Environmental toxicity and genotoxicity of antibiotics on organisms of the aquatic food chain

Drugs are not environmentally different from other chemicals. High quantities of pharmaceuticals are discharged into sewage treatment plants when used for human cure and directly into surface waters or on soil when used for veterinary purposes. Drugs generally occur in low concentrations (ng-g/L) in various compartments of the aquatic environment Though antibacterial agents are known to have irreversible, no quantifiable effects on the gene pool of microrganisms (resistance), few data exist about the disturbance they cause to the wastewater treatment process, the microbial life in surface waters and their effects at low concentrations on other organisms. The ecotoxicity of the following six antibiotics on aquatic organisms was investigated: Erythromycin, Oxytetracyclin, Sulfamethoxazole, Ofloxacin, Lincomycin and Clarithromycin . Bioassays were performed on bacteria, algae, rotifers, microcrustaceans and fish to assess acute and chronic toxicity, while SOS chromotest and Ames test were used to detect the genotoxic potential of the investigated drugs. For risk assessment, the environmental impact was calculated by MEC/PNEC ratio using the available data from the literature regarding the occurrence in the aquatic environment of the pharmaceuticals investigated and the toxicity data obtained from the bioassays performed. The ecotoxicological results showed that acute toxicity was in the order of mg/L while, for the chronic data the antibiotics were bioactive at concentrations in the order of µg/L, mainly for the algae. The toxicity ratios of acute and chronic effect (A/C ratio) ranged for Brachionus calyciflorus from 3 (clarithromycin and sulphametoxazole) to 56 (ofloxacin) and for Ceriodaphnia dubia from 2 (clarithromycin and lincomycin) to 104 (oxytetracyclin), confirming that chronic assays are more appropriate than acute ones to detect the impact of pharmaceuticals. Ofloxacin was the only genotoxic compound and Sulfamethoxazole, Ofloxacin and Lincomycin were mutagenic. As for environmental risk, the macrolides were found to be the most harmful for the aquatic environment.