Environmental risk assessment of antibiotics: comparison of mecillinam, trimethoprim and ciprofloxacin

The effects of mecillinam, trimethoprim and ciprofloxacin, antibiotics used in the treatment of urinary tract infections, on the aquatic environment w ere assessed, Mecillinam and ciprofloxacin were both readily biodegradable (primary degradation) in activated sludge, whereas trimethoprim persisted. The toxicity of these antibiotics towards sludge bacteria, a green alga, a cyanobacterium, a crustacean and a fish were investigated; both mecillinam and ciprofloxacin were highly toxic to the cyanobacterium Microcystis aerug inosa (EC50 in the range 560 mu g/L). Risk characterization for the aquatic environment was performed for the three compounds by calculating the predi cted environmental concentration (PEC) and the predicted no-effects concent ration (PNEC). A PEC/PNEC ratio of <1 indicates that, with the present patt ern of use, no environmental risk is expected. PEC/PNEC ratios of <1 for pr esent usage in Europe were found for mecillinam and trimethoprim whereas a PEC/PNEC ratio >1 was found for ciprofloxacin.