Can "plastic" really be put into the microwave? New research: There is no real safety

Experts interviewed:

Ding Xuejia, Associate Professor, School of Materials Science and Engineering, Beijing University of Chemical Technology

With the popularization of science, many people know that ordinary plastic products cannot be used to heat food, and only plastics marked as food grade can be used for heating. However, not long ago, the magazine "Environmental Science and Technology" published an experiment by a research team from the University of Nebraska-Lincoln, and the results were shocking. It turns out that food grade plastics are not safe when heated.

The researchers selected food-grade plastic containers made of polypropylene and polyethylene. The team placed them in a 1-kilowatt microwave for 3 minutes and then analyzed the liquid in the container and found a lot of microplastics (about 1 micron in diameter) and smaller nanoplastic particles. It is estimated that 4.22 million micron plastic particles and 2.11 billion nanoplastic particles will be released in 1 square centimeter of plastic.

The researchers also found that if the container of this material is used for heating liquids, including water, milk, etc., the number of microplastic particles produced is the highest; if it is only used for refrigerated storage of food or beverages, the microplastic released will be much less. The researchers pointed out: "We hope that one day the labels of these products will say 'no microplastic particles' or even 'no nanoplastic particles'."

Coincidentally, on April 20, 2022, a team of experts from the National Institute of Standards and Technology conducted a study using food-grade nylon bags and products made of low-density polyethylene (LDPE). The results showed that after a disposable take-out coffee cup filled with 100°C water was left to stand for 20 minutes, an average of trillions of plastic nanoparticles could be detected per liter of water. In addition, millions of microplastic particles were detected after adding 70°C water to a polypropylene baby bottle and shaking it for 1 minute. The researchers found that when the water temperature rose from 25°C to 95°C, the number of microplastic particles detectable per liter of water increased from 600,000 to 55 million.

In this regard, the reporter interviewed Ding Xuejia, an associate professor at the School of Materials Science and Engineering of Beijing University of Chemical Technology. He pointed out: "The so-called 'food grade' only means that it is relatively safe for a period of time. With the advancement of detection methods and the extension of the research time span, the regulations on food safety will continue to upgrade and the standards will become higher and higher. Therefore, the above experiment is a reminder to people."

Ding Xuejia introduced that at present, the concept of microplastics is in a vague stage both at home and abroad. When the concept of microplastics was first proposed, it referred to plastic particles smaller than 5 mm. At that time, this concept was mainly limited to the field of marine pollution research. The hazards of microplastics initially proposed were all based on the millimeter scale, and their hazards also mostly pointed to the release of various toxic additives. For microplastics smaller than 1 micron or even nanometer scale, current research is very controversial and inconclusive, and there is even less research on their hazards. "But what is clear is that humans have been using plastics for more than a hundred years, and there has not been a single case of disease caused by the ingestion of these tiny plastics reported." Ding Xuejia said.

Ding Xuejia said that people do not need to worry too much about the above issues. The absorption, distribution, accumulation, metabolism and final toxicity of these tiny plastic particles in the body depend on many factors, and most of them can be excreted due to their small size.

In my country, all plastic products are marked with a triangle sign, which is equivalent to its identity "label". The triangle formed by three arrows means "recyclable and reusable"; the numbers in the triangle range from 1 to 7, and each number represents a plastic material, which is mainly for the convenience of recycling and understanding its use conditions. Among them, the main manufacturing material marked with "5" is polypropylene, or PP, which is currently the only material that can be used to make microwave lunch boxes.

Ding Xuejia reminded that PP plastic is only relatively safe and can be reused after careful cleaning. At the same time, be careful with colorants and try to choose colorless products. Before using plastic products for the first time, try to wash them several times with hot water to ensure that the items are clean. Use plastic products as little as possible and replace them with products made of other materials (glass, ceramics). (Global Times Health Client reporter Dong Changxi)