Contrary to the common belief that glass bottles are more hygienic than PET bottles, a French study has revealed a surprising result: beverages in glass bottles contain 5 to 50 times more microplastic particles than those in PET (plastic) bottles.

The French Agency for Food, Environmental and Occupational Health & Safety (ANSES) measured the amount of microplastics found in lemonade, iced tea, soft drinks, and beer contained in glass and plastic bottles. The results showed that beverages in glass bottles contained about 100 microplastic particles per liter. This is 5 to 50 times higher than the amount found in beverages contained in plastic bottles or metal cans.

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Iseline Schaive, a doctoral student who led the study, told AFP, "We expected the exact opposite result." The research team estimated that the microplastic particles found in beverages from glass bottles originated not from the glass itself, but from the paint on the bottle caps. Schaive explained, "We confirmed that the microplastic particles found in samples from glass bottle beverages had the same shape, color, and polymer composition as the paint on the outside of the caps that seal the glass bottles." ANSES stated, "The paint on the bottle caps had small scratches that were invisible to the naked eye, likely caused by friction between the caps during storage." They concluded that microplastic particles separated from the surface of the caps due to these scratches and dissolved into the beverages.

An image created by generative AI DALL·E3 with the command "a comparison of the hygiene conditions of bottle caps and PET bottle caps."

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The amount of microplastics varied depending on the type of beverage. Both carbonated water and mineral water had the lowest microplastic content, with about 4.5 particles per liter in glass bottles and 1.6 particles per liter in plastic bottles. In contrast, the number of microplastics detected in sweetened beverages was much higher. Carbonated drinks in glass bottles contained about 30 particles per liter, lemonade in glass bottles about 40, and beer in glass bottles about 60 microplastic particles per liter. Interestingly, wine showed almost no detectable microplastics, regardless of the type of bottle. Guillaume Duplois, the lead researcher at ANSES, said, "The reason for this is still unknown." ANSES explained that since there is currently no established toxicity threshold for microplastics, it is not possible to determine what health risks these numbers may pose.

The research team also suggested a simple way to reduce the amount of microplastics coming from bottle caps. When they blew air to remove dust from the caps and then rinsed them with water or alcohol, the amount of microplastics decreased by as much as 60%. Washing the caps before sealing the bottles can significantly reduce the amount of microplastics entering beverages.