Combined Impact of Nanoplastics and Temperature on Green Algae: Implications for Growth, Lipid Content and Organic Exudates

Freshwater ecosystems are under significant environmental stress due to warming and plastic pollution. However, our understanding of their combined effects on primary producers is scarce. We investigated the effects of plain spherical polymethylmethacrylate (PMMA) nanoparticles (NPs) and the acute temperature increases on the growth and fatty acid content of the freshwater green algae Pseudokirchneriella sp. over a 5-day exposure period. The experiment was conducted at three NP concentrations (0.05, 0.5, and 5 mg/L) and two temperature levels (20°C and 25°C). We analysed algal organic matter (AOM) produced during the experiments. Higher temperature stimulated cell growth at lower NP concentrations, but not at the highest NP concentration. Fatty acid composition was affected by temperature but not by NPs. At 20°C, the fractions of low, intermediate, and high molecular weight (MW) AOM had a higher tryptophan-like fluorescence, pointing to a higher protein-like content. Humic-like fluorescence of low MW AOM fractions was higher at higher temperature. At 25°C, the fluorescence response increased slightly with increasing NP concentrations. The findings suggest that temperature has a greater effect on altering fatty acid composition and AOM chemistry than NPs.