Ultratrace extraction of persistent organic pollutants

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Ultratrace extraction of persistent organic pollutants Yves Tondeur, Jerry Hart We review and discuss ultratrace extraction as a high-volume technique for quantifying persistent organic pollutants in aqueous matrices, including its evolution, its acceptance by scientific and regulatory communities, influential factors, published validation efforts and analytical issues to bring to light existing assumptions concerning its effectiveness. We identify important methodological gaps, which may affect potential analytical outcomes, to orient future validation efforts or to pursue more effective alternatives. We also review the function and the purpose of quality-control features. Regarding analytical issues, we examine those related to sample definition (e.g., the distinction between high-volume sampling and extraction) and the major sources of bias associated with measurement technology – particularly sample-preparation and analysis steps in the laboratory. We discuss challenging old ways of viewing sampling and analysis as independent entities, emphasizing that a change in sample configuration (i.e. multi-component, multi-matrix and voluminous samples) must result in changes in the analytical protocol, if reliable data are desired. Current methods are not structured to facilitate the adaptation needed to ensure data are reliable, even if they are based on powerful isotope-dilution technology. We review the literature to identify deficiencies related to validation of the technique, to provide a basis for experiments that scientists can consider to test expressed concerns (confirm or refute) and to evaluate their effects on data quality (precision and accuracy). It is necessary to review the state of the science to ensure that we do not develop and validate a procedure whose design is at odds with its purpose. ª 2009 Elsevier Ltd. All rights reserved. Abbreviations: ASE, Accelerated solvent extraction; DOM, Dissolved organic matter; EPA, US Environmental Protection Agency; fg/L, Femtogram per liter; GC-MS, Gas chromatography coupled to mass spectrometry; GFF, Glass-fiber filter; HOC, Hydrophobic organic contaminant; HVE, Highvolume extraction; OPR, Ongoing precision and recovery; PCB, Polychlorinated biphenyl; PCDD/F, Polychlorinated dibenzo-p-dioxins and furans; PM, Particulate matter; POP, Persistent organic pollutant; ppq, parts per quadrillion; ppqt, parts per quintillion; PUF, Polyurethane foam; QA/QC, Quality assurance/quality control; SPMD, Semi-permeable membrane device; TCDD, Tetrachlorodibenzo-p-dioxin; TCDF, Tetrachlorodibenzofuran; WQC, Water-quality criterion Keywords: Aqueous matrix; Data quality; Dioxin; Dioxin-like compound; Isotope dilution; Persistent organic pollutant; Quality control; Sample preparation; High-volume extraction; Validation

Yves Tondeur*, Jerry Hart Analytical Perspectives, 2714 Exchange Drive, Wilmington, NC 28405, USA

*

Corresponding author. Tel.: +1 (910) 794-1613; Fax: +1 (910) 794-3919; E-mail: [email protected]

1. Introduction With the advent of isotope dilution with high-resolution gas chromatography coupled to high-resolution mass spectrometry (ID-HRGC-HRMS) [1,2], the limits of detection (LODs) significantly improved. Concurrently, the drive for reliable data in risk-assessment studies continued to support the development of methodologies capable of achieving even lower levels of detection for substances, such as dioxins and dioxin-like compounds. Since the early 1980s, we have seen advances in ultratrace analyses with sample-preparation techniques [3], sample-introduction approaches [4] and enhanced detector performance [5].

0165-9936/$ - see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2009.07.009

One area of interest – not mentioned above – is the development of sampling techniques designed to increase sample size significantly as a means to lower the LODs. Most recognized is the concentration of organics onto sorbents (e.g., XAD-2 resin for flue-gas samples [6] and polyurethane foam (PUF) for ambient-air samples [7]). However, this review focuses on the use of similar sampling modules to extract minute quantities of dioxins and dioxin-like compounds from large volumes of water (e.g., 1000 L). In 1984 [8], when the US Environmental Protection Agency (EPA) established the ambient surface water-quality criterion (WQC) of 0.013 ppq for 1137

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2,3,7,8-tetrachlorodibenzo-p-dioxin, analytical methodologies could not achieve this level of detection unless a larger sample volume was employed. Even today, stateof-the-art methodologies – principally relying on 1-L extractions – are only able to achieve limits of quantitation (LOQs) that are three orders of magnitude greater than the EPA quantitative criterion. The idea of high-volume extraction (HVE) is simple; a large volume of water is forced through a series of filters followed by solid-phase extraction sorbent beds. Dissolved minute amounts of hydrophobic organics are adsorbed by the sorbent. The retained solids, the filters and the sorbent cartridges are then returned to the laboratory for analysis.

2. Pioneering studies At two Dioxin symposia [9,10], Rappe presented data about the use of PUF for concentrating dioxins from large volumes of drinking water, seawater and river waters. Volumes timidly started at 150–430 L, and went up to 1500 L, depending on the types of water being sampled. Like many others who followed his lead, he found numerous practical issues that were eventually addressed over the years, through the introduction of prefilters to remove large particulates, filters capable of retaining particles above 1 lm, filters used with a centrifuge or configured in parallel, increasing the size and the number of resin columns, and more robust sampling equipment. Generally, clogging of the filters requiring frequent replacements and interruptions of the sampling efforts were reported.

