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A Risk-Management Strategy for PCB-Contaminated Sediments Appendix F Methods of Analysis of PCBs in Sediments, Water, and Biota METHODS OF QUANTIFICATION A number of methods are available to quantify concentrations of PCBs in sediments and tissues. Each technique has advantages and disadvantages. The resources and equipment required vary greatly among methods. The method selected for use in quantifying PCBs, either in the exposure quantification phase or in the subsequent monitoring phases, should be matched to the requirements of the analysis in which the data will be used. Some of the methods are sufficiently robust to allow congener-specific analyses while allowing the generation of total concentrations of PCBs that can be compared with historical information. Below is an overview of the available methods and their utility for use in risk assessment and monitoring efforts. Gas-Chromatography-Based Methods The gas chromatography schemes that are used in the quantification of PCBs can generally be divided into two types: PCB quantification based on analogy to Aroclor technical mixtures is referred to as the Aroclor method and that based on quantification of individual PCB congeners present in samples is referred to as the congener-specific method. The typical Aroclor analysis is based on estimating residue PCB concentrations by measuring a subset of PCB congeners or by approximating the profile as an appropriate set of technical mixtures (Newman et al. 1998). In the United States, PCB water-quality
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A Risk-Management Strategy for PCB-Contaminated Sediments criteria established by the Clean Water Act (Title 40 CFR part 125.58) to protect humans and wildlife are based on Aroclor values (EPA 1995). Unfortunately, the environmental weathering of Aroclors modulates mixture toxicity (Quensen et al. 1998). As such, carcinogenic risk-assessment guidelines recommend the calculation of congener-specific or total PCB data when available (EPA 1994c). Congener-specific analyses utilize the direct quantification of each unique PCB congener. The result is a precise description of PCB profiles, which can highlight physiological, spatial, and temporal changes that might not be apparent in Aroclor values. Both the Aroclor and the congenerspecific methods of PCB analysis rely on gas chromatography. Gas-chromatography methods require the extraction of PCB from the environmental matrix and usually require the cleanup of the PCB extract by one or more methods before analysis. A gas chromatograph (GC) is used to separate individual PCB congeners or combinations of congeners based on physical properties, such as volatility and polarity. Over the past 20 years, open tubular capillary GC columns have replaced older packed GC columns for routine laboratory work. The capillary GC columns offer improved resolution, better selectivity, and increased sensitivity compared with packed GC columns. For that reason, many standard EPA methods have been rewritten to allow the use of capillary GC columns for the analysis of environmental samples. The use of open tubular capillary GC columns in a GC system is termed high-resolution gas chromatography (HRGC). All the analytical methods presented below for PCB analysis use HRGC. Within a GC system, PCBs are then detected with electron capture detection (ECD), electrolytic conductivity detection (ELCD), or mass spectrometry (MS). For MS detection of PCBs, two systems are considered: low- or medium-resolution MS and high-resolution MS. The data output of a GC is called a chromatogram and individual PCBs are identified as peaks on the chromatogram. For GC-ECD and GC-ELCD, PCBs are identified by order of elution from the GC, also called retention time. For MS systems, PCBs are also identified by molecular mass. Certain coplanar PCBs, which are known or suspected carcinogens, are sometimes measured with high-resolution mass spectrometry (HRMS) techniques originally developed for the analysis of dioxins and furans in environmental samples. The HRMS technique provides lower limits of detection for PCB congeners but requires additional sample cleanup beyond that normally required and requires special instrumentation, the high-resolution mass spectrometer. The utility of the two GC-based methods of PCB analysis (Aroclor and congener-specific), based on costs and benefits, is summarized in Table F-1. These two methods are discussed in detail in the following sections.
