The researchers found an average of around 100 microplastic particles per liter in glass bottles of soft drinks, lemonade, iced tea and beer. That was five to 50 times higher than the rate detected in plastic bottles or metal cans.
“We expected the opposite result,” Ph.D. student Iseline Chaib, who conducted the research, told AFP.
“We then noticed that in the glass, the particles emerging from the samples were the same shape, color and polymer composition—so therefore the same plastic—as the paint on the outside of the caps that seal the glass bottles,” she said.
The paint on the caps also had “tiny scratches, invisible to the naked eye, probably due to friction between the caps when there were stored,” the agency said in a statement.
This could then “release particles onto the surface of the caps,” it added.
Bottle caps are stored in big bags of some sort before being placed on bottles.
They have sharp edges and they scratch each other’s paint as they shift around in the bags.
The scratching produces a fine dust of plastic/paint particles. The dust covers all sides of the bottle caps in the bags.
The caps are placed on the bottles. The dust goes into the liquid inside the bottle. People drink it.