3. Validation studies As mentioned earlier, the idea is simple. However, the complexities associated with both sampling and analytical aspects become evident in the sections to follow. When the objective is to determine the presence and the concentrations of dioxins at levels 1000 times lower than the state-of-the-art, a new technique must be developed. Its feasibility and applicability need to be assessed before undertaking comprehensive validation efforts. Our review of published studies reveals that efforts have mostly been directed toward sampling, not laboratory analysis. Moreover, there seems to be lack of agreement on what constitutes validation or when the technique is regarded as reliable. In effect, very little information to assess the effectiveness of the HVE systems can be found in the literature. Often, we discover that, mistakenly, authors refer to a validated sampling technique in their conclusions or mention the word validation in their article titles when 1138

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they present no definitive data for validating the technique. It is desirable that we hold our conclusions as provisional, pending further data because unsupported conclusions regarding validated techniques become leaps of abstraction that are in danger of being accepted as facts. For instance, if the sampling equipment is modified to boost the flow rate and thus shorten the collection time by increasing the amount of resin and the number of columns, appropriate controls need to be in place to ensure that the contact time between the dissolved dioxins and the resin remains optimal for physico-sorption under a particular set of conditions (e.g., water temperature, pH, flow rate, total organic contents, and sorbent-bed crosssection and length). Perhaps, an understanding of the sorption mechanism can help orient future validation efforts. Without supportive data, it becomes difficult for the reader to distinguish a maximum flow rate from an effective flow rate. The latter relates to the extraction efficiency, whereas the former speaks of equipment limitations. Furthermore, we need to be cautious about assumptions. For example, optimal flow rates were determined during breakthrough studies involving 200 L of spiked water and a given resin-bed volume [11,12]. To accommodate larger flows, systems were reconfigured so the numbers of columns and their sizes were increased. Therefore, compared with todayÕs design, the original column sizes, the types of filter and the configurations were different (i.e. the information about system performance obtained in the past may not represent the level of performance today). The first attempt at clarifying what is desired in a validation effort can be found in an article describing an automated preconcentration sampler for drinking water [12]. In the article, the authors stated that a final validation for the equipment required a comparison with conventional liquid-liquid extraction methodologies. Obtaining a suitable aqueous standard reference material presented challenges, so an excellent alternative using split samples from a contaminated source was suggested rather than dynamically spiking the water with known quantities of target analytes, since the hydrophobic nature of dioxins and dioxin-like compounds causes difficulties when mimicking naturallydissolved organics. Future validation efforts might consider different varieties of target analytes. For instance, if humus [13] can dissolve compounds that are normally insoluble in water and act as a transporter for dioxins in the water, we might consider an aquatic humus dynamic spiking regime. Similarly, persistent organic pollutants (POPs) spiked onto 1–10-lm carbon particles could be considered.

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3.1. Cubic Meter Water study [14, 15] and application [17] EPAÕs first efforts to determine parts per quintillion (ppqt) levels of dioxins using a cubic-meter water sample were presented in 1996. The undertaking comprised tap water plus dynamically spiked polychlorinated dibenzop-dioxins and furans (PCDD/Fs), a method LOD study by one laboratory and field applications involving another laboratory. Samples from various sources were collected using an earlier model of the sampling equipment [16]. The primary objective of the study was to establish the

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ability to collect enough water to measure tetrachlorodibenzo-p-dioxin (TCDD) at the 13 fg/L (ppqt) level. Several challenges surfaced during the sampling sessions [14,15] because the equipment was not reliable (e.g., frequent interruptions). From an analytical point of view, the absence of important details (e.g., amount of resin used per module and its particle-size distribution, number of filters and nominal pore size, certain critical details on how the laboratory actually carried out the extractions, quality assurance and quality control (QA/ QC)-sample results, and the way the samples were

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Figure 1. Illustration of what was done to generate data from the Cubic Meter Sample study. The chart shows the complexity of the study design, whereby individual components of the sampler received a fraction of the labeled extraction standards, were separately extracted, analyzed separately as well as after combining the corresponding extracts, and then analyzed together after combining the combined extracts. The results are compared to the arithmetic sums. Note that up to four resin columns were used here (i.e. two sets of resin-column pairs).

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prepared) all pointed to the analytical phase not receiving the attention necessary. In the discussion that follows, critical analytical issues will be discussed in more detail. At this point, we identify certain practices used in the study that are objectionable. For instance, Fig. 1 shows two serious flaws: 1. the first flaw relates to the resin-column pairs each receiving a fraction of the labeled extraction standards, being extracted separately and the resultant extracts then combined before analysis; and, 2. the second flaw relates to the action of combining the previously-analyzed final extracts and analyzing them as combined. From an analytical point of view, the data obtained in such manner cannot be used (vide infra) to assess the performance of the technology, which is perhaps the reason for the observed disparities (e.g., concentrations differing by a factor of 2). After the study, measurement at the 20-fg/L level was considered feasible, although the need for improvements to reduce labor costs and sampling time was recognized. Later studies incorporated design changes to accommodate higher filtration capacities. In 2000, as part of an on-going evaluation of the applicability of the sampling system, EPA reported on the HVE technique for pulpand-paper-mill effluents [17]. The technique shows good precision. The study included an interesting comparison between the conventional 1-L grab sample and the 1000-L continuous HVE sample. From a validation point of view, such a comparison between conventional and new approaches is sensible. Table 1 summarizes the findings for 2,3,7,8-TCDD/F for the two types of samples. Although the sampling events display good precision despite the fact that sample collections took place on different days, the most disturbing observation is the factor of 5–6 difference between the two sets of results. Even after the application of a correction factor to the dissolved-phase results based on the recoveries of the field spikes (11–12%), the ratio between the grab sample and HVE remains elevated. Incidentally, this correction assumes that the field-spike recovery reflects breakthrough; something that remains unproven. Besides, why would we settle for 10% extraction efficiency?

