Biosorption of PFHxS by two freshwater microalgae: A preliminary investigation of temporal partitioning and algal growth responses

This preliminary research investigated the growth responses and temporal distribution of PFHxS in two freshwater microalgae, Chlorella vulgaris and Tetradesmus obliquus, during a 12-day exposure to 0.05, 0.5, and 5 mg L⁻¹ PFHxS. Cell density, specific growth rate, dry biomass, photosynthetic pigments, and PFHxS concentrations in the dissolved, biosorbed, and uptake fractions were determined. The obtained results showed that PFHxS exposure did not significantly affect specific growth rate in either species, while cell density increased from 2.63 × 10⁶ to 99.87–130.33 × 10⁶ cells mL⁻¹ in C. vulgaris and from approximately 0.31 × 10⁶ to 5.0–6.4 × 10⁶ cells mL⁻¹ in T. obliquus. Transient treatment-related differences in dry biomass occurred in C. vulgaris, whereas no consistent growth response was observed in T. obliquus. Pigment contents varied mainly with exposure time rather than PFHxS concentration. PFHxS remained predominantly in the dissolved fraction. In C. vulgaris, the dissolved fraction at 0.05 mg L⁻¹ decreased from 100% to 68.88 ± 12.31% of the initial PFHxS mass between Days 0 and 12, whereas 87.86–93.85% remained dissolved in T. obliquus at Day 12. Most biomass-associated PFHxS was recovered in the biosorbed fraction. The uptake fraction was generally below the limit of quantification at 0.05 and 0.5 mg L⁻¹ and remained comparatively small at 5 mg L⁻¹. In C. vulgaris at 5 mg L⁻¹, biosorbed PFHxS decreased from 141.99 ± 25.68 to 78.58 ± 14.27 µg g⁻¹ DW, while the corresponding percentage remained at 1.28–1.72%.