Algal extracellular polymeric substances (algal-EPS) for mitigating the combined toxic effects of polystyrene nanoplastics and nano-TiO2 in Chlorella sp.

Abstract

The continuous release of nanoparticles and nanoplastics into the marine environment necessi-tates the examination of their combined effects in marine organisms. Natural Organic Matter(NOM) can significantly influence the behavior of nanomaterials in the marine environment. Thepresent study explores the effects of algal Extracellular Polymeric Substances (EPS) in reducingthe combined toxic effects of three different polystyrene nanoplastics (PSNPs)—aminated (NH2-PSNPs), carboxylated (COOH-PSNPs), and plain PSNPs—and P25 titanium dioxide nanoparticles(Nano-TiO2) towards the marine alga,Chlorellasp. Two doses (0.25 and 2.5 mg/L) of nano-TiO2mixed with the PSNPs (1 mg/L) were employed. The COOH-PSNPs with 2.5mg/L nano-TiO2exhibited higher growth inhibition toward algal cells. Addition of algal EPS to the mixture ofNMs decreased the negative effect significantly. The mean hydrodynamic diameter increasedsignificantly from 666 to 797nm and 1248 to 3589 nm at concentrations 0.25 and 2.5mg/L,respectively when the mixtures of nano-TiO2and COOH-PSNPs were incubated with the algalEPS. In comparison to the pristine NMs, the EPS-NMs were found to significantly reduce thesuperoxide and hydroxyl radical production. The results were further validated with the estima-tion of lipid peroxidation (LPO), esterase activity, photosynthetic efficiency, and membrane per-meability in the cells. The major outcomes from this study highlight the role of algal EPS insignificantly reducing the toxic impact of binary mixture of NMs in marine organisms.