Antialgal Effects of Nonanoic and Palmitic Acids on Microcystis aeruginosa and the Underlying Mechanisms

Algal blooms caused by Microcystis aeruginosa are a common occurrence and pose significant threats to freshwater ecosystems. This study investigates the antialgal effects and underlying mechanisms of two plant-derived fatty acids, nonanoic acid and palmitic acid, on Microcystis aeruginosa . The results show that the inhibitory effects of both fatty acids on M. aeruginosa increase with higher concentrations. Algal recovery occurs when nonanoic acid concentrations are below 0.5 mg/L and palmitic acid concentrations are below 50 mg/L. Acute toxicity tests indicate that the safe concentrations of nonanoic acid and palmitic acid are below 1.87 mg/L and 263.3 mg/L, respectively. The inhibitory effect of nonanoic acid is more pronounced under conditions of pH 5.5, 15 °C temperature, 0.75 mg/L nitrogen, and 2 mg/L phosphorus, with inhibition efficiency remaining unaffected by increased light intensity. Both fatty acids exert their strongest inhibitory effects in the early stages of addition (0–8 days), causing cell death and the release of extracellular organic matter primarily consisting of aromatic compounds and proteins. Oxidative stress analysis reveals that high concentrations of fatty acids can cause irreversible damage to the algae’s antioxidant defense system. These findings provide valuable insights for the prevention and control of cyanobacterial blooms, which can help promote the sustainable development of freshwater ecosystems.