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

Abstract

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. Hazardous risks linked to microplastic degradation are a significant concern in every urban system. Our study addresses this issue by developing an integrated approach to understand polyethylene degradation in both real-world and controlled laboratory settings. Through this approach, the proportion of biotic degradation is estimated relative to abiotic degradation. Studying polyethylene transfer in urban hydrosystems allows assessment of the critical degradation phases of this polymer in the environment and the formulation of effective mitigation strategies. The integration of laboratory results enables recommendations on aging processes for experimental researchers, in particular to carry out representative degradation studies of microplastics in situ. • In-situ microplastics exhibit elevated levels of both abiotic and biotic degradation • Our protocol mimics the abiotic degradation observed in in-situ microplastics • Comparable carbonyl index values are observed between in-situ and laboratory samples • Carbonyl bonds persist as the predominant form in in-situ microplastics • Critical degradation phases were identified during transfer in urban hydrosystems

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