A study published on September 13, 2019, in the peer-reviewed journal Water Research, investigated whether “mechanical stress cause[s] microplastic release from plastic water bottles.” Anna Winkler and colleagues from the Department of Environmental Science and Policy, University of Milan, Italy, analyzed microplastics (MP) in the screw-cap single-use polyethylene terephthalate (PET) bottles with high-density polyethylene (HDPE) caps after subjecting these bottles up to 100 open/close cycles or to a mechanical stress (squeezing).

There was “a considerable increase of MP particle occurrence on the surface of PET and HDPE material (bottlenecks and caps) after opening and closing the bottles.” After 100 times, the effect was “impressive, especially on caps.” The authors also reported “great differences . . . in cap abrasion” observed for bottles from different brands. In contrast, exposure to mechanical stress (squeezing) did not lead to a significant increase of MP concentrations in the bottled water, which implies that the bottle walls “are not a consistent source of MP particles after this extent of mechanical stress.”

Winkler and colleagues conclude that “chances of MP ingestion by humans increase with frequent use of the same single-use plastic bottle, though only from the bottleneck-cap system.” They also emphasize that, according to their results, “though being declared as food-safe, PET and HDPE used for food packaging exhibit deficiencies such as the release of MPs due to frequent use” and suggest that the revealed differences between different brands “should be considered to an optimization of the admission criteria for food contact substances.”

The MP content measured in the analyzed mineral waters currently “is not considered a safety concern.” However, there is “a lack of information regarding the potential toxicity of plastic polymers to human health,” the authors warn and call for “intensification” of research on “the degradation of plastic material and the release potential of particles and additives, especially regarding plastics used for food packaging.”


Winkler, A., et al. (2019). “Does mechanical stress cause microplastic release from plastic water bottles?Water Research 166: 115082.