Distribution and Biological Response of Nanoplastics in Constructed Wetland Microcosms: Mechanistic Insights into the Role of Photoaging

Concern over nanoplastic contamination of wetland ecosystems has been increasing. However, little is known about the effect of photoaging on the distribution and biological response of the nanoplastics. Here, palladium-labeled polystyrene nanoplastics (PS-Pd NPs) at 0.05-50 mg/L were exposed to constructed wetland microcosms containing floating (<i>Eichhornia crassipes</i>) and submerged (<i>Vallisneria natans</i>) macrophytes. Results demonstrate that PS-Pd NPs' concentration in surface water after 2-4 weeks of exposure was decreased by over 98.4% as compared with that in the 1st week. Photoaging enhanced the surface charge and colloidal stability of PS-Pd NPs, with a subsequent increase of the content of PS-Pd NPs in surface and middle layer water by 264.6 and 207.4%, respectively. Additionally, photoaging significantly enhanced the accumulation of PS-Pd NPs in <i>E. crassipes</i> roots by 6.9-65.0% and significantly decreased it in <i>V. natans</i> shoots by 59.7-123.0%. PS-Pd NPs inhibited the growth of <i>V. natans</i> by 43.8% at 50 mg/L. Mechanistically, PS-Pd NPs induced oxidative stress in <i>V. natans</i>, leading to the disruption of the metabolic pathway. Interestingly, PS-Pd NP exposure inhibited nitrification in wetland ecosystems due to the alteration of the related bacterial community (<i>Ellin6067</i> decreased by 13.19%). These findings deepen our understanding of the environmental fate and risk of plastic particles in wetland ecosystems.