Assessment of Potential Antibiotic Contaminants in Water and Preliminary Occurrence Analysis

Antibiotics are among the emerging microcontaminants in water because of concerns of their potential adverse effects on the ecosystem and possibly on human health. Antibiotics are likely to be released into the aquatic environment via wastewater effluent and agricultural runoff as a result of incomplete metabolism, ineffective treatment removal or improper disposal because large quantities of antibiotics are used annually in human therapy and in agriculture. Despite large quantities of use, published data on the amounts and use patterns of antibiotics are scarce. To assess the magnitude of the potential risks associated with antibiotics, a comprehensive literature review was conducted on the usage, occurrence, and behavior of antibiotics. To identify antibiotics that are likely to be present in water sources, concentrations of antibiotics in municipal wastewater and animal waste in the United States (U.S.) were estimated and were classified according to chemical properties. The estimation of human health antibiotics was based upon the number of prescriptions administered. The estimated concentrations of antibiotics in untreated wastewater range from 3.9 ng/L to