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Glass bottles too carry hidden microplastics risk 

Glass bottles too carry hidden microplastics risk 
Row of empty wine bottles in storage. Image used for representational purposes only. PHOTO/Pexels

For long, glass bottles have been considered a safer alternative to plastics. However, a new study has revealed that they actually release up to fifty times more microplastics into drinks. 

The study conducted by France’s food safety agency ANSES reveals that though microplastics are present in all beverages, those packaged in glass bottles contain more microplastic particles than those in plastic bottles, cartons or cans.  

“This revelation underscores a previously overlooked source of contamination and highlights the complex nature of microplastic pollution,” reads part of the report. 

For most of the drinks studied, the level of microplastics was found to be higher in glass bottles than in other containers.

For example, on average, in glass bottles of cola, lemonade, iced tea and beer, there were around 100 microplastic particles per litre. This number was five to 50 times lower in plastic bottles and cans. 

Source of contamination 

According to the report, researchers traced the unexpected source of contamination to the paint used on glass bottle caps.

Over time, the painted coating on the caps deteriorates and releases tiny plastic particles into the liquid during storage and transport. 

Two key clues pointed to this source: first, the microplastics detected matched the colour and chemical makeup of the cap paint.

Second, microscopic analysis revealed tiny scratches on the caps — invisible to the naked eye — likely caused by friction when caps rub against each other during storage.

This friction scrapes off paint particles, which then find their way into the drinks. 

“We expected the opposite result when we were conducting this research, but instead we found that glass bottles are a bigger source of microplastics than we ever imagined,” said PhD student Iseline Chaib, one of those who conducted the research. 

Beer bottle most contaminated 

Among the beverages tested, beer was the most contaminated, with an average of 60 microplastic particles per litre. Lemonade followed closely at 40 particles per litre, while other soft drinks showed around 30.  

Surprisingly, bottled water, both flat and sparkling, contained far fewer microplastics when packaged in glass, averaging 4.5 particles per litre, compared to 1.6 in plastic bottles. Wine exhibited surprisingly low microplastic counts because wine bottles were closed with cork stoppers rather than metal caps. 

“The reasons why microplastic levels vary between beverages is still unknown, just as it is not yet possible to determine whether these levels pose a health risk,” Chaib adds. 

To confirm how drinks in glass bottles become contaminated and to explore ways to reduce microplastic levels, the research team tested the impact of different cleaning methods.

They examined three scenarios: first, they cleaned the bottles and filled them with filtered water to ensure no microplastics were present, then sealed them with untreated caps.  

Next, they tested the effect of blowing air on the caps with an air blower, and finally, they combined air blowing with rinsing the caps in filtered water and alcohol before sealing the bottles.

The results were striking: bottles sealed with uncleaned caps contained an average of 287 particles per litre.  

This number dropped significantly to 106 particles per litre when the caps were blown with air before use, and fell even further to 87 particles per litre when the caps were both blown and rinsed. 

“Encapsulation experiments with new caps and clean bottles filled with water revealed the presence of microplastics identical to the cap paint in the water. These results demonstrated that cap paint was a source of microplastics contamination in bottles,” adds Chaib. 

Reducing microplastic contamination 

But what can be done to prevent plastic particles from being released into drinks contained in bottles sealed with caps?

The report has identified a practical method to reduce contamination: cleaning the caps. By blowing air and rinsing the caps with a mixture of water and alcohol, microplastic levels can be reduced by up to 60 per cent.

This simple intervention could significantly decrease the number of microplastics entering beverages, offering a straightforward approach to improving consumer safety. 

Manufacturers can 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. 

“A cleaning step before encapsulation can significantly reduce beverages’ contamination. However, cleaning does not remove all the MPs from the capsule,” reads part of the report. 

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