Evaluation of the toxic effects of polylactic acid on green microalgae using flow cytometric methods

Bioplastics such as polylactic acid (PLA) are increasingly promoted as environmentally friendly alternatives to conventional plastics; however, their toxicological effects on aquatic primary producers remain insufficiently characterized. This study investigated the oxidative stress responses and genotoxic effects of PLA on two freshwater green microalgae species, Desmodesmus pannonicus and Scenedesmus aldavei using spectrophotometric and flow cytometric approaches. Algal cultures were exposed to PLA at concentrations of 0–50 µg mL⁻ 1 for 96 h according to the experimental exposure design. A solvent control was prepared using 1% DMSO. Growth inhibition was evaluated by optical density (OD₇₅₀) and pigment analysis, while reactive oxygen species (ROS) production was evaluated using DCFH-DA (2′,7′-dichlorodihydrofluorescein diacetate), and DNA damage was assessed by flow cytometric methods via the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. PLA exposure caused a significant concentration- and time-dependent reduction in growth in both species (p ≤ 0.05). The percentage of non-viable cells ranged from 3.32–7.26% in S. aldavei and 3.95–18.44% in D. pannonicus . ROS levels increased markedly at 50 µg mL⁻ 1 , reaching 55.58% in S. aldavei and 73.09% in D. pannonicus , compared with control values of 14.65% and 4.5%, respectively. TUNEL analysis revealed minimal DNA fragmentation in controls (1.51–4.75%), while PLA induced concentration-dependent DNA damage up to 67.39% in S. aldavei and 57.41% in D. pannonicus . The findings indicate that PLA induces oxidative stress and genotoxic effects in freshwater algae, highlighting the need to consider chemical toxicity alongside biodegradability in sustainable plastic evaluation.