Per- and Polyfluoroalkyl Substances (PFAS) in Foodstuffs

Simon Hird | Waters Corporation

Introduction?

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals with a myriad of industrial and cosmetic uses. Despite decades of research on PFAS, fundamental barriers remain to address worldwide contamination by these chemicals and their associated impacts on environmental quality and health [1], they are highly mobile, ubiquitous, persistent, toxic environmental contaminants that accumulate in humans, animals, and the environment. PFAS are characterized by their high chemical stability, enormous structural diversity and consistent presence in both the scientific literature and mass media, alike. An ongoing challenge regarding PFAS has been the shifting definition of what qualifies a substance to be a member of the PFAS class and their nomenclature. The basic structure of a PFAS consists of a carbon chain with substituted fluorine atoms replacing hydrogen atoms on the chain. Different categories of PFAS can be grouped based on the different substituents and functional groups within or terminal to the chain [2]. Where maximum or advisory limits exist for water and food, the actual specific PFAS included in the legislation varies hugely.?

Mandatory Regulatory Requirements in Europe?

The negative impacts on human health are extensive and continue to be investigated [3]. Dietary intake is considered as one of the main human exposure pathways of these chemicals and, having entered the human body, PFAS are not metabolized and accumulate in tissues [4]. The first regulatory limits for some PFAS have recently been agreed upon in some foods in Europe with recommended indicative limits in many other foods. Commission Regulation (EU) 2022/2388 [5], amending Regulation (EC) No 1881/2006 [6], came into force from 1 January 2023, and sets out mandatory individual maximum levels for a limited number of PFAS (perfluorooctanoic acid [PFOA], perfluorooctanesulfonic acid [PFOS], perfluorononanoic acid [PFNA] and perfluorohexane sulfonic acid [PFHxS]), together with a maximum level for the sum of those PFAS, in various foods of animal origin. The regulation was restricted to food of animal origin as this group is thought to be the most important contributor to the human exposure to PFAS.?

Food with levels of contaminants, including the specified PFAS, higher than those listed in the annex to Commission Regulation (EC) No 1881/2006, may not be sold. The competent government authorities in each Member States are responsible for the enforcement of this legislation and organize official control systems in their countries to verify food business compliance. In addition, all food business operators must ensure their products are compliant. Controls include sampling and analysis of the relevant commodities, by both parties, to check compliance with the maximum levels. As the amended regulation also applies to goods entering the EU from countries outside the EU, pre-export testing for PFAS by relevant authorities and those companies operating in those countries, is highly likely.?

Scope of Analysis?

In addition, Commission Recommendation (EU) 2022/1431 [7], which came into force from September 2022, recommends Member States, in collaboration with food business operators, should include the same four PFAS in their monitoring programs during the years 2022 to 2025, in a wider range of foodstuffs than covered in 2022/2388. This should include a wide variety of foodstuffs reflecting consumption habits, including fruits, vegetables, starchy roots and tubers, seaweed, cereals, nuts, oilseeds, food for infants and young children, non-alcoholic drinks, wine, and beer. Member States that have the analytical capability should also monitor PFAS in feed, whereas those lacking that? capability should look to validating suitable analytical methods for PFAS in feed. The testing described is not mandatory, so further investigation of the causes of the contamination is recommended when a range of indicative levels are exceeded (between 0.005 to 1.5 μg/kg, depending upon the substance and the commodity).? It also suggests the monitoring for a much larger list of PFAS (see below), but no proposed values for expected limits of quantification (LOQ) or indicative levels are provided.?

In order to ensure the results generated for official control are comparable, Commission Implementing Regulation (EU) 2022/1428 [8] provides instructions on methods of sampling and analysis for the control of PFAS in certain foodstuffs should be followed. It also provides acceptance criteria for the validation of methods and information on reporting and interpretation of results. Laboratories may select any validated method of analysis for the respective matrix provided that the selected method meets the specific performance criteria set out in the document. For example, the within-laboratory reproducibility (RSDR) of the method selected must be demonstrated to be ≤20% and trueness between -20 and +20%.? It is only applicable to the official control of the levels of PFAS's in foodstuffs for which maximum levels have been established in Commission Regulation (EU) 2022/2388 but I suspect it will be implemented, at least in part, more widely. This regulation complements an extremely useful guidance document from the EURL POPs [9].?

Controlling Contamination?

