For years, glass bottles have been marketed as the eco-conscious consumer’s choice – a cleaner, greener alternative to plastic bottles and cans. But a new study from France – first reported by our colleagues of Green Prophet – has turned this assumption on its head. It reveals that glass bottles may contain far more microplastics than their plastic or metal counterparts.
The research was conducted by the Boulogne-sur-Mer unit of the ANSES Laboratory for Food Safety and published in the Journal of Food Composition and Analysis. The source of contamination: the painted metal caps sealing glass bottles.
Beyond beverages, microplastics are infiltrating everyday products like toothbrushes, teeth aligners, and chewing gum, raising urgent questions about their impact on human health and the environment.
In this article I will explore the study’s findings, the broader issue of microplastic exposure, and what consumers and manufacturers can do to address this pervasive problem.
The French Study: Glass Bottles Under Scrutiny
The ANSES study, led by PhD student Iseline Chaïb, analyzed 56 beverage samples – including water, soda, iced tea, beer, and wine – to assess microplastic contamination across different packaging materials: glass bottles, plastic bottles, cartons, and cans. The results were unexpected. Contrary to expectations, glass bottles consistently showed higher microplastic levels, with popular beverages like cola, lemonade, iced tea, and beer containing an average of 100 microplastic particles per liter, or five to 50 times higher than plastic bottles or cans.
“We were expecting the opposite result when we compared the level of microplastics in different drinks sold in France,” Chaïb admitted in a statement to ANSES. “We then noticed that in the glass, the particles emerging from the samples were the same shape, colour, and polymer composition – so therefore the same plastic – as the paint on the outside of the caps that seal the glass bottles.”
The researchers pinpointed the painted metal caps as the primary culprit. These caps, coated with plastic-based paint on their interior, develop microscopic scratches during storage and transport. Friction among the caps’ edges causes tiny plastic particles to flake off, contaminating the beverage inside when the bottle is sealed.
Needless to say that this discovery challenges the long-held belief that glass is inherently safer for avoiding plastic pollution.
The Data: Microplastics by Beverage and Packaging
The ANSES study provides detailed data on microplastic contamination, which is summarized in the table below based on figures reported in the study and supporting sources. While the full dataset is not publicly available, the reported values offer a clear picture of the contamination levels across different beverages and packaging types.
| Beverage Type | Packaging Type | Microplastic Particles per Liter | Notes |
|---|---|---|---|
| Soft Drinks (e.g., Cola) | Glass Bottle | ~100 | 5–50 times higher than plastic bottles or cans. Source: Painted metal caps. |
| Lemonade | Glass Bottle | ~40 | Higher contamination linked to cap paint. |
| Iced Tea | Glass Bottle | ~100 | Similar to soft drinks, cap paint is the primary source. |
| Beer | Glass Bottle | ~60 | Highest among beverages tested, linked to painted caps. |
| Water (Flat/Sparkling) | Glass Bottle | ~4.5 | Relatively low contamination compared to other beverages. |
| Water (Flat/Sparkling) | Plastic Bottle | ~1.6 | Lower than glass bottles. |
| Water (Flat/Sparkling) | Carton | ~1.6 | Comparable to plastic bottles. |
| Soft Drinks | Plastic Bottle/Can | ~2–20 | Significantly lower than glass bottles. |
| Wine | Glass Bottle (Cork) | Minimal (~0–5) | Low contamination, likely due to cork stoppers instead of painted caps. |
| Cleaning Test (Water) | Glass Bottle (Uncleaned Caps) | 287 | Control test with filtered water and untreated caps. |
| Cleaning Test (Water) | Glass Bottle (Air-Blown Caps) | 106 | Reduced by ~63% compared to uncleaned caps. |
| Cleaning Test (Water) | Glass Bottle (Air-Blown + Rinsed Caps) | 87 | Reduced by ~70% compared to uncleaned caps. |
Sources: ANSES Laboratory for Food Safety (2025), Interesting Engineering (June 21, 2025), The Independent (June 25, 2025), ScienceAlert (June 24, 2025), Business Standard (June 23, 2025), NDTV (June 22, 2025)
Painted Caps on Glass Bottles
The high microplastic levels in glass bottles stem from an overlooked detail: the painted metal caps used to seal them. These caps, coated with a plastic-based paint to prevent corrosion and ensure a tight seal, shed particles due to mechanical wear. During storage, transport, or handling, caps rub against each other, creating tiny scratches that release microplastics into the beverage. The particles detected in the drinks matched the chemical makeup and color of the cap paint, confirming the source.
