Grantee Research Project Results
Final Report: Development of a New, Simple, Innovative Procedure for the Analysis of Bromate and Other Oxy-Halides at Sub-ppb Levels in Drinking Water
EPA Grant Number: R825952Title: Development of a New, Simple, Innovative Procedure for the Analysis of Bromate and Other Oxy-Halides at Sub-ppb Levels in Drinking Water
Investigators: Weinberg, Howard S. , Singer, Philip C.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 1997 through August 31, 1999 (Extended to December 31, 2000)
Project Amount: $198,460
RFA: Drinking Water (1997) RFA Text | Recipients Lists
Research Category: Water , Drinking Water
Objective:
Bromate is a disinfection by-product (DBP) that has mostly been associated with ozonation of drinking waters containing background bromide. It has been identified more recently as a contaminant in sodium hypochlorite, which is used in the chlorination process. This project evaluated a relatively simple analytical methodology to provide the tools for assessing exposure to bromate in drinking water at the 10-6 cancer risk level of 0.05 µg/L. Occurrence data for bromate in the range of 0.05-2 µg/L had been impeded by the lack of sensitivity of existing methodologies. This new analytical methodology provides the U.S. Environmental Protection Agency (EPA) and the water monitoring community with the ability, using existing analytical equipment with simple add-on accessories, to set the criteria for future drinking water regulations by achieving the required sensitivity very easily in oxyhalide analysis. The method is designed for the simultaneous analysis of routine anions as well as other oxyhalide species, including iodate, chlorite, and chlorate. The developed method was applied to a variety of waters in treatment plants that would not otherwise be suspected to contain bromate. In particular, the project targeted ozonation plants with nondetectable bromide in the source water and chlorination plants using liquid hypochlorite known to contain bromate contamination in the feedstocks.
Summary/Accomplishments (Outputs/Outcomes):
A relatively unconventional approach to the analysis of chemical components in drinking water was employed. The optimized method utilizes a high capacity anion exchange column, enabling large injection volumes (up to 1 mL) of samples to be loaded. The resolved oxyhalide species first pass through a conductivity detector and then undergo a postcolumn reaction (PCR) at 60?C with sodium bromide in the presence of nitrous acid generated from sodium nitrite via a chemical suppressor unit. A stable tribromide species is formed and detected by ultraviolet (UV) absorption spectrophotometry at 267 nm. The commonly occurring anions in typical drinking water samples (e.g., chloride, sulfate, phosphate, and nitrate) are invisible to the detector and therefore do not interfere with the UV-PCR chromatography. This method is very sensitive for bromate with a limit of quantitation that has been extended down to 0.05 µg/L and also is very selective. This ion chromatographic-postcolumn reaction method (IC-PCR) also has been optimized for similar sensitive quantitation for the oxyhalides iodate and chlorite. Additionally, with the use of a higher capacity ion exchange column, chlorate also can now be quantified at the submicromolar level. Optimization of the methodology has involved reducing the amount of accessories required to achieve the stated sensitivity in a variety of aquatic media. In effect, the postcolumn reaction now only requires a single anion micromembrane suppressor to produce the required postcolumn reagents in situ.
As a preliminary screening of the method, synthetic waters were prepared to mimic the ionic strength of anion species and organic content of natural organic matter (NOM) present in tap water. This matrix was used to establish analyte retention times. The total number of equivalents contributed from each anionic species in tap water was then calculated to ensure that a column capacity well below its maximum would be achieved for routine analyses with a 1,000 mL sample injection volume. The method was then applied to two specific scenarios of water treatment: (1) ozonated water low in bromide, and (2) hypochlorite treated water.