Excellent details on the dynamic spiking of the field standard are offered in the 2000 study [17]. The solvent used, the delivery system, the delivery rate and the concentrations of the spiking solution provide valuable information about the procedures. The configuration of the injection port is not described, and the reader cannot assess how far from the inlet side of the resin column the injection took place, or if the injection took place under turbulent conditions. The solubility of dioxins in water varies between congeners, so, as part of a validation effort, a representative of each of the homologue groups should be considered instead of limiting the evaluation to one of the target analytes. Missing from this report [17] are the recoveries of extraction and clean-up standards, as well as details of how the recoveries for both field (dynamic) and breakthrough (static) standards were computed. The reader cannot determine whether the recoveries of 11–12% for dynamically spiked 13C6-1,2,3,4-TCDD were corrected for the laboratory extraction-fractionation efficiencies. Normally, field-standard recoveries corrected for laboratory operations are expected to be near the 100% mark plus or minus an allowance for the response-factor variations [6]. It is not known where the missing spiked compounds might be (i.e., still inside the resin? breakthrough? never made it to the resin?). The spike level for 13 C6-1,2,3,4-TCDD [18] was 300 times the WQC and at approximately 5 ppq. The dynamic spike is performed just before the resin-sorbent modules, so, presumably, it can provide information about only the dissolved dioxins and not the performance of the equipment for the particle-bound and chelated dioxins (e.g., humus). Finally, the spike levels for the three PCB congeners inside the resin are 10–20 times the TCDD level with recoveries in the range 56–173%. The latter are said to be within the recovery limits of Method 1668A [19]. However, the method was not designed for such types of sample, so the concept of field standards is foreign and the statement on the recovery limits is irrelevant. 3.2. Other relevant studies Interestingly, other reports make it appear that the technology is validated. Following an in-stream study of dioxin levels at several river sites, Dinkins and Heath [20] remarked that the technology is extremely valuable

Table 1. Comparison of the conventional 1-L grab wastewater sample with the 1000-L continuous high-volume extraction (HVE) wastewater sample. The data shows that the grab sample results are 5–6 times higher than the HVE time-weighted-average data [17] Collection Date Volume Units

13-Jul-99 1,000 L Filter + Resin fg/L

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542 4,450

492 4,280

2,440 27,600

2,440 24,800

10% 4%

0% 11%

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and should continue to be refined and expanded upon. Some recommended changes were made to accommodate larger flow rates to reduce the sampling time. The concentration of dioxins in the particulate phase was much higher than in the dissolved phase. In addition, total 2,3,7,8-TCDD (filter and resin) exceeded the WQC in 85% of the samples collected. In a recent publication [21], the same technique, without dynamic field spiking, was applied to stormwater run-off. In light of the results in the EPA report [17], the system continues to be described as capable of rapidly adsorbing dioxins to the resin and thus of completely collecting the dissolved dioxins from the sampled water although no unambiguous proof has been published. Furthermore, the pumping rate was selected based on the technical specifications for the sampling unit to prevent breakthrough of dioxin in the resin, which appears to counter EPAÕs observations [17]. At one location [21], a second resin column mounted in series was analyzed separately and showed 10–25% of potential breakthrough of the first column. The result is quite a difference with the estimated 90% breakthrough from the EPA study. However, as we lack details, it is difficult to assess the impact of laboratorybackground contamination on this latest observation. A separate analysis of the second resin column placed in series remains valuable.

4. Dynamics As a whole, the development of the sampling technology to support the WQC standard focused disproportionately on sampling aspects without consideration of how and why the standard was established. As far as we can make out, the fixation on the LODs achievable with state-of-the-art analytical instrumentation diverted attention from the purpose of WQC and led to a fragmented approach. Sampling-technique selection is beyond our abilities and the scope of this article, which considers important issues associated with the analytical aspects (vide infra). Nevertheless, fundamental questions should be asked. Issues embodied in Figs. 2 and 3 show subtle influential factors that ought to be considered during the development and the validation of the HVE technique. Fig. 2 presents a linear path, from the standard to its measurement and reporting, whereas Fig. 3 shows the interactions of the standard, and the sampling and analytical aspects. The resulting pattern of organization shown in Fig. 3 – when considered with what has been reported thus far – shows an emphasis on sampling efficiency (e.g., lots of water in as little time and with as little interruption as possible to reduce labor costs). It also reveals the weak links where little attention has been paid to why we do things in a certain way. For

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EPA WQC Approach 0.013 ppq Current State-of-the-Art (1,000 times too short)

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Figure 2. The linear path from an established water-quality criterion (WQC) standard to its measurement and reporting.

example, from a validation standpoint, the importance of the target analytesÕ extraction efficiency appears to have received little consideration, not to mention the possible effect of the sample complexity on the analytical bias, or whether the sampling is consistent with the rationale of WQC. We should manage the relationships in Fig. 3 so these factors can develop together because they will transform and shape the way the future process develops toward more purpose-oriented research efforts. 4.1. WQC rationale – sampling – definition relationships During the development phase, designers need to interact with regulators to ensure that the sampling methodology is consistent with the intent of the WQC. It is unclear whether the regulator, the engineer or the toxicologist should decide what is ‘‘dissolved’’ versus ‘‘particle-bound’’ contaminant. The issue centers on the definition of the sample so it objectively answers our concerns about exposure and remains consistent with the rationale followed for the establishment of the criterion. Some of the dioxins captured by the resin could originate from dioxins bound to particles of less than 1 lm. Are particle-bound dioxins considered dissolved when the particle size is less than 1 lm? Of course, this question has potential ramifications for not only bioavailability modeling but also sampling-system designs, http://www.elsevier.com/locate/trac

