Polystyrene microplastics photo-aged under simulated sunlight influences gonadal development in the Pacific oyster

Microplastics (MPs) aging in natural ecosystems are caused by solar irradiation. Photo-aged MPs in aquatic systems are a major threat to molluscs. In this study, polystyrene (PS) photo-aging was simulated using a sunlight simulator. After exposure of Crassostrea gigas to photo-aged PS, a decreased gonadosomatic index, coupled with histological alterations, suggested an inhibitory effect on the gonadal development of bivalves. As the concentration of aged PS increased, the inhibitory effects on gonadal development became more severe. The sex hormone (testosterone and estradiol) and energy metabolism (glycogen, lipid, and protein content) differences between C. gigas males and females suggested a disruption of sex hormonal homeostasis and a shift in energy allocation strategy, which may have affected reproduction, especially female oysters. In addition, the substantial downregulation of SOX-8, SOX-E, Piwi1, and TGF-β genes may be contributing factors causing the inhibitory effect of aged PS on the gonadal development of C. gigas. This study provides an essential reference for evaluating the reproductive health risks posed by aged MPs and offers novel insights and perspectives for exploring the impact of MPs under natural conditions.