22 1.00 1.04 1.30 1.60 2.33 4.71 33.0 9 2.33 6.45
a
On the basis of means of replicates counted as a single sample.
maximum concentrations of 1.32, 0.76, and 0.89 µg/L, respectively. SIM and PROP were both detected in some water samples with maximum concentrations of 0.48 and 0.10 µg/ L, respectively. Only 5% and 1% of individual raw and finished water samples had ATZ concentrations that exceeded the 3.0 µg/L MCL. The TCT ranged from undetected to 89.6 µg/L in raw water and undetected to 7.7 µg/L in finished water. Review of the data in Table 1 shows that ATZ was, on average, the dominant species contributing to the TCT with DEA as the second most important triazine. Full analyses of the relative concentrations of triazines contributing to the TCT are presented below. Concentrations in Raw Water by Source. The raw water results were binned into three groups, based on their source waters, for comparison. These groups included surface water only (SW), groundwater only (GW), or a mix of surface water and groundwater (MIX). GW included plants that may have drawn groundwater from deep wells as well as plants utilizing alluvial aquifers. It should be noted that alluvial aquifers may be under the direct influence of surface-water sources, especially if they are located along a surface-water source that provides direct recharge. MIX plants are those that utilize both SW and GW for their source supply. No distinction was made for the percentage of either SW or GW or temporal variation, which could have shifted between SW or GW sources exclusively at certain times. The data showed that the GW systems had the lowest concentrations of all triazines and TCT. For example, in raw waters, median ATZ concentrations were 0.07 µg/L for GW compared with 0.32 for SW and MIX sources (Table 1). Similarly, in finished waters, median ATZ concentrations were 0.05 µg/L for GW compared with 0.20 µg/L for SW and MIX sources (Table 1). For the remaining analyses in this manuscript, the combined SW and MIX plant data were analyzed (and the GW plants were excluded). This was to focus analysis on the utilities that have more significant ATZ and other triazine concentrations.
Concentrations by Utility Service Population and Watershed. Concentration data was binned or grouped by the number of customers or service population for each utility as 100k customers. The data were plotted for all study compounds and TCT in raw waters as shown in Figure 1. For raw waters, there were no significant differences (R ) 0.05) between population groups for any triazine or TCT concentrations with three exceptions: TCT and DIA were greater in >100k than 100k) than for either of the small systems groups. No differences (R ) 0.05) were observed between groups for DDA. The analysis showed that the highest ATZ and TCT concentrations were generally observed in the Ohio River watersheds (HUC 5), the Lower Mississippi watershed (HUC 8), and the Missouri watershed (HUC 10). The smallest ATZ and TCT concentrations were observed in the South Atlantic Gulf watershed (HUC 3) and the Texas-Gulf watershed (HUC 12). These trends are consistent with regions in which the highest ATZ use occurred for crops including corn (HUC 10 and 5) and sugarcane (HUC 8). The Lower Mississippi watershed (HUC 8) also serves as the ultimate drainage for the entire Midwestern United States. These patterns are in general agreement with Thurman et al. (20). Temporal Variations. Temporal variations in ATZ, other triazine, and TCT concentrations were examined by plotting the data binned by quarter for the study period (Figure 2). VOL. 40, NO. 11, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Triazine concentrations in raw (top) and finished (bottom) surface waters binned by utility service population. Plots show median (symbol), 5th- and 95th-percentile values (box), and min/max (whiskers). Any maximum values off the chart are indicated numerically at the top. In the initial quarter of the study (January-March 2003), the 95th-percentile concentrations for all compounds were less than 0.5 µg/L. When the growing season for corn was reached during April-June, ATZ was applied throughout many of the watersheds which led to a large increase in the median and 95th-percentile ATZ concentrations (Figure 2) as is commonly observed (21). Rain events cause surface runoff (as well as infiltration into groundwater), causing transport of the applied parent compound into these surface-water supplies. Between the 2nd and 3rd quarters, ATZ, DEA, and TCT decreased significantly (R ) 0.05) while DDA increased as more DEA was converted to DDA. Overall, the 2004 ATZ concentrations were relatively low in comparison to the regulatory limits (data not shown). ELISA tests for ATZ, conducted as part of this study, offer more detailed examination of the ATZ trends (17, 18). This decreasing trend between 2003 and 2004 may suggest a declining ATZ problem for water utilities with respect to compliance. The reason for this decline may be due to stricter labeling requirements, better education of ATZ users in the agriculture industry, and more effective regulation in general. Trends in finished water samples were similar to those observed in raw water supplies, with the exception that concentrations were generally lower and, specifically, the high peak concentrations were reduced (Figure 2). For example, important significant differences (R ) 0.05) observed in finished water included the increase in ATZ, DEA, 3612
