Environ. Sci. Technol. 2005, 39, 4996-5004
Development of U.S. EPA Method 527 for the Analysis of Selected Pesticides and Flame Retardants in the UCMR Survey BARRY V. PEPICH,* BRAHM PRAKASH, MARK M. DOMINO, AND TERI A. DATTILIO Shaw Environmental, Inc., 26 W. Martin Luther King Drive, Cincinnati, Ohio 45268 DAVID J. MUNCH U.S. EPA Office of Ground Water and Drinking Water, 26 W. Martin Luther King Drive, Cincinnati, Ohio 45268 ED K. PRICE Teledyne Tekmar, 4736 Socialville Foster Road, Mason, Ohio 45040
Method 527 was developed to address the occurrence monitoring needs of the U.S. Environmental Protection Agency (EPA) under its second unregulated contaminant monitoring rule (UCMR 2). This method includes a wide range of semivolatile organic contaminants, including pesticides that were deferred during the first UCMR, flame retardants, and pyrethroid pesticides. This paper discusses the rationale for selection and inclusion of the various contaminants included in Method 527 and describes the challenges associated with developing analytical methods that will be used for the occurrence monitoring of such a diverse group of organic molecules. Method 527 employs solid-phase extraction with analysis by gas chromatography/ mass spectrometry (GC/MS). The final method preservation scheme requires the storage of samples in amber bottles buffered at pH 3.8 using citric acid to prevent degradation from acid-catalyzed hydrolysis and from UV light. Citric acid is also an effective antimicrobial reagent, preventing this mode of loss during storage. Ethylenediaminetetraacetic acid (EDTA) is added to remove transition metals such as copper, which was determined to degrade target analytes upon storage. Finally, free available chlorine (FAC), which is present in many finished waters and found to degrade a number of the targets, is removed using ascorbic acid. The final method meets all of the EPA UCMR survey requirements for sample storage, precision, accuracy, and sensitivity and will be proposed for use under the UCMR 2.
Introduction The Safe Drinking Water Act, as amended in 1996, required the U.S. Environmental Protection Agency (EPA) to establish a program for the determination of contaminants that are priorities for future regulation (1). In response to this * Corresponding author phone: (513)569-7439; fax: (513)569-7837; e-mail:
[email protected]. 4996
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mandate, the EPA worked with stakeholders to develop the contaminant candidate list (CCL 1), a list of the 34 highestpriority contaminants and contaminant groups, and established a means of collecting occurrence data under the unregulated contaminant monitoring rule (UCMR) (2, 3). Through active participation by the U.S. water industry, the EPA has collected valuable occurrence data since UCMR sampling commenced in 2001 that will be used to make regulatory decisions on the CCL 1 contaminants. The EPA will soon propose the design for the second UCMR cycle (UCMR 2). In conjunction with the proposed rule, the EPA advanced a new list of 25 contaminants for monitoring (CCL 2). This list was compiled from a broad list of over 200 contaminants that were selected based on five criteria: (i) compounds identified as CCL 1 occurrence priorities without acceptable analytical methods; (ii) contaminants that were monitored under the UCMR 1 screening survey that require additional information; (iii) priority pesticides initially identified during CCL 1 that were “deferred”; (iv) endocrine disrupters for which little information was available for during the development of the CCL 1; and (v) other emerging contaminants based on new occurrence and/or health research since the development of CCL 1. This list was further pared down to 127 contaminants based on compounds that were registered for use in the U.S. that had available analytical standards and potentially suitable methods. To expedite the regulatory process, the EPA initiated parallel efforts in analytical method development and in prioritization of the 127 contaminants based on available health effects research. The first step in the method development process was to divide the 127 contaminants into groups based on their solubility properties and analytical techniques. A total of 45 pesticides and flame retardants were identified as potential candidates for inclusion in a UCMR 2 gas chromatography/mass spectrometry (GC/MS) method, EPA Method 527. Included in the list were a number of deferred pesticides, synthetic pyrethroids, and flame retardants. Flame retardants are a broad group of brominated organic compounds used in many applications, including plastics, electronic circuits, textiles, and clothing. Compounds that were considered for inclusion in EPA Method 527 include hexabromocyclododecane (HBCD), polybrominated biphenyls (PBBs), and polybrominated diphenyl ethers (PBDEs). Each of these subgroups are classified as “additive” flame retardants because they are not chemically bonded to the plastic, thus making them more likely to leach out over time. The families of PBB and PBDE flame retardants each contain 209 congeners. HBCD is a mixture of three isomers (4, 5). Of these three subgroups, PBDEs have been studied the most extensively because of their widespread use and because of concern that their toxicological endpoints may act as thyroid disrupters and/or potentially cause neurodevelopmental deficits and cancer (6). They are ubiquitous contaminants that have been found throughout the environment (7-11), in our food chain (12-17), and in human tissue and breastmilk (18, 19). In a recent review of PBDE occurrence data dating back as far as 1970, Hites concluded that PBDE concentrations are doubling in our environment and in the human population approximately every 4-6 years and that levels in the U.S. are much higher than those in Europe (20). Pyrethroids are a family of pesticides that are structurally similar to pyrethrum, a natural extract of flowers (21). As a group, they are acute neuorotoxicants that have strong insecticidal activity yet relatively low mammalian toxicity 10.1021/es050374y CCC: $30.25
2005 American Chemical Society Published on Web 05/24/2005
(22). The first synthetic pyrethroid, allethrin, was introduced in 1949 (23). Since then, research has focused on synthesizing structurally modified pyrethroids with improved photostability and insecticidal efficacy. By 1995, pyrethroids were second only to organophosphorus pesticides in world economic market value (24). Developing a method for use in the UCMR 2 survey places stringent requirements on method robustness and data quality because the method will be employed by a wide range of laboratories and the data will be used by the EPA to support regulatory decisions. This article describes the research that was necessary to meet these requirements for Method 527, including the development of a suitable extraction procedure for this wide range of analytes, ensuring adequate preservation of method analytes from microbial and chemical degradation during sample storage, and steps that were undertaken to improve the reliability and robustness of the method. The final method contains 7 of the 25 contaminants proposed for monitoring under the UCMR 2 based on health effects analysis and prioritization but has a much wider potential scope that may be useful for laboratories interested in collecting reliable data on some of these emerging contaminants.