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A Risk-Management Strategy for PCB-Contaminated Sediments TABLE F-1 Utility of Aroclor and Congener-Specific Methods of PCBs Analysis Analysis Method Cost High Utility Low Utility Aroclor analysis Low Identification of neat mixture Preliminary site screening; soil Preliminary site screening; sediment Biological samples PCB quantification Soils and sediments siangle PCB mixture low organic carbon short residence time Weathered PCBs Congener-specific analysis High Biological samples Weathered PCBs Data utilized for toxicology analysis Aroclor Method of PCB Quantification For many years, PCB concentrations in environmental media have been quantified by comparison to Aroclor standards. Early gas chromatography-electron capture detection (GC-ECD) methods, such as the EPA’s solid waste 846 (SW 846) methods 8080 and 8081 (EPA 1994a,b), relied on comparing the chromatographic pattern of peaks in the environmental sample with the pattern or number of peaks in a series of pure Aroclor standards. However, due to biological processes, such as biodegradation and metabolism, or environmental processes, such as volatilization, congener profiles of PCBs in environmental samples are different from technical Aroclor standards. The alteration of the congener pattern in environmental samples can be influenced by several factors, including source and type of PCBs, type of environmental media (air, water, soil, sediment, and biota), physical-chemical properties of the media (temperature, pH, organic carbon content), the congeners present in technical mixtures, and the type and abundance of microfauna and flora. Therefore, the methods might not be applicable to environmental samples containing weathered Aroclors or complex mixtures of Aroclors. Aroclor analyses are estimations that are prone to error. Two important sources of variance in the methodology as defined by EPA are the subjective assignment of Aroclor speciation and response factors (Draper et al. 1991) and the assumption that Aroclor response factors are representative of weathered profiles. As an example, determination of the concentrations of PCBs based on the COMSTAR algorithm, a statistical procedure to determine total PCBs based on marker congeners and peak ratios (Burkhard and Weininger 1987),
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A Risk-Management Strategy for PCB-Contaminated Sediments overestimated the concentrations determined by summing the concentrations of individual congeners. This artifact occurs because COMSTAR estimates total concentrations of unweathered PCB congeners that would have been present in the original technical Aroclor mixtures (Giesy et al. 1997). Similarly, several other computer programs incorporating multivariate analysis have been developed to normalize PCB concentrations in samples to those in Aroclor standards (Stalling et al. 1985). Despite that, the Axoclor method does not adequately represent the concentrations found in weathered environmental samples. The discrepancies in the congener composition between the commercial mixture and real-world environmental exposures imply that the predictive value of studies based on commercial mixtures might be limited with respect to estimating risks from environmental exposure. Determination of all PCB isomers and congeners present in environmental matrices using a mixture of technical PCB preparations (such as an equivalent mixture of Aroclors 1016, 1242, 1254 and 1260) as standards might provide a better estimate of PCB concentrations for use in risk assessment. The advantage of the Aroclor method is its simplicity, cost, and comparability to historical and contemporary PCB concentrations. Detection Limits and Method Performance The method detection limits (MDLs) for Aroclors vary in the range of 0.054 to 0.9 mg/L in water and 57 to 70 ng/g in soils, with higher MDLs for the more heavily chlorinated Aroclors. Estimated quantification limits for PCBs as congeners vary by congener in the range of 5 to 25 ng/L and 160 to 800 pg/g in soils, the higher values being for the more heavily chlorinated congeners. Cost Aroclor analysis is relatively inexpensive in comparison to congener-specific methodologies. The cost on a per sample basis ranges from $50 to $500, depending on the sample matrix, number of samples to be analyzed, and extent of quality-assurance-quality-control protocols. Implications of Aroclor Analysis in Risk Assessment The differences in the composition of PCB residues in environmental
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A Risk-Management Strategy for PCB-Contaminated Sediments matrices have implications not only for quantification but also in hazard evaluation, particularly when considering the differences in the biological activity, both qualitatively and quantitatively, among isomers as well as congeners. Several studies have demonstrated the differences in both mechanisms and toxic potentials of individual PCB congeners (see Giesy and Kannan 1998). Thus, the impacts of PCBs on the environment and biota are due to the individual components of these mixtures and the additive and/or nonadditive (synergistic and antagonistic) interactions among them and other chemical classes of pollutants. Therefore, the development of scientifically based regulations for the risk assessment of PCBs requires analytical and toxicological data on the individual PCB congeners present in any technical mixture and information regarding interactive