Four antibiotics and copper interactive effects on the growth and physiological characteristics of Hydrilla verticillata (L.f.) Royle

Co-pollution of antibiotics and heavy metal copper (Cu) is common in freshwater environments because of their wide use as antimicrobial agents, especially in aquaculture. However, the toxic effects of coexisting antibiotics and heavy metals on aquatic plants remain unclear. This study investigated the effect of four antibiotics (i.e., enrofloxacin, ENR; tetracycline, TC; sulfamethoxazole, SMX; erythromycin, ERY), Cu, and their mixture on the growth and physiological responses of Hydrilla verticillata (L.f.) Royle. Results showed that the four antibiotics exhibited toxic effects on the growth and physiological indicators of H. verticillata, and root elongation was the most sensitive endpoint of the phytotoxicity test. The median effect concentration (EC50) of root elongation indicated that TC (EC50 = 10.05 mg/L) has the highest level of growth toxicity, and the toxicity of ENR to aquatic plants was close to TC (EC50 = 10.44 mg/L), followed by SMX (EC50 = 20.08 mg/L). However, there was no significant toxic effect of 20 mg/L ERY on the root elongation. Hydrophobicity may be a key factor affecting the phytotoxicity of antibiotics. Moreover, antagonistic toxic effects were observed under ENR + Cu, TC + Cu, SMX + Cu, and ERY + Cu co-exposures at all the experimental concentrations (0.01-20 mg/L). Due to the concentrations of antibiotics in natural waters usually with ng/L levels, our results suggested that environmental antibiotic concentrations probably pose low ecological risk to aquatic plants and indicated the H. verticillata could be used as phytoremediation candidate to remove antibiotic or antibiotic-Cu pollutions in general nature water.