Article pubs.acs.org/est
Identifying New Persistent and Bioaccumulative Organics Among Chemicals in Commerce. III: Byproducts, Impurities, and Transformation Products Philip H. Howard*,† and Derek C. G. Muir‡ †
SRC, Inc. Defense and Environmental Solutions (DES), 7502 Round Pond Road, North Syracuse, New York 13212, United States Environment Canada, Aquatic Contaminants Research Division, 867 Lakeshore Road, Burlington, Ontario, Canada
‡
S Supporting Information *
ABSTRACT: The goal of this series of studies was to identify commercial chemicals that might be persistent and bioaccumulative (PB) and that were not being considered in current wastewater and aquatic environmental measurement programs. In this study, we focus on chemicals that are not on commercial chemical lists such as U.S. EPA’s Inventory Update Rule but may be found as byproducts or impurities in commercial chemicals or are likely transformation products from commercial chemical use. We evaluated the 610 chemicals from our earlier publication as well as high production volume chemicals and identified 320 chemicals (39 byproducts and impurities, and 281 transformation products) that could be potential PB chemicals. Four examples are discussed in detail; these chemicals had a fair amount of information on the commercial synthesis and byproducts and impurities that might be found in the commercial product. Unfortunately for many of the 610 chemicals, as well as the transformation products, little or no information was available. Use of computer-aided software to predict the transformation pathways in combination with the biodegradation rules of thumb and some basic organic chemistry has allowed 281 potential PB transformation products to be suggested for some of the 610 commercial chemicals; more PB transformation products were not selected since microbial degradation often results in less persistent and less bioaccumulative metabolites.
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INTRODUCTION In 2006, we published a paper1 challenging environmental chemists to start looking for new persistent and bioaccumulative (PB) chemicals. In 2010, we published an additional paper2 identifying 610 compounds that are potential PB chemicals from a list of 22 000 commercial chemicals from the Canadian Domestic Substances List (DSL) or from the Toxic Substance Control Act (TSCA) with reported production ranges in 1986, 1990, 1994, 1998, 2002, and 2006 under the Inventory Update Rule (IUR). In 2011, we published3 another paper that developed a database of 3193 pharmaceuticals of which 275 had already been detected in the environment. After subtracting the 275 and selecting high production volume (HPV) pharmaceuticals, 58 potentially PB and HPV pharmaceuticals were identified. Our motivation was that analytical chemists would be more successful in identifying new PB chemicals if they know what they are looking for and several successes have been noted in one of the earlier papers.2 This screening of thousands of chemicals has become possible due to the developments in quantitative structure property relationships (QSPRs) and the availability of large chemical structural databases. The approach we used to identify the 610 commercial organic chemicals and the pharmaceutical chemicals relied on QSPR, expert scientific judgment, and several large databases some of which had production volume information on the chemicals being © 2013 American Chemical Society
considered. In this study, we have focused on possible byproducts and impurities that might be found in the 610 commercial organic chemicals and on potential transformation products from their commercial use. Most of these chemicals have persistent structures (e.g., highly branched or with halogen substitution) or have part of the parent chemical that appears to be persistent and possibly bioaccumulative. Therefore, these chemicals have considerable potential to have PB byproducts, impurities, or transformation products. Most commercial chemicals are synthesized from starting materials and reagents and result in the desired product plus left over starting materials and byproducts or impurities. These leftover starting materials, byproducts, or impurities can be environmental contaminants just like the desired commercial products. An example of a leftover starting material is linear alkylbenzenes (LAB) which is a starting material and impurity found in linear alkylbenzenesulfonates (LAS), one of the highest production surfactants used today. LAB has been found as an environmental contaminant where LAS is used.4 An example of byproducts are some compounds formed during the synthesis of Dechlorane Plus (DP) which is formed Received: Revised: Accepted: Published: 5259
