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New insights into the size-independent bioactive potential of pristine and UV-B aged polyethylene microplastics
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Scientists tested how UV light aging changes polyethylene microplastics and their effects on human immune cells (lymphocytes) from blood samples. Both new and UV-aged microplastics reduced cell viability and triggered DNA damage, regardless of particle size. This suggests that microplastics in the environment may harm human immune cells whether they are freshly produced or have been weathered by sunlight.
The present study investigates the morphological, physicochemical, and structural changes occurred by the UV-B aging process of low-density polyethylene microplastics (LDPE MPs), as well as the bioactive potential of both pristine and UV MPs towards healthy peripheral blood lymphocytes. Specifically, LDPE MPs (100-180 μm) prepared by mechanical milling of LDPE pellets, were UV-B irradiated for 120 days (wavelength 280 nm; temperature 25 °C; relative humidity 50 %) and further examined for alterations in their particle size and surface, their functional groups, thermal stability, and crystallinity (by means of SEM, FTIR spectroscopy, XRD patterns, and TGA measurements, respectively). In parallel, isolated human peripheral blood lymphocytes were treated with different concentrations (25-500 μg mL) of either pristine or aged MPs (UV and UV LDPE MPs) for assessing the cytogenotoxic (by means of trypan blue exclusion test and the cytokinesis-block micronucleus assay using cytochalasin-B) and oxidative effects (using the DCFH-DA staining) in both cases. According to the results, UV and UV-LDPE MPs, with a size ranging from 100 to 180 μm, can differentially promote cytogenotoxic and oxidative alterations in human lymphocytes. In fact, UV LDPE MPs not being able to be internalized by cells due to their size, could indirectly promote the onset of mild oxidative and cytogenotoxic damage in human peripheral lymphocytes, via a dose-dependent but size-independent manner. The latter is more profound in case of the irregular-shaped UV-LDPE MPs, bearing improved dispersibility and sharp edges (by means of cracks and holes), as well as oxygen-containing and carbonyl groups. To our knowledge, the present findings provide new data regarding the bioactive behavior of pristine and UV-B aged LDPE MPs, at least in the in vitro biological model tested, thus giving new evidence for their size-independent and/or indirect mode of action.
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