In February 2024, a group of Canadian and American researchers published a study in the journal Environmental Pollution that analyzed the presence of microplastics in 16 protein-based foods commonly found in supermarkets (Environ Pollut. 2024;343:123233). The products included plant and animal proteins from both marine and terrestrial animals and with different levels of processing, such as breaded shrimp, Pollock fillets, chicken nuggets, pork loin chops, plant-based nuggets, and tofu.
The analysis found microplastics contamination in all sampled foods, with no significant difference between animal and plant-based proteins. Another takeaway was that more processed products, such as chicken nuggets and tofu, contained more microplastics particles than those with minimal processing, such as Pollock fillet or pork chops.
The correlation between levels of processing and microplastics contamination is not surprising. As Madeleine Milne, PhD, a researcher at the University of Manitoba and co-author of the study says, “as food goes through additional processing steps, there might be more opportunities for contamination from microfibers of synthetic polymers used for workers’ clothing or rubber pieces from conveyor belts.”
This study is not the first one indicating microplastics contamination generated in food processing environments. In 2001, in Japan, a research study found that the levels of phthalates in retail packed lunch meals substantially decreased after PVC (polyvinyl chloride) gloves containing DEHP (a common phthalate plasticizer) were banned during production and cooking processes (Food Addit Contam. 2001;18:569-579). In 2020, researchers from the Instituto Politécnico Nacional in Mexico analyzed milk samples and found microparticles of sulfone polymers, which are commonly used for membrane materials in dairy processes (Sci Total Environ. 2020;714:136823).
Microplastics contamination in food products creates a potential new food safety risk for manufacturers, especially when one of the pathways is the very processing environment they are responsible for; exactly how to manage that risk is something researchers are still trying to determine.
Worrying Signs
One of the main questions about microplastics is their actual toxicity. “Humans have been exposed to different types of particles for thousands of years; they ingest them and digest them without anything bad happening. We don’t know yet whether microplastics are any different,” says Mohamed A. Abdallah, PhD, associate professor in persistent organic pollutants and emerging contaminants at the University of Birmingham in the U.K. and a member of the Birmingham Plastics Network, an interdisciplinary team of experts aiming to address the global plastics waste problem. “We still don‘t have a full understanding of the toxic implications of human exposure to microplastics, and we haven’t been able to establish a toxic dose level (TDL), which is the lowest dosage known to have produced signs of toxicity. We have reasons to worry, though.”
One of those reasons is the small size of microplastics, which allows them to potentially reach any corner of the human body. Most microplastics are the product of the breakdown of plastics into smaller particles. Their size ranges from one micrometer (one thousandth of a millimeter) up to five millimeters. “Current findings are focusing on microplastics in the smaller size range, less than 50 micrometers, which can be carried around by blood and accumulate in organs,” says Dr. Abdallah. “Microplastics were found in tissues, bones, genitals, and there are even indications that they can cross the cerebral spinal barrier and reach the brain.”
The very presence of these extraneous particles in the human body may be reason for concern: “There have been studies on mice pointing to microplastics as a cause of myocardial toxicity,” says Susanne Brander, PhD, an associate professor in the College of Agricultural Sciences at Oregon State University in Corvallis, who focuses on endocrine disrupting compounds and microplastics in aquatic organisms. “The hypothesis is that these particles could interfere with cell function and cause muscle tissue inflammation.”
Another potential source of toxicity are the additives used to give plastic certain attributes, such as color, texture, or flexibility: “A lot of those chemicals, bisphenol A for example, have been shown to be endocrine disruptors, which means they can bind to hormone receptors on cells and disrupt the messaging that happens between them and organs,” says Dr. Brander.
The damage that these plastic additives cause to human health are well known. In 2022, a research study published in the US was able to quantify the societal costs of cardiovascular mortality associated with phthalate exposures to at least $39 billion per year (Environ Pollut. 2022;292:118021).