Experimental Section Chemical and Standard Materials. The following method analytes were obtained as a special order from AccuStandard, Inc. (New Haven, CT); amitrole, atrazine, bifenthrin, bromacil, chlorpyrifos, deltamethrin, desethyl atrazine (DEA), desisopropyl atrazine (DIA), dicofol, dimethoate, esbiol, esfenvalerate, fenamiphos, fenvalerate, 2,2′,4,4′,5,5′-hexabromobiphenyl (PBB-153), 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153), hexazinone, kepone, malathion, mirex, nitrofen, norflurazon, oxychlordane, parathion, phenothrin, 2,2′,4,4′,5pentabromodiphenyl ether (BDE-99), 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100), permethrin, prometryn, propazine, resmethrin, terbufos-sulfone, tetramethrin, 2,2′,4,4′tetrabromodiphenyl ether (BDE-47), thiobencarb, and vinclozolin. The target analytes, allethrin, cyfluthrin, cypermethrin, and hexabromocyclododecane (HBCD), were purchased from Fluka (Buchs, Switzerland). Thiazopyr and ethofenprox were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). An internal standard solution of acenaphthene-d10, phenanthrene-d10, and chrysene-d12 and a surrogate standard solution of 1,3-dimethyl-2-nitrobenzene, triphenyl phosphate, and perylene-d12 were obtained from Accustandard, Inc. (New Haven, CT). The reagents used in the dechlorination studies included L-ascorbic acid (99+% grade) ACS Certified from SigmaAldrich (Milwaukee, WI), sodium sulfite (98% grade) from EM Science (Gibbstown, NJ), sodium thiosulfate (>99% grade) from Fisher Scientific (Pittsburgh, PA), and glycine (99% grade) from Sigma-Aldrich. The buffers investigated included potassium dihydrogen citrate, sodium hydrogencitrate sesquihydrate, and Trizma pre-set crystals at pH 7 and 9, all from Sigma-Aldrich. Ethylenediaminetetraacetic acid trisodium salt (Na3EDTA) (97%) was obtained from Sigma-Aldrich, and a concentrated solution of CuSO4 was prepared from cupric sulfate (CuSO4‚ 5H2O) (99%) obtained from Fisher Scientific (Pittsburgh, PA) in reagent water that was used to fortify the reagent water samples to yield a Cu++ concentration of 1.3 mg/L for the transition-metal studies. Anhydrous sodium sulfate, 5-7 g (ACS certified), suitable for pesticide residue analysis from Fisher Scientific (Pittsburgh, PA) was used to dry the extracts. Reagent water was obtained using a Millipore MilliQ Plus TOC system. The solvents included methanol, ethyl acetate (EtOAc), and methylene chloride (CH2Cl2), all obtained from Burdick & Jackson (Muskegon, MI).
Instrumental Conditions. Detailed instrumental conditions are described elsewhere (25). Briefly, extracts were analyzed on a Hewlett-Packard Gas Chromatograph/Mass Selective Detector (GC/MSD) System (model 6890/5973, Wilmington, DE) equipped with a HP model 7683 autosampler and a standard split/splitless injector. A 1-µL splitless injection was made into a 2-mm i.d. quartz liner. The compounds were separated using a DB-5MS fused silica capillary column (30 m × 0.25 mm i.d. × 0.25 um film thickness) obtained from J&W Scientific, Inc. (Folsom, CA). The compounds were quantitated using an internal standard calibration with the MS operating in full scan mode. Sample Extraction. The extraction efficiencies were evaluated for six different solid-phase extraction (SPE) media. The C18 SPE disks (47 mm), styrenedivinylbenzene (SDVB) Reverse Phase Sulfonate (RPS) disks (47 mm), Abselut cartridges (10 cm3/60 mg), and the SDVB disks (47 mm) were all obtained from Varian (Palo Alto, CA). Oasis HLB cartridges (6 cm3/200 mg) were obtained from Waters (Milford, MA), and Strata cartridges (6 cm3/200 mg) from Phenomenex (Torrance, CA). Extraction efficiency studies were conducted by fortifying a 1-L aliquot of unbuffered reagent water with the target analyte and surrogate compounds at 5.0 µg/L. Because these studies were only for preliminary assessment of extraction efficiency, preservation reagents were omitted and samples were extracted immediately. All of the SPE materials were conditioned according to the manufacturers’ recommendations. Additional information regarding the elution conditions are provided in Table 2 below. The final extraction conditions used to collect the storage stability and method performance data involved collecting a 1-L aliquot of either reagent water, a local chlorinated surface water, or a hard groundwater (342 mg/L calcium carbonate) in amber glass bottles (Wheaton, Millville, NJ) that contained all of the final method preservatives (9.4 g/L potassium dihydrogencitrate, 0.10 g/L ascorbic acid, and 0.35 g/L of EDTA) prior to fortifying them with target and surrogate compounds at the desired concentration. The entire sample was then passed through the SDVB disks to extract the target analytes, dried by pulling air through the filter for 10 min to remove excess water, and then eluted with a 5-mL aliquot of ethyl acetate, followed by 5 mL of