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and TCT between the 1st and 2nd quarters and the decrease in ATZ and TCT and increase in DDA between the 2nd and 3rd quarters. No statistically significant differences (R ) 0.05) in DIA were observed throughout the year in finished water. Overall, no ATZ samples exceeded the 3 µg/L MCL for ATZ in the first (January-March) or fourth (OctoberDecember) quarters and relatively few exceeded in the second (April-June) and third (July-September) quarters. Specifically, only six samples in the 2-year study had ATZ concentrations in finished drinking water that were greater than 3 µg/L (Figure 2). Again, these samples would not be likely to trigger a violation of the MCL because they would be averaged with three other quarters to calculate an annual average. Degradate Concentrations to ATZ Ratios. A key objective of this study was to determine the relative and absolute concentrations of degradates of ATZ (i.e., DEA, DIA, and DDA) and assess their contribution to the TCT. Because the TCT concentration may potentially be used as a regulatory endpoint based on endocrine disruption, it is of critical concern to ascertain the importance of each compound with respect to the TCT. For all paired data, ratios of the three degradates or TCT relative to ATZ are presented in Figure 3, grouped or binned into quarters. For all of the ratios calculated for Figure 3, only data sets with ATZ concentrations greater than 0.2 µg/L were included to eliminate very high ratios simply due to dividing by low ATZ concentrations. Overall for raw water, the DEA/ATZ ratio was significantly greater (R ) 0.05) than
FIGURE 2. Triazine concentrations in raw surface waters (top) and finished (treated) waters (bottom) binned by quarter for 2003 and 2004. Plots show median (symbol), 5th- and 95th-percentile values (box), and min/max (whiskers). Any maximum values off the chart are indicated numerically at the top. either the DIA/ATZ or DDA/ATZ ratios (which were not significantly different). In finished water, the DEA/ATZ and DDA/ATZ ratios were both significantly greater (R ) 0.05) than the DIA/ATZ ratio (but not significantly different from each other (R ) 0.05)). In fact, for each quarter of the study, the median raw water DEA/ATZ ratio (denoted previously as the DAR for “deethylatrazine-to-atrazine ratio” (4)) was greater than the corresponding percentile values for the DIA/ATZ or DDA/ATZ ratios (Figure 3). The fact that the DEA/ATZ is highest supports that ATZ preferentially loses its ethyl moiety as compared with the isopropyl moiety in the environment as has been seen or suggested by others (22-25). Analysis of the 95th-percentile raw water ratios, however, shows that the DDA/ATZ exceeds the DEA/ATZ late in the year. This observation would result from DEA (and DIA) converting to DDA in the environment throughout the growing season coupled with some persistence of the DDA. Little has been published on DDA in the environment. There was a concern initially that DDA might be a major contributor to the TCT if it were to degrade very slowly and, hence, would build up in the environment. The results of this study show that the median DDA/ATZ ratios remain well below unity (that is, ATZ . DDA) in all cases (Figure 3). However, in greater than 5% of the samples (i.e., at the 95th
percentile), the DDA/ATZ ratio is greater than unity (except during the application season (April-June)). Overall, DDA concentrations tend to be low, which suggests that DDA eventually degrades to other byproducts. The significance is that the buildup of DDA, and its significant impact on a potential TCT regulatory endpoint, does not appear to be a major issue from a regulatory standpoint. The median and 95th-percentile values for TCT/ATZ in raw waters ranged from 1.4 to 2.7 and 3.9 to 6.3, respectively (Figure 3). In finished water, the median and 95th-percentile values for TCT/ATZ ranged from 1.4 to 2.2 and 3.2 to 6.7, respectively, over the four quarters (Figure 3). These ratios can be used as a preliminary basis for the prediction of TCT concentrations based on the large volume of ATZ occurrence data available from many different and varied studies. Specifically, ATZ concentrations in various watersheds and conditions and over various previous time periods can be multiplied by an assumed TCT/ATZ ratio (based on quarterly data in Figure 3) to develop initial estimates of historic TCT concentrations. Many factors could impact the assumed ratio, including residence time, dilution, infiltration from GW sources, and average temperatures, with a resultant impact on the estimated maximum, median, and other parameters. Further, it should be noted that as degradate/ATZ or TCT/ATZ ratios increased in the third quarter (Figure 3) (and potentially in the fourth and first VOL. 40, NO. 11, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Ratios of degradate or TCT to ATZ in raw water (top) and finished (treated) water (bottom). (Data for raw ATZ concentrations less than 0.5 ppb were excluded.) Plots show median (symbol), 5th- and 95th-percentile values (box), and min/max (whiskers). Any maximum values (and two 95th-percentilve values) off the chart are indicated numerically at the top. quarters), the ATZ concentrations tended to decrease, resulting in an overall declining or stable absolute TCT concentration late in the season (Figure 