Interactions between typical antibiotics and Microcystis aeruginosa in aquatic environment

The interactions of six typical antibiotics, including azithromycin, clarithromycin (CLR), ciprofloxacin, sulfathiazole, sulfamethoxazole, and tetracycline (TCY), with Microcystis aeruginosa were investigated, discussing the effects of antibiotics on algal growth in terms of mono- and co-antibiotics, and the removal of six antibiotics by the alga. The results showed that all the antibiotics showed “low-promoting and high-inhibiting” effects, except for sulfonamides, which showed a promotion trend on algal cell density and chlorophyll a. The tests of half effective concentrations (EC₅₀s) of antibiotics against M. aeruginosa showed that the antibiotics of the same category had similar EC₅₀s, and the toxicity effects of co-antibiotics were higher compared to mono-antibiotics. The toxic effects of antibiotics against M. aeruginosa were antagonistic in most binary co-antibiotics, and synergistic and simple additive effects in the ternary co-antibiotics. For removal tests of antibiotics by the alga, it could be seen that at the same concentration (10 µg L⁻¹), M. aeruginosa showed the best removal of TCY with 22.8% and the lowest removal of CLR with only 5.8%. It was found that both antibiotics and M. aeruginosa had mutual influences; therefore, the interaction might be favorable to the permanent removal of antibiotics and reduce the impact on the aquatic ecological environment.