methylene chloride and then 5 mL of 1:1 ethyl acetate/methylene chloride. The extracts were dried by passing them through a column of anhydrous sodium sulfate and concentrated to a volume of slightly less than 1 mL by blowdown with nitrogen. Internal standards were added, and the extracts were diluted to 1 mL with ethyl acetate for analysis. The SDVB cartridges evaluated in this portion of the study were Varian Bond Elute ENV (1000 mg, lot no. 9522003, Palo Alto, CA). Performance Studies. During method development, studies were performed to evaluate the effect of pH, UV light, residual free available chlorine (FAC), and transition metals such as copper on compound stability over time. These studies were performed at room temperature over a 7-day period rather than at the temperature used to store samples to accelerate degradation. The effect of pH was evaluated using four buffers: pH 3.8 potassium dihydrogen citrate (9.4 g/L), pH 5.0 sodium hydrogencitrate sesquihydrate (11.5 g/L), pH 7.0 tris buffer (7.75 g/L of Trizma pre-set crystals), and pH 9.0 tris buffer (6.2 g/L of Trizma pre-set crystals). Potential dechlorinating reagents were evaluated initially in the absence of FAC and included ascorbic acid (100 mg/L), sodium sulfite (100 mg/ L), sodium thiosulfate (100 mg/L), and glycine (250 mg/L). Subsequent evaluations were conducted in the presence of FAC that was prepared by fortifying each 1-L sample with a 100-µL volume of diluted bleach solution so that the final concentration was 6 mg/L (as determined using a Hach test kit). VOL. 39, NO. 13, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Initial Evaluation of Proposed Method 527 Analytesa compound amitrolef dicofol mirex kepone oxychlordane
classification
aminotriazole chlorinated hydrocarbon chlorinated hydrocarbon chlorinated ketone chlorinated phenyl/ nitrophenyl ether thiobencarb chlorobenzyl thiocarbamate vinclozolin dicarboximide BDE-47 flame retardant BDE-99 flame retardant BDE-100 flame retardant BDE-153 flame retardant BDE-209d flame retardant hexabromobiphenyl flame retardant HBCD flame retardant chlorpyrifos organophosphate dimethoate organophosphate fenamiphos organophosphate malathion organophosphate parathion organophosphate terbufos sulfone organophosphate nitrofen nitrophenyl ether allethrinb pyrethroid bifenthrin pyrethroid cyfluthrinb pyrethroid cypermethrinb pyrethroid deltamethrin pyrethroid esbiol pyrethroid esfenvalerate pyrethroid ethofenprox pyrethroid permethrinc pyrethroid c phenothrin pyrethroid fenvaleratec pyrethroid resmethrinc pyrethroid tralomethrine pyrethroid tetramethrinc pyrethroid norflurazon pyridazinone thiazopyr pyridinecarboxylate desethyl atrazine triazine desisopropyl atrazine triazine hexazinone triazine prometryn triazine propazine triazine bromacil uracil
UCMR 2 group iv iv iv iv iv v iv v v v v v iv v v i iii v iv iii iv iv iv iv iv iv iv iv iv iv iv iv iv iv iv iii iii i ii iii iii ii iii
a (i) CCL 1 occurrence priorities without adequate methods; (ii) contaminants monitored from UCMR 1 that require additional information; (iii) deferred pesticides; (iv) endocrine disrupters; (v) emerging contaminants. b Eliminated because the standard contained 4-5 isomers. c Contained two isomers that did not coelute. d Removed because it did not elute at the maximum recommended column temperature. e Coeluted with deltamethryn and had the same spectra. f Removed due to solubility issues.
Antimicrobial and Storage Stability Studies. Microbes have the potential to degrade the target analytes. Chlorination reduces the microbial load to a low level, and acidification of the samples protects analytes from degradation. Citric acid has been reported to be a suitable antimicrobial agent under similar conditions (26). Studies were conducted to test the effectiveness of the preservation scheme in the presence of microbial activity in order to confirm that the preservation scheme inhibited biodegradation and that regrowth of the microbes did not occur after dechlorination. Finished surface (tap) water samples were collected in 1-L sampling bottles and fortified with 4 mL of Ohio River water per liter of sample and with all of the target and surrogate analytes at 5.0 µg/L on day 0 of the study. This was sufficient to challenge the preservation scheme with a large population of microbes. The effectiveness of the biocide was evaluated at 7-day intervals up to 28 days. The samples were stored at the maximum temperatures allowed in the method, which 4998
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are 10 °C for the first 2 days and then 6 °C for the remainder of the study. The biocidal efficacy of the preservation scheme was determined by enumerating culturable microorganisms detected with a heterotrophic plate count method. Colony forming units (CFUs) per milliliter of sample were used as an indication of viable microorganisms.
