Effects of humic acids on biotoxicity of tetracycline to microalgae Coelastrella sp

The release of antibiotics into aquatic environments would induce adverse effects on organisms, so the environmental impact and fate of antibiotics must be paid close attention. In this paper, the effects of tetracycline on the growth of microalgae Coelastrella sp. in the presence of humic acids were investigated at various tetracycline concentrations ranging from 0.5 to 10 mg/L in Blue-Green medium, and the underlying mechanisms were also discussed. Results revealed that the microalgae growth showed a hormesis dose-response phenomenon under tetracycline stress with stimulation at low levels (≤2 mg/L) while inhibition at higher levels (>2 mg/L). More importantly, tetracycline biotoxicity to Coelastrella sp. decreased significantly due to the increase in humic acids concentration, as evidenced by the increased biomass, chlorophyll-a and total proteins contents, as well as the reduced oxidative stress response in Coelastrella sp. cells. The strong complexation between tetracycline and humic acids was responsible for the reduced tetracycline biotoxicity. These findings are helpful for better understanding the environmental risk of antibiotics in eutrophic waters. •Microalgae Coelastrella sp. exhibited hormesis response under tetracycline stress.•Humic acids significantly mitigated the toxicity of tetracycline to the microalgae.•Complexation of humic acids with tetracycline is the main mechanism.