The past few years have seen increasing regulation targeting plastic packaging, including the EU’s ban on single-use cutlery, plates, and straws in 2021, followed by similar legislation in Canada in 2022. In the fast food industry, many manufacturers have responded by introducing more sustainable packaging from paper and other plant-based sources.
However, a recent analytical study of paper-based containers and wrappers from Canadian fast food restaurants suggests that these ‘greener’ options may have undesirable consequences. The results indicate that polymeric PFAS coatings used to repel fat and water from paper can eventually transform into compounds of toxicological concern.
“Our broader – and ambitious – goal is to identify all major sources of PFAS around us,” explains Marta Venier from the O’Neill School of Public and Environmental Affairs at Indiana University, one of the study’s main authors. “We knew that fast food packaging has a need for grease repellency to keep the containers intact, so we saw a possible connection to our research.”
Analyzing fluorine concentration
After collaborators from Miriam Diamond’s group at the University of Toronto, Canada, collected food packaging samples including 'compostable' fiber bowls, burger wrappers, popcorn bags, and dessert covers, the researchers used particle-induced gamma-ray emission spectroscopy (PIGE) performed by Graham Peaslee’s group at Notre Dame University to screen for total fluorine content. PIGE is a nuclear excitation technique that enables non-destructive testing for fluorine contaminants.
The PIGE analysis revealed significant differences in fluorine levels across various types of fast food packaging. Approximately half of the samples had no detectable fluorine. However, certain materials, including donut and pastry bags, contained fluorine at concentrations ranging from 10,000 to 30,000 μg F/m2. Meanwhile, molded fiber bowls were found to contain fluorine at a concentration of 1,000,000 μg F/m2. This higher concentration underscores the greater structural demands placed on these bowls.
“The advantage of PIGE is that it gives you a really quick answer if fluorine is there or not, and it requires little sample preparation,” says Venier. “We then take the resulting few with high fluorine content and put them through secondary analysis.”
The team selected eight products for targeted analysis based on their high fluorine concentrations. Following solvent extraction, they analyzed the targets using LC-MS/MS with an ultrahigh performance LC coupled to a triple-quadrupole MS, and with GC-MS in the positive chemical ionization mode. Among the 55 PFAS compounds originally targeted, two short-chain species appeared most frequently: 6:2 fluorotelomer alcohol (6:2 FTOH) and 6:2 fluorotelomer methacrylate (FTMAc) at levels ranging from 300 to 5,700 ng/g.
A recent study suggests that previous research may have underestimated the health risks associated with 6:2 FTOH. Furthermore, the authors believe this is the first instance of FTMAcs reported in food packaging.
Elusive PFAS
Venier and her team noticed a significant disparity after completing the targeted analysis – the total fluorine concentrations derived from PIGE measurements were 100 to 5,000 times higher than results obtained through gas and liquid chromatography.
“In general, there could be both organic and inorganic fluorine associated with PFAS. In the case of bowls, when you detect fluorine, it’s clearly organic,” says Venier. “With organic PFAS there’s the issue of fluorinated precursors that we can’t get out through regular extractions. One way to close the gap is through a hydrolysis treatment.”
Using assays based on strong alkaline treatments, the team successfully retrieved a portion of the fluorine balance, with recoveries reaching as high as 30% in certain instances. Nevertheless, some PFAS components remained elusive. Eventually, the demands of a meticulous reviewer led them to a partial explanation.
“We had samples that we sealed in the lab for two years, and we decided to re-extract them to get the data the reviewer was asking for,” recalls Venier. “When we saw from the results that the composition had changed, we began to look at the volatility of some of these chemicals.”
The PFAS concentrations in the re-extracted samples were notably lower than the initial measurements, showing reductions of up to 85%. The new contaminant levels ranged from 130 to 2,430 ng/g. Since the concentrations of less mobile ionic PFAS contaminants remained consistent, the researchers hypothesize that some of the mass losses might have occurred due to the volatilization of certain FTOH and FTMAc compounds.
The findings from the team's targeted analysis suggest that consumers might encounter PFAS concentration levels in their fast food wrappers that exceed conventional exposure thresholds. Furthermore, these results highlight previously overlooked implications for indoor air quality.
“Our next work is looking at PFAS from other products, including building materials, as we’re trying to map out all major sources in the environment,” Venier remarks. “I think we'll be busy for quite some time.”
Adam Dickie is a science writer for Separation Science. He can be reached at adickie@sepscience.com.
This article is featured in our October publication, 'PFAS: Unraveling the Analytical Challenges.' From cutting-edge analytical methods to the unexpected avenues of PFAS exposure in everyday items, explore the multifaceted challenges and solutions surrounding these pervasive contaminants.