Many raw water feeds appear to have ambient levels of bromate at the 0.5 µg/L level. Ozonation of such waters that have levels of bromide below detection (< 10 µg/L) can on occasion elevate the bromate level to 2 µg/L. Hypochlorite solutions were quenched of free chlorine immediately at the time of preparation of a 1:10,000 dilution through use of ethylene diamine. IC-PCR analysis of each facility's dilute feedstock indicated bromate present as a contaminant. Reported values reflected a 1 percent relative percent difference (RPD) from replicate analyses of each feedstock sample. Significant levels of chloride mask the measurement of bromate by conductivity at 6.6 minutes. However, the IC-PCR method is ideal in that chloride is not detected by UV, and allows for good chromatographic resolution of bromate from the other oxyhalides. As an example of analysis at one site, bromate concentration was determined as 36 µg/L from the original 15.4 percent solution and a good spike recovery for the analyte was demonstrated at 92 percent. Entering raw water received at this treatment plant was prechlorinated with sodium hypochlorite upstream about 80 miles away at a dose of 0.5 µg/L. However the chlorine residual in the water once reaching the facility was essentially zero. The raw water underwent coagulation, flocculation, and sedimentation, and the clarified water was then treated with a 15.4 percent hypochlorite solution at a dose of 2.5-3.0 µg/L prior to filtration (ammonia was added postfiltration at this facility). The 0.14 (?0.01) µg/L concentration of bromate observed in the raw water is likely attributed to contamination present in the hypochlorite solution used 80 miles upstream. Using the dose information provided and the amount of bromate per gram of free chlorine determined by IC-PCR analysis of the hypochlorite feedstock, a mass balance of 117 percent was achieved based on the actual predicted level of bromate (0.12 µg/L) present in the raw water. As would be expected, the chlorite, bromate, and chlorate levels increased after the addition of hypochlorite. A mass balance of 101-122 percent was calculated between measured and predicted bromate concentrations for this particular sample due to hypochlorite addition. An increase in iodate concentration (up to 4 µg/L) is suspected to be due to the presence of iodide in the water being rapidly oxidized by the treatment process through a hypoiodous acid intermediate. Multiple low-level calibration curves (from 0.05 to 10.0 µg/L) of iodate, chlorite, and bromate in deionized water by IC-PCR showed good linear regression coefficients (r2) of 0.9999, 0.9953, and 0.9999, respectively. A higher level chlorate calibration (up to 150.0 µg/L) measured by conductivity detection, produced a regression coefficient of 0.9973. Spike recoveries obtained for all the target analytes from the real water matrices ranged between 86 and 113 percent.
Depending on the dosage of, and number of points of hypochlorite addition during treatment, the levels of bromate resulting from its usage at the plants surveyed are indicated in the range 0.1-3 g/L. Among 20 plants surveyed using this technique, the average level of bromate contributed by the use of hypochlorite was 0.94 g/L. A mass balance between the levels of bromate in the hypochlorite feedstocks and finished water proved beyond doubt the source of the added contaminant. Iodate and chlorate, which are not currently classified by the EPA as a health concern, also were evaluated by the method. The results do suggest that the level of contamination of bromate in hypochlorite varies across the country with those plants sampled in EPA Region 5 exhibiting the highest levels of contamination. With discussions towards future regulation of bromate in drinking water required to balance risk with the cost of alternative treatment, this finding may seriously impede attempts to regulate bromate closer to 0.05 g/L from its current regulated level of 10 g/L in the United States.
This user-friendly IC-PCR method successfully demonstrates the capability of detecting down to a 0.05 µg/L level of bromate in chlorinated drinking waters. The good chromatographic separation and detection of target oxyhalides by UV-PCR is achieved with the simultaneous analysis of routine anions by conductivity. Nonhazardous materials are utilized, and the PCR setup can be easily adapted to existing IC instrumentation typically found onsite at drinking water facilities. In its current configuration, this method demonstrates another level of diversity for IC in that it offers an additional path for monitoring environmental contaminants that are otherwise below detection by direct analysis.
This method has been demonstrated as a viable technique for utilization in the drinking water industry to assess sub-µg/L levels of bromate in waters treated by ozone and/or hypochlorite. The PCR method conformed to quality control protocols generating bromate recoveries from spiked matrices, both aquatic samples and diluted hypochlorite feedstocks, in the average range of 80-99 percent. The average spike recoveries obtained for chlorite in water and dilute hypochlorite matrices ranged 75-123 percent. Iodate recovery from water matrices averaged 93 percent. The few outliers for chlorite and iodate observed for some of the spike recoveries were attributed to a unique property present in the corresponding sample matrix that interfered with the PCR. The practical quantitation limit (PQL) of target oxyhalides established for the method utilizing UV-PCR detection were 0.06 µg/L for iodate, 0.10 µg/L for chlorite, and 0.05 µg/L for bromate. Samples require no pretreatment prior to analysis other than filtration to remove particulates and the addition of ethylene diamine to quench free chlorine.
The facilities that participated in this study had source waters low in bromide. Treatment processes included ozone followed by hypochlorination and/or chloramination, or hypochlorination alone. The level of bromate contamination in various hypochlorite feedstocks was determined by IC-PCR analysis of quenched dilute solutions. Although dependent on the manufacturer, hypochlorite feedstock solutions were found to contain between 12 and 700 mg bromate per g free chlorine. With most of the water treatment facilities examined averaging a daily free chlorine dose of 3 µg/L, the predicted level in the finished waters analyzed would contribute between 0.06 µg/L and 2.8 µg/L bromate. A mass balance of 101-143 percent was observed for most of the finished waters supplied in the survey, based on the amount of bromate actually measured to the predicted amount that would be contributed from a hypochlorite treatment at a given dose. The level of chlorate found in the water samples due to hypochlorite treatment ranged from 40 to 200 µg/L. Of seven waters analyzed in this survey, five produced reasonable mass balances for chlorate ranging from 50-182 percent. Some error may be attributed to the reported dose information provided by the facility. The value may have represented a daily average, established from minimum and maximum doses that varied according to the flow rate of the water passing through the system within that day. Also, the hypochlorite feedstock sample provided might not have been representative of the feedstock solution used for treatment at the time the samples were collected.