To explore solutions, the ANSES team conducted controlled experiments using filtered water in glass bottles. They tested three scenarios for cap preparation:
- Uncleaned Caps: Bottles sealed with untreated caps contained 287 microplastic particles per liter.
- Air-Blown Caps: Blowing air on the caps reduced contamination to 106 particles per liter, a 63% decrease.
- Air-Blown and Rinsed Caps: Combining air-blowing with rinsing in filtered water and alcohol further reduced levels to 87 particles per liter, a 70% reduction.
These results suggest that simple changes in cap handling – such as cleaning protocols or reducing friction during storage – could significantly lower contamination. More ambitiously, reformulating the paint used on caps or exploring alternative materials could address the issue at its source.
Exceptions: Wine and Cork Stoppers
Not all glass-bottled beverages showed high microplastic levels. Wine, particularly when sealed with cork stoppers, had minimal contamination, averaging 0–5 particles per liter. The reason for this is tied to the absence of the painted metal caps.
Cork, a natural material, does not introduce plastic particles, making it a safer option for reducing microplastic exposure. This finding suggests that the choice of closure type is as critical as the bottle material itself.
Beyond Bottles: Microplastics in Everyday Life
The ANSES study’s findings are alarming, but microplastics are not limited to beverages. A lot of common products contribute to daily microplastic exposure, infiltrating our bodies through unexpected routes:
- Toothbrushes: Nylon bristles on toothbrushes fray over time, shedding microplastic fibers that can be swallowed or absorbed into oral tissues. Alternatives like miswak sticks, a natural chewing stick used in many cultures, are gaining attention as plastic-free options.
- Teeth Aligners and Retainers: Made from thermoplastics, these devices can release microplastics, especially when exposed to hot liquids or worn overnight. Heated plastics in the mouth may leach hormone-disrupting chemicals, posing potential health risks.
- Chewing Gum: Modern chewing gum is often made from synthetic rubber, a plastic polymer, rather than natural chicle. Chewing releases microscopic plastic particles into saliva, which may be swallowed. Few regulations require manufacturers to disclose these polymers, leaving consumers unaware of their exposure.
These sources of microplastics are particularly concerning because particles smaller than 5 microns can cross cellular membranes, potentially accumulating in the bloodstream, lungs, or brain. Emerging research has detected microplastics in human tissues, including the placenta and brain, raising questions about their long-term effects on health.
The Health and Environmental Toll
The health risks of microplastic exposure remain understudied, with no toxicological reference data to definitively assess the danger of the levels found in beverages or other products. However, early studies suggest potential effects on the liver and other organs, as well as disruptions to hormonal systems due to chemical leaching. Microplastics also act as carriers for environmental contaminants like heavy metals and bacteria, amplifying their impact.
Environmentally, microplastics are a global crisis as we reported about in the past. They have been found in oceans, rivers, soil, air, and even Arctic ice, affecting ecosystems and wildlife. In aquatic organisms, microplastics disrupt feeding, growth, and reproduction, with ripple effects up the food chain.
What Can Consumers Do?
For consumers, the study obviously complicates the quest to avoid microplastics. Glass bottles, once seen as a safe haven, are as we now see not a guaranteed solution. Here are practical steps to reduce exposure:
- Choose Cork-Sealed Bottles: Opt for wines or other beverages sealed with cork stoppers, which showed minimal microplastic contamination.
- Consider Cans or Cartons: These had significantly lower microplastic levels than glass bottles in the ANSES study.
- Filter Water at Home: High-quality water filters can reduce reliance on bottled beverages, minimizing exposure to microplastics from packaging.
