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Micro- and nanoplastics are released from food packaging
Microplastics have been detected in several foods and beverages including salts, fish, and bottled water and more recent studies showed that plastics food packaging can be one source of microplastics into food. Several studies published in November and December 2022 further broaden the evidence around micro- and nanoplastic sources and exposure by investigating their release from several types of food contact materials and articles into foodstuffs.
Yunlong Luo from the University of Newcastle, Callaghan, Australia, and co-authors, investigated the release of small plastic particles from non-stick cookware. In their article published on December 10, 2022, in the journal Science of The Total Environment, they described purchasing six non-stick cooking pots with Teflon coatings (four new and two old ones) and turners made of stainless steel or wood in supermarkets in Australia. They mimicked the cooking process by stirring and cycling the turner around on the pot surface. Using a scanning electron microscope (SEM), the researchers counted the released fragments. They also recorded Raman spectra and developed a new algorithm that combines principal component analysis (PCA) and an algebra-based algorithm which allows for effective detection and analysis of Teflon's Raman activity. According to the authors, this "algorithm enables better detection of nanoplastics" since Teflon's Raman activity is very weak.
Applying their newly developed approach, they reported that one scratch in the Teflon surface may generate around 9,100 micro- and nanoplastics. Overall, broken coatings could result in a release of approximately 2,300,000 plastic particles. However, the authors clarified that their "dry-run" (cooking without food and oil) as well as the type and quality of cookware and the style of cooling might affect the particles' release. Comparing 2 year old pots with the new ones showed that old pots release more and bigger particles than new ones even when wood turners are used to cook instead of steel.
The study results demonstrate that "Teflon microplastics and nanoplastics are potentially released during our daily cooking processes." Teflon is a family member of per- and polyfluoroalkyl substances (PFAS) which have been associated with several negative human health outcomes. Given their newly developed method, Luo et al. concluded that "it is recommended that Raman imaging, along with the signal recognition algorithms, be combined with SEM to characterize and quantify microplastics and nanoplastics."
In an article published on December 7, 2022, in the journal Toxics, Jun Hu from the Zhejiang University of Technology, Hangzhou, China, and co-authors analyzed the abundance of microplastics prone to be released from polypropylene (PP) takeaway food containers. For their study, they acquired 210 clean containers from restaurants in seven Chinese cities and flushed their inner wall several times with pure water of different temperatures. To isolate microplastics, they filtered the water though 50 µm glass membranes and analyzed microplastics on dried filters by stereomicroscopy and Fourier Transformed Infrared (FT-IR) spectrometry.
Hu and co-authors detected microplastics in all samples ranging from three to 43 items per container. Particles were mostly between 201 and 500 µm in size and fibers were the most predominant shape accounting for 66-87% of all microplastics. The authors speculated that they may mainly be "from the deposition of atmospheric microplastics during production, storage, and transportation" of the takeaway food containers. Most plastic particles were made of PP, representing 56-73% of all microplastics. The abundance of the small particles varied between the seven cities from 25 particles/container acquired in Chengdu to 9 particles/container acquired in Shanghai. The authors also estimated the daily microplastic intake for the general Chinese population and reported a range of 0.042–0.14 particles/kg body weight/day.
Shadi Taheri and co-authors from the Isfahan University of Medical Sciences, Isfahan, Iran focused on plastic particle release into bottled water. In their article published on November 3, 2022, in the journal Environmental Monitoring and Assessment, they described that they purchased 23 single-use polyethylene terephthalate (PET) bottles of different brands in Iranian (Isfahan) supermarkets, removed organic material by wet peroxide oxidation and vacuum filtered the water through a polytetrafluoroethylene (PTFE) membrane with a pore size of 0.22 mm. The scientists also investigated if particle release is affected by mechanical stress (rolling of water bottle on a wavy surface under a 5 kg vessel for 30 min), freezing (-20 °C for 48 hours), or sunlight (sunlight exposure for 3 months). SEM was used to evaluate the plastic particles' size and shape and FTIR to identify and quantify them.
Taheri and co-authors reported that water samples contained an average of 1497 ± 1452 particles/L with significant differences between the brands tested. Over 90% of the particles had a size smaller than 5 µm and most were made of PET, while also PP and other polymer types were identified. While freezing the bottled water did not affect microplastic release, mechanical stress increased particle numbers in the water. Sunlight especially exaggerated particle release with 2817 particles/L detected on average after three months. The authors emphasized the study was limited since the "possible effects of chemical properties of water on plastic structure of bottles and microplastic release… was not investigated due to limited number of bottled water brand in Iranian market."
In a review article published on November 12, 2022, in the journal Trends in Analytical Chemistry, Clementina Vitali from Wageningen University & Research, the Netherlands, and co-authors highlighted that to date a fully validated method to analyze micro- and nanoplastics in food is missing. For their literature review, the authors searched Google Scholar for relevant studies published before August 2021 and extracted data on sample matrix type, sample preparation, detection methods, and quality parameters of the analytical method. The data analysis showed "that even the most widely used methods are still under development and microplastic/nanoplastic analysis is still far away from method validation and standardization."
The authors further highlighted that no single method would suffice to assess plastic particle occurrence in food due to the multidimensionality of the data. Instead, they suggested combining microscopic with analytical techniques as a promising approach to detecting and identifying microplastics. The researchers concluded that "there is a strong need to encourage and establish rigorous best practices in order to yield reliable data and build a comprehensive knowledge of their [micro- and nanoplastic] occurrence in food."
Hu, J. et al. (2022). "Microplastics in Widely Used Polypropylene-Made Food Containers." Toxics. DOI: 10.3390/toxics10120762
Luo, Y. et al. (2022). "Raman imaging for the identification of Teflon microplastics and nanoplastics released from non-stick cookware." Science of The Total Environment. DOI: 10.1016/j.scitotenv.2022.158293
Taheri, S. et al. (2022). "Investigating the pollution of bottled water by the microplastics (MPs): the effects of mechanical stress, sunlight exposure, and freezing on MPs release." Environmental Monitoring and Assessment. DOI: 10.1038/s43016-020-00171-y
Vitali, C. et al. (2022). "Microplastics and nanoplastics in food, water, and beverages, part II. Methods." Trends in Analytical Chemistry. DOI: 10.1016/j.trac.2022.116819
This article was originally published by Lisa Zimmermann at the Food Packaging Forum.
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