effects. Although developments in high-resolution isomer-specific PCB analysis have enabled identification and quantification of individual PCB congeners present in commercial mixtures and environmental samples, there are important challenges associated with risk assessment of PCBs due to their different mechanisms of biological activity and toxicity. Most of the earlier in vivo animal exposure—and in vitro bioassay—studies have exposed animals to commercially available technical PCB mixtures. Only in the past 10 years has the toxicity of individual congeners been studied. Due to the differences in metabolism and/or biodegradation rates of individual congeners, the compositions of the original commercial technical mixtures are different from the compositions of the mixtures to which humans or wildlife are exposed (McFarland and Clarke 1989). Due to changes in the relative proportions of individual congeners in PCB mixture, reference doses (RfDs) derived from laboratory studies for technical Aroclor mixtures might not be appropriate for the PCB mixture found in environmental samples. The environmental weathering of PCB mixtures can result in a reduction or enrichment of toxic potency over time (Quensen et al. 1998, Corsolini et al. 1995a,b; Williams et al. 1992). For example, microbially mediated anaerobic reductive dechlorination is common in sediments in which chlorines are removed from the PCB biphenyl rings (Bedard and Quensen 1995). Dechlorination of PCBs can eliminate the most toxic coplanar congeners (Zwiernik et al. 1998). As a result, the toxic potency of the resulting PCB mixture can be reduced by as much as 98% (Quensen et al. 1998). Moreover, Aroclor-based analysis will not detect a change in either the quantity or the quality of the above PCB mixture, including toxic coplanar congeners. In this case, estimation of hazard based on RfDs from laboratory exposure to technical PCB mixtures would overestimate the risk. In contrast, certain aquatic animals selectively enrich arylhydrocarbon receptor (AhR)-active congeners, an enrichment that can result in greater relative proportion of these toxic congeners in tissues than in technical mixtures (Williams et al.
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A Risk-Management Strategy for PCB-Contaminated Sediments 1992; Corsolini et al. 1995a,b). In this case, estimation of hazard based on RfDs from laboratory exposure to technical PCB mixtures would underestimate the risk. Aroclor-based analysis and risk assessment offer minimal insight into toxicokinetics, because animals exhibit interspecies differences in their abilities to metabolize specific PCB congeners. Toxicity of PCB congeners to different species might be modulated by species-specific differences in lipid metabolism, quantitative differences in binding of PCBs to receptors in target organs, enzyme induction, or other differences in toxicokinetics. Another uncertainty associated with estimates of toxicity based on exposure to commercial PCB mixtures (i.e., Aroclors) is related to the relative amounts of polychlorinated dibenzofurans (PCDFs) and polychlorinated naphthalenes (PCNs) identified as contaminants in technical PCB preparations or as covariates in complex environmental mixtures. Concentrations of total PCDFs and PCNs in Aroclor preparations were in the ranges of 0.6 to 7.5 μg/g and 2.6 to 170 μg/g, respectively. Certain PCN congeners are bioaccumulative and exhibit toxic effects similar to those reported for PCBs. In most studies, the PCDF and PCN contents were not quantified, and their contribution to technical PCBs-induced toxicity is unknown. Accepted Methods for Aroclor-Based Analysis The recent EPA method 8082 is a performance-based procedure that describes a dual capillary-column gas-chromatographic analysis of PCBs as Aroclors or as individual PCB congeners in extracts from solid or aqueous matrices (EPA 1996a). This procedure also relies on Aroclor pattern recognition techniques. This method is an improvement of earlier iterations of the procedure and provides greater laboratory flexibility. Unfortunately, the method has procedural recommendations that might be counterproductive. The use of decachlorobiphenyl (PCB 209) as an internal standard will result in negative bias if Aroclor 1268 is present in environmental samples (Aroclor 1268 contains 4.8% of PCB 209) (Kannan et al. 1997). More important, method 8082 suggests instrument calibration with appropriate Aroclors when a PCB contaminant source mixture is known but relies on 1:1 mixture of Aroclors 1016 and 1260 to calibrate for samples containing PCBs from an uncharacterized source. Single concentrations of subjectively identified Aroclors are then analyzed, and the 1016 and 1260 calibration is transformed based on the results. This practice has two underlying problems. First, the use of single-point extrapolations assumes linear-response factors throughout the range of PCB concentrations to be analyzed, when in fact that assumption
