Simulation model to predict the fate of ciprofloxacin in the environment after wastewater treatment

The extent hospital effluent contributes to antimicrobial presence in the environment and its impact on resistance dissemination remains unknown. To investigate the fate of the antimicrobial ciprofloxacin in hospital effluent a Monte Carlo simulation model was developed to model levels from hospital use to wastewater treatment plant (WWTP) effluent release, in addition to modeling resistance formation potential, hazard quotient (HQ) and swimmer exposure. The mean predicted concentration (PC) of ciprofloxacin in hospital effluent, urban effluent, WWTP effluent, sludge, soil and sea water was 579, 6.06, 2.59, 3.48, 0.006 and 0.15mg/m3, respectively. A parallel surveillance study confirmed levels of ciprofloxacin above or below the limit of detection. The model predicted levels would never exceed the ECOSAR toxicity value. The model predicted a 98% probability of ciprofloxacin exhibiting a HQ > 1 (low toxicity concern). The mean ciprofloxacin PC in WWTP effluent was less than the minimum inhibitory concentration (MIC). The probability of conditions in WWTP effluent being favorable for resistance at 20% and 80% of the MIC was 3% and 72%, respectively. In all instances, when the MIC was bound, the probability for resistance formation within soil and sea water was < 1%. The probability of a swimmer being exposed to a level of ciprofloxacin greater than the acceptable daily intake was negligible. The study concluded that release of hospital effluent into the environment may lead to concentrations of ciprofloxacin which are of low toxicity concern but may be conducive to resistance formation and allow for the dissemination of resistance.