Sometimes after the takeaway is cold, we will "bake" it in the microwave for a few minutes, and the delicious food in the plastic box will return to its steaming and attractive appearance, which is efficient and convenient! As everyone knows, millions of tiny plastic fragments accompany the food in your mouth.
Since the discovery of microplastics in the human body, scientists have found multiple ways for microplastics to invade the human body: drinking water, seafood, clothing, cosmetics, air, etc. Humans have no escape and inevitably ingest a certain amount of microplastics every day. But in some scenarios, the amount of microplastics we ingest will skyrocket beyond imagination—from tens of thousands per year to millions per day.
In June this year, a study published in Environmental Science & Technology experimentally measured the amount of microplastics released from plastic containers under different scenarios. Researchers found that plastic containers released surprisingly high amounts of microplastics when microwaved compared to refrigerated or room temperature storage. At the same time, they also revealed the damaging effects of microplastics on cell activity.
In the experiment, the researchers did not use any unfamiliar experimental equipment, but chose the most common plastic containers in our lives that are used to hold food and are marked "microwave-heatable".
The origin of this research is very special. It originated from a father's love for his son.
In the third year of his PhD in environmental nanotechnology at the University of Nebraska, Kazi Albab Hussain became a new dad. Since he has been engaged in plastic-related research, Hussain is well aware of the seriousness of microplastic pollution.
Just in 2020, an article published in Nature Food revealed in detail the process of infants ingesting huge amounts of microplastics. The study found that when infant formula is brewed, millions of microplastic particles are shed from the inner walls of plastic bottles due to heating and sloshing of liquid. Eventually, these fragments get mixed into the milk and flow into the baby's body. But what impact do they have on baby health? There has never been a conclusion.
However, the unknown is the scariest thing. Looking at the baby bottles, pacifiers and plastic-wrapped food, Hussein couldn't help but worry about his child. He decided to take matters into his own hands and measure exactly how much microplastics were released from various plastic containers under different conditions.
To measure the amount of microplastics that babies might be exposed to, Hussein and colleagues selected three baby-specific food containers available at a local store: two that were FDA-approved and labeled “microwaveable.” A polypropylene (abbreviated as PP) plastic jar with a "heat" label, and a reusable polyethylene (abbreviated as PE) plastic grocery bag.
The researchers used deionized water to simulate aqueous foods such as milk, and used acetic acid to simulate acidic foods such as oranges and tomatoes. Then, based on the FDA's food contact testing recommendations, they used three containers to simulate three daily usage scenarios: storing food at room temperature, refrigerated, and higher-temperature spaces. In addition, they heated two polypropylene plastic jars in a microwave oven at high power for 3 minutes.
Experimental results show that the higher the storage temperature of the container, the more plastic particles will enter the food. For example, polypropylene containers in higher temperature environments will release 400,000 more microplastics per square centimeter than those stored in refrigerators. In comparison, microwave heating is even more terrifying.
When two different liquids were placed in containers under three different storage conditions, microwave heating caused the most microplastics and nanoplastics to fall off the containers. After testing, researchers found that the polypropylene container in the microwave oven released as many as 4.2 million microplastics per square centimeter, and even smaller nanoplastics reached 1.2 billion. “It really scares me to see the amount of microplastics under the microscope,” Hussain said.
In our understanding, the safety level of baby products must be the highest, because newborns are far more fragile than adults, and they are more susceptible to the effects of pollutants and health risks. Whether it is a baby bottle or a plastic packaging box for takeaway, they are clearly marked: microwaveable. So why do such research results still appear?
In fact, to evaluate whether a certain material can be used for microwave heating of food, you must first see whether it can withstand high temperatures: it cannot melt at the temperature at which food is heated, let alone release plasticizers, curing agents and other harmful substances at slightly higher temperatures. . The more important indicator is: the migration speed and amount of harmful substances to food under high temperature conditions need to be limited to standards.
On the basis of meeting these conditions, plastics such as PP (common takeout packaging box material) and PE (commonly used for plastic wrap) still have many restrictions (for example, the temperature of PP should not be too high, and PE should not come into contact with oily food, etc.) , but they are indeed microwave safe. However, microplastics are not included in these evaluation criteria.
So what effects will microplastics have on our bodies? Do they really affect human health?
Some studies have found that the human kidneys can actually filter out most of the relatively large microplastics. However, nanoscale plastic particles are extremely tricky. They are small enough that they can pass through cell membranes and reach places they are not meant to go. Nanoplastics can even coat themselves in proteins to sneak into the immune system invisibly. Once they break through the body's defense line, the chemicals carried by nanoplastics (such as bisphenol A, phthalates, etc.) will interfere with the body's hormone secretion, thereby affecting metabolism, sexual development and even fertility.
To test the effects of microplastics when they enter the human body, the team soaked kidney cells from human embryos in a mixture of high concentrations of microplastics and nanoplastics that had flowed from baby food containers. After two days, about 75% of the kidney cells were dead.
Hussain said that although the concentration of microplastics used in the experiment was higher than the concentration that babies were exposed to when eating, over time, microplastics will inevitably be released from many aspects (such as the air, other foods, and skin surfaces, etc.) Enters the baby and accumulates. Therefore, it is important to study the health effects of high concentrations of microplastic exposure. Regardless, this study is a wake-up call for everyone, from parents of newborns to those of us who eat takeout every day, to avoid heating food in plastic containers in the microwave.
If you've been heating food in plastic boxes for years, don't panic. From clothing to food to food packaging and even in the air, these tiny plastic particles are all around us and we can never truly get rid of them. But it’s never too late to make changes and reduce exposure.