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A Risk-Management Strategy for PCB-Contaminated Sediments is rarely the case. Second, the Aroclor mixture has a distinct congener percent composition; therefore, the assumption that 1016:1260 congener co-elution domain response factors represent the response factors for individual Aroclors is fundamentally unsound (Newman et al. 1998) Despite the concerns discussed above, Aroclor determination might be required when compliance measurements specify Aroclors. The details of one Aroclor-based method are given below and summarized in Table F-2. Method: EPA SW 846 Method 8082/PCBs by Gas Chromatography for Aroclor (EPA 1996a) Analytes Measured: PCBs are measured as Aroclor formulations or congener. Aroclor 1016, Aroclor 1221, Aroclor 1232, Aroclor 1242, Aroclor 1254, Aroclor 1248, Aroclor 1254, and Aroclor 1260 have been tested. Instrumentation: High-resolution gas chromatography with electron capture detection (HRGC-ECD) or electrolytic conductivity detection (ELCD). Quantification Method: Uses the external standard method to quantify Aroclor. A solution of Aroclor 1016 and Aroclor 1260 is used for a 5-point calibration, which is then used for all Aroclors. All Aroclors are also analyzed separately for pattern identification and single-point calibration. Decachlorobiphenyl (PCB209) is used as a surrogate to determine recovery. MDL: The MDL ranges from 57 to 70 μg/kg of soil and from 0.054 to 0.090 μg/L of water. Discussion: EPA method 8082 was released in December 1996, replacing EPA method 8080. PCBs can be measured as Aroclors or congeners by this TABLE F-2 Summary of One Aroclor-Based Analytical Method Used for the Examination of PCB in the Environment Method Analytes Instrumentation Quantification method MDL Typical cost per sample EPA SW 846 method 8082/ PCBs by gas chromatography PCBs as Aroclor formulation HRGC-ECD or HRGC-ELCD External standard method, single surrogate, 5-point calibration of Aroclor solution 57 to 70 μg/kg, soil/sed. $250–300
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A Risk-Management Strategy for PCB-Contaminated Sediments method. The surrogate compound is spiked into the sample, the sample is then extracted by an appropriate method, and the extract is concentrated. Typically for PCBs, the extracts are cleaned up using concentrated sulfuric acid cleanup. The internal standard is added to the clean extract, and the sample is analyzed by HRGC-ECD. Individual PCB peaks are identified by retention time. The peaks should be confirmed by dual-column analysis. The method recommends the analysis of reference material and samples spiked with compounds of interest following SW 846 guidance. The method warns users that acceptable qualitative and quantitative analysis of Aroclor in environmental samples using this method or other methods is difficult to obtain because of weathering. Aroclor analysis is recommended only for compliance measurements where Aroclor concentrations need to be specified. Congener-Specific Analysis of PCBs As analytical capabilities have increased over the past 30 years, the standard approach applied to the analysis of PCBs has slowly shifted from technical grade approximation to component-based analyses. Component-based analysis or congener-specific analysis has improved the quality and the toxicological relevance of the resulting data. Many research applications, particularly those investigating ecological effects require comprehensive, quantitative, congener-specific analysis of PCBs (Frame 1997). By this method, congener profiles resulting from combinations of technical mixtures can be easily identified. Likewise, congener profiles differing from the original technical mixtures in profile and toxicity because of weathering can now be addressed effectively. Congener-specific analysis can be performed by both GC-MS and GC-ECD techniques. Both techniques use analyte separation via a split valve injector and capillary-column stationary phase. Mass-spectrometric detection of ions selective for individual congener groups provides confirmation. Selective mass analysis is used to individually quantify sets of co-eluting congeners. By this method, interfering compounds can be identified easily and therefore false-positives can be eliminated. Detection Limits and Method Performance: The GC-MS method provides better precision and resolution than the GC-ECD techniques. Detection limits of individual congeners can be achieved in the lower parts per billion to parts per trillion. The non-ortho coplanar PCBs can be more reliably measured by GC-MS because of their low concentration
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A Risk-Management Strategy for PCB-Contaminated Sediments in most environmental media compared with other congeners. Non-ortho coplanar PCBs can be measured in biological tissues (20 g matrix) at 1 to 10 ppt range, depending upon the nature of the matrix (egg, liver, or fat). Data Summing The manner of summing and reporting PCB congener data is a data-reporting issue, not an analytical one, and the approach varies depending on the application and data need. Typical approaches for handling PCB congener data include Reporting and using only individual congener data. Summing the identified congeners to arrive at a total observed PCB concentration. Summing the identified congeners and using a regression analysis based on environmental data to report levels assumed present. Summing the individual congeners by level of chlorination; (e.g., summing all congeners containing three chlorine atoms and reporting Σ Cl3-PCB). Summing the individual congeners identified as toxic or potentially toxic and calculating a TODD-equivalent concentration. Individual congener data provides the most flexibility for supporting environmental management decisions, because the congeners provide the raw data that can be analyzed numerically or statistically by the environmental manager, case by case, as needed. For example, advanced numerical analysis using hierarchical cluster analysis (H.A.) and principal component analysis (PCA) of PCB congeners may be used to evaluate the linkage between the samples and likely point or nonpoint sources—PCB “fingerprinting” analogous to techniques used to identify fugitive petroleum products (Stout et al 1998). Costs Congener-specific analysis is costlier than Aroclor-based methodologies. The cost on a per sample basis for GC-MS analysis ranges from $800 to $2,000, depending on the sample matrix, number of samples to be analyzed, and the extent of QA/QC required. GC-ECD congener-specific methods are slightly less costly at $500 to $1,200 per sample. These higher costs are in part related to the necessity of highly trained professionals to perform rigorous
