A major new study of microplastics contamination of popular beverages shows that the highest levels are often found in glass bottles. 

The study was conducted by France’s Food Safety Agency and is published next month in the Journal of Food Composition and Analysis. 

The researchers created special laboratory conditions consistently and accurately test for presence of microplastics in water, wine, beer, soft drink and tea products in a range of container types including plastic, cans, glass and collapsible cubtainers (use for wine boxes). They found an average of around 100 microplastic particles per litre 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. 

The researchers suspect that painted bottle caps are the principal source of the much higher presence of microplastics in glass bottle, as the majority of particles isolated in beverages corresponded to the colour and polymeric composition of the paint on the caps, which are coated with alkyd thermosetting resin or PES/PET-based paint. 

The researchers say the contamination from the paint on the outside of the bottle caps raises an additional significant safety (over and beyond microplastic contamination), since additives may be present. Additional cleaning of the caps prior to bottling may help to reduce MP levels, but not climate them, the study authors suggest.