Cellular Responses of Microcystis aeruginosa to Environmentally Relevant PFBA Concentrations under Different Nutrient...

Perfluorobutanoic acid (PFBA), a short-chain alternative to perfluorooctanoic acid (PFOA), has been increasingly detected in aquatic environments due to its widespread applications. However, its ecological effects on aquatic organisms under environmentally relevant exposure levels and different nutrient conditions remain poorly understood. In this study, Microcystis aeruginosa was exposed to PFBA concentrations of 0.2 and 200 μg/L under different nitrogen (N) and phosphorus (P) availability, resulting in a 7 × 3 nutrient condition × PFBA concentration experimental design including the PFBA-free controls. The acute toxicity test showed that PFBA inhibited algal growth in a concentration-dependent manner, with a 72-h half-maximal effective concentration (EC₅₀) of 24.83 mg/L, indicating that the concentrations used in this study were far below acute toxic levels. On Day 3, 200 μg/L PFBA significantly inhibited algal growth under N-limited conditions, with inhibition rates of 29.80% and 23.13% in the LN (1 mg/L N, 7.1 mg/L P) and LNP (1 mg/L N, 0.05 mg/L P) groups, respectively. In contrast, 0.2 μg/L PFBA showed a slight growth-promoting effect under moderate nutrient conditions. However, after 10 days of exposure, PFBA did not significantly affect algal density in most treatment groups, and the effects of PFBA observed during the early exposure stage were attenuated over prolonged cultivation. Nutrient limitation significantly reduced algal growth, chlorophyll a content, and intracellular microcystin-LR levels, while promoting oxidative stress responses and extracellular polymeric substance (EPS) secretion. Under the experimental conditions, N limitation exerted stronger inhibitory effects on algal growth than P limitation and induced more pronounced oxidative stress responses. Although PFBA did not significantly alter the final algal density, it still was associated with changes in several physiological and molecular responses under specific nutrient conditions, including changes in reactive oxygen species accumulation, antioxidant enzyme activities, extracellular polymeric substances secretion, and the expression of photosynthesis-related genes (psaB, psbD, and rbcL). This study provides insights into the toxicological effects of PFBA on microalgae in aquatic environments.