Once they’ve snuck past the body’s defense systems, “the chemicals used in plastics hack hormones,” says Leonardo Trasande, a professor at the NYU Grossman School of Medicine and the director of the Center for the Investigation of Environmental Hazards. Hormones are signaling molecules underlying basically everything the body does, so these chemicals, called endocrine disruptors, have the potential to mess with everything from metabolism to sexual development and fertility.
“Babies are at greater risk from those contaminants than full-grown people,” Hussain says. So to test how much plastic babies are exposed to, Hussain’s team chose three baby-food containers available at a local grocery store: two polypropylene jars labeled “microwave-safe” according to US Food and Drug Administration regulations, and one reusable food pouch made of an unknown plastic.
They replaced the original contents of each container with two different liquids: deionized water and acetic acid. Respectively, these simulate watery foods like yogurt and acidic foods like oranges.
They then followed FDA guidelines to simulate three everyday scenarios using all three containers: storing food at room temperature, storing it in the refrigerator, and leaving it out in a hot room. They also microwaved the two polypropylene jars containers for three minutes on high. Then, for each container, they freeze-dried the remaining liquid and extracted the particles left behind.
For both kinds of fluids and polypropylene containers, the most microplastics and nanoplastics—up to 4.2 million and 1.2 billion particles per square centimeter of plastic, respectively—were shed during microwaving, relative to the other storage conditions they tested.
In general, they found that hotter storage temperatures cause more plastic particles to leak into food. For example, one polypropylene container released over 400,000 more microplastics per square centimeter after being left in a hot room than after being stored in a refrigerator (which still caused nearly 50,000 microplastics and 11.5 million nanoplastics per square centimeter to shed into the stored fluid). “I got terrified seeing the amount of microplastics under the microscope,” Hussain says.
To test what these plastics do to our bodies once they’re consumed, the team bathed human embryonic kidney cells in the plastic roughage shed by the baby-food containers. (The team chose this kind of cell because kidneys have so much contact with ingested plastic.) After two days of exposure to concentrated microplastics and nanoplastics, about 75 percent of the kidney cells died—over three times as many as cells that spent two days in a much more diluted solution.
While the concentration of plastic used in these solutions was higher than what a baby would be exposed to by eating from a microwaved food jar in real life, Hussain notes that the full extent of plastic particle accumulation over time—from food and from the air and surfaces—is unknown, and might be high. So, he says, it’s important to study the health effects of high levels of exposure.
While Hussain’s team was the first to test the toxicity of plastics on cells using the particles released from commercially available food containers, a review published in the Journal of Hazardous Materials last year found that exposure to microplastics can cause cell death, inflammation, and oxidative stress. “Plastics are a huge problem for human health,” says Trasande. “This study just pushes the concern even further.”
