At the beginning by his third year at graduate school, Kazi Albab Hussain became a father. As a new father and PhD student studying environmental nanotechnology, plastic was on his mind. The year before, scientists had discovered that plastic baby bottles secrete millions of particles into formula, which infants end up swallowing (while also sucking on the plastic bottle’s nipples). “At that time,” says Hussain, “I was buying a lot of baby food and I could see that even in baby food there is a lot of plastic.”
Hussain wanted to know how much was released from the kind of containers he had bought. So he went to the grocery store, picked up some baby food, and brought the empty containers back to his lab at the University of Nebraska-Lincoln. In a study published in June i Environmental science and technologyHussain and his colleagues reported that when these containers were used in the microwave, they released millions of pieces of plastic, called microplastics, and even less nanoplastics.
Plastics are complex cocktails of long chains of carbon, called polymers, mixed with chemical additives, small molecules that help mold the polymers into their final shape and imbue them with resistance to oxidation, UV exposure and other wear and tear. Microwaves deliver a triple whammy: heat, UV radiation and hydrolysis, a chemical reaction through which bonds are broken by water molecules. All of these can cause a container to crack and shed small pieces of itself such as microplastics, nanoplastics and leachatestoxic chemical components in the plastic.
The human health effects of plastic exposure are unclear, but researchers have suspected for years that they are not good. First, these particles are sneaky. Once inside the body, they coat themselves with proteins and slip past the immune system incognito, “like Trojan horses,” says Trinity College Dublin chemistry professor John Boland, who was not involved in this study. Microplastics also collect a complex community of microbes, called plastisphereand transport them into the body.
Our kidneys remove waste and place them on the front lines of exposure to pollutants. They are OK for filtering out the relatively larger microplastics, so we probably excrete a lot of them. But nanoplastics are small enough to slip across cell membranes and “make their way to places they shouldn’t,” says Boland.
“Microplastics are like plastic roughage: They come in and they get thrown out,” he adds. “But it’s quite likely that nanoplastics could be very toxic.”
Once they sneak past the body’s defense systems, “the chemicals used in plastics disrupt hormones,” says Leonardo Trasand, a professor at the NYU Grossman School of Medicine and director of the Center for the Study of Environmental Hazards. Hormones are signaling molecules that underlie virtually everything the body does, so these chemicals, called hormone disrupting drugshas the potential to mess with anything from metabolism to sexual development and fertility.
“Babies are at greater risk from these pollutants than full-grown humans,” says Hussain. 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 regulationsand a reusable lunch bag made of unknown plastic.