Results from recent laboratory experiments show that microwaving water- and milk-based beverages in common baby food containers releases levels of microplastics and nanoplastics that could potentially be toxic over time.

The experiments were not conducted on humans. Instead, they involved exposing human cells in a laboratory to the tiny plastic particles released during microwaving. The findings were published in the journal Environmental Science & Technology.

Researchers from the University of Nebraska-Lincoln conducted experiments on three types of commonly sold baby food packages: two different baby food containers made from polypropylene, and a reusable baby food pouch made of polyethylene. The container types are approved by the FDA, the authors noted. One set of containers was filled with water and another set of containers with an acidic liquid to mimic the properties of common baby foods and beverages like fruit, vegetables, or dairy products. The filled containers were microwaved at full power for three minutes in a 1,000-watt microwave. Afterward, researchers analyzed the liquids to see if they contained micro- or nanoplastic particles.

Microplastic particles are those at least 1/1000th of a millimeter, and nanoplastic particles are smaller than that size. Researchers concluded that the most concentrated consumption of the tiny plastic particles would occur when infants drank products with microwaved water or when toddlers consumed microwaved dairy products.

Study author Kazi Albab Hussain, a doctoral student in civil and environmental engineering at the University of Nebraska–Lincoln, recently became a father, which inspired the research. “For my baby, I was unable to completely avoid the use of plastic,” Hussain said in a statement. “But I was able to avoid those (scenarios) which were causing more of the release of micro- and nanoplastics. People also deserve to know those, and they should choose wisely.”

Researchers conducted an additional laboratory experiment that exposed human embryonic kidney cells to the microplastics and nanoplastics detected after microwaving the baby food containers. They exposed the kidney cells to many more particles than would be released in just a single microwave-and-drink session. The amount of particles used in the experiment equaled what researchers estimated would add up to particle concentrations accumulated over the course of many days or from multiple sources.