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A Risk-Management Strategy for PCB-Contaminated Sediments cleanup techniques to remove interferences from coplanar PCBs. In addition, GC-ECD congener-specific methods require second column confirmation. Implications of Congener-Specific Analysis in Risk Assessments: Congener-specific analysis is recommended for risk assessment because of the differences in the toxic potentials of individual congeners in technical mixtures. Not all 209 PCB congeners are toxic. Several studies have confirmed a correlation between the structure-activity relationships for PCBs. Non-ortho coplanar PCBs 77 (3,3′,4,4′-T4CB), 126 (3,3′,4,4′,5-P5CB), and 169 (3,3′,4,4′,5,5′-H6CB), which are substituted in both para, at least 2 meta. and no ortho positions, are clearly the most toxic congeners of PCBs (Giesy and Kannan 1998). Similar to non-ortho PCBs, mono-ortho congeners, which have one chlorine atom substituted in the ortho position can also elicit AhR binding activity (Safe 1994). However, mono-ortho congeners are relatively less toxic than non-ortho congeners. These studies suggested a need for measuring PCBs at a congener level for application in risk assessment. Toxicological studies conducted in the past 10 years have focused on individual congeners rather than technical mixtures. There is considerable toxicological information for individual congeners from which risk assessment can be performed more reliably than that based on Aroclor measurements (Van den Berg et al. 1998). Total PCB concentrations can also be measured by summing concentrations of all the individual PCB congeners identified in samples. The homologue and congener profile might reveal the source or origin of the contamination. Evaluation of these profiles might indicate whether mixed Aroclors were present and the degree of weathering. Accepted Methods for Congener-Based Analysis This section presents a technical summary of several of the accepted congener-based methods for the analysis of PCBs in environmental samples, including relevant instrumentation, limits of detection, and quality-assurance issues. The technical summary is not intended to be comprehensive. Interested readers are requested to review the original methods. All of the GC analytical methods below are appropriate for the analysis of PCBs in sediments, soils, water, or biological tissue, provided appropriate extraction and cleanup methods are used. The methods below identify between 18 and 78 congeners, which are reported individually or as two or three co-eluting congeners. The 18 to 78
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A Risk-Management Strategy for PCB-Contaminated Sediments congeners represent a subset of the total 209 possible congeners but include those most commonly found in environmental samples. Collectively, about 18 to 22 congeners usually represent about one-half of the total PCB that might be found in an environmental sample, if an exhaustive analysis of all congeners is performed. The EPA method 1668 measures 13 toxic or suspected toxic congeners that usually constitute a small fraction (<5%) of the PCBs found in environmental samples. Although the standard HRGC-ECD methods presented below identify and report between 18 and 22 PCB congeners, it is important to note that each method can be expanded to include additional PCB congener analytes. All PCB congeners are chemically similar and behave similarly in terms of their extraction and analysis. The addition of new congeners to an existing method is a simple matter of adding the new congener to the calibration standards and performing appropriate validation steps to demonstrate the method. PCB congener standards of documented purity are available for all 209 PCB congeners. The methods presented for congener-specific PCB analyses are summarized in Table F-3. Detailed descriptions of the methods follow the table. Method: EPA SW 846 Method 8082/PCBs by Gas Chromatography for Congener (EPA 1996a) Analytes Measured: The 19 PCB congeners tested by the method include PCB 1, PCB 5, PCB 18, PCB 31, PCB 44, PCB 52, PCB 66, PCB 87*, PCB 101*, PCB 110, PCB 138*, PCB 141, PCB 151, PCB 153, PCB 170*, PCB 180, PCB 183, PCB 187*, PCB 206. (Reported in the EPA congener list: *PCB 87 comprises three co-eluting congeners PCBs 87/115/81, PCB 101 is the co-eluting pair PCBs 101/90, PCB 138 is PCBs 138/160/163; PCB 170 is PCBs 170/190, and PCB 187 is PCBs 187/182.) Instrumentation: High-resolution gas chromatography with electron capture detection (HRGC-ECD) or electrolytic conductivity detection (ELCD). Quantification Method: Uses the internal standard method with a decachlorobiphenyl (PCB 209) as the single internal standard is used. A solution of the 19 target congeners is used for a 5-point calibration. Tetrachloro-m-xylene is used as a surrogate to monitor recovery. MDL: The MDLs for congeners are not provided in the method but are assumed similar to the National Oceanic and Atmospheric Administration (NOAA) method and the U.S. Army Corps of Engineers (USAGE) New York
