Day: July 31, 2023

At the start of his third year of graduate school, Kazi Albab Hussain became a father. As a new dad and a PhD student studying environmental nanotechnology, plastic was on his mind. The year before, scientists had discovered that plastic baby bottles shed millions of particles into formula, which infants end up swallowing (while also sucking on plastic bottle nipples). “At that time,” Hussain says, “I was purchasing many baby foods, and I was seeing that, even in baby foods, there are a lot of plastics.”

Hussain wanted to know how much was being released from the kinds of containers he’d been buying. 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 in Environmental Science & Technology, Hussain and his colleagues reported that, when microwaved, these containers released millions of bits of plastic, called microplastics, and even tinier nanoplastics.

Plastics are complex cocktails of long chains of carbon, called polymers, mixed in 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. Microwaving delivers a triple whammy: heat, UV irradiation, and hydrolysis, a chemical reaction through which bonds are broken by water molecules. All of these can cause a container to crack and shed tiny bits of itself as microplastics, nanoplastics, and leachates, toxic chemical components of the plastic.

The human health effects of plastic exposure are unclear, but scientists have suspected for years that they aren’t good. First, these particles are sneaky. Once they enter the body they coat themselves with proteins, slipping 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 the plastisphere, and transport them into the body.

Our kidneys remove waste, placing them on the front lines of exposure to contaminants. They are OK at filtering out the relatively larger microplastics, so we probably excrete a lot of those. But nanoplastics are small enough to slip across cell membranes and “make their way to places they shouldn’t,” Boland says.

“Microplastics are like plastic roughage: They get in, and they get expelled,” he adds. “But it’s quite likely that nanoplastics can be very toxic.”

Once they’ve snuck past the body’s defense systems, “the chemicals used in plastics hack hormones,” says Leonardo Trasand, 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.

Around a third of human-generated greenhouse gas emissions comes from the global food system, and lost or wasted food is known to contribute some amount—but it has never been clear to exactly what degree. Now, by following specific foods through their entire life cycle, researchers have determined just how much this wasted food adds to emissions through phases such as harvest, transportation and disposal.

For a study in Nature Food, Xunchang Fei of Singapore’s Nanyang Technological University and his colleagues used 164 countries’ food supply data from 2001 to 2017 to estimate emissions across 54 food commodities and four categories: cereals and pulses; meat and animal products; vegetables and fruits; and root and oil crops.

Roughly a third of food is lost during harvest, storage and transportation or is wasted by consumers. The team found this food was responsible for greenhouse gases equivalent to 9.3 billion metric tons of carbon dioxide—about half the global food system’s total emissions—in 2017. Four countries (China, the U.S., India and Brazil) contributed 44.3 percent, mainly owing to their dietary habits and large populations. Of the four food categories, meat and animal products were the source of almost three quarters of emissions that occurred during the supply-chain phase for food that was ultimately lost.

The study considered emissions across nine postfarming stages, which vary among regions—for instance, developed countries’ advanced waste-treatment technologies can create fewer emissions. Such intricate details show how “different countries should set different targets for [food loss and waste] reductions,” Fei says—such as reducing meat production in some areas, and switching from landfills to anaerobic digestion or composting processes in others.

Food systems expert Prajal Pradhan of the Potsdam Institute for Climate Impact Research in Germany notes that the United Nations Sustainable Development Goals aim to halve food waste in the coming years—which Pradhan says wouldn’t be enough to limit global warming but would be a start. Based on this study, he says, emissions could decrease if “high-income countries could focus on saving food discarded by consumers, and low- and middle-income countries could prioritize avoiding food loss during harvesting, processing, storage and transport.”