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Definition Issues

Sampling Issues • Sampling Time • Filter Design / Configuration / Type • Equipment Ruggedness • Governing Factors (effectiveness)

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• Driven by sampling technology? Risk Model? • To assess exposure, what is the sample? • High-Volume Sampling or Extraction? • What is dissolved? • Significance of the 140- µm pre-filter

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Final Report Final Report Issues • Validation of the Technology • Regulatory Filters • Summing Data • Interpretation

Figure 3. Various interdependent and influential factors to consider during the validation of the new high-volume extraction technique. The relationships between the influential factors help delineate their function or purpose. The current pattern of organization shows an emphasis on sampling efficiency and reveals the weak links where little attention has been paid to why we do things in a certain way. The validation of the methodology needs to consider the purpose of the water-quality criterion (WQC) and the total picture.

reporting, and interpretation of the data. Indeed, when the limit of 13 fg/L was established, what kinds of dioxins were the target [22] or, from the point of view of risk exposure, which ought to be considered – truly or freely dissolved in solution (i.e., less than 1 nm and bioavailable [23]), colloid particulates in the range 0.001–1 lm, or adsorbed on particulates in the range 1–140 lm, or all the above? When a supplier of equipment provides a particular specification, of say, 1-lm pore size, is it really 1 lm? Once installed on the system, is it done so that only particulates <1 lm pass through, or should we expect leaks? The questions extend to what the prefilter, which removes particles larger than 140 lm, was intended to accomplish when the WQC was formulated. Is the assumedly optimal 140-lm pore size consistent with protection of human health? Or is it selected because this is what is available on the shelf, or particles larger than 140 lm damage the pump head of the sampling equipment? If we believe that dioxins typically adsorb onto small particulate matter (PM), can the larger than 140-lm particles, filtered and discarded, become a filter for smaller particles? If 80% of the dioxins are expected to be associated with the particulates, and certain authors have justifiably suggested limiting the sampling to the particle-bound dioxins to control cost, how does this suggestion fit relative to the underlying principle of WQC? In essence, the current approach suggests that the bioavailable fraction corresponds to truly dissolved plus adsorbed dioxins on less than 140-lm particles. 1142

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However, according to Suarez [24], Morehead [25] and Burgess [26] showed that colloid-sorbed PCBs and PAHs are not retained by the XAD-2 resin. In fact, Morehead [25] showed that hydrophobic organic contaminants (e.g., PAHs bound to dissolved organic matter) pass through gravity-flow reversed-phase C18 column while freely dissolved hydrophobic organic contaminants are retained by the C18 column. Burgess [26] came to the same conclusion as Morehead for PCBs with PUF or large C18 particles (>63 lm). Suarez suggested that PCDD/Fs (i.e., including 2,3,7,8-TCDD) sorbed to colloidal organic constituents (i.e., fine PM-bound and dissolved organic matter partially bound) are not included in the measurements relying on HVE XAD-2 resin-based systems. 4.2. WQC rationale – analytical – sampling relationships Now, the tools at the chemistÕs disposition cannot adapt to changing circumstances. A linear thinking mindset can take us away from our original goals for data reliability if we assume that what works for 1-L water or 10-g solid matrices will automatically work for 1000-L water subjected to HVE. As previously described, HVE produces 500 g of resin plus water, several large filters containing large amounts of solid materials (Fig. 4), and several wet glass-wool plugs that are sent to a laboratory for analysis. Truly, chemists, engineers and regulators need to interact closely, so that the purpose of the WQC is not compromised by adapting the sampling design – without

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Figure 4. A typical glass-fiber filter (GFF) obtained during a highvolume extraction (HVE) session.

also adapting the analytical methodology – to suit the needs of a more practical approach above those of the WQC rationale. Specifically, when designing any sampling system, we need to keep in mind the various relationships (Fig. 3). In particular, sampling and analytical aspects are not independent. Treating them as such can only lead to serious errors, resulting from underestimating the limitations associated with the powerful ID methodology. To establish that ID works, we must be aware of the technologyÕs traits and applicability, and take appropriate precautions. As a start, we should refrain from introducing too many components or modifying them so that the complexity of the sample submitted to the laboratory increases (e.g., variety of matrices, number of components, and volume or weight). Adding several thick particulate-laden 10-cm long 1-lm filters significantly complicates the analytical procedures at the risk of reducing the credibility of the data. Next, we discuss other details and critical aspects. Other approaches designed to determine the biologically relevant concentrations are available [27]. Whatever the case, the ideal approach has the added benefit of being more aligned with the laboratory sample-handling practices as delineated in todayÕs analytical protocols.

5. Analytical perspectives Most studies focus on the sampling aspects, as if the analytical aspects are a given. Typically, no analytical issues are identified in the published studies, probably as a result of lack of awareness about the limitations associated with the technology in use, and linear thinking (whereby it is assumed that what works on small, simple sample matrices automatically works on more complex samples). Unaware of the potential ramifications, many assume that there are no hurdles associated with transitioning from the extraction of 1-L

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water or 10-g solid matrices to highly complex multicomponent, multi-matrix and voluminous samples (e.g., those obtained from HVE), so it is natural for researchers to direct their attention to sampling equipment. However, it is the chemistÕs responsibility to help reveal the analytical issues associated with the transition. In the introduction, we mentioned that one can lower the measurement limits by either improving the sensitivity of the instrumentation or increasing the sample size. Because we have reached a plateau with regard to analytical instrument performance, increasing sample size is deemed more practical, so our attention should be directed to sample preparation. First, we need to return to our WQC goal and examine what is being done in that context (Fig. 3). Indeed, there is a difference between the terminology HVE and high-volume sampling. HVE leads to a measurement of what is present in the river water, whereas high-volume sampling leads to a measurement of what is present in the sample submitted to the laboratory. The WQC wants to know what is biologically relevant in the surface water, which should define the sample. However, the laboratory can report only what is in the sample submitted for analysis. Like the laboratory extraction of a submitted sample, if the sample must be river water, then extraction of POPs from the river water requires adequate controls to monitor the efficiency of the extraction step. In wanting to do so, we effectively move the extraction step from the laboratory to the field. Thus, according to Methods 8290/1613B, labeled extraction standards should be introduced into the river-water sample before HVE – but this is not done at present because of practical concerns. Consequently, it is necessary to recognize that our current practices are not really telling us what is in the river water (bioavailable or not) – and can fall short of meeting the WQC objectives. Second, we need to acknowledge that Method 1613B, or, for that matter, any other method (e.g., Methods 8290 and 1668B) does not have the proper infrastructure to handle these unique types of sample. The reason for this apparent inability to recognize the potential repercussions can be traced back to lack of understanding of ID-based technology, and the factors governing precision and accuracy. Some of the most questionable practices that we were able to identify included:  splitting the spiked compounds into the various components before separate extractions and combining the resulting extracts;  combining the fractionated final extracts before analysis;  extraction of the tightly woven glass-fiber filters without freeing the strands; and,  citing financial constraints to justify what comes across as poor science. http://www.elsevier.com/locate/trac

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5.1. Spiking and extraction issues When the sampling event is completed, the laboratory typically receives several components per sample. On a per-sample basis, the amounts of particulate can be quite large (e.g., 20 g to >40 g). Moreover, some tests can result in several large glass-fiber filters per sample (Fig. 4), along with 500 g of resin plus water and several wet glass-wool plugs [28]. The multi-component, multimatrix, voluminous nature of these samples is evident. This kind of sample is clearly outside the scope of Method 1613B. It is fair that we ask how the laboratory spiking and extraction operations are carried out, so that we can judge how the sample preparation of Method 1613B is adapted to ensure we continue to generate reliable results in support of the WQC. Explicitly, we want to know where and how the spikes are applied (i.e., filter, PMs or resin) and how extractions are carried out, so that one analysis and one report is generated per sample to control costs, all the while maintaining the quality of the results. We are concerned with the scientific validity (and defensibility) of extracting voluminous samples where several Soxhlet extraction vessels are required. A change in sampling design – both for the sampling module and the filter – and/or accepting the higher cost for more than one analytical run per sample may be required to generate meaningful data. None of the aforementioned infrastructures of methods took into account the importance of the spiking and extraction scheme in achieving data reliability. As already stated, the size of each sample is completely outside the scope of the methods. Solid matrices in Method 1613B are in the size range 10–25 g. Merely adapting the dimensions and the number of the extraction vessels to meet these unique challenges amounts to thinking linearly. Alas, the production of reliable data does not follow such a simple model. As it happens, in response to the special size requirement, the laboratory typically sets up several extraction vessels (Fig. 5). Alternatively, the laboratory can use larger thimbles for the Soxhlet extraction with the requisite improvements to limit heat losses and prevent channeling. In such cases, it is necessary to validate the solvent selection, extraction time and other influential factors. Validation usually relies on spiking experiments. As discussed below, there are important issues associated with adding labeled standards inside a large, complex sample. Under ID conditions, the most critical step involves the spiking [29] of the standards inside the matrix. In particular, one of the three key aspects of spiking [30] requires proper and timely integration of the labeled compounds so that some sort of equilibrium exists between endogenous and labeled compounds. When the sample is spread over many extraction vessels, the integration cannot be carried out in a satisfactory manner. Often, laboratories have no other choices than to spread the spiking solution over the contents of the 1144

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Figure 5. 1-lm filter cut to free the tightly woven glass-fiber strands; the cut filter typically requires more than one conventional Soxhlet thimble holder. Placing the filter unopened inside the thimble will prevent exhaustive extraction of the tightly woven strands.

various extraction vessels, separately extract the various components, and combine the extracts before fractionation and analysis. Notwithstanding the difficulties with integrating the spiked compounds within each sub-sample being extracted, to have valid results, the practice of dividing the spiking solution implicitly assumes that the extraction efficiencies in the laboratory are identical. In reality, there is inherent bias that is a function of the way the endogenous compounds are initially distributed among the various components (e.g., a first filter was used for 75% of the sampling time before it was replaced by a second filter when the flow rate dropped considerably) and of the difference in extraction efficiencies in the laboratory between the two components. For a given distribution of the target analytes (e.g., 75% in Filter A and 25% in Filter B) and a true 1-1 split of the spiked labeled standards, the bias increases with the difference in the recoveries (e.g., from 10% to 30%

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off the correct result when the difference between the two extraction efficiencies in the laboratory increases from 25% to 75%). For cases where the distribution ratio of the native compounds is large (e.g., 95% in Filter A and 5% in Filter B), large differences in extraction efficiencies in the laboratory (e.g., from 50% to 80%) can lead to elevated biases (e.g., from 45% to more than 70% off the correct result). It is worth mentioning that – in a multi-component scenario, where separate extractions are carried out as indicated above – losses from laboratory spills occurring before combining the extracts are not recovery-corrected, as normally occurs for a single-component sample. It is easy to imagine what would happen to the analytical bias when more than two components per sample are spiked separately, extracted separately and the combined extracts analyzed. These flawed practices result in the production of data of unknown quality. Finally, other sources of errors common to current ID methodologies (e.g., response-factor variations) and other spiking errors not caught by the ongoing precision and recovery (OPR) [30] can alter the biases illustrated above, including self-compensations that can lead to correct results by chance. When it comes to the generation of reliable data, the volume or the size of the sample and the successful integration of the spike are not independent. For samples containing large amounts of resin, many particulates, and several filters, the location (i.e., one aspect of the integration) for the application of the spike as well as its dispersal (i.e., the other aspect of the integration) are important if we want to benefit fully from ID methodology. Any error associated with the spiking [30] – including those cited above – can result in what we refer to as a catastrophic failure of ID (i.e., the data are meaningless). ID is a ratio game. Any action taken to break the ratio (e.g., poor integration of the standards inside the sample matrix) will create the conditions for ID to fail should unusual circumstances develop. Laboratories following Method 1613B typically spike 20 lL of the labeled extraction standards dissolved with 1 mL acetone inside the sample. The method does not really specify where, although it is usually done locally on the top of the sample inside the Soxhlet thimble. In addition, the method does not address the integration-dispersal aspect. 5.1.1. Integration location. Multi-component samples force the chemist to decide where to apply the spiking solution. Initially, the choices are between the components (e.g., filter, PM or resin) and then where within each component. For instance, when large amounts of carbonaceous particulates are present on or in the filters, there is a genuine concern about the extraction efficiency of certain target analytes (e.g., with strong pcomplex affinities) from the filter versus the resin.

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Additionally, POPs associated with particulates located on the surface of the filter are more accessible than those buried deep down the layers of the tightly woven strands. If, during application of the spikes, we do not reach these deep layers, no account can be taken of the POPs trapped deep inside the filter structure. 5.1.2. Integration-dispersal. An issue directly linked to the large volume of filters and resin that has to be analyzed is dispersal of the labeled standards across the entire sample matrix. The objective of the spiking step is to keep the ratio between endogenous and labeled compounds constant throughout the sample matrix. Achieving this objective presents major challenges for extra-large and bulky samples (e.g., a 1-mL spike in a sample containing several large filters loaded with 20–40 g of particulates, 500 g of resin plus water, and many wet glass-wool plugs amounts to localized spiking). To help place things in perspective, considering just the amount of resin, it corresponds to more than 15 Method 23 stack-sampling modules or 50 Soxhlet setups for soil or sediment extractions by Method 8290/ 1613. In the latter case, these amount to a room full of extraction vessels where the labeled extraction standards are only introduced into one of the 50 units, and, following the extraction, the laboratory combines all 50 extracts – including those from the unspiked units where the Soxhlet extraction was mechanically faulty – before fractionation and analysis. There is therefore no accounting for losses of POPs within sections of the sample that are not readily accessible by the spiking solution and the extraction solvent, or not reflecting regional losses when an undocumented leak develops. If the laboratory extracts the filters by placing them as one piece inside the Soxhlet thimble holder (i.e., the tightly woven strands are not taken apart), there is no assurance that the spiked compounds will reach the inner sections of the filters. Using this method, the labeled compounds are not given a chance to distribute across the majority of the sample before the extraction starts. As a result, POPs trapped deep inside the filter have no representation [31] in the ID ratio game, whose effectiveness is therefore undermined. 5.1.3. Reality check. In a comprehensive study [24] that looked at the spatial distributions of PCDD/Fs in the water column and bottom sediments of a shipping channel, the analytical methods section described how the 250-g resin plus water and particulate-laden 10-cm long 1-lm filters from the water samples were homogenized, spiked with the labeled extraction standards, and mixed with sodium sulfate, allowing 12–24 h to dry before extraction with methylene chloride-hexane (1:1) in a Soxhlet extractor. From a practical perspective, it is difficult to imagine how such homogenization can be http://www.elsevier.com/locate/trac