Results and Discussion Compound Selection and Initial Evaluation. Table 1 summarizes the 45 contaminants that were identified initially as Method 527 candidates together with their reason for inclusion on the list. The flame retardants and the synthetic pyrethroids have many more family members than those that appear in the Table 1 list and warrant additional discussion. The use of PBDEs is significant and increasing. Alaee et al. reported a global production of 106 700 metric tons in 1989 that increased to 203 500 tons in 1999 (5). Despite the potential for 209 distinct PBDE congeners, the synthetic pathway favors substitution, in particular, ring positions resulting in technical products that have a few predominant constituents. Five PBDE congeners were chosen based on their environmental occurrence and on their commercial production. These PBDEs represent the most common tetra-, penta-, hexa- and octabrominated analogues. The PBB family of flame retardants, which also contain 209 congeners, are no longer manufactured in the U.S. or Europe, and therefore are of lesser concern for UCMR 2. When in use, the commercial product, FireMaster, typically contained one primary isomer, 2,2′,4,4′,5,5′-hexabromobiphenyl that comprised 48-68% of the technical grade material (27, 28). This isomer was available as an analytical standard and was therefore included in the method. The last flame-retardant family, HBCD, is used primarily in polystyrene foam used for construction and is manufactured by the bromination of cyclododecatriene (5). Bromination of the double bonds results in three isomers (R, β, and γ) that are not resolvable by GC. It was available as an analytical standard and therefore included in the method. As noted above, pyrethroids have been researched actively and used over the past 50 years, resulting in many commercial products. These pesticides are not persistent, so the list was confined to the pyrethroids that are currently registered for use in the U.S. This list was further restricted to pyrethroids that had analytical standards of acceptable purity. A preliminary assessment was made of single component standards to confirm that the method analytes were compatible with gas chromatography and to examine solubility properties and standard purity. This evaluation identified several problem molecules. Amitrole, although available as a solid standard of acceptable purity, was not sufficiently soluble in ethyl acetate to permit preparation of a standard solution of adequate concentration for method development work. As a result, it was excluded from the list. Many of the pyrethroid standards contained isomers that yielded chromatographic peaks that were chromatographically resolved but had essentially identical mass spectra. The single component standards for allethrin, cyfluthrin, and cypermethrin each had 4-5 fully separated chromatographic peaks with identical mass spectra. Because this had the potential to add a significant layer of complexity to the quantitation method, these three compounds were removed. With a molecular weight of 959.2 g/M, BDE-209 was determined to require an injector and column temperature that were much higher than those of the other method analytes. It was therefore excluded from the analyte list because the optimal conditions for this analyte were not compatible with the lessstable analytes.
TABLE 2. Recovery Comparison for Six Different SPE Materials Based on Five Replicates Prepared and Extracted the Same Daya solid phase
SDVB
C-18
SDB-RPS
Oasis-HLB
Abselut
Strata
type cartridge sample volume elution solvent and volume
disk 47 mm 1L EtOAc/CH2Cl2 15 mL
disk 47 mm 1L EtOAc/MeCl2 15 mL
disk 47 mm 1L EtOAc 13 mL
cartridge 6 cm3/200 mg 1L EtOAc/CH2Cl2 13 mL
cartridge 10 cm3/60 mg 0.3 L EtOAc/CH2Cl2 13 mL
cartridge 6 cm3/200 mg 1L EtOAc/CH2Cl2 13 mL
a
surrogates
% rec
% rec
% rec
% rec
% rec
% rec
1,3-dimethyl-2-nitrobenzene triphenyl phosphate perylene-d12
106% 108% 132%
76% 94% 113%
108% 102% 40%
112% 115% 16%
100% 111% 11%
128% 113% 7%
target analyte
% rec
% rec
% rec
% rec
% rec
% rec
desisopropyl atrazine desethyl atrazine dimethoate atrazine propazine vinclozolin prometryn bromacil thiazopyr malathion chlorpyrifos thiobencarb parathion terbufos sulfone oxychlordane esbiol fenamiphos tetrabromobisphenol A nitrofen kepone norflurazon hexazinone resmethrin isomer resmethrin tetramethrin isomer bifenthrin tetramethrin dicofol BDE-47 phenothrin isomer phenothrin mirex permethrin isomer BDE-100 permethrin BDE-99 ethofenprox HBB fenvalerate esfenvalerate BDE-153 tralo/deltamethrin HBCD
16% 50% 71% na 94% 99% 91% 100% 99% 98% 94% 94% 94% 98% 97% 96% 38% 99% 102% 105% 102% 95% 72% 71% 105% 94% 96% 97% 84% 111% 95% 91% 101% 90% 105% 90% 134% 105% 104% 100% 102% 111% 128%
12% 20% 19% na 83% 88% 91% 82% 86% 84% 83% 83% 79% 84% 84% 86% 23% 96% 88% 99% 95% 95% 63% 65% 90% 79% 81% 79% 76% 103% 83% 76% 89% 88% 97% 88% 125% 93% 92% 84% 94% 94% 106%
45% 50% 77% 57% 67% 102% 17% 89% 93% 98% 95% 91% 93% 96% 93% 93% 10% 78% 95% 96% 98% 85% 65% 63% 92% 46% 83% 80% 88% 67% 58% 42% 53% 74% 57% 74% 91% 74% 44% 41% 73% 39% 84%
87% 90% 96% 100% 103% 109% 103% 106% 107% 108% 101% 100% 105% 107% 95% 97% 79% 86% 112% 92% 113% 98% 57% 51% 95% 14% 85% 85% 96% 55% 37% 10% 29% 75% 34% 75% 99% 72% 22% 19% 71% 17% 78%
28% 70% 70% 99% 103% 108% 100% 95% 105% 108% 89% 99% 104% 107% 57% 92% 45% 85% 99% 107% 107% 94% 18% 15% 86% 9% 77% 55% 66% 18% 16% 4% 14% 65% 14% 64% 63% 63% 14% 11% 62% 10% 55%
65% 90% 97% 99% 107% 109% 103% 103% 91% 107% 99% 99% 106% 105% 92% 86% 65% 94% 106% 105% 114% 102% 53% 45% 89% 9% 75% 75% 12% 38% 28% 7% 20% 10% 21% 10% 49% 5% 14% 12% 6% 10% 43%
% rec ) percent recovery.
