A Step in the Right Direction for Dioxin Detection
To produce the chemicals and products that we need to survive and thrive in our lives, we require industry. Unfortunately, as well as creating the targets we aim for, unwanted byproducts are also frequently generated. Some of these are well known, such as carbon dioxide, but there are also a host of chemicals that, if not handled correctly and safely, can be harmful to the environment and health. Amongst these byproducts are the group of chemicals known as dioxins.
To detect, quantify and ultimately instigate remedial action in relation to dioxin contamination, scientists require suitable analytical tools and techniques. The United States Environmental Protection Agency (USEPA) recently approved a new dioxin testing method which could assist these efforts.
We spoke to Frank L. Dorman, PhD, FRSC, associate professor of biochemistry, microbiology and molecular biology at Penn State University and senior principal environmental market manager at Waters Corporation about the hazards posed by dioxins, challenges in their identification and the future detection landscape.
Karen Steward (KS): What are dioxins and why are they a concern? Is this problem increasing?
Frank L. Dorman (FD): Commonly, when the word “dioxin” is used in scientific applications where human health and/or environmental exposure are concerned it is a simplification for a series of molecules that are more formally known as polychlorodibenzo-p-dioxins and polychlorodibenzofurans. Together there are 210 possible configurations of these molecules (referred to as congeners), but generally our concern has to do with a subset of 17 of them that are considered toxic to living organisms, including humans. They are the specific molecules that have the chlorine substitutions located at the lateral positions, numbered 2, 3, 7 and 8 using the conventional naming system, and thus a congener-specific determination is needed in order to characterize a sample’s overall toxic equivalency (TEQ) value.
These molecules are persistent and bioaccumulative and coupled with their potential health implications, represent a very important class of compounds for analytical determination. Since they have come under scrutiny by the scientific community, a number of regulatory actions have diminished the amount of dioxins entering the environment. As a result, overall dioxin contamination entering the environment has been decreasing, but the long lifetimes and accumulative nature of these compounds require that continued vigilance to prevention or reduction of exposure efforts remain active. This is best directed to the control of industrial processes as they are the main source of release from which can then enter the food supply and ultimately result in human impact.
While the annual amounts of dioxins and furans entering the environment may be on the decline, the impact to human health continues to be of concern to scientists. Especially concerning is the potential impact to the developing fetus, and continued research is directed to the measurement of even lower levels of detection in much smaller sample volumes than those called for in conventional environmental analytical methods. As we continue to transition from bulk environmental sample testing towards samples with more direct human relevance (food commodities, serum, blood spots, etc.) the need for additional sensitivity becomes greater as science tries to understand fully the effect of various exposures to exogenous compounds such as the polychlorodibenzo-p-dioxins and polychlorodibenzofurans.
KS: How are dioxins currently detected? Are there any shortcomings with existing methods?
FD: For the last few decades, dioxins have been analyzed using gas chromatography (GC) followed by high-resolution mass spectrometry (HRMS) based on double-focusing magnetic sector technology. This separation and detection approach has allowed for the necessary sensitivity, selectivity and specificity necessary to report results to the levels required by the various methodologies (United States Environmental Protection Agency (USEPA) Method 1613, for example). This approach relies on chromatographic separation of the “toxic” congeners within each homolog group (chlorination level), followed by detection of an accurate-mass, specific ion, for each target compound. These instruments utilize multiple stages of mass spectrometry to achieve the mass-resolution necessary for target-to-matrix separations where there may be chromatographic coelutions. While this technology is quite effective, it comes at the cost of instrumental complexity; these instruments require a high-level of operator sophistication. Additionally, these instruments, tend to be rather “finicky” and overall robustness of the system is not as high as many users would desire. Lastly, these instruments are getting harder to find as some historic manufacturers have exited this market in preference to other types of instruments due to the cost and complexity of manufacturing them.
In addition to these shortcomings, these instruments also do not achieve the sensitivity desired by some researchers. While they are capable of around a 100 fg, or so, detectability, some analyses, most notably, human-relevant samples where sample mass/volume can be limited (blood, blood spots, etc.), would benefit from a further increase in sensitivity. For more routine applications, an increase in instrument sensitivity may also allow for smaller amounts of sample to be extracted and/or sample extracts to be concentrated to larger volumes. Both would save commercial laboratories time and expense, increasing laboratory throughput.
KS: The USEPA, recently accepted a new technology for dioxin detection. How might this benefit laboratories and human health?
