Effect of different polystyrene nano-plastic concentrations on Chlorella pyrenoidosa

Nanoplastics have become an emerging contaminant in water bodies that adversely affects aquatic biodiversity. The present study investigated the effect of different concentrations of polystyrene (PS) nano-plastics (NP), 500 nm in size, on green microalgae Chlorella pyrenoidosa in terms of its growth, chlorophyll-a synthesis, oxidative stress, and cell viability. The morphological and compositional alterations in microalgae were observed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) analysis. Seven concentrations (1, 10, 100, 200, 500, 1000, and 5000 mg L- 1) of PS NP were used for experimentation. Overall, a negative trend in the growth of C. pyrenoidosa was observed with increasing nano-plastics concentration. The chlorophyll-a synthesis was reduced to 3.0 %, 15.6 %, 25.9 %, 30.1 %, 37.6 %, 39.2 %, and 52.8 %, respectively, in all seven concentrations compared to control. The results of the cell viability assay confirmed that PS NP was toxic to microalgal cells and enhanced the production of reactive oxygen species. The results suggested that higher concentrations (1000 and 5000 mg L-1) were more toxic to microalgal cells. Furthermore, FTIR analysis revealed substantial alterations like nucleic acid degeneration at 1262 cm- 1 in biomass exposed to 1000 and 5000 mg L-1 PS NP compared to other concentrations. Enhanced extracellular polymeric substances (EPS) secretion of 157 mg g- 1and 253 mg g-1 by 1000 and 5000 mg L-1 PS NP exposed cells, respectively, compared to control i.e., 92.2 mg g- 1was also noticed. SEM images showed aggregated nano-plastics adsorbed on the microalgal surface, whereas Transmission electron microscopy (TEM) micrographs revealed the internalization of nano-plastics with a slight deformation in the cell wall at higher concentrations (1000 and 5000 mg L-1 PS NP). Conclusively, higher concentration leads to high exposure risk, negatively impacting cellular functionality and their metabolic secretions.

Automated summary

The study investigated the effects of nanoplastics on the growth and functionality of green microalgae. The results showed that increasing concentrations of nanoplastics inhibited the growth of microalgae, reduced chlorophyll-a synthesis, and exhibited toxicity to the cells. Furthermore, the exposure to nanoplastics led to abnormal cellular functionality and metabolic secretions.