Plastic baby bottles are light-weight and convenient — no wonder they make up more than 80% of the baby bottle market around the world.

But a recent study published in Nature Food found they can expose infants to thousands or even millions of particles of microplastics per day, higher than previously thought.

The study estimated the average microplastics exposure level for a bottle-fed baby was more than 1.5 million particles a day, or 2,600 times that of an adult. Infants in North America and Europe consumed even more plastic bits based on the preference for plastic baby bottles in those regions.

The researchers selected 10 types of plastic baby bottles, representative of nearly 70% of the global market, and measured the levels of microplastics released when they were used to prepare infant formula according to guidelines set by WHO. Those guidelines call for mixing powdered formula with water heated to at least 158 degrees Fahrenheit to reduce bacteria loads.

What they found was that the release of microplastics was highly temperature sensitive, Boland said. "What's happening is that there's an interaction between the [plastic] polymer and the water," Boland said. "It's almost like a flaking of the surface of the actual plastic itself." Hotter water exacerbates that flaking, and so does shaking the bottle.

When the researchers filled the plastic baby bottles with room temperature water and shook them for about 60 seconds, to simulate normal formula preparations, "you get hundreds of thousands of microplastics," he said. When they increased that temperature to 158 F, the bottles released anywhere from 1 million to 16 million particles per liter. The bottles also released trillions of even smaller nanoplastics — tiny bits of plastic ranging in size from 10 nanometers up to 1 micron – so many that "we stopped counting them," he said.

The plastic bottles continued to release microplastic particles over 21 days of testing.

The researchers then used global sales data for plastic baby bottles and information on national breastfeeding rates to estimate the potential exposure to microplastics for infants around the world in the first 12 months of life. Overall, they estimated that the average infant consumes more than 1.5 million microplastics particles per day.

But those estimates varied drastically depending on the region of the world. Infants in higher-income parts of the world, including North America and Europe, where breastfeeding rates are lower, could potentially be consuming well over 2 million microplastic particles per day, they estimated. Meanwhile, in China, where glass baby bottles are more popular, the average infant's consumption of microplastics is estimated to be in the "tens of thousands" of particles, Boland said.

The big question is if — or how — that could affect a baby’s health.

Microplastics are tiny bits of plastic smaller than a sesame seed, according to the National Oceanic and Atmospheric Administration. They can be harmful to ocean and aquatic life, and have been detected in human stools, human testis, in human blood and even in placentas from pregnancies.

The plastics industry said reporting about such small particles can sound alarming, but detecting something does not mean it presents a health risk...

But pediatricians said parents would be right to be alarmed by the study findings.

 “The science is still just scratching the surface of the concerns there. But when you see microplastics, you know the plastic is breaking down and the deeper concern is actually the less visible concern,” said Dr. Leonardo Trasande, a pediatrics professor at NYU Grossman School of Medicine and director of the Center for the Investigation of Environmental Hazards at NYU Langone in New York City.

Chemicals that absorb into foods from plastics and are of particular concern include phthalates, which can disrupt metabolism and reduce the male sex hormone testosterone; and bisphenols like BPA, which is essentially a synthetic estrogen and can make fat cells bigger, said Trasande, who was the lead author of the American Academy of Pediatrics’ policy statement on food additives and child health.

“I do think parents should worry about this,” added Dr. Claire McCarthy, a pediatrician at Boston Children's Hospital and an assistant professor of pediatrics at Harvard Medical School.

“The problem is we don’t know how much they should worry… We don’t know exactly how much exposure causes harm, or what factors might increase or decrease the harm. But it’s fair to say that we should all be using less plastic, especially when it comes to feeding our babies and children.”

Advice to parents:

To lower the amount of plastic bits a baby consumes, the authors of the new study advised shaking and heating the plastic bottle as little as possible. Wang said the four main steps to do that are:

• Rinse sterilized feeding bottles with cool sterile water to wash away some of the microplastics that might have leached out.
• Always prepare formula in a non-plastic container.
• After it has cooled to room temperature, transfer the formula into the cooled, sterilized feeding bottle.
• Avoid rewarming prepared formula in plastic containers, especially in a microwave oven, which can generate "micropockets" of superheated liquid.

But the simpler solution is to switch to 100% plastic free bottles - stainless steel and glass bottles are the best alternatives!

 Sources used in the article:

• Nature Food "Microplastic release from the degradation of polypropylene feeding bottles during infant formula preparation"
• Oxford Academic "Microplastic presence in dog and human testis and its potential association with sperm count and weights of testis and epididymis"
• Science Direct "Discovery and quantification of plastic particle pollution in human blood"
• Science Direct "Temporal trends in microplastic accumulation in placentas from pregnancies in Hawaiʻi"