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CASRN for the new impurities, byproducts, or transformation products, but it is expected that many of these chemicals will not have CASRN numbers since their identification by this study may be the first time that such structures appear in the scientific literature. Chemicals were evaluated in the same order as the existing spreadsheetbrominated, chlorinated, fluorinated, other (nonhalogenated), phosphorus containing, and organosilicone compounds. Besides the 610 PB commercial chemicals previously identified to be screened, it seemed worthwhile that we also reexamine commercial chemicals with high production volume (2455 HPV chemicals and 541 EHPV14 which are produced annually >1 Mlbs/y [450 t/y]). However, these HPV chemicals were already screened during the selection of the 610 PB chemicals, and therefore, HPV chemicals that had persistent and bioaccumulative properties were already included in the 610 chemicals. Only two chemicals in the HPV list provided chemicals of interest as potential byproduct, impurity, or transformation PB chemicals that were not already identified from the 610 commercial chemical list. Each of the new records in the separate ISISBase database which is available from the authors in a variety of formats has a SMILES notation13 for the new chemical. Most of these SMILES notations were developed by taking the parent compound SMILES and using the new draw feature of EPI Suite software5 to alter the parent two-dimensional chemical structure to the related byproduct, impurity, or transformation product; the software automatically provides the corresponding SMILES notation. The SMILES notation was used with the ChemSpider structure search Web site15 to determine if there was an available systematic chemical name and CASRN available for the new byproduct, impurity, or transformation product. The SMILES notation was also used with the EPI Suite software5 to provide the data from a database in the software or estimate the data from the chemical structure for the following properties: chemical name; chemical formula; molecular weight; KOWWIN estimated log octanol−water partition coefficient (log Kow); experimental log Kow; estimated Henry’s law constant; log air−water partition coefficient (derived from the Henry’s law constant); log BCF, (from the BCFBAF program); log octanol−air partition coefficient (from the KOAWIN program); atmospheric hydroxyl (OH) radical rate constant (from the AOPWIN program); atmospheric ozone rate constant (from the AOPWIN program); atmospheric half-life (calculated from the OH radical and ozone rate constants); and two biodegradation estimates from the BIOWIN program (BIOWIN 1 and 5). The properties that are relevant to determination of PB include the octanol/water partition coefficient, BCF, and the estimated biodegradability. Once these values were estimated and added to the database, they were used to sort chemicals for potential to be PB starting materials, byproducts, impurities, and transformation products. Other fields that were added included (1) the IUR production volumes for the related parent commercial chemical to provide an indication of the commercial importance of any byproducts, impurities, or transformation productions; (2) comments on the synthetic commercial pathway, starting materials, possible byproducts, possible transformation pathways, and how they were determined along with citations; (3) an indication of whether the chemical was a starting material, byproduct, impurity, and/or transformation product (some chemicals were in more than one category); and (4) an indication of whether
by a Diels−Alder reaction combining 2 mol of hexachlorocyclopentadiene and 1 mol of 1,5-cyclooctadiene. If only 1 mol of hexachlorocyclopentadiene reacts with 1 mol of 1,5cyclooctadiene, a byproduct monoadduct compound is formed which is a hexachloro adduct instead of the 12 chlorine chemical, DP. This monoadduct has an estimated log Kow of 7.4 and an estimated bioconcentration factor (BCF) of 8700 (using EPI Suite)5 which is predicted to be considerably more bioaccumulative than DP. If the cyclooctadiene starting material has some 1,3-cyclooctadiene and 1,4-cyclooctadiene impurities, it is possible to get both the mono- and diadduct of both of these. All of these byproducts can be predicted from an understanding of the synthesis of 1,5-cyclooctadiene and DP, and many of these byproducts/impurities have recently been detected in the environment.6 An example of transformation productions/metabolites of commercial chemicals is transformation products from triclocarban, 3,4,4′-trichlorocarbanilide, a widely used antibacterial and antifungal chemical in disinfectants, soaps, and household products. Unfortunately, with the exception of some pharmaceuticals and pesticides, most chemicals do not have known transformation pathways so potential pathways will have to be estimated using scientific judgment and available software. In the case of triclocarban, Higgins et al. have identified some metabolites including 4,4′-trichlorocarbanilide.7 Understanding the starting materials, byproducts, and impurities that could be or are found in commercial chemical products or transformation products that may be formed during commercial use of a chemical or from its release to the environment will help synthetic chemists prepare standards and analytical chemists develop new analytical methods. To our knowledge, a systematic examination of large numbers of commercial chemicals for potential starting materials, byproducts, impurities, and transformation products has not been conducted. Some approaches for identifying transformation products have been suggested but have been applied to limited numbers of chemicals.8,9 These approaches and ours are similar in that we assume aerobic degradation conditions and used the University of Minnesota Biocatalysis/ Biodegradation Database Pathway Prediction System (UMPPS)10 software since experimental information on metabolites is not available. The compounds identified here could be useful for identification of unknowns by high resolution mass spectrometry in nontarget screening programs.11,12
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METHODS Identification of Potential PB Starting Materials, Byproducts, Impurities, and Transformation Products. Databases. A spreadsheet of 610 potential PB commercial chemicals from our previous study2 was used for individual chemical assessment (see Table S-1, Supporting Information). Columns were added to the original spreadsheet to cover starting materials, impurities, and byproducts as well as transformation products so that notes on the searches that were conducted could be recorded (e.g., if no information on the commercial synthesis pathways could be found). A separate ISISBase database13 was also developed for capturing any chemicals that appear to be PB as determined during the searches and evaluations; this software allows for the chemical structure and data to be seen at the same time. Chemicals in this database were indexed back to the original 610 PB chemicals by the Chemical Abstracts Service Registry Number (CASRN). The new ISISBase database does have a field for the 5260
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Table 1. Examples of HPV Commercial Chemicals with Potential Persistence and Bioaccumulative Byproducts, Impurities, and Transformation Products
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Table 1. continued
a B and P criteria.1,2 These are discussed in the Results and Discussion section. bKOWWIN: estimates the log octanol−water partition coefficient (log Kow) of chemicals using an atom/fragment contribution method. A high log Kow indicates a compound will partition into organic matter rather than water. cBIOWIN1: biodegradation probability program (BIOWIN) includes a linear probability model that estimates the rapid aerobic biodegradation of organic chemicals. dBIOWIN5 is the Japanese MITI (Ministry of International Trade and Industry) linear model that estimates the probability of rapid aerobic biodegradation of organic chemicals. eK-O is Encyclopedia of Chemical Technology16 and Ullmann’s Encyclopedia of Industrial Chemicals;17 UM-PPS is Biocatalysis/Biodegradation Database Pathway Prediction System.10 All of the above estimation programs are in the EPI Suite software.5
there were any journal articles that examined the commercial synthetic process and analyzed for any impurities or byproducts. In many cases, none of these sources provided any information and some basic synthetic organic chemistry was used to deduce likely synthetic pathways and possible impurities and byproducts. Transformation Products. Several approaches were used to identify potential transformation products. One was to use computer-aided predictions similar to that used by Ng et al.8 and Kern et al.9 using the UM-PPS software.10 This software requires the input of the SMILES notation of the parent commercial chemical (list of 610). The UM-PPS software then
the chemical was assessed as persistent and/or bioaccumulative (the same criteria that were used as in our earlier papers).2,3 Evaluation for Starting Materials, Byproducts, and Impurities. The first step in evaluating one of the 610 commercial potential PB chemicals was to determine the likely commercial synthetic method that was used by industry to produce the chemical. This included searches of the KirkOthmer Encyclopedia of Chemical Technology,16 Ullmann’s Encyclopedia of Industrial Chemistry,17 and the Methods of Manufacturing field of the National Library of Medicine’s Hazardous Substances Data Bank (HSDB).18 In some instances, searches of Google Scholar were also used to see if 5262
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transformation pathways were understood. In our case, the commercial chemicals do not have known biodegradation pathways, so comparisons and uncertainties between estimated pathways and known pathways was not possible. However, these biodegradation pathways of UM-PPS10 and the “rules of thumb”19 have been widely tested on numerous pesticides and other environmental contaminants and have reliably predicted persistent compounds and degradation pathways.
provides possible transformation pathways including an indication of the likelihood of each step occurring (six categories: very likely, likely, neutral, unlikely, very unlikely, and unknown). Potential PB transformation products were then identified by selecting pathways that had the higher likelihood as well as having structures that still appear to be persistent based upon the rules of thumb of BIODEG software19 in EPI Suite software.5 Occasionally, a reaction database of microbial pathways that was developed by SRC from a 30-year collection of Dr. Martin Alexander of Cornell University was used. In order to handle the problem of simplifying the number of metabolites from the hundreds that may be possible, Ng et al.8 used a simplication scheme that consisted of (1) only one metabolite for a biodegradation rule that gives many; (2) only most likely metabolites; and (3) only two generations (steps) in the metabolite pathway. As chemicals are degraded, the metabolites generally become more water-soluble/lower Kow partition (less bioaccumulative) and less persistent (there are many exceptions to this rule). So like Ng and co-workers,8 we focused on the earlier metabolic steps and selected representative chemicals for individual biodegradation rules. For example, if the first step is to add a hydroxyl group in a number of places on the parent molecule, we would pick one metabolite that was most likely to be persistent (e.g., an OH on a tertiary carbon that would not allow further oxidation). Unlike Ng and co-workers,8 we did not select pathways that had all the steps rated “likely” by the UM-PPS software since the intermediate metabolites would not accumulate and be detected. Instead we looked for the first or second pathways that had no further “likely” pathways and thus the metabolites were possibly persistent. Also, there were exceptions to the two generation rule; some persistent metabolites were found further down the metabolite pathway (e.g., an aromatic ring is broken and metabolized to a carboxylic acid that is next to a quaternary carbon). In our earlier papers, expert judgment criteria for biodegradability was based upon the “rules of thumb” that have been available for many years19 and the criteria were applied very conservatively. If part of the molecule had persistent functional groups in our earlier studies on parent commercial products, it was considered as a potential PB chemical even if part of the molecule could be chemically oxidized or hydrolyzed which is not predicted by the BIODEG software. Therefore, basic organic chemistry was also used to identify potential transformation products from the 610 chemical list of commercial chemicals by determining compounds that could be chemically photolyzed, hydrolyzed, oxidized, or be reduced to PB transformation products. The list of byproducts and transformation products was also reviewed to determine whether suitable analytical methods were available and, if not, what methodology for analysis of related compounds might be adapted. Information sources for this evaluation included ChemSpider, Scopus, and Google Scholar. Uncertainties Associated with Properties and Biodegradation Pathways. The uncertainty in the estimated properties obtained from the EPI Suite software5 has been widely published and has been reviewed by Ng et al.8 Very few of the relatively new chemicals have actual measured values, and therefore, comparison of estimated to measured values was not possible. Ng et al. 8 were able to compare the biodegradation pathways estimated by UM-PPS10 to known pathways because they selected current use pesticides where the
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RESULTS AND DISCUSSION A total of 320 potential PB byproducts, impurities, and transformation products were identified and listed in Table S1 of the Supporting Informationthe table indicates if the chemical is considered to be P or B or both. Some of the individual 610 chemicals had numerous byproducts, impurities, or transformation products while some chemicals had no potential PB chemicals. Sometimes this is due to (1) complex synthesis pathways with impurities in the starting material or (2) multiple byproducts as well as several transformation products. In other cases, no information on the synthesis pathway was available and none of the potential transformation