Solid Phase Selection. Following the initial refinement of the Method 527 analyte list, evaluations of six potential SPE media were completed. In each case, five reagent water solutions were fortified at 5.0 µg/L and extracted immediately using each SPE material. The extractions were performed using similar elution solvents and volumes, and all of the extracts were processed and analyzed identically. As can be seen in Table 2, the SDVB disk exhibited the best recovery for the targets. By using SDVB, we found that all of the potential target analytes exhibited good extraction efficiencies with the exception of the atrazine degradation
products and fenamiphos, which are known to be unstable and problematic in other methods (29). The atrazine degradates (DIA & DEA) percent recoveries were best when extracting the samples using the Oasis-HLB cartridge, but poor results for many other targets were observed using this phase. Because of these factors, atrazine degradates were removed from the analyte list for this method. Preventing Analyte Loss Due to Hydrolysis and UV Degradation. There are several avenues that can lead to analyte loss during storage. It is important that the occurrence data generated under the UCMR 2 reflect the actual sample VOL. 39, NO. 13, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 3. The Effect of pH and UV Light on Target Recovery for Reagent Water Samples (n ) 5) Fortified at 5.0 µg/L and Then Held at Room Temperature for 7 Daysa
a
pH 3.8, AB (% rec)
pH 3.8, CB (% rec)
pH 5, CB (% rec)
pH 7.0, CB (% rec)
pH 9.0, CB (% rec)
surrogate 1,3-dimethyl-2-nitrobenzene triphenyl phosphate perylene-d12
83% 86% 78%
84% 97% 77%
76% 85% 67%
83% 79% 61%
82% 63% 64%
target compound dimethoate atrazine propazine vinclozolin prometryn bromacil thiazopyr malathion chlorpyrifos thiobencarb parathion terbufos-sulfone oxychlordane esbiol fenamiphos nitrofen kepone norflurazon hexazinone resmethrin isomer resmethrin tetramethrin isomer bifenthrin tetramethrin dicofol BDE-47 phenothrin isomer phenothrin mirex permethrin isomer BDE-100 permethrin BDE-99 ethofenprox HBB fenvalerate esfenvalerate BDE-153 tralo/deltamethrin HBCD
81% 88% 87% 90% 91% 102% 97% 91% 87% 90% 92% 92% 93% 96% 60% 99% 70% 93% 88% 97% 99% 103% 94% 93% 114% 76% 104% 97% 85% 97% 83% 97% 83% 118% 78% 96% 88% 80% 82% 78%
87% 97% 90% 100% 97% 114% 105% 97% 93% 99% 98% 101% 99% 96% 69% 107% 98% 105% 96% 0% 0% 91% 93% 85% 118% 73% 17% 12% 90% 99% 88% 104% 88% 106% 84% 97% 93% 87% 85% 88%
75% 94% 96% 54% 88% 89% 94% 86% 83% 89% 84% 86% 88% 79% 78% 84% 61% 88% 91% 7% 4% 58% 86% 53% 94% 70% 6% 5% 86% 83% 71% 105% 71% 81% 59% 66% 62% 56% 57% 41%
74% 103% 103% 14% 92% 90% 94% 67% 84% 90% 86% 87% 87% 75% 101% 85% 52% 84% 91% 7% 0% 0% 84% 7% 24% 69% 2% 6% 85% 81% 64% 104% 64% 82% 55% 89% 46% 52% 41% 38%
48% 106% 105% 11% 96% 89% 80% 7% 82% 91% 88% 69% 87% 65% 135% 86% 20% 83% 85% 0% 1% 0% 87% 8% 0% 80% 0% 2% 88% 81% 65% 107% 65% 79% 56% 85% 39% 52% 24% 32%
AB ) amber bottle, CB ) clear bottle, % rec ) percent recovery.
concentration at the point and time of sample collection. Sample preservation during storage is a key consideration during the development of all drinking water methods. The mechanisms for analyte loss during the storage of finished drinking water samples include degradation caused by acid, base and/or transition-metal-catalyzed hydrolysis, degradation from residual disinfectants, photodegradation, and microbial degradation. Experiments were first designed to examine the stability of target compounds as a function of pH. Five replicates of buffered reagent water at pH 3.8, 5.0, 7.0, and 9.0 were fortified with method compounds at 5.0 µg/L and extracted using SDVB disks. These sample sets were compared to a control set that contained no buffer and was treated identically with respect to extraction and analysis. The samples were stored in 1-L clear glass bottles and, as mentioned previously, were held for 7 days at room temperature as a rough initial holding time study to hasten method development. As shown in Table 3, degradation was considerably more pronounced at higher pH. The reagent water control, which was near pH 7, had recoveries similar to the solution buffered 5000
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at pH 7. Results of the study also indicated that a majority of the target analytes were most stable at pH 3.8. Exceptions to this were several of the pyrethroid pesticides, namely, resmethrin, phenothrin, and their isomers. As mentioned above, instability of the pyrethroid pesticides to UV light has driven much of the synthetic research since their commercial introduction over 50 years ago. To investigate the effect room light had on sample storage, we prepared a set of samples buffered to pH 3.8 in 1-L amber bottles and allowed them to sit at room temperature for 7 days before extraction and analysis. An identical set of samples was prepared in clear bottles as a control. The control behaved nearly identically to the data presented in Table 3. The data from the amber bottles clearly indicate that the source of the low percent recovery for the pyrethroids was photodegradation. On the basis of these results, Method 527 samples were adjusted with a citric acid buffer (pH 3.8) and stored in amber glass bottles. Removing Residual Disinfectant. A residual disinfectant is often imparted to drinking waters to prevent microbial contamination during distribution. As a result, many finished
