Ageing with algal EPS reduces the toxic effects of polystyrene nanoplastics in freshwater microalgae Scenedesmus obliquus

Abstract

The increase in the daily usage of the plastics aggravates their risk of accumulation in the freshwater bodies. The extra polymeric substances (EPS) secreted by the freshwater algae can interact with these particles altering their physicochemical behaviour and fate in the process. The effects of the EPS coated polystyrene nanoparticles (EPS-PSNPs) in freshwater microalgae are still not very clear. The current work investigates the role of ageing the PSNPs (plain, aminated and carboxylated) with EPS in the freshwater medium in influencing their toxic effects towards a freshwater microalga Scenedesmus obliquus. A significant increase in the hydrodynamic size of the PSNPs was noted upon ageing in the EPS-containing medium due to induced agglomeration. The aged PSNPs had significantly lesser toxic effects compared to the pristine forms. The surface functionalization of the PSNPs and the duration of ageing played a significant role in the process. A substantial decline in the levels of the reactive oxygen species, activity of the oxidative stress markers (SOD and CAT) and cell membrane damage corroborated well with observed increase in the cell viability. Improved photosynthetic efficiency parameters (electron transport rate and maximum quantum yield of PS II system) correlated well with decreased levels of the reactive species in the cells. The principal component analysis of the results helped to gain better understanding of how ageing of the PSNPs influenced the various biological parameters.