A new study from the University of Nebraska-Lincoln suggests that the fastest way to heat food and drink may also be the fastest way to ingest large amounts of tiny plastic particles.
Experiments show that microwave heating of plastic baby food containers on US store shelves can release large amounts of plastic particles. Over 2 billion nanoplastics and over 4 million microplastics per square centimeter of container.
The health effects of ingesting microplastics and nanoplastics are not yet known, but the Nebraska researchers also found that three-quarters of cultured fetal kidney cells died two days after ingesting the same particles. A 2022 report from the World Health Organization recommends limiting exposure to such particles.
“Knowing how much microplastics and nanoplastics we are ingesting is very important,” says Kazi Al-Bab Hussein, lead author of the study and a Ph.D. student in civil and environmental engineering at the University of Nebraska-Lincoln. “When we eat a particular food, we are usually informed or aware of its caloric content, sugar content and other nutrients.
“In the same way that we understand the effects of calories and nutrients on our health, knowing the amount of plastic particles we ingest is crucial in understanding the potential harm they can cause. Numerous studies, including ours, demonstrate that the toxicity of micro- and nanoplastics is highly correlated with exposure levels.”
The research team began work in 2021, the year Hussein became a father. While previous studies had looked at the release of plastic particles from baby bottles, the researchers noted that none had looked at the kinds of plastic containers and pouches that Hussein shopped for himself, and that millions of other parents shop for on a regular basis.
Hussain and his colleagues decided to experiment with two polypropylene baby food containers and a reusable polyethylene pouch, both of which are FDA-approved plastics. In one experiment, researchers filled a container with either deionized water or 3% acetic acid (the latter intended to simulate dairy products, fruits, vegetables, and other relatively acidic consumables) and heated it in a 1,000-watt microwave at full power for three minutes. They then analyzed the liquid for evidence of microplastics and nanoplastics. Micros are particles at least 1/1000th of a millimeter in diameter and nanos are smaller particles.
The actual number of each particle emitted by microwave heating depends on multiple factors, including the plastic container and the liquid inside. But based on a model that takes into account particle emissions, body weight, and per capita intake of various foods and drinks, the researchers estimated that infants who drank products containing microwaved water and those who consumed microwaved dairy products had the highest relative plastic concentrations. Experiments designed to simulate refrigerated and room temperature storage of food or beverages over six months also suggested that both could lead to the release of micro- and nanoplastics.
“I couldn’t completely avoid using plastic because of my baby,” Hussein said. “However, we have been able to avoid scenarios (scenarios) that lead to further releases of microplastics and nanoplastics. People also have a right to know about them and need to choose wisely.”
With the help of Svetlana Romanova of the University of Nebraska Medical Center, the team then cultured the fetal kidney cells and exposed them to the actual plastic particles released from the container. This was the first time Hussein knew. Instead of just introducing the number of particles released from a single container, the researchers exposed the cells to particle concentrations that infants and young children could accumulate for several days or from multiple sources.
After two days, only 23% of kidney cells exposed to the highest concentration were viable, a much higher mortality rate than that observed in previous studies of micro- and nanoplastic toxicity. The researchers suspect that kidney cells may be more susceptible to particles than other cell types examined in previous studies. However, these early studies also tended to examine the effect of larger polypropylene particles, some of which may be too large to penetrate cells. If so, the Hussein-led study could have particularly grave consequences. The Husker team found that polypropylene containers and polyethylene pouches typically released about 1,000 times more nanoplastics than microplastics, regardless of experimental conditions.
Hussain said the question of cell invasion is just one of many that need answers before determining the true risks from ingesting microplastics and nanoplastics. But to the extent that plastic poses a health threat, and that plastic remains a go-to for baby food storage, parents will be keenly aware that companies that make plastic containers are looking for viable alternatives, he said.
“We need to find a polymer that emits less[particles],” Hussein said. “Perhaps researchers will be able to develop plastics that do not emit microplastics or nanoplastics, or, if they do, the emissions will be negligible.
“We hope that one day these products will have labels that say ‘microplastic free’ or ‘nanoplastic free’.”
The research team reported their findings in a journal environmental science & technology. Hussain and Romanova, along with Yusung Lee, Matthias Schubert, Yongfeng Lu, Lucia Fernandez-Ballester, Binh Wang, Shi Huang, Jesse Kubler, Dong Jiang, and Ilhami Ocul of the University of Nebraska-Lincoln, authored the study. The researchers received support from the National Science Foundation and the Buffett Institute for Early Childhood Research.