Growing Pains
In fact, the research on microplastics contamination in food and its toxicity in humans is relatively new. It evolved from the study of plastic pollution in marine environments and then in fish. “Up until a few years ago, most of the studies were focused on the occurrence of microplastics in oceans and in waterways. Funding sources for research focused on humans have just started to materialize. If you got a grant, and it‘s a three-year or five-year grant, you’re probably still working on it,” says Dr. Brander.
A significant issue confronting research on microplastics in food is measurement techniques. Measuring the content of microplastics typically goes through three stages: chemically digesting the sample, removing the food part, and using microscopy and spectroscopy to identify and count the particles. Currently, however, there is no standard method for measuring microplastics. “The protocol is well established, the problem is, it takes a lot of time and it‘s a very intensive and expensive process due to the labor that‘s required. One sample has been estimated to take up to 60 hours from start to finish,” says Dr. Brander.
“A lot of labs are trying to figure out how to reduce the manual labor of having to look under a microscope at samples and pick particles. But until then, it will definitely be a challenge, because each measuring method has its benefits and limitations. Some techniques can only measure larger microplastics, while others can examine smaller particles,” says Dr. Milne.
Because not all techniques are available to all researchers, the size range of microplastics they investigate might be limited by the instrumentation they have access to. These limitations make it difficult to compare results of different studies: “If a hypothetical study on fish found 50 particles of microplastics in a sample and another one found 100 particles, you couldn’t simply say the second one was more contaminated, because they may be measuring completely different size ranges,” says Dr. Abdallah.
Once these issues are resolved, however, the progress on microplastic detection will pave the way to the study of nanoplastics, whose size can be as small as a nanometer, which is the thousandth part of a micrometer. Nanoplastics are still a largely unexplored side of plastics contamination: “They’re the next frontier and one of the biggest challenges,” says Dr. Brander. “We know that they’re there, and the technology to quantify them is improving, but it’s still expensive and it‘s not available to most labs that work on microplastics.”
Reducing Microplastics in Food
Food safety regulations and standards don’t yet have any specific requirements around microplastics—this may change in the future. “Microplastics in food products is a rising concern among both food manufacturers and the public,” says Bosco Ramirez, senior director of the North American Laboratory Division of NSF International, a global certification body for food safety schemes. “Hopefully, as research progresses and methodologies improve, specific requirements for microplastics will be introduced to existing food safety standards. It’s also possible that new standards or government regulations will be developed. Collaboration among experts, industry stakeholders and regulatory agencies will be key in deriving robust methodologies to detect and quantify microplastics.”
Right now, there’s not a lot that food companies can do to tackle the issue of microplastics contamination directly: “A lot of food and non-food companies are concerned about whether they’re inadvertently generating microplastics or are using materials that contain microplastics,” says Caroline Potter, VP of sustainability at Sagentia Innovation, an R&D consultancy based in the U.K. “But if you find microplastics contamination in a food processing environment, it would be very difficult to understand how much of it came from the processing line, from water, from air pollution, or from the people working in the facility. And without knowing that, it would be very difficult to take precautionary measures.”
The best strategy for food manufacturers is to reduce the use of plastics across the board: “Part of the problem is coming from plastic packaging and the way it’s mismanaged after use, which leads to the breakdown that generates microplastics,” says Potter. “Food companies should definitely look at using alternative materials or use plastic packaging designed in a way that it can be easily recycled, so that it won‘t make its way into the environment.”
The problem, however, is more nuanced, Potter adds. “Sustainability isn’t just one thing. Plastic leakage is an important aspect, but companies are also looking at their carbon footprint, and with plastic being a very lightweight material, it can be the lower carbon footprint packaging option in some cases. When evaluating the alternatives, our advice is to try and balance all the different sustainability trade offs, whether it‘s carbon footprint, water usage, or impact on biodiversity. There’s no point in finding a solution that has a better impact in one area of sustainability, just to have a worse impact on another.
Tolu is a freelance writer based in Barcelona, Spain.
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