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A Risk-Management Strategy for PCB-Contaminated Sediments TABLE F-4 Immunoassay Method for PCB Screening Method Typical Sample Size Summary of Method EPA method 4020, screening for PCBs by immunoassay 5 g of soil or sediment, or nonaqueous waste liquids Soil samples are extracted with methanol and test kit reagents. A sample extract and an enzyme conjugate reagent are added to immobilized antibody that binds both. A second enzyme and dye are added, and the color intensity is measured with a spectrophotometer. The signal is indirectly proportional to the amount of PCB. The results are compared against three calibrators of 5, 10, and 50 ppm. PCB concentrations are semiquantitatively classified as below 5 ppm, between 5 and 10 ppm, between 10 and 50 ppm, and greater than 50 ppm. Sensitivity can be optimized to detect samples in the low (0.5–1.5 ppm) range semiquantitative not quantitative. Different commercial PCB formulations show a wide range of sensitivity to the test method (factor of 8 between Aroclor 1254 and Aroclor 1268). However, because of the ease of use and rapidity, the method is often used for field screening of PCBs. Cell Bioassays—H4IIE Cells The H4IIE-luciferase induction assay is an in vitro technique for the identification of AhR-active compounds (Hilscherova et al. 2000). The technique uses rat hepatoma cells (H4IIE-luc) stably transfected with an AhR-controlled luciferase reporter gene construct (Sanderson et al. 1996). The assay is also referred to as the chemical-activated luciferase gene expression (CALUX) system (Murk et al. 1996). These cells express firefly luciferase in response to AhR agonists. Luciferase activity is measured conveniently and with high sensitivity as light emission using a plate-scanning luminometer. Luciferase induction potential is assessed by comparison of the response to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TODD), the most potent agonist for the mammalian AhR. This cell bioassay has been utilized for the screening and monitoring of Ah-active components in environmental extracts of sediment, water, air, and tissue (invertebrates, fish, birds, and mammals). The H4IIE rat hepatoma cell bioassay (Tillitt et al. 1991) is widely used for this purpose. In this assay, ethoxyresorufin-O-deethylase (EROD)-inducing potencies (ED50 values) of
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A Risk-Management Strategy for PCB-Contaminated Sediments single compounds and environmental samples are determined from complete dose-response curves and compared with EC50 values of TODD to express the biological potency of the tested samples in TODD-equivalents. The bioassay integrates potential nonadditive interactions among AhR agonists and other compounds by measuring a final receptor-mediated response (Giesy et al. 1994). One of the primary purposes of this bioassay is to prioritize samples for more extensive quantification by instrumental analysis. It can also be used to direct fractionation steps in a toxicity identification and evaluation approach and to detect novel compounds that have biological activity similar to that of TODD. Excellent correlation has been observed between the TODD-equivalent concentrations determined from this bioassay and instrumental analysis when these methods have been applied to the same sample (Tillitt et al. 1996, Quensen et al. 1998). For a sample size of 20 g of tissue or soil and a final extract volume of 0.25 mL, the H4IIE-luc assay will detect 1 part per trillion (ppt; pg/g of wet weight) TODD-equivalents. Sample Extraction Methods The above analytical methods must be used with appropriate extraction and extract cleanup techniques to be effective. Broadly, PCBs are extracted from environmental matrices along with a potentially wide range of hydrophobic organic compounds of similar polarity and volatility. For example, in EPA method 1625, PCBs are extracted from water along with 175 other listed compounds extracted from water. In EPA method 8270, PCBs are listed with 243 other analytes. The selectivity of the extraction and cleanup procedures to isolate PCBs from other extracted compounds (so-called matrix interferences) usually determines the MDL—that is, the greater the level of interfering compounds in individual sample extracts, the greater the level of PCB required to overcome the interference. Ecological risk assessments currently require PCB MDLs in the low parts per billion for sediments and biological tissue. Appropriate and rugged sample extraction and extraction cleanup procedures are required to deliver those low MDLs routinely. All of these methods use surrogate materials added at the beginning of the process to monitor performance. Fortunately, environmental samples have been extracted for PCBs for over 25 years. During this time, sample extraction and cleanup procedures have been refined, and procedures delivering MDLs in the low parts per billion are well recognized. Quality-assurance programs have been established supporting low-level detection methods. Multiple standard reference materials, interim reference materials, and other quality-assurance samples are available to support PCB analytical programs.
