Quantitative study of microplastic degradation in urban hydrosystems: Comparing in situ environmentally aged microplastics vs. artificially aged materials generated via accelerated photo-oxidation

The degradation of plastic waste is a major research challenge due to the adverse impacts of microplastic weathering on the environment and ecosystems. As a major source of plastic contamination comes from urban hydrosystems, studying MP degradation prior to their environmental dissemination is crucial. Through a combination of field sampling and laboratory experiments, this study provides a thorough statistical degradation comparison analysis between polyethylene in situ environmentally aged microplastics and artificially aged films. In the laboratory, pristine nonadditivated low-density polyethylene films were exposed to controlled ultraviolet (UV) radiation to simulate aging for various durations. Firstly, the study aims to assess the representativeness of controlled UV degradation to mimic urban in situ MPs. The second goal is to identify polyethylene (PE) degradation characteristics in various environmental matrices such as stormwater, suspended solids and sediment samples from a stormwater detention basin in a large urban area in France. Artificially aged plastics exhibit distinct alterations in physical and chemical properties, corresponding solely to the abiotic degradation observed in situ. In contrast, environmental particles display notable markers of biotic chemical degradation and hydrolysis. Moreover, the degradation environment varies significantly: it is predominantly abiotic for MPs collected in stormwater samples, while it is largely biotic for MPs collected in sediment and suspended solid samples. Besides, MPs from stormwater and suspended solid samples show a higher degree of hydrolysis degradation. Finally, additional comparisons with common consumer materials, before and after use, show almost no signs of notable degradation compared to the environmentally and artificially aged materials considered in this study.