Comparative biotoxicity of N-Phenyl-1-naphthylamine and N-Phenyl-2-naphthylamine on cyanobacteria Microcystis aeruginosa

Abstract

N-Phenyl-1-naphthylamine (P₁NA) and N-Phenyl-2-naphthylamine (P₂NA) are both widely used as antioxidant and plant secondary metabolites. In this study, growth, esterase, photosynthetic activity and cell membrane integrity were used as biomarkers to compare biotoxicity of P₁NA and P₂NA on Microcystis aeruginosa. According to the results, a dose-response relationship was observed only between P₁NA concentrations and growth inhibition. The EC₅₀ (48 h) of P₁NA calculated from growth inhibition was 16.62 μM, while that of P₂NA was not detected. When the esterase and photosynthetic activity were applied to evaluate the biotoxicity, it was found that a concentration of 20 μM P₁NA, P₂NA caused reduction of esterase activity and Fv/Fm of M. aeruginosa to 22.2 and 3.3%, 97.5 and 92.1%, respectively, after 48 h exposure. The percentage of membrane-damaged cells was increased as P₁NA exposure concentration increased, but that was not detected when exposure to P₂NA. The difference substituted position in the molecular structure of P₁NA and P₂NA leads to different toxicological properties and only P₁NA was found highly toxic to M. aeruginosa. The toxicity is due to that only P₁NA can be biotransformed to 1,4-naphthoquinone, which could induce overproduction of intracellular ROS as well as result in oxidative damage and growth inhibition of test organism.

Keywords: Microcystis aeruginosa; N-Phenyl-1-naphthylamine; N-Phenyl-2-naphthylamine; Reactive oxygen species; Toxic effects.