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A Risk-Management Strategy for PCB-Contaminated Sediments This section is intended to provide a brief overview of the available approaches to sample extraction and extract cleanup and compares several of the methods. There are literally hundreds of combinations of methods currently in use for PCB extraction and cleanup, and no effort has been made for this review to be all inclusive. The methods presented are those in use by EPA, EPA regions, state agencies, and NOAA for determination of PCBs at environmental levels. An experienced laboratory will have little difficulty using the methods to determine PCBs at concentrations ranging from low parts per billion to high parts per million. Note that many PCB extraction and cleanup methods, as well as the analytical methods, are performance based. That is, the methods are not prescriptive but rather present procedures that may be followed directly or used as guidelines for analysis at laboratory discretion. Instead of prescriptive methods, the federal and state agencies using PCB data establish quality-assurance requirements, including matrix-specific performance data. Examples of this method include the EPA method 8082 (including extraction method 3510 and 3520 for water and method 3540 and method 3541 for solid samples, and multiple cleanup options) and the NOAA NS&T method. A summary of accepted extraction methods for sediments and soils, water, and biological tissue is presented below. Table F-5 presents and compares several extraction procedures suitable for soils and sediments with a percent solids content of greater than 20%. Methods suitable for biological tissue extraction are presented in Table F-6. In general, many more methods exist for the extraction of PCBs from soils and sediments than for extraction from biological tissue. The EPA Office of Solid Waste and Office of Water have published method for soil and sediment. In addition, the NOAA NS&T method is presented. EPA has no published methods for extraction of PCB from tissue. However, the FDA has published methods for tissue, as well as NOAA NS&T. Used by an experienced laboratory, any of the listed methods will provide suitable results. Cleanup Procedures Cleanup methods—that is, laboratory techniques that remove interfering materials from extracts of environmental samples before analysis—are also presented. Table F-7 presents and compares several cleanup procedures suitable for the isolation of PCB from other classes of organic compounds in extracts of environmental samples. All the above analytical methods presented in Tables F-3 and F-4 call for at least one cleanup method to remove chemical or biological interferences with the PCB analysis.
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A Risk-Management Strategy for PCB-Contaminated Sediments TABLE F-5 Sediment and Soil Extraction Methods Method Typical Sample Size Summary of Method EPA 3540C, soxhlet extraction 10 g of soil or sediment Water layer, if any, is discarded. Any foreign objects, such as sticks, leaves, and rocks, are removed. Sample is mixed thoroughly and blended with equal amounts drying agent (sodium sulfate). PCB is extracted into acetone/ hexane or acetone/methylene chloride using soxhlet extraction technique. Solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method. EPA 3541, automated soxhlet extraction 10 g soil or sediment Sample preparation as above. Sample may be air dried with no loss of PCB. Sample is mixed thoroughly and blended with equal amounts drying agent (sodium sulfate). PCB is extracted into acetone/hexane using an automated soxhlet extraction apparatus. Solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method. EPA method 3550, ultrasonic extraction 30 g of soil or sediment Sample preparation as above. Sample is mixed thoroughly and blended with equal amounts anhydrous sodium sulfate. The sample is extracted 3× with acetone/hexane or acetone/methylene chloride using an ultrasonic disrupter. Solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method. EPA methods 3560 and 3561, super-critical extraction 3 g soil or sediment Sample preparation as above. Wet samples may be mixed with drying agent or diatomaceous earth to enhance porosity. The sample is extracted with supercritical CO2. PCBs that are extracted with the CO2 are trapped in an organic solvent. Solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method. NOAA NS&T method (MacLeod et al 1993) 10 g soil or sediment Sample preparation as above. The sample is mixed thoroughly and blended with equal amounts anhydrous sodium sulfate. The sample is extracted 3× with dichloromethane using shaker or tumbler apparatus. Solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method.