products appear to be P or B. Table 1 provides a few examples of commercial chemicals that are produced in large quantities and have byproducts, impurities, or transformation products that are potential PB emerging contaminants. A few of the more commercially important chemicals are discussed in the following. Tetrabromobisphenol-A (TBBPA; CASRN 79-94-7) is one of the largest commercial brominated flame retardant (BFR) chemicals (100−500 Mlbs/y [45 000−227 000 t/y])23 (see Figure 1). According to Ullmann’s Encyclopedia of Industrial Chemicals,17 it is made by direct bromination of bisphenol A in a variety of organic solvents. Great Lakes Chemical Corporation makes TBBPA (trade nameBP-59) which contains less than 3% tribromobisphenol A (tribromoBPA shown in Figure 1; CASRN 6386-73-8) according to its
Figure 1. Metabolism pathway for tetrabromobisphenol A and tribromobisphenol A. 5263
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aromatic rings have been hydrogenated.16 This commercial product is produced in 10−50 Mlbs/y (4500−22 500 t/y)23 and worldwide production has been reported as 9 Mkg/y.16 If one assumes that 40% hydrogenation results in one terminal benzene ring being fully hydrogenated (this is just one assumptionmany other hydrogenation products are possible), there would be three isomers (o-, m-, and p-) in the commercial mixture, each of which could have three possible transformation products as predicted by UM-PPS (Figure S2 Supporting Information). Thus, there are numerous isomers in the commercial product and numerous possible transformation products. Hydrogenated terphenyls are used in industrial heattransfer systems, as a direct heating medium for the condensation of polyester, as dye solvents by European carbonless copy paper producers, in certain plasticizer applications (primarily PVC), and minor amounts for other uses (lubricant, hydraulic, nuclear reactor coolant, etc.).16 Many of these applications could result in release to the environment during use or during disposal of the commercial products in which they are used. Another commercial chemical that has become commercially important only recently is decabromodiphenylethane (DBDPE) (CASRN 84852-53-9) which was produced in 10− 50 Mlbs/y (4500−22 500 t/y) in 2006 (IUR)23 but had no reported production in the five previous reporting years. It has been detected in air over the Great Lakes24 and in Great Lakes herring gull eggs and in biota from the Baltic Sea.22 During production by bromination (U.S. Patent 6,743,825),21 gas chromatography analysis indicates that the commercial product contains 0.23% of the octabromo isomer (DPE-Br8) (could be several isomers) and 0.93% of the nonabromo isomer (BPEBr9) (could be three isomers; see Table 1). Estimated transformation metabolites include the decabromodiphenylethane alcohol followed by the decabromodiphenylethane ketone (see Table 1); both of these steps are given a neutral probability by the UM-PPS software. Analytical Challenges. The combined 320 potential PB byproducts, impurities, and transformation products provided in the Supporting Information (see Table S1) include 88 with acidic moieties (i.e., COO−, PO4−, SO3−), 138 alcohols or phenolics, and 95 mainly neutrals (e.g., byproducts with fewer halogens). In Supporting Information Figure S3 estimated log Kow and BIOWIN1 and BIOWIN5 values are plotted for 268 parents and 281 biotransformation products. While almost all have lower log Kow than their parent compounds the differences are not large due to the selection of persistent transformation products (also phenolics and acids are assumed to protonated for Kow estimation in KOWWIN). Similarly the probabilities of biotransformation of the products were only slightly higher than the parents because persistent transformation products were selected. Thus, we may expect to see these products partitioning in environmental media similar to the parent compounds. We may also expect that extraction methods that recover the parent compounds are also likely to recover transformation products. However, since the majority have phenolic or acid moieties the pH of the extraction and analyte isolation conditions may be important. There are relatively few studies on the determination of transformation products of most industrial or commercial chemicals listed under TSCA in environmental samples such as wastewaters, surface and ground waters, and sediments. However, the determination of transformation products of commercial chemicals in environmental samples is certainly not