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carried out. Furthermore, the selection of the solvent system is not according to the Method 1613B requirement where toluene is expected. This solvent selection is particularly significant for carbon-containing matrices where it is difficult to recover planar molecules with such a solvent system. The paper indicated that recoveries of the labeled extraction standards were in the range 72–92%. However, recoveries of the labeled extraction standards do not mean much unless the spiking is carried out in a manner that is consistent with ID. One can ask: ‘‘How much of the spiked compounds dissolved in 1 mL of acetone interacted with the carbonaceous materials dispersed among 250-g resin plus water, a large volume of (shredded?) filters and particulates, and an unknown amount of sodium sulfate (granular or powder?) so that they can be recovered with a solvent system, such as hexane-methylene chloride in 18-24 H by Soxhlet extraction?’’ Note that the extraction time is not very different from that of Method 1613B for a 10-g solid sample. 5.2. Quality-control samples Field and laboratory QC samples need to be defined with regard to their role, function or purpose, so that we appreciate the aspect of quality that they are supposed to control. We then need to make sure that they are treated and used accordingly. For instance, the same lot of prepared resin and in the same amount as used for the field activities should be utilized for the laboratorymethod blank. Moreover, the collection of field blanks should ideally be between two samples collected at a particular site. Finally, if the recoveries of the dynamically spiked standard or the breakthrough standard are outside expectations – which need to be defined ahead of time – what does this mean in terms of data quality? 6. Conclusions Nearly two decades have gone by since the pioneering work involving the first HVE systems. During that time, remarkable efforts were expended toward refining the sampling equipment to reduce downtimes, sampling times and labor costs. Today, one commercial system is available; it is capable of sampling 1000 L water in about 12 h. Unfortunately, the development efforts neglected or avoided the ramifications of the sampling equipment and its changes for the performance of the analytical measurement system. It is as if we solved one problem (achieving lower LODs) by introducing a solution (HVE) and, unknowingly, displaced the problem to another location (the analytical performance). In particular, the state-of-the-art analytical protocols for trace levels of POPs are not configured to handle

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large, bulky samples, such as those generated by HVE. Multi-component, multi-matrix and voluminous samples require special attention during the sample-preparation steps if we want to fully benefit from ID methodology. Ignoring this reality can lead only to sub-optimal performance. Indeed, questionable laboratory analytical data would undeniably have a significant effect on the conclusions of any study. It is therefore vital that we pay attention to the reliability of the analytical data, especially when linear thinking is applied to the preparation of complex samples of that sort. There is no really good answer to the problems associated with such intricate samples, except to keep the size of the samples to a reasonable level – a size that is more aligned with the requirements of ID. As far as we can assess, there are no validation studies proving the effectiveness of the HVE technique to support the WQC. Finally, HVE does not necessarily address the bioavailable form of POPs, so future development and validation efforts ought to consider the pattern of organization between influential factors (Fig. 3) so that we do not look at only one part of the elephant and end up developing and validating a procedure whose design is at odds with its purpose. Other sampling approaches for biologically relevant organics should be considered, particularly if they measure contaminants in water by mimicking the parts of the fish that cause concentration of specific chemicals in fish tissues [32]. Many of the issues that we helped reveal in this article affect ambient testing in a similar fashion (e.g., several PUF cartridges per sample) or stack testing (e.g., for each sample, spreading 40 g of XAD-2 resin, glass-wool and filters over several 30-mL ASE cells).

References [1] US Environmental Protection Agency, US EPA Method 8290: Analytical procedures and quality assurance for multimedia analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans by high-resolution gas chromatography/high-resolution mass spectrometry, US EPA, Environmental Monitoring Systems Laboratory, Las Vegas, NV, USA, 1987. [2] US Environmental Protection Agency, US EPA Method 1613: Tetra- through octachlorinated dioxins and furans by isotope dilution HRGC/HRMS. Revision B, US EPA, Office of Water, EAD, Washington, DC, USA, 1994. [3] H.R. Buser, Chapter 5: Review of Methods of Analysis for Polychlorinated Dibenzodioxins and Dibenzofurans, in: Environmental Carcinogens Methods of Analysis and Exposure Measurement, Vol. 11 – Polychlorinated Dioxins and Dibenzofurans, IARC Scientific Publication No. 108, IARC, Lyon, France, 1991. [4] P.J. Marriott, P. Haglund, R.C.Y. Ong, Clin. Chim. Acta 328 (2003) 1. [5] S. Richardson, Chem. Rev. 101 (2001) 211. [6] US Environmental Protection Agency, US EPA Standards of performance for new stationary sources. Test Method 23. 40 CFR Part 60, US EPA, Washington, DC, USA, 1990. [7] US Environmental Protection Agency, US EPA Compendium Method TO-9A: Determination of polychlorinated, polybrominated

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[12] [13] [14]

[15]