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A Risk-Management Strategy for PCB-Contaminated Sediments TABLE F-6 Tissue Extraction Procedures Method Typical Sample Size Summary of Method Organo-chlorine residues, general methods for fatty foods (FDA 1999) Ca. 30 g of wet tissue Wet tissue is placed in a Teflon or glass extraction container along with equal amounts of anhydrous sodium sulfate and extracted with petroleum ether using a commercial high-speed blender. The solvent is filtered and dried before further clean up. Solvent concentration is by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method. NOAA NS&T method (MacLeod et al 1993) Ca. 30 g of wet tissue This method is similar to the FDA method, from which it was originally taken. Wet tissue is placed in a Teflon extraction container along with equal amounts of anhydrous sodium sulfate and extracted with methylene dichloride using a commercial high-speed homogenizer. The solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration is by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method. NOAA NS&T soxhlet method (NOAA 1998 Ca. 30 g of wet tissue This method is similar to the soxhlet method presented above for sediment or soil. The sample is mixed thoroughly and blended with equal amounts drying agent (sodium sulfate). PCB is extracted into methylene chloride using soxhlet extraction technique. Solvent is exchanged to hexane or other solvent for cleanup and analysis. Solvent concentration by Kuderna-Danish concentrator, nitrogen evaporation, or equivalent method.
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A Risk-Management Strategy for PCB-Contaminated Sediments TABLE F-7 Methods Appropriate for the Cleanup of Environmental Extracts for PCB Analysis Method Summary of Method EPA method 3610B, alumina cleanup Alumina, a porous and granular form of aluminum oxide, is adsorptive and is used to separate classes of organic compounds based on their chemical polarity. A sample extract is added to an alumina column, which is eluted with a series of solvents of increasing polarity to isolate PCB. The method 3610B, which includes the use of commercial solid-phase extraction cartridges, is one of many written methods of the use of alumina PCB cleanup. Alumina is one of several adsorbents commercially available for this purpose. Others include silica gel and florisil, and accepted methods for using these also can be found in the literature. The method for extracts from water, waste water, soil, sediments, biological tissue, and other environmental samples upon method validation. EPA method 3665A sulfuric acid/ permanganate cleanup The sample extract is reacted with concentrated sulfuric acid alone or acid and potassium permanganate. This procedure destroys most organic chemicals, including most pesticides and other compounds that interfere with the PCB HRGC-ECD analysis. For this reason, the method cannot be used if non-PCB analytes are to be measured in the same extract. Acid cleanup is generally followed by alumina or other adsorption column cleanup to further isolate PCB. Method 3640A, Gel-permeation (size-exclusion) chromatography The method separates classes of compounds based on molecular size. The sample extract is passed through a porous gel or porous solid bead of uniform pore size, which is chosen to exclude molecules of a certain size or larger. Excluded molecules elute before smaller molecules that pass through the pores in the beads. The method is particularly effective at removing common interferences from environmental extracts, such as sulfur and plant or animal fats. Krahn et al (1988) presents an automated HPLC cleanup method based on the size exclusion principle that has been used extensively in the NOAA NS&T program. NOAA NS&T copper method (MacLeod et al 1993) Elemental sulfur, often present in freshwater or marine sediments, is extracted under most conditions presented in the above methods tables and must be removed. Activated copper is one of several reagents that can be used for this purpose. The activated copper is commonly added to concentrated extracts, but it also may be added in the thimbles of soxhlet extractors and extraction vessels of supercritical fluid extractors.
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Representative terms from entire chapter: