UV-aged nanoplastics induced stronger biotoxicity to earthworms: Differential effects and the underlying mechanisms of pristine and aged polystyrene nanoplastics

Nanoplastics (NPs) are widely distributed in a variety of environments, including soil, and are known to adversely affect soil organisms. Currently, most studies have focused mainly on the ecological risks of pristine nanoplastics (PNPs), ignoring the fact that they are subjected to ultraviolet (UV) aging into aged nanoplastics (ANPs) in real environments that can change their traits. Therefore, this study aimed to investigate the differences and potential mechanisms of ecotoxicity of PNPs and ANPs at relevant environmental concentrations (0.2, 1, and 2 g kg) on the earthworm Eisenia fetida. Findings indicated that day 28 of exposure to PNPs and ANPs impacted earthworm mortality, weight loss, and reproductive success. At 2 g kg, ANPs increased earthworm mortality by 11.1 % and reduced cocoon production by 2.33 cocoons relative to PNPs, demonstrating a greater impact. Oxidative stress was also induced, leading to lipid peroxidation, DNA damage, genetic system damage and intestinal damage, resulting in decreased resistance to exogenous stress, and the effects of ANPs were more pronounced. Histopathology revealed that ANPs induced more serious tissue damage in earthworms. The integrated biological response index (IBR) revealed differences in the toxicity of PNPs and ANPs to Eisenia fetida, with oxidative stress and DNA damage being the most sensitive biomarkers. The IBR values of ANPs were 1.5-2.3 times higher than those of PNPs, indicating that UV-aged NPs were more toxic to earthworms than PNPs. This study enhances our understanding of the toxicological impacts of UV-aged NPs on soil organisms, using Eisenia fetida as a model organism.