Microplastics in Food and Their Impact on Human Health

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.”