Does mechanical stress cause microplastic release from plastic water bottles?

Plastic particle ingestion has become of concern as a possible threat to human health. Previous works have already explored the presence of microplastic (MP) in bottled drinking water as a source of MP intake. Here, we consider the release of MP particles from single-use PET mineral water bottles upon exposure to mechanical stress utilizing SEM plus EDS, which allows the implementation of morphological and elemental analysis of the plastic material surface and quantification of particle concentrations in sample water. The aim of this study was to better evaluate the sources of MP intake from plastic bottles, especially considering the effect of daily use on these bottles such as the abrasion of the plastic material. For that, we analysed MP release of PET bottlenecks and HDPE caps on their surfaces after a series of bottle openings/closings (1 x, 10 x, 100 x). Furthermore, we investigated, if the inner surface of the PET bottles released MPs, counted particle increase of the water and identified MPs in the PET bottled water after exposing the bottles to mechanical stress (squeezing treatment; none, 1 min, 10 min). The results showed 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. Moreover, great differences exist in cap abrasion between brands which uncovers a discrepancy in plastic behavior of brands. Interestingly, particle concentrations in the bottled mineral water did not significantly increase after exposure to mechanical stress (squeezing treatment). The morphological analysis of the inner wall surface of the bottles supported this observation, as no stress cracks could be detected after the treatment, implying that the bottles itself are not a consistent source of MP particles after this extent of mechanical stress. However, chances of MP ingestion by humans increase with frequent use of the same single-use plastic bottle, though only from the bottleneck-cap system.