The Toxicity of Nonaged and Aged Coated Silver Nanoparticles to Freshwater Alga Raphidocelis subcapitata

The transformation of coated AgNPs and their impacts on aquatic organisms require further study. This study investigated the role of ageing on the transformation of differently coated AgNPs and their sub‐lethal effects on the freshwater alga, Raphidocelis subcapitata. The stability of AgNPs was evaluated over 32 days and the results indicated that transformation of AgNPs occurred during the incubation; however, coating‐specific effects were observed. AgNPs increased reactive oxygen species (ROS) formation, while aged AgNPs induced excessive ROS generation compared with their fresh counterparts. Increased ROS levels caused increased lipid peroxidation in treatment groups exposed to both fresh and aged NPs while lipid peroxidation was comparatively higher in algae exposed to aged AgNPs. The observed increase in catalase (CAT) activity of algal cells was attributed to early stress responses induced by excessive intracellular ROS generation while the CAT levels were higher in the aged NP treatment groups. In conclusion, AgNPs increased ROS levels and lipid peroxidation in algae, and caused the activation of antioxidant enzymes such as CAT. Overall, the results suggest that ageing and coating of AgNPs have major impacts on AgNP transformation in media and their effects to algae.