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Fact check: Do glass bottles contain more microplastics than plastic bottles?
Executive Summary
A series of studies and news reports in 2025 found that beverages sold in glass bottles often show higher counts of microplastic particles than the same beverages in plastic bottles, cans, or cartons, with the principal contamination source identified as the painted plastic coatings on metal bottle caps. The French food safety agency ANSES led the core research, reporting that drinks in glass bottles had markedly greater microplastic counts — often many times higher — than other packaging types, and multiple outlets summarized and echoed these findings [1] [2] [3]. This analysis synthesizes the claims, methods, and caveats from those reports and related studies to place the result in broader scientific and regulatory context and to highlight what remains uncertain.
1. Why glass bottles showed more microplastics — the contamination story that surprised regulators
ANSES’s laboratory work found that the majority of microplastic particles detected in beverages in glass bottles originated from the painted coatings on metal caps, not from the glass itself or the beverage manufacturing process alone, indicating a packaging-derived contamination pathway that had been underappreciated [2] [3]. The studies analyzed many beverage types — water, soft drinks, beer, wine, iced tea — and reported that glass-sealed products often contained significantly higher particle counts per liter than the same products in PET or aluminum packaging, with some reports quantifying differences in the range of several-fold to tens of times higher counts [4] [3]. The paint and polymer layers on metal caps can shed tiny flakes or fragments during capping, transport, or storage, which then enter the liquid, producing a distinct contamination vector tied to closure materials rather than the glass substrate [3] [5]. Regulators noted that addressing closures could reduce this source of exposure.
2. What the studies measured — methods, scope, and limitations that matter
The core ANSES assays applied particle counting and material identification techniques, including spectroscopy, to classify particles as plastic and to quantify particles per liter across packaging types; those methods detected higher particle loads in glass-bottled beverages but also revealed significant variability by product and cap type [1] [5]. Reporting outlets emphasize the headline difference but provide limited methodological detail in news summaries, so the breadth of sample sizes, representativeness of brands and bottling lines, and analytical detection limits are critical technical gaps for fully generalizing the result beyond the sampled products [6] [3]. Independent studies of bottled water using Raman spectroscopy and other analytic tools have previously reported low but variable microplastic levels across PET, rPET, and glass, suggesting that detection methods and lab protocols substantially influence reported concentrations; without standardized, widely adopted protocols, cross-study comparisons remain imperfect [5].
3. How big is the exposure — particle counts, not toxicity, are the current metric
Reports summarized average particle counts like roughly a hundred particles per liter for some glass-bottled soft drinks in the ANSES dataset and noted glass often had higher median and mean counts compared with other packaging [4] [3]. These counts describe particle abundance and size distribution, but they do not by themselves quantify health risk: toxicological significance depends on particle composition, size (e.g., nano vs micro), shape, chemical additives, and human exposure pathways, which the current reports do not fully resolve [1] [5]. Regulatory agencies and scientists emphasize that particle counts are an exposure metric that must be combined with toxicology and epidemiology to assess health implications, and the ANSES reports were framed as an identification of a contamination source rather than a direct health hazard determination [2].
4. Conflicting perspectives and reporting differences — nuance lost in headlines
Media coverage has sometimes reduced the findings to a simple “glass worse than plastic” headline, but the underlying scientific narrative is more nuanced: the elevated microplastics are tied to specific closure materials and production practices rather than intrinsic properties of glass as a container [6] [2]. Some outlets emphasize the magnitude of difference and potential regulatory consequences, while others foreground methodological caveats or prior studies showing low overall concentrations across packaging types [5]. Stakeholders’ agendas can influence emphasis: public health advocates highlight exposure increases, packaging manufacturers and beverage producers may point to closure design fixes, and journalists may favor striking comparisons; the full picture requires reading the technical reports, not only summaries [3].
5. What this means for consumers and policy — practical fixes and scientific next steps
The actionable takeaway from the collective reporting is that closures matter: changing cap coatings, improving capping processes, and testing closure materials could reduce microplastic shedding into glass-bottled beverages, and regulators are likely to focus on those interventions first [2] [1]. For consumers, switching packaging type is not a simple health-preserving choice because risk implications remain unresolved; instead, transparency about cap materials and industry adoption of low-shedding closures would address the immediate contamination pathway identified by ANSES. Scientifically, the field needs standardized sampling and analytical methods, larger multi-brand surveys, and toxicological studies that link particle exposures to biological effects before definitive health guidance can be established [5] [3].