Antagonistic effect of polystyrene nanoplastics and sliver nanoparticles on Chlorella pyrenoidosa

Nanoplastics and silver nanoparticles (AgNPs) have been widely detected in aquatic environments, but their combined effects on phytoplankton have not been extensively studied. We investigated the effects of AgNPs and polystyrene nanoplastics (PSNPs) on the microalgae Chlorella pyrenoidosa. The results showed that AgNPs and PSNPs significantly inhibited the growth of C. pyrenoidosa, and binary mixture of AgNPs and PSNPs exhibited antagonistic effects on algal growth. The adsorption between AgNPs and PSNPs led to increased particle size, reducing the bioavailability of nanoparticles and thus the toxicity of binary mixture on the algae. In the presence of AgNPs and PSNPs, nuclear region dissolution and plasmolysis were observed. Correspondingly, a decrease in soluble protein content was detected, while soluble sugar content increased in the early stage and decreased in the late stage to regulate cellular osmotic pressure. Photosynthetic pigment content decreased, cell membrane damage increased, and oxidative stress levels rose. Malondialdehyde content and catalase activity increased, while superoxide dismutase activity initially rose but decreased later due to the collapse of the antioxidant system. Compared to the single exposure groups, the adverse effect on the algae on the cellular membrane, photosynthetic pigments, soluble sugar, soluble protein and oxidative stress was reduced exposed to the binary mixture. These findings provide evidences for understanding the effects and potential ecological risks of PSNPs and AgNPs.