Ageing characteristics and microplastic release behavior from rainwater facilities under ROS oxidation

Reactive oxygen species (ROS) are ubiquitous in the natural environment that are generated by chemical or biochemical processes. Plastic rainwater facilities, as an important part of modern rainwater systems, are inevitably deteriorated by ROS. As a consequence, microplastics will be released. However, information on how ROS affect the ageing characteristics of plastic rainwater facilities and the subsequent microplastic release behavior is still insufficient. To address this knowledge gap, Fenton reagents were used to simulate the reactive oxygen species (ROS) induced ageing process of three typical plastic rainwater components (rainwater pipe, made of polyvinyl chloride; modular storage tank, made of polypropylene; inspection well, made of high-density polyethylene) and the subsequent microplastic release behavior. After 6 days of Fenton ageing, an increase in sharpness, holes, and fractures on the rainwater facilities' surface was observed by scanning electron microscope (SEM). The functional group changes on the rainwater facilities' surface were analyzed by Fourier transform infrared spectrometer (FTIR) and two-dimensional correlation spectroscopy (2D-COS) and compared with the results of X-ray photoelectron spectroscopy (XPS). During the ageing process, oxygen-containing functional groups were generated and the carbon chains were broken, which promoted peeling and the release of microplastics. The amount of released microplastics (ranging from 158 to 6617 items/g facility) varied with the type of rainwater facilities, and the order was modular storage tank > inspection well > rainwater pipe. The release amount increased with ageing time, and a significant linear relationship was observed (r² > 0.91). The particle size of the released microplastics ranged from 2 to 1362 μm, among which 10-30 μm particles accounted for the largest proportion (62.7 %). The release amount increased exponentially with decreasing particle size (r² > 0.71). This study indicates that large amounts of microplastics could be released from plastic rainwater components during ROS-induced ageing.