Laboratory contamination is the main threat to the determination of PFAS in water or foods. Such contamination can lead to reporting of false positives and/or higher reporting limits due to elevated background. PFAS from fluoropolymers and coating are ubiquitous in common sampling and analytical equipment and can easily contaminate solvents and reagents and laboratory contamination is common and near impossible to eliminate completely but there are actions that can be taken to mitigate the issue. Avoiding all products likely to contain fluoropolymers such as vials with Teflon seals, and minimising the risks from contaminated dust and air, are both essential. Screening all analytical consumables, solvents and reagents including water purifying systems and implementing extensive use of procedural blanks, from sample storage to LC-MS/MS, helps to locate the sources of the contamination. One useful option is to modify the LC system by changing the tubing, fittings, filters, and other components, to replace those that can contribute to contamination and to use an isolator column that helps isolate the background contaminants from the analytes in a sample [10]. The isolator column is in the flow path between the mixer of the solvent manager and the injector of the sample manager. During analysis, the isolator column retains the background PFAS, separating them from the analytes of interest. The increased retention time of the background PFAS makes them easily distinguishable by mass analysis.?

Achieving Necessary Sensitivity?

The next critical aspect associated with the determination of PFAS in food is the sensitivity required to confidently check for compliance with the maximum and indicative levels set now or in the future. Commission Recommendation (EU) 2022/1431 sets out the expected limits of quantification for the four most important PFAS.??

To achieve such low LOQs in food, Waters evaluated two analytical approaches: methods based upon QuEChERS [11,12] and those using an alkaline digestion, solvent extraction solid-phase extraction (SPE) by Weak Anion Exchange (WAX) [13]. Both products suitable extracts for determination using UPLC-MS/MS, ideally on a high-performance tandem quadrupole system [14]. The US FDA have successfully employed a QuEChERS approach for the determination of PFAS in foods obtained through their various Total Diet Study projects [15] but the second approach has been used for much longer [16]. The figure below shows some chromatograms of PFAS detected of samples of beef liver and egg, purchased from local grocery stores in the USA, using the later approach. Waters also arranged a successful interlaboratory study to further demonstrate reliability of the method selected for the analysis of fish [17].??

Conclusion?

Concerns about the impact of human exposure to PFAS continue to grow and focus has now expanded to an evaluation of exposure from food. To protect the public and understand dietary exposure, accurate and sensitive analytical methods for the analysis of a large variety of food products are required. These comprehensive methods allow for high confidence in results from the determination of PFAS in complex food matrices to check compliance with regulatory and indicative levels and to better understand the impact of PFAS on our food sources.?

References

[1] Addressing Urgent Questions for PFAS in the 21st Century

[2] Assembly and Curation of Lists of Per- and Polyfluoroalkyl Substances (PFAS) to Support Environmental Science Research

[3] A review of the pathways of human exposure to poly- and perfluoroalkyl substances (PFASs) and present understanding of health effects

[4] Occurrence of Selected per- and polyfluorinated alkyl substances (PFASs) in food available on the European market - A review on levels and human exposure assessment

[5] Commission Regulation (EU) 2022/2388 of 7 December 2022 amending Regulation (EC) No 1881/2006 as regards maximum levels of perfluoroalkyl substances in certain foodstuffs.?OJ L?316:38–41

[6] Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs.?

[7] Commission Recommendation (EU) 2022/1431 of 24 August 2022 on the monitoring of perfluoroalkyl substances in food.?OJ L?221:105–109?

[8] Commission Implementing Regulation (EU) 2022/1428 of 24 August 2022 laying down methods of sampling and analysis for the control of perfluoroalkyl substances in certain foodstuffs.?OJ L?221:66–73?

[9] Guidance Document on Analytical Parameters for the Determination of Per- and Polyfluoroalkyl Substances (PFAS)

[10] PFAS Analysis Kit for ACQUITY UPLC Systems User Guide

[11] QuEChERS Extraction of Per- and Polyfluoroalkyl Substances (PFAS) from Edible Produce with Sensitive Analysis on Xevo TQ-XS

[12] Matrix Matching or Isotope Dilution? A Comparison of Two Quantitation Approaches to Determine PFAS in Dairy Milk

[13] Total Workflow for the Sensitive Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Fish, Meat, Edible Offal, and Eggs

[14] Improved Sensitivity for the Detection of Per- and Polyfluorinated Alkyl Substances in Environmental Water Samples Using a Direct Injection Approach on Xevo??TQ Absolute

[15] Analysis of Per- and Poly(fluoroalkyl) Substances (PFASs) in Highly Consumed Seafood Products from U.S Markets

[16] Dietary intake estimate for perfluorooctanesulphonic acid (PFOS) and other perfluorocompounds (PFCs) in UK retail foods following determination using standard addition LC–MS/MS

[17] Evaluation of the Performance of a Total Workflow Approach for the Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Fish, Using an Interlaboratory Study