TABLE 4. Comparison of Ascorbic Acid and Sodium Thiosulfate as Dechlorinating Reagents for Reagent Water Samples (n ) 5) Fortified at 5.0 µg/L and Then Held at Room Temperature for 7 Daysa
TABLE 5. Results of Copper Hydrolysis at the EPA Action Limit for Reagent Water Samples (n ) 5) Fortified at 5.0 µg/L and Held at Room Temperature for 7 Days 6 mg/L FAC pH 3.8 6 mg/L FAC 6 mg/L FAC 100 mg/L AA pH 3.8 pH 3.8 1.3 mg/L Cu++ 100 mg/L AA 100 mg/L AA 350 mg EDTA 1.3 mg/L Cu++ (% rec) (% rec) (% rec)
buff RW buff RW buff RW buff RW plus FAC plus FAC control plus FAC and AA and NaThio (% rec) (% rec) (% rec) (% rec) surrogate 1,3-dimethyl-2nitrobenzene triphenyl phosphate perylene-d12
93%
81%
83%
84%
94% 97%
87% 89%
94% 97%
82% 90%
targets dimethoate atrazine propazine vinclozolin prometryn bromacil thiazopyr malathion chlorpyrifos thiobencarb parathion terbufos-sulfone oxychlordane esbiol fenamiphos tetrabromobisphenol A nitrofen kepone norflurazon hexazinone resmethrin isomer resmethrin tetramethrin isomer bifenthrin tetramethrin dicofol BDE-47 phenothrin isomer phenothrin mirex permethrin isomer BDE-100 permethrin BDE-99 ethofenprox HBB fenvalerate esfenvalerate BDE-153 tralo/deltamethrin HBCD
74% 76% 76% 99% 93% 106% 103% 99% 87% 96% 119% 97% 91% 105% 48% 99% 108% 91% 104% 88% 91% 80% 128% 101% 105% 118% 78% 114% 100% 100% 98% 83% 115% 82% 113% 81% 120% 99% 72% 121% 107%
39% 67% 62% 93% 57% 99% 87% 60% 54% 67% 59% 59% 87% 49% 0% 95% 97% 98% 97% 78% 63% 64% 57% 90% 47% 107% 78% 80% 80% 91% 85% 81% 105% 79% 98% 80% 100% 92% 71% 109% 117%
81% 81% 82% 101% 105% 112% 102% 102% 90% 97% 123% 98% 95% 103% 117% 107% 103% 111% 108% 93% 96% 88% 123% 109% 105% 126% 105% 115% 108% 109% 106% 105% 126% 105% 124% 102% 137% 111% 97% 125% 124%
58% 53% 55% 102% 64% 110% 97% 52% 84% 94% 136% 78% 88% 91% 49% 99% 76% 85% 95% 66% 60% 56% 62% 58% 61% 92% 98% 105% 93% 91% 83% 108% 98% 106% 113% 98% 63% 52% 84% 70% 121%
a Buff RW ) buffered reagent water, AA ) ascorbic acid, FAC ) free available chlorine, NaThio ) sodium thiosulfate.
drinking waters contain small amounts of FAC or chloramines. Dechlorination is a required step in EPA drinking water methods because residual chlorine may degrade target analytes. EPA methods employ several different types of dechlorinating agents. Most of these reagents are reducing agents of varying strength, including ascorbic acid, sodium thiosulfate, sodium sulfite, and glycine. As reactive molecules, they too can degrade target compounds. Reaction with target compounds with either a residual disinfectant or a dechlorinating reagent is generally quick, and may proceed to completion in hours assuming the reagents are in sufficient concentration. Glycine, sodium thiosulfate, and sodium sulfite were first evaluated for compatibility with the target analytes in the absence of free available chlorine by preparing 1-L reagent
surrogate 1,3-dimethyl-2nitrobenzene triphenyl phosphate perylene-d12 targets dimethoate atrazine propazine vinclozolin prometryn bromacil thiazopyr malathion chlorpyrifos thiobencarb parathion terbufos-sulfone oxychlordane esbiol fenamiphos tetrabromobisphenol A nitrofen kepone norflurazon hexazinone resmethrin isomer resmethrin tetramethrin isomer bifenthrin tetramethrin BDE-47 phenothrin isomer phenothrin mirex permethrin isomer BDE-100 permethrin BDE-99 ethofenprox HBB fenvalerate esfenvalerate BDE-153 tralo/deltamethrin HBCD
85%
93%
65%
95% 96%
108% 90%
61% 80%
67% 79% 73% 88% 92% 98% 89% 84% 81% 85% 92% 89% 97% 86% 102% 111%
76% 87% 80% 104% 98% 103% 97% 92% 93% 99% 101% 95% 98% 98% 92% 108%
43% 65% 61% 64% 75% 68% 59% 52% 55% 59% 54% 55% 81% 45% 66% 79%
100% 94% 96% 97% 103% 105% 93% 89% 81% 84% 103% 89% 84% 94% 86% 93% 86% 101% 92% 104% 97% 97% 99% 118%
104% 98% 106% 105% 108% 105% 93% 85% 84% 88% 97% 89% 85% 93% 86% 91% 94% 99% 92% 91% 90% 89% 93% 93%
72% 82% 69% 70% 56% 70% 20% 80% 17% 83% 68% 70% 83% 79% 82% 74% 84% 82% 89% 82% 80% 85% 83% not spiked
water samples that were fortified with target compounds at 5.0 µg/L containing one of the dechlorinating reagents. The solutions were mixed and allowed to sit on the bench for 1-2 h prior to extraction. Sample sets that contained glycine and sodium sulfite showed significant loss of target analytes, with average recoveries of 66 and 84%, respectively. The recoveries for the pyrethroids and esbiol were affected in both dechlorinating reagents. Recoveries for malathion, chloropyrifos, parathion, and terbufos sulfone were also significantly depressed by the glycine reagent. The average recovery for the target compounds was 97% with sodium thiosulfate. The addition of sodium thiosulfate to the samples produced sulfur peaks in the chromatogram, which can diminish the method precision and accuracy, and often requires more frequent GC maintenance. Ascorbic acid was VOL. 39, NO. 13, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 6. Precision and Accuracy of Method 527 Analytes Fortified at 5.0 µg/L in Three Matrices. All Samples Were Extracted the Same Day They Were Prepareda reagent water
a
surface water
groundwater
final method 527.0 analytes
% rec
% RSD
% rec
% RSD
% rec
% RSD
