A Comparative Multi-Bioassay Assessment of Tetracycline Mixture Toxicity in Water and Soil Using Harmonized Dose–Response Modeling

Tetracyclines (TCs) are antibiotics widely used in human and veterinary medicine as well as in agricultural practices. They may be retained in soil or drift into freshwater, thereby exerting effects on non-target organisms and deteriorating ecological quality. In this study, tetracycline (T), oxytetracycline (OT), chlortetracycline (CT), and their binary and ternary mixtures were evaluated using a battery of bioassays including terrestrial plants, aquatic crustaceans, a ciliate protist and a bacterial species. Results showed a concentration-dependent effect for parameter immobilization in Daphnia magna and Artemia salina, seed germination in the terrestrial plants, and bioluminescence inhibition and growth inhibition in Aliivibrio fischeri and Tetrahymena thermophila, respectively. For A. fischeri, statistically significant interactions were observed between dose and exposure time. A. salina demonstrated greater sensitivity than D. magna in all cases. Both A. salina and A. fischeri showed increased toxicity to OT and the ternary mixture. Dicots presented greater sensitivity than the monocot species in all cases. In the combined exposures, there was a deviation from the concentration addition (CA) model, with possible synergism for CT + T and the ternary mixture for A. fischeri. The concurrent environmental exposure of non-target organisms to TCs should be investigated further.