Assessment of endogenous and exogenous silver nanoparticles effects on the microalgae Chlorella vulgaris

Microalgae are susceptible to most pollutants in aquatic ecosystems and can be potentially damaged by silver nanoparticles (AgNPs). This study aims to clarify the potential consequences of Chlorella vulgaris internalizing AgNPs. The exposure of C. vulgaris to AgNPs stabilized with citrate led to the accumulation of NPs in the cell wall, increasing permeability, which allowed the entry of AgNPs and Ag ⁺ ions resulting from the dissolution of AgNPs. Ag ⁺ accumulated inside the cell could be converted into AgNPs (endogenous) due to the reducing potential of the cytoplasm. Both exogenous and endogenous AgNPs caused damage to all biological structures of the algae, as demonstrated by TEM images. This damage included the disorganization of chloroplasts, deposition of AgNPs on starch granules, and increased amounts of lipids, starch granules, exopolysaccharides, plastoglobuli, and cell diameters. These changes caused cell death by altering cell viability and interfering with organelle functions, possibly due to reactive oxygen species generated by nanoparticles, as shown in a lipid bilayer model. These findings highlight the importance of considering the exposure risks of AgNPs in a worldwide distributed chlorophyte.