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and brominated/chlorinated dibenzo- p-dioxins and dibenzofurans in ambient air, in: Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air. EPA/625/R-96/ 010b, US EPA, Office of Research and Development, Center for Environmental Research Information, Cincinnati, OH, USA, 1999. US Environmental Protection Agency, Ambient Water Quality Criteria for 2,3,7,8-Tetrachloro-p-Dioxin, EPA 440/5-84-007 February 1984, US EPA, Washington, DC, USA, 1984. (Assumes a lifetime exposure occurring from the consumption of both drinking water and aquatic life from waters containing 0.013 ppq of 2,3,7,8-TCDD and an estimated human increased cancer risk of 10 6). C. Rappe, L.O. Kjeller, R. Andersson, Chemosphere 19 (1989) 13. C. Rappe, L.O. Kjeller, S.E. Kulp, Organohalogen Compd. 2 (1990) 207. G. Lebel, D.T. Williams, B.R. Hollebone, C. Shewchuk, L.J. Brownlee, H. Tosine, R. Clement, S. Suter, Int. J. Environ. Anal. Chem. 38 (1990) 21. M. Uza, R. Hunsinger, T. Thompson, R.E. Clement, Chemosphere 20 (1990) 1349. G. Carlberg, K. Martinsen, Sci. Total Environ. 25 (1982) 245. D. Rushneck, Determination of CDDs and CDFs at part-perquintillion levels using a cubic meter sample, 10-9 to 10-35, 19th Annu. EPA Conf. Analysis of Pollutants in the Environment, Norfolk, VA, USA, May 1996. W.A. Telliard, Feasibility study for the determination of TCDD at the part-per-quintillion level in water, US Environmental Protection Agency, Office of Water, Washington, DC, USA, 1997. Infiltrex-100 and 300, Axys Environmental Systems, BC, Canada. US Environmental Protection Agency, Report on High-Volume Sampling of Pulp and paper Mill Effluent for Determination of CDDs/CDFs by EPA Method 1613, Revision B; Final, August 2000, US EPA, Washington, DC, USA, 2000. A resolving power of 12,000 is required to separate 13C6-1,2,3,4TCDD (dynamic sampling standard) from the 13C12-1,2,3,4-TCDD (injection standard). Typical resolving powers used in such assays are 8,000 to 10,000. US Environmental Protection Agency, US EPA Method 1668, Revision A: Chlorinated Biphenyl Congeners in Water, Soil, Sediment, and Tissue by HRGC/HRMS; United States Office of Water EPA, EPA-821-R-00-002, US EPA, Washington, DC, USA, 1999. S.A. Dinkins, J.P. Heath, Quantification of dioxin concentrations in the Ohio River using high volume water sampling, Presented at NWQMC National Monitoring Conf., Reno, NV, USA, 7–9 July 1998. M.P. Suarez, H.S. Rifai, J. Schimek, M. Bloom, P. Jensen, L. Koenig, J. Environ. Eng. 132 (2006) 1633. Experimentally, 2,3,7,8-TCDD is administered in the animalÕs diet or gavages in an oil vehicle. When the administration is based on aqueous suspension of soil, it decreased the hepatic levels compared to using 50% ethanol. When an aqueous suspension of activated carbon is used, absorption is almost totally eliminated [8]. P.M. Cook, L.P. Burkhard, Proc. Natl. Sediment Bioaccumulation Conf., US EPA, EPA 823-R-98-002 (1998) 3-19. M.P. Suarez, H.S. Rifai, R. Palachek, K. Dean, L. Koening, Chemosphere 62 (2006) 417. N.R. Morehead, B.J. Eadie, B. Lake, P.F. Landrum, D. Berner, Chemosphere 15 (1986) 403.

Trends [26] R.M. Burgess, R.A. McKinney, W.A. Brown, J.G. Quinn, Environ. Sci. Technol. 30 (1996) 1923. [27] a) B. Vrana, G.A. Mills, I.J. Allan, E. Dominiak, K. Svensson, J. Knutsson, G. Morrison, R. Greenwood, Trends in Analytical Chemistry 24 (2005) 845–868; b)If SPMD is considered, we recommend the use of labeled standards spiked inside the lipophilic phase before mobilization in the field to monitor complications such as destruction or chemical modifications of the extracted analytes during long sampling periods, if any. [28] The use of glasswool plugs in the preparation of the sorbent modules is never mentioned in any study. [29] Y. Tondeur, The light and shadow-side of ultratrace analyses, Invited Plenary Lecture, Dioxin 2003, 23d International Symposium on Halogenated Environmental Organic Pollutants and POPs, Boston, MA, USA, 24–29 August 2003. [30] Y. Tondeur, J. Hart, Isotope Dilution: A Bifurcation Point in Ultratrace Analyses, Monograph (in preparation). [31] ‘‘Quantitation without representation’’. [32] D. Chapman, SPMD Fact Sheet ‘‘The Virtual Fish; SPMD Basics’’, 6th International SPMD Workshop and Symposium, USGS Columbia Environmental Research Center, MO, USA, 2000 (http:// www.aux.cerc.cr.usgs.gov/spmd/). Yves Tondeur PhD is cofounder and owner of Analytical Perspectives, a contract laboratory specializing in ultratrace analyses based on comprehensive and stable ID high-resolution gas chromatography and high-resolution mass spectrometry. He is the author of the original version of USEPA Method 8290, and has been instrumental in the development of several other related methods, such as Method 1613, EN1948, and the analytical portion of Method 23. He has been retained as a consultant and expert witness for chemical and pulp & paper companies. Analytical Perspectives has performed analyses of HVE samples for engineering firms. He has been retained as a paid observer by Georgia-Pacific (GP) during an EPA-initiated HVE session at one pulp and paper mill. His involvement in methodsÕ development for more than 30 years, analyses of HVE samples, and witnessing an HVE session led to the identification of a series of concerns associated with the analytical aspects. Before the inception of this manuscript, some of the concepts and ideas presented in this article were discussed with GP. As a courtesy, a draft version of this manuscript was provided to GP for review. Financial support for this work was solely from Analytical Perspectives. Jerry Hart is cofounder and owner of Analytical Perspectives. He has worked in high-resolution mass spectrometry since joining VG Analytical (later Micromass) in 1981. In 1990, he was appointed Product Manager for Environmental Applications, having become increasingly involved with the growing needs of both hardware and software requirements of government and commercial laboratories world-wide in the ÔdioxinÕ business. In this position, he led the development of the AutoSpec-Ultima mass spectrometer – a high-sensitivity version specifically aimed at users in the environmental arena (and which subsequently also found a niche at certain Olympic laboratories for drug testing in sports). He also traveled extensively to present seminars and provided training in the analysis, and subsequent data processing, of dioxins and related compounds across Asia, Europe and North America. In 2000, he joined Yves Tondeur to form Analytical Perspectives; he now takes responsibility for strategic development of new mass spectrometry and software initiatives.

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