dimethoate atrazine propazine vinclozolin prometryn bromacil malathion chlorpyrifos thiobencarb parathion terbufos-sulfone oxychlordane esbiol nitrofen kepone norflurazon hexazinone bifenthrin BDE-47 mirex BDE-100 BDE-99 hexabromobiphenyl fenvalerate esfenvalerate BDE-153 1,3-dimethyl-2-nitrobenzene (SUR) triphenyl phosphate (SUR) perylene-d12 (SUR)
85.8 85.8 82.3 93.8 85.6 103 86.4 84.6 87.0 87.4 93.2 84.0 97.2 100 82.8 106 94.1 78.7 81.3 75.4 83.6 86.8 82.0 95.6 86.3 85.4 87.7 88.4 78.5
4.5 8.7 9.1 6.0 5.6 5.7 4.5 5.4 4.7 5.1 4.3 6.0 5.2 4.6 4.3 5.8 6.8 4.3 4.1 4.7 3.9 5.4 3.6 4.4 4.8 9.3 9.1 4.8 5.6
89.3 102 89.8 103 91.0 104 95.4 91.1 95.0 93.8 97.3 90.6 104 98.8 88.1 105 101 89.8 88.8 86.6 91.0 93.4 95.2 105 97.3 91.3 96.5 97.7 92.6
2.6 2.9 4.1 6.0 4.1 3.2 4.0 4.8 4.5 4.7 4.6 3.4 4.8 3.7 4.0 3.2 3.1 5.1 2.9 5.6 1.8 2.7 2.5 3.9 3.3 5.3 14 4.2 4.2
78.0 89.7 82.5 95.8 84.5 93.3 85.3 84.8 85.8 86.6 87.3 85.8 94.8 89.2 75.0 94.5 92.9 76.7 78.0 72.7 79.8 82.7 79.5 93.7 87.7 82.7 85.5 86.1 82.9
4.3 9.6 9.5 8.9 9.7 9.5 10 10 9.6 9.8 11 10 8.6 8.4 7.4 7.8 7.5 11 5.6 12 3.8 4.2 6.1 7.2 9.4 4.6 12 9.6 8.5
additional analytes studied thiazopyr fenamiphos tetrabromobisphenol A resmethrin-isomer resmethrin tetramethrin-isomer tetramethrin phenothrin-isomer phenothrin permethrin-isomer permethrin ethofenprox
81.6 72.9 93.5 97.8 90.5 99.0 80.4 110 85.8 90.8 96.8 107
4.1 3.6 4.7 4.9 4.5 4.9 4.0 5.5 4.3 4.5 4.8 5.3
95.8 69.7 107 104 99.0 108 90.9 127 96.8 99.2 103 115
4.8 3.5 5.3 5.2 5.0 5.4 4.5 6.4 4.8 5.0 5.1 5.8
85.3 85.3 92.8 75.1 70.4 92.5 81.1 96.5 82.5 84.9 83.8 96.5
4.3 4.3 4.6 3.8 3.5 4.6 4.1 4.8 4.1 4.3 4.2 4.8
SUR ) Method 527 surrogates used to track extraction efficiency, % rec ) percent recovery, % RSD ) percent relative standard deviation.
compared to thiosulfate as a potential dechlorinating reagent for this reason. Because thiosulfate seemed to be chemically compatible with the target compounds, these studies were conducted in the presence of free available chlorine. To challenge the system, we fortified the samples with FAC at 6 mg/L, which is 1.5 times the maximum residual disinfectant level for chlorine in finished drinking waters. Two sets of samples were buffered, dechlorinated with either reagent, fortified with the target compounds at 5.0 µg/L, and then held at room temperature for 7 days prior to extracting and analyzing. Two sets of controls were also prepared, stored, and processed. These included a chlorinated reagent water that was buffered at pH 3.8 but did not contain a dechlorinating reagent and a buffered reagent water without free available chlorine or dechlorinating reagent. These results are presented in Table 4. Based on these data, ascorbic acid was chosen as the dechlorinating reagent for Method 527. Protection from Transition-Metal-Catalyzed Hydrolysis. The presence of catalytic metals such as copper have been shown to increase the rate of hydrolysis for some organic compounds even when copper is present at its EPA Action Limit in drinking water of 1.3 µg/L (29). EDTA has a very high chelate-forming quotient that can be used to prevent 5002
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transition metals such as copper from accelerating the degradation of labile organic molecules. To determine the potential effect of copper ion on the Method 527 target analytes, we buffered four sets of samples to a pH of 3.8 and fortified them with 6 mg/L of FAC. The samples were then dechlorinated with ascorbic acid and fortified with the target compounds (5 µg/L). In one set of samples, an amount of copper sulfate was added to yield a concentration of the copper ion at the action limit (1.3 mg/L). A second set was prepared identical to the first, but EDTA was added, and a third set without copper or EDTA was included as a control. These samples were stored in amber glass bottles at room temperature for 7 days and then extracted and analyzed. Data from these experiments, presented in Table 5, warranted the inclusion of EDTA as a preservative. Improving Method Ruggedness. Several factors were identified during method development that can effect method ruggedness. Many of the flame retardants are highly brominated. The bromine atom has two isotopes. The smaller isotope, Br(79), has a weight of 78.91 (50.69% abundance) and the larger isotope, Br(81), has a weight of 80.91 (49.31% abundance). As the degree of bromination increases, the mass of the PBDE must be determined to four significant figures
to avoid potential issues associated with mass defect during quantitation. For example, the isotopic mass for the tetra-, penta-, hexa-, and decabrominated biphenyl ethers are 481.7, 559.6, 637.5, and 949.2, respectively. Although this concept is well understood by most mass spectroscopists, the quantitation ions for the PBDEs were expressed to four significant figures in Method 527 for clarity. As noted above, the PBDEs have a high molecular weight relative to the other compounds in the target list, which is a consideration during the optimization of injection port parameters. Discussions with standard manufacturers indicated that some of the PBDEs have a tendency to decompose before they reach their boiling point, so the injection port temperatures were carefully evaluated for two manufacturer’s split/splitless injection ports over 210-290 °C. The optimal injection temperature varied for our Agilent and Varian instruments, with the Agilent GC having a higher optimal temperature for the PBDEs and better precision, presumably due to