Material Safety Data Sheet (MSDS). Using the EPI Suite estimation programs5 as reported in Table 1, tribromoBPA has an estimated log Kow of 6.3 and an estimated BCF of about 7000, and all of the BIOWIN estimates suggest persistence, which is the same as TBBPA, indicating that the tribromo isomer impurity is also a P&B chemical. Given the high production of TBBPA, 3% of tribromoBPA could amount to as much as 3−5 Mlbs/y (5000−25 000 t/y). As indicated in Figure 1, the UM-PPS software suggests that TBBPA may be degraded to the tribromo isomer (although rather unlikely which confirms that TBBPA is probably persistent) and that the tribromo isomer will be degraded to the diol followed by ring breakage. The two “neutral” likelihood pathways of aerobic biodegradation for the diol are from UM-PPS, but the rules of ring breakage suggest that the diacid will be more likely to be formed. Using the EPI Suite software,5 the estimated values in Table 1 were calculated for the various fate and physical properties of the transformation products. From these results, the TBBPA diol, TBBPA ketoacid, and TBBPA diacid metabolites all appear to be P from the Biodeg1 and Biodeg5 model estimates and the estimated log Kow values are all over 3.0, which would suggest the potential to bioaccumulate. The TBBPA tert acid appears to also be a likely persistent metabolite as the alkyl side chain of the ketoacid or diacid are metabolized, but then further metabolism will be blocked by the quaternary carbon. This metabolite is not estimated by UM-PPS but is suggested by the biodegradation rules of thumb.19 In addition, TBBPA tert acid’s log Kow of 3.6 suggests that it may also bioaccumulate. Another interesting chemical that has byproducts, impurities, and transformation products that are noted in Table 1 is hexabromocyclododecane (HBCDD); this commercial chemical is produced in about 10−50 Mlbs/y (4500−22 500 t/y).23 Barontini et al. studied two commercial HBCDD products and identified six impurities in the product.20 A few of these are noted in Table 1 and provided in the Supporting Information (Figure S1 presents the chemical structures). These authors also examined thermal transformation isomers that could be formed using thermogravimetric analyzers and identified a total of 55 polybrominated cycloalkane isomers. Since HBCDD is a BFR, it seems reasonable that when HBCDD containing products are in a fire or during brominated epoxy resin production, some of the above isomers could be thermally formed, released to the environment, and be potential PB chemicals. There were no other thermal transformation studies like this that we identified, but when they are available, these types of products should be considered and more studies should be encouraged. A third commercial chemical that is a complex mixture and has some potential PB transformation products is hydrogenated terphenyls. This complex mixture is made by thermal dehydrocondensation of toluene to benzene.16 Since it proceeds by a free-radical mechanism, large amounts of biphenyl (1 kg/100 kg of benzene) and lesser amounts of terphenyl and quaterphenyl are formed. Pure biphenyl is then separated leaving a polyphenyl residue of approximately 4% oterphenyl, 44% m-terphenyl, 25% p-terphenyl, 1.5% triphenylene, and 22−27% higher polyphenyl and tars.16 Distillation then leaves the mostly terphenyl mixture with some quaterphenyl. The terphenyls produced are then partially hydrogenated to afford a complex hydrocarbon mixture (CASRN 61788-32-7) in which approximately 40% of the 5264
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Unfortunately for many of the 610 chemicals, little or no commercial synthesis information was available. Similarly, there was very little experimental information available on transformation products for the 610 chemicals, but the use of computer-aided software to predict the aerobic degradation pathways in combination with the biodegradation rules of thumb19 and some basic organic chemistry has allowed transformation products to be suggested. These compounds may themselves be emerging PB contaminants or useful for tracking sources of the parent compounds.
