Sitting Down With… Stefan van Leeuwen, Senior Scientist, Wageningen Food Safety Research, University of Wageningen, The Netherlands
What is the overarching theme of your work?
Environmental contaminant analysis is really the core of my work – particularly substances that persist in the environment for long periods. These so-called persistent organic pollutants (POPs) eventually enter our food chain, so they are of special concern for human health. I started my career studying polychlorinated biphenyls (PCBs) and brominated flame retardants with Jacob de Boer’s group at Wageningen Marine Research, but, by the early 2000s, our international coworkers had pointed us towards a new pollutant of interest – perfluorooctane sulfonate. Soon many more per- and polyfluoralkyl substances (PFASs) were detected, and their study became a field in its own right. After 5 years at the VU University in Amsterdam, where I obtained my PhD developing analytical methods for detecting the occurrence of POPs in fish for human consumption, I started in my current position at Wageningen Food Safety Research, where research on POPs in food has continued.
Have there been any landmark moments during your time in the field?
In 2006, we published the results of the first international proficiency test for PFASs in environmental and human samples. The data was very scattered and not comparable between labs; it was obvious that these analytes required different analytical approaches than the field was used to. In the following years, enormous effort was made to improve method development – commercial standard providers have devoted considerable time and energy to developing high-quality standards and mass-labelled analogues. This has resulted in a huge increase in the quality of reported results, which will in turn improve our understanding of the effects associated with PFASs in the years to come. Regarding chlorinated paraffins, a new high-resolution MS (HRMS) and statistical approach from the Bogdal lab has recently provided researchers with a more powerful tool to probe these industrial contaminants in food.
What are the “tools of the trade”?
We use several techniques including LC-MS/MS and GC-HRMS to conduct targeted analysis of a number of environmental contaminants, including dioxins, PCBs, and PFASs. Chlorinated paraffins in food present a particularly challenging phenomenon, requiring HRMS (Orbitrap) coupled with LC to ensure the resolution necessary for complete analysis.
What technological developments does the field need?
The OECD has published a list of over 5,000 PFASs; of these, we routinely analyze about 20 using a targeted LC-MS/MS approach. Although not all 5,000 PFASs may be relevant for food or environmental contamination, it’s clear that a more holistic approach is needed. The solution lies in complementary approaches: in vitro effect assays, oxidizable PFAS detection, total organic fluorine detection, and untargeted identification. Several groups in our institute are joining forces to develop and combine these approaches, and so far, the results have been promising.
Elsewhere, the accumulation of contaminants in the “circular economy” is gaining considerable attention. When materials are recycled, undesirable substances like brominated flame retardants can be unintentionally introduced into products. We need to better understand how recycling processes lead to contamination and where these substances accumulate, which will – of course – require new analytical approaches.
What are the biggest misconceptions facing the field?
Some people say that environmental contaminants are no longer a problem. I disagree –evidence is mounting that even very low levels of contaminants such as dioxins, PCBs, and PFASs lead to subtle yet undesirable effects for organisms. Moreover, we’ve seen that chemical industries will cease production of a specific contaminant due to social, political, or environmental pressure, only to switch to another, similar compound down the line – potentially introducing yet another new contaminant to our food or drinking water. This surely provides more than enough evidence to support the importance of environmental analysis… And this importance will only increase over time.
What’s next for your group?
I would like to further increase separation power when studying chlorinated paraffins by combining complementary analytical approaches. We hope to be able to separate individual isomers from mixtures of thousands of very similar compounds within a sample. This level of precision is crucial for food analysis, and to support toxicology studies into individual congeners.
Another important goal is to design strategies that will allow the identification of unknown PFASs. Untargeted identification of PFASs in food and environmental samples is currently very time- and resource-consuming; HRMS data evaluation is a particularly limiting step. Speeding up data analysis by using software and combinations of complementary techniques would not only be beneficial for studying PFASs, but also for identifying many other food contaminants.