improved inertness of the port. An injection port temperature of 250 °C was chosen as a “middle ground” for the method. This parameter should be reevaluated at each analytical laboratory based on instrument configuration and the application of the method. Some of the Method 527 analytes such as the PBDEs and HBCD had a tendency to build up in the syringe, causing the syringe plunger to stick during injection. This issue was resolved by adding additional ethyl acetate and methanol rinses between sample injections. Sample extracts that were not carefully dried according to the procedure had the tendency to reduce the lifetime of the injector port and/or require column maintenance. This is believed to be associated with residual acid from the citric acid buffer and/or ascorbic acid dechlorinating reagents retained in the water portion of the extracts that are not properly dried. The amount of sodium sulfate recommended in the procedure is adequate for drying the extracts, assuming of course that the analyst is familiar with SPE techniques. The initial work on Method 527 utilized SDVB disks. Experiments conducted to evaluate SDVB cartridges determined that the later eluting compounds, from bifenthrin on, had lower recoveries even though the surrogate, triphenyl phosphate, recovered acceptably. Recoveries for the PBDEs ranged from 67 to 69%. Cartridges were omitted from Method 527 for this reason. Antimicrobial and Storage Stability Studies. EPA drinking water methods commonly contain microbial inhibitors to prevent biodegradation during sample storage (30). Citric acid was chosen as the buffer for this method because it had previously been shown to be an effective antimicrobial agent during the development of EPA Method 531.2 (26). A series of experiments were conducted to confirm the storage stability of the method analytes under the method preservation requirements and the antimicrobial effectiveness of the preservation reagents. Triplicate 1-L samples from experiment 1 were stored at the maximum allowed temperatures in the method (as described above) and analyzed at 7-day increments over a 28-day period. Analyte recoveries showed acceptable stability over this period for most analytes (25). However, bifenthrin, BDE-47, mirex, BDE-100, BDE-99, and HBB began to show diminished recovery on day 21 that continued through day 28. Recoveries on day 28 and their change relative to day 1 were 73% ((-17%), 71% ((-16%), 65% ((-19%), 75% ((-13%), 79% ((-14%), and 75% ((-18%), respectively. Based on these data, a sample holding time of 14 days was established for the method. The extract storage stability was also examined at -20 °C and determined to be acceptable over 28 days (25). Method Performance. The Method 527 detection limits were evaluated in accordance with the procedure described
by Glaser et al. (31) and ranged from 0.025 to 0.14 µg/L for the method analytes. The lowest concentration minimum reporting levels (LCMRLs) were determined in accordance with the new EPA Office of Ground Water and Drinking Water (OGWDW) procedure (32) and ranged from 0.12 to 1.1 µg/L. In each case, the method had adequate sensitivity for the compounds that will be monitored under the UCMR 2. The precision and accuracy of the method were determined for the 38 method analytes and the 3 surrogate compounds in reagent water, a chlorinated surface water, and a chlorinated groundwater at 2 fortification concentrations. The average recoveries and percent relative standard deviations for five replicate samples fortified at 5.0 µg/L (the higher concentration studied) are summarized in Table 6. The precision and accuracy of the method were determined to be acceptable. An independent second laboratory evaluation of Method 527 yielded similar data. Prior to publication of the method, 12 of the Table 6 analytes were removed. Eight of these compounds were pyrethroids that had a second isomer, and single isomer standards were unavailable. This would have required manual quantitation to report “total” values because these isomers were chromatographicly separated. Single component, second source standards were obtained for each target analyte. Thiazopyr, ethofenprox, and tetrabromobisphenol A were removed from the list because the second source standards did not meet the quality control acceptance criteria (within 70-130% of the primary standard concentration). In its final form, Method 527 contains 25 analytes. Sample preservation techniques were refined carefully to ensure that the sample analytes are stable during the permitted storage time. The ruggedness of the method was optimized to yield a method that performs well and should be readily mobilized by the analytical community to generate survey data that meet the Agency’s UCMR 2 accuracy, precision, and completeness goals.
Acknowledgments All of this work was supported on-site at EPA’s Drinking Water Laboratory located in Cincinnati, Ohio. This work has been funded wholly or in part by the United States Environmental Protection Agency under an on-site contract (contract no. 68-C-01-098) to Shaw Environmental, Inc. This paper has been subject to the Agency’s review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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Received for review February 23, 2005. Revised manuscript received April 13, 2005. Accepted April 18, 2005. ES050374Y