new. Pesticide and pharmaceutical degradates in surface and ground waters and in wastewaters have been studied extensively.9,25−27 More frequently the analysis of transformation products of HPV industrial chemicals has been conducted for biological tissues, for example, the analysis of the mono- and dialkyl/aryl phosphate hydrolysis products in urine28 and the determination of dimethyl silanediol transformation products of dimethylsiloxanes in biological samples.29 Potential analytical methods for trace analysis in environmental media were reviewed for all 320 compounds. In most cases (270 compounds), specific analytical methods did not exist. Exceptions were the monohexachlorocyclopentadiene adducts of Dechlorane Plus analyzed by Sverko et al.,6 the polyfluoro- and perfluoroalcohols formed from the hydrolysis of polyfluoroalkyl phosphosphates and phosphonates,30 and the perfluoroalkyl acids formed from the alcohols. Methodology is well established for both groups.31−34 In the case of debromination products of TBBPA, HBCDD, and DBDPE, while no specific methods were available they would be analyzable under the same conditions as the parent compounds although, since reference standards are not currently available for all congeners, analysis might be semiquantitative. The lack of analytical reference standards for the transformation products as well as for most of the parent compounds from the original list of 610, is a major impediment to development of analytical methods. However, our list of transformation products can serve to direct nontarget analysis of environmental samples as has been done for selected pesticides and pharmaceuticals.8,9 Using the structures provided (see Table S1, Supporting Information) the mass spectral fragmentation pathways can be predicted. High resolution mass spectra of the analytes can then be compared using peak matching software. Liquid chromatography with electrospray ionization tandem mass spectrometry (ESI/MS/MS) in negative ion mode appeared to be the most appropriate methodology for attempting to identify the majority of the transformation products and byproducts based on its wide use for parent compounds or structurally related compounds. In total, LC-MS/MS was recommended for 220 compounds (see Table S1, Supporting Information). As noted by Kern et al.9 given the lack of standards, the most appropriate instrumental methodology would be to acquire high resolution mass spectra in full scan mode using quadrupole time-of-flight tandem mass spectrometry or ion trap orbitrap tandem mass spectrometry (LTQ orbitrap MS/MS). Very high resolution MS using FTICRMS may be another approach.12,35 A viable alternative for some compounds (125) that are readily derivatized (e.g., phenolics and carboxylates) would be gas chromatography (GC) high resolution MS using GC-QTOF or magnetic sector instruments. About 90 compounds appeared to be analyzable by GC-MS without derivatization based on their structure and reported GC separations for related molecules analyzed (see Table S1). As indicated in our earlier publication,2 many of the 610 chemicals that were selected as potential PB chemicals had only part of the structure that appeared to be persistent as indicated by the rules of thumb.19 Evaluating the 610 chemicals and the HPV chemicals resulted in several hundred chemicals that could be potential PB chemicals (see Table S1, Supporting Information). The examples above had a fair amount of information on the commercial synthesis and byproducts and impurities that might be found in the commercial product.
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ASSOCIATED CONTENT
S Supporting Information *
Tables and figures providing a list of 320 potential persistence and bioaccumulative byproducts, impurities, and transformation products (see Table S1); a figure of the impurities in commercial HBCDD (see Figure S1); the isomers of commercial hydrogenate terphenyl and possible environmental metabolites (see Figure S2); and plots of log Kow version BIOWIN values for the parent compounds and transformation products (see Figure S3). This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Phone: 315-727-0679. Fax: 315-452-8440. E-mail: howardp@ srcinc.com. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Financial support for the study was provided by the U.S. EPA Great Lakes National Program Office (Chicago, IL) and by Environment Canada (Great Lakes 2020 program). We thank Ted Smith (U.S. EPA, GLNPO) for his interest in the project. Thanks to Joanne R. White and to Bill Meylan (SRC, North Syracuse, NY) for editorial corrections and physical−chemical property estimates, respectively.
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REFERENCES
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Environmental Science & Technology
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dx.doi.org/10.1021/es4004075 | Environ. Sci. Technol. 2013, 47, 5259−5266
