Ready-to-heat meals packaged in plastic trays and containers are often labeled as safe for microwave or oven cooking. However, a new review of peer-reviewed research suggests that heating food in plastic packaging may significantly increase the release of microplastics and chemical additives into food.

The analysis, conducted by Greenpeace International, outlined findings from 24 peer-reviewed scientific studies examining the migration of microplastics and chemical substances from food-contact plastics.

Heating Can Accelerate Microplastic Release from Food Packaging

According to the report, several studies found that microwaving plastic food containers can rapidly release large quantities of microplastic and nanoplastic particles.

For example, one study found that polypropylene and polystyrene containers released between 100,000 and 260,000 microplastic particles when microwaved after refrigerated or frozen storage. In another experiment, two polypropylene containers released an estimated 326,000–534,000 microplastic particles into a food simulant after five minutes of microwave heating, a level four to seven times higher than that observed during oven heating.

Other research cited in the review found that higher microwave power levels and longer heating times increased the number of particles released from plastic food contact materials (FCMs), and that old or scratched containers released nearly twice as many microplastics as new containers.

At present, there is currently no regulatory guidance specifically addressing microplastics released from FCMs. However, the European Food Safety Authority (EFSA) is expected to deliver a scientific opinion on the potential health risks posed by microplastics in food by end-2027. Interestingly, a preliminary review published by EFSA concluded that, while there is clear evidence of microplastic release from FCMs, the actual quantities are likely lower than many studies suggest, and current evidence does not support reliable exposure estimates.

Chemical Migration from Food Packaging

Plastic food packaging also contains chemical substances that can migrate into food under certain conditions.

Plastics may contain intentionally added substances (e.g., stabilizers, plasticizers, and antioxidants) as well as non-intentionally added substances that form during manufacturing, storage, or degradation of the material. According to the report, more than 4,200 chemicals that are known to be hazardous have been identified as used or present in plastics, although many are not specifically regulated in food packaging.

The review found that chemical migration during heating is common. In one study cited in the report, microwaveable plastic containers released at least 42 intentionally added substances and more than 100 non-intentionally added substances into food simulants. Another experiment reported that polystyrene and polypropylene lunch containers leached chemical additives into food simulants in every tested sample during microwave heating. One study found that 20 different additives migrated into a ready meal during microwave heating.

Additional studies found that antioxidants and plasticizers migrated from heated plastic packaging into foods such as meat and vegetables, demonstrating that migration can occur not only in laboratory simulants but also in real foods.

Researchers also identified cases where chemical reactions between food and packaging occurred during heating, producing previously unknown compounds. In one study, a UV stabilizer used in plastic packaging reacted with potato starch during microwave cooking, forming a previously unknown chemical compound.

Potential Health Impacts of Microplastics, Chemical Migration from Food Packaging

The report also referenced a growing body of research examining the potential health implications of plastic exposure.

Microplastics and plastic-associated chemicals have been detected in various human tissues and biological samples, including blood, placenta, breast milk, lungs, liver, and stool. While research on health outcomes is ongoing, some studies have suggested that smaller particles, particularly nanoplastics, may move through the body and interact with cells.

Reviews of existing research have also associated exposure to plastic-related chemicals with a range of health concerns, including endocrine disruption, metabolic disease, reproductive disorders, and certain cancers. Additionally, at least 1,396 food-contact plastic chemicals have been detected in human bodies, according to research cited in the report.

However, experts emphasize that hazard detection does not necessarily equate to risk, as risk assessments must consider exposure levels and dose-response relationships.

Implications for Food Safety

For food safety professionals, the findings highlight the importance of evaluating FCMs not only for their chemical composition but also for how they are used by consumers. Heating conditions, packaging design, and the interaction between food ingredients and packaging materials can influence the migration of particles and chemicals. (To hear an expert perspective on the regulatory, sustainability, and technical considerations for food companies regarding chemicals of concern in packaging, listen to a recent episode of the Food Safety Matters podcast with packaging scientist Claire Sand, Ph.D., here.)

Notably, most of the studies reviewed used food simulants (e.g., water, ethanol, acetic acid) rather than real foods, meaning actual exposure levels in typical meal preparation scenarios remain uncertain. Still, the report argues that the evidence warrants closer regulatory scrutiny of plastic food packaging and the conditions under which it is used.

Based on the findings, Greenpeace urged regulators to implement the precautionary principle to prevent the use of hazardous plastics and chemicals in FCMs as a priority, based on their intrinsic hazard and not on a risk assessment that determines safe levels. The group also calls for action to phase out the use of known endocrine-disrupting chemicals and prohibit “microwave safe” and “oven safe” label claims on ready meal packaging.