2). This analysis showed that watersheds that are not exceeding a 3 µg/L concentration of ATZ would likely not exceed a potential 37.5 µg/L level of concern for TCT (based on a 90-day average). In general, these data suggest that for most utilities the potential level of concern on TCT may impose no significantly greater concern about compliance than that which exists about compliance for ATZ with its current MCL. Removal of Triazines in Drinking Water Treatment Plants. Degradate-to-ATZ Ratio. There was no significance difference (R ) 0.05) between the DEA/ATZ ratio in raw and finished water overall, suggesting that DEA and ATZ may, on average, be similarly removed from water treatment plants. The DIA/ATZ, however, was significantly less (R ) 0.05) in finished water compared with raw water, suggesting potentially more effective removal of DIA compared with ATZ. Conversely, the DDA/ATZ was significantly greater (R ) 0.05) in finished water compared with raw water, suggesting less effective removal of DDA compared with ATZ. Activated Carbon. Removal of a SOC during water treatment may be important both in terms of mass removal in micrograms per liter as well as percentage removal. Mass (concentration) and percentage removals were calculated for all raw/finished sample pairs. In the calculations of 3614
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removal percentages below, any systems with less than 0.2 µg/L of a compound in the raw water were excluded to limit the bias of the division by small concentrations. Mass removal data showed median removals ranged from 0 to 0.5 µg/L (except PROP) (Figure 4). GAC achieved removals up to 84 µg/L for ATZ but less that 2.5 µg/L for all other compounds. Only a few differences between treatment categories were significant. For mass removals, PAC provided significantly greater (R ) 0.05) removals than NONE or GAC + PAC. Similarly GAC + PAC provided significantly greater (R ) 0.05) mass removal than using no carbon. Median percent removals ranged from near 0% to 100% (Figure 4). PAC provided significantly greater removal (R ) 0.05) than no carbon (NONE) for ATZ. PAC also provided significantly greater removal (R ) 0.05) than GAC + PAC for DEA. Overall, these data suggest that a wide range of removals are possible for each process, depending on the specific process conditions and source water characteristics. Generalizations with respect to the effectiveness of a particular process (i.e., PAC, GAC, or GAC + PAC) are clearly difficult and may not prove valid. In comparing systems that used NONE, PAC, GAC, and GAC + PAC, some examples of apparent “negative” removals were observed for all compounds with all systems (Figure 4). In a typical water treatment plant utilizing PAC, the PAC dose is varied in response to variations in raw water ATZ concentrations. The results of this study show that generalities
FIGURE 4. Removal (µg/L) (top) and percent (bottom) of triazines from surface water for utilities using no carbon, GAC only, PAC only, or both GAC and PAC. (Percent removals for raw triazine concentrations less than 0.5 µg/L were excluded.) Plots show median (symbol), 5th- and 95th-percentile values (box), and min/max (whiskers). Any maximum values (and two 95th-percentilve values) off the chart are indicated numerically at the top. regarding plant performance, with respect to ATZ (or other SOC) removal in a plant that “uses PAC”, must be viewed cautiously with the knowledge that the PAC dosing may vary significantly and result in removals ranging from low (or negative) to very high within the same plant. Apparent “negative” ATZ (or other SOC) removal can occur in a drinking water treatment plant when raw and finished water samples are collected at the same time rather than accounting for the residence time within the plant. These considerations are important when interpreting the PAC (and other) results from the full-scale studies presented in this paper. Insufficient PROP concentrations to perform meaningful percent removal calculations were observed in any sample pairs. The removal data for both PAC- and GAC-only systems show that PAC and GAC were both capable of high mass removals (e.g., >5 µg/L) of ATZ and TCT. Removal of all compounds by PAC and GAC was observed (micrograms per liter except for DDA in GAC-only systems due to the lack of significant DDA in the raw waters). An advantage of GAC is that it is always in place in the process and reduction and control of very high spike concentrations of ATZ (or other SOCs) as observed in this study (i.e., 84 µg/L ATZ). Ozone. Ozone was utilized in three of the plants studied. In two of these plants, the raw water ATZ and other triazine
concentrations were too low to provide meaningful insight into the effects of ozone. In the third plant, however, the raw and finished water sample concentrations of the study compounds (which used no activated carbon) were sufficient to provide insight as to the effects of ozone on triazines. Influent ATZ concentrations for the plant ranged from approximately 0.3 to 1.8 µg/L (data not shown). For each of the seven sample pairs, the ATZ concentration decreased significantly between the raw and finished water. The degradation of ATZ led to a slight increase in DEA concentrations in four of the seven raw and finished sample pairs. With one exception, DIA and DDA were not detected in the finished water samples. An increase in DIA of from
