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 were 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 aeruginosa (EC50 in the range 5-60 microg/L). Risk characterization for the aquatic environment was performed for the three compounds by calculating the predicted environmental concentration (PEC) and the predicted no-effects concentration (PNEC). A PEC/PNEC ratio of <1 indicates that, with the present pattern of use, no environmental risk is expected. PEC/PNEC ratios of <1 for present usage in Europe were found for mecillinam and trimethoprim whereas a PEC/PNEC ratio >1 was found for ciprofloxacin.