Ecotoxicity of mixtures of antibiotics used in aquacultures

Abstract

More or less well-defined mixtures of antibiotics used in aquacultures may be distributed in the aquatic environment. Therefore, a systematic mixture ecotoxicity study was performed with the aquaculture antibiotics oxytetracycline, oxolinic acid, erythromycin, florfenicol, and flumequine. Test organisms were freshwater algae (Pseudokirchneriella subcapitata), activated sludge microorganisms, and luminescent bacteria (Vibrio fischeri). Design and statistical analysis of test results were based on isobolographic analysis. Synergistic effects were observed when combinations of erythromycin and oxytetracycline were tested on activated sludge microorganisms, and in these cases model predictions indicate independent action on the different bacterial species in the sludge. As predicted from the modes of action, concentration addition was evident when flumequine and oxolinic acid were mixed and tested on sludge bacteria. In the algae test, the combined toxicity of antibiotics could not be predicted based on knowledge of the modes of action of the individual compounds. Independent of the test species, our results gave examples of combined effects that were higher than predicted based on the assumption of concentration addition. This result underlines the need to consider the effects of mixtures of antibiotics on environmental organisms. The isobolographic method appears to be a suitable tool for this purpose, particularly for well-defined mixtures with few substances.

Comparing the sensitivity of algal, cyanobacterial and bacterial bioassays to different groups of antibiotics

“…Yet, in the classical acute Microtox test with V. fischeri as test organism, no effects were observed for any of the test compounds after 30 min of exposure. This is in agreement with previous studies applying the Microtox test (Ferrari et al, 2004;Isidori et al, 2005;Christensen et al, 2006) and is most likely due to the very short exposure time (15-30 min) rather than to insensitivity of V. fischeri to antibiotics. This is confirmed by Thomulka et al (1993) who reported substantial effects of several antibiotics on reproduction of the microbe Vibrio harveyi after 5 h of exposure, but obtained little evidence for shortterm effects on bioluminescence.…”

“…04.011 expected that toxicity assessment with bacteria would provide a sensitive method to determine the effects of antibiotics in the aquatic environment. Yet, the classical acute Microtox test system, with a marine bacterium (Vibrio fischeri) as test organism, has not proven very sensitive to antibiotics (Ferrari et al, 2004;Isidori et al, 2005;Christensen et al, 2006). Alternatively, cyanobacteria could be used as test organisms and it has indeed been found that cyanobacteria were up to two orders more sensitive to antibiotics than green algae (Holten-Lützhøft et al, 1999;Halling-Sørensen, 2000).…”

Medicines, shaken and stirred: a critical review on the ecotoxicology of pharmaceutical mixtures

“…Slight deviations ( predicted EC 50 values lower than predicted by a factor of roughly 2-unfortunately, the authors do not provide numerical values for the observed and predicted EC 50 s) from the predictions by CA and IA were also observed by Schnell et al [53] for an equitoxic mixture of diclofenac, bezafibrate, fluvoxamine, musk ketone and galaxolide. Clear synergistic effects to algae were observed for mixtures of flumequine þ erythromycin and oxytetracycline þ flumequine by Christensen [45].…”

Shelf life of antibiotic treated rohu fish, Labeo rohita (Hamilton) under ice storage condition

“…These drugs are applied as a means to treat diseased fishes or for prevention of diseases (Christensen et al, 2006) as the production may get hampered by unpredictable mortalities that may be due to negative interactions between fish and pathogenic bacteria. Although they are used to improve aquaculture production, residues of these antibiotics and chemicals could influence quality of the final product.…”