FD: With the USEPA formally accepting a revised approach to the traditional Method 1613B, this has significantly changed the landscape for potential adoption of tandem mass spectrometers for dioxin testing. The SGS-AXYS Method 16130 allows wastewater to be tested for dioxins and furans using tandem mass spectrometry. Laboratories now have a precedent-setting alternate test procedure (ATP) that can be cited and followed by other laboratories to hopefully make it much easier for them to obtain an ATP of their own. Additionally, the revisions in the SGS-AXYS method will be moved forward for planned inclusion in the Federal Register as an update to the promulgated method 1613B in the future. When that occurs, then the technique would be accepted without any further need for laboratories to petition for acceptance.
Regulations aside, the benefits of the adoption of tandem mass spectrometry, and specifically the WatersTM XevoTM TQ-XS atmospheric pressure gas chromatography-tandem mass spectrometer (APGC-MS/MS) (one of the two instruments that the SGS-AXYS Method 16130 was developed on) is a large gain in sensitivity as compared to the conventional HRMS approach. This gain in sensitivity can allow for measurement and quantification of target compounds where other instruments will only be able to report a “non-detect”. For those researchers investigating the cause/effect between exposure and disease, measurement of actual values is critical for performing correlation studies. Additionally, this sensitivity opens up the world of possibility for measurement of very small samples, as discussed in the previous question, so this becomes even more important when you consider at-risk subjects. Examples of this would be infants and health-compromised individuals where the risks of obtaining a larger volume of sample would be prohibitive.
Again, for more routine analyses, this gain in sensitivity of APGC-MS/MS allows for modifications in the sample preparation steps so that increases in laboratory throughput may be realized, where these were not practicable with the historic approach.
Lastly, this instrument also allows for the monitoring of multiple compound classes at once, another limitation of the historic HRMS approach, enabling additional target compounds to be measured. Specifically, the mixed-halo dioxins and furans have been reported in environmental samples and their biological activities have also indicated that they likely play a similar role as the polychloro-congeners that have historically been monitored. The use of this instrument allows for all of these compounds to be measured in a single analysis, which should reflect a more realistic TEQ.
KS: What barriers might exist to the uptake of newer instrumentation and how might these issues be overcome?
FD: Of course, with any new technology, there will be an adoption period and this is no exception. Decades of data have been reported using the HRMS approach and there is a resistance by potential users of the data to change for fear that it may cause a discontinuity in the reported findings. Additionally, regulatory methods are typically slow to adapt to new instrumental approaches for the same reasons. The reality is, however, that HRMS instruments are harder to operate and maintain and are becoming more scarce. Maybe most concerning is that with the HRMS approach, human exposure to environmental and occupational sources is not being monitored to the fullest extent, possibly because of instrumental limitations, so from a strict scientific view it would be better to adapt to a platform that does not have these same limitations.
Researchers have been using APGC-MS/MS for a number of years already, and there are numerous publications in the scientific literature demonstrating not only equivalence to the HRMS approach, but improved performance. The regulatory world is beginning to adopt this technique as well now and as laboratories become more comfortable with the performance of these systems, regulations will adapt. We have seen that the European Union has already allowed for tandem quadrupoles to be used for food and feed samples and now with the USEPA recognizing it for wastewater the time for general acceptance is drawing nearer. Once the clients of the commercial labs gain a level of comfort, the adoption is likely to happen rather fast I would predict.
KS: Does the USEPA’s acceptance of this technology mean that all laboratories can immediately utilize this technique? Have many already made the switch?
FD: As discussed in an earlier question, laboratories performing work directly under the USEPA Method 1613B must submit for an ATP, but they have the SGS-AXYS precedent to now reference and use as a template. Of course, if a laboratory is not doing work directly covered by 1613B, then they can ask their clients for and approval to use tandem MS/MS and again reference the ATP already granted. It is important to note that the SGS-AXYS ATP does not give carte blanche to all labs performing dioxin analysis in all samples, but it is certainly a major hurdle that has been overcome. It should allow for much more simple petitioning to other clients. The USEPA has also setup a website to detail their current position on these regulations and laboratories should also consult that source. There are already a number of laboratories, research and commercial, that are using the XevoTM TQ-XS APGC-MS/MS instruments for dioxins and furans analysis. These same labs are also expanding the range of compounds they monitor with this system to include polychlorinated biphenyls (PCB’s), Polybrominated diphenyl ethers (PBDE’s) and a wide range of pesticides in addition to others. To date, no laboratory has found any negative impact of this technology relative to the HRMS approach for any sample but rather many have been very happy with the gains in performance. It is likely that this technique will replace the HRMS technique in a relatively short amount of time and the market has seen several manufacturers follow suit.
Dr Frank L. Dorman was speaking to Dr Karen Steward, Senior Science Writer for Technology Networks.