The acute toxicity in water of a series of drugs, including antibiotics, antihistamines, antifungals, steroidal and non-steroidal antiinflammatories, was evaluated through the measurement of bioluminescence from the bacterium Vibrio fischeri. The drugs were spiked in water at concentration in the range 1.0-50.0 μg ml-1, distributed over six concentration levels, and their toxicity evaluated in terms of response rate calculated along 30 min of incubation. The test was also applied to real river samples previously assayed by the HPLC method. The parameters LOEC (lowest observable effect concentration) and EC50 (half effective concentration) were calculated. Chlortetracycline, promethazine, betamethasone, ketoconazole and econazole were found to be very toxic. Diclofenac and ketoprofen showed toxicity only at the highest concentrations tested. Clindamycin, neomycin and oxatomide induced a decrease in bioluminescence but below the toxicity limits. In contrast, erythromycin and diphenhydramine showed an increase in bioluminescence, known as hormesis. The toxicity was amplified in samples containing drug mixtures, demonstrating additive o synergistic activity.
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