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Weird Science: Drinks in glass bottles can contain more microplastics than those in plastic

Microplastics are present in all beverages, but those packaged in glass bottles can contain more microplastic particles than those in plastic bottles, cartons, or cans.

This was the surprising finding of a study conducted by the Boulogne-sur-Mer unit of the ANSES Laboratory for Food Safety in France. The scientists hypothesized that these plastic particles could come from the paint used on bottle caps. Water and wine are less affected than other beverages. These findings have highlighted a source of microplastics in drinks that manufacturers can easily take measures to address.

"We were expecting the opposite result when we compared the level of microplastics in different drinks sold in France," explained Iseline Chaib, a PhD student in the Aquatic Food Safety Unit (SANAQUA, Boulogne-sur-Mer site), which conducted the study at the ANSES Laboratory for Food Safety. In the absence of toxicological reference data, it is not possible to say whether the levels of microplastics found pose a health risk, said the researchers.

In the specific case of water, the level of microplastics was relatively low, regardless of the container, with an average of 4.5 particles per liter in glass bottles and 1.6 particles per liter in plastic bottles and cartons. Wine also contained few microplastics, including in glass bottles with corks. The origin of these variations in the level of microplastics in drinks remains to be explored, except for drinks contained in glass bottles with caps.

The scientists investigated the origin of the microplastics found in drinks packaged in glass bottles with caps. Given their characteristics, they concluded that these particles probably came from the metal caps, and more specifically from the paint that covered them. The first clue: The microplastics found in the drinks were mostly the same color and had the same composition as the paint on the caps. The second clue: The paint on these caps had tiny scratches that were invisible to the naked eye and had probably been caused by friction between the caps when they were stored before use. This friction, which released particles from the surface of the caps, was thought to be the source of the microplastics found.

To confirm the route of contamination of drinks in glass bottles and explore the possibility of reducing microplastic levels, the laboratory tested the effects of different cleaning operations. "We studied three scenarios" said Chaib. "We cleaned the bottles and filled them with filtered water, so that no microplastics could be detected, then we placed caps on the bottles without treating the caps, after blowing on the caps with an air bomb, or after blowing air and rinsing the caps with filtered water and alcohol."

The result? While an average of 287 particles per liter were found in the water of the bottles sealed with uncleaned caps, this number decreased significantly, to 106 particles per liter, when air was blown on the caps before they were placed on the bottles. It fell further to 87 particles per liter when blowing was followed by rinsing.

To prevent plastic particles from being released into drinks contained in bottles sealed with caps, manufacturers could also explore other lines of action, such as changing the conditions in which the caps are stored before use, to avoid friction, or modifying the composition of the paint used on the caps.

Read "Microplastic contaminations in a set of beverages sold in France."

Source: ANSES Laboratory for Food Safety

Published July 2025

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