Polypropylene baby bottles­—which comprise 82 percent of the global baby bottle market—release an “extraordinary” number of microplastic particles, reports a new study by Trinity College Dublin. In a study published in Nature Food, which covered 48 regions worldwide, researchers found that flexible plastic baby bottles release as many as 16.2 million particles per liter. “A study last year by the World Health Organization estimated adults would consume between 300 and 600 microplastics a day—our average values were on the order of a million or millions,” study co-author John Boland told The Guardian. He called for more studies to understand the implications, saying the researchers were “absolutely gobsmacked” by the numbers. The microplastics are released when heated liquid is used to sterilize the bottles and to dissolve powdered formula and when the bottle is shaken to dissolve the powder. The higher the water temperature, the greater the release of particles. Polypropylene bottles have a “5” on the recycling symbol on the bottom.