Bromate contamination to finished waters via treatment with hypochlorite is a reasonable concern with regard to proposed drinking water regulations in the United States. Although chlorine gas will most likely not contribute bromate to finished water, its use has operational risks that are not beneficial to water treatment facilities. Modifications to the manufacturing process of hypochlorite solutions might be able to minimize the presence of bromate contamination. A source of salt containing a very low trace of bromide could be used in the electrolysis process, as well as employing different electrolysis cells for hypochlorite manufacture. Time, cost, technology, and economics are major issues of concern to the hypochlorite industry in that water utilities are only a very small portion of their market. Therefore, it might be in the best interest of the drinking water industry to develop a technology for removing bromate from finished waters that have been treated by ozone and/or hypochlorite. A comprehensive study would assess that bromate levels contributed in processes that vary in water quality and treatment. Further bench-scale and pilot-scale studies also would be needed to evaluate a viable bromate removal technology.
Based on the results of the application of this method, the major issue becomes the feasibility of a future, more stringent regulation on bromate (some have suggested 5 µg/L in the short-term) in drinking water. The level of bromate generated from bromide-containing waters that undergo ozonation will vary according to raw water quality and ozone dose. Similarly, the reaction of ozone with carbonate alkalinity or NOM may affect the dose required for inactivation of pathogenic microorganisms. Dissolved ozone and hydroxy radicals existing in the water would be potentially consumed, or scavenged, by carbonate alkalinity and/or NOM, therefore requiring a higher ozone dosage for disinfection. An increase in ozone dose, particularly with a significant presence of bromide, would result in an increased production of bromate. Lowering the ozone dose would reduce bromate levels, but disinfection capability would be sacrificed. Ozonation plants would have to cut bromate formation to less than 2 µg/L to prevent compliance infractions from the subsequent addition of bromate into the drinking water from hypochlorite use. At a 5 µg/L or higher dose of hypochlorite, ozonation would then not be permitted to generate any bromate. Because disinfection credits could not be compromised by reducing the ozone dose, the only long-term solution would be the commercial production of an economically feasible higher grade of liquid hypochlorite feedstock.
Regarding the rule-making process, a proposed lowering of the maximum contaminant level (MCL) for bromate from its current level of 10 µg/L by the EPA involves several issues. The health risks associated with establishing MCL values for DBPs are statistically extrapolated and take into account numerous uncertainty factors. Also, the best available technology must be developed such that it may be uniformly implemented at facilities nationwide. The adoption of stringent MCLs would mean less disinfectant applied and a corresponding increased risk to infectious microorganisms. Consequently, more rigorous disinfection would not only inactivate pathogenic microorganisms but also produce hazardous disinfection by-products. No matter what the source of hypochlorite in the United States, its use as a pre- and/or terminal disinfectant at dosages of between 1 and 5 ppm may impart an additional 1-2 µg/L of bromate into the finished water as demonstrated in this study. This latter finding suggests that any attempt to lower the current MCL for bromate will require the chlorine industry to first reengineer its hypochlorite manufacturing process. Furthermore, the long-term MCL goal of 0.05 µg/L may be unattainable based on the levels often found in raw water.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 4 publications | 2 publications in selected types | All 2 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Delcomyn CA, Weinberg HS, Singer PC. Use of ion chromatography with post-column reaction for the measurement of tribromide to evaluate bromate levels in drinking water. Journal of Chromatography A 2001;920(1-2):213-219. |
R825952 (2000) R825952 (Final) |
Exit Exit |
|
Weinberg HS, Yamada H, Joyce RJ. New, sensitive and selective method for determining sub-μg/l levels of bromate in drinking water. Journal of Chromatography A 1998;804(1-2):137-142. |
R825952 (1998) R825952 (1999) R825952 (2000) R825952 (Final) |
Exit Exit |
Supplemental Keywords:
drinking water, exposure, risk, analytical methods., RFA, Scientific Discipline, Water, Environmental Chemistry, Drinking Water, Environmental Engineering, monitoring, public water systems, oxy-halides, animal model, disinfection byproducts (DPBs), treatment, bromate formation, brominated DPBs, carcinogenicity, chlorine-based disinfection, anion chromatographic resolution, tribromide ion, DBP risk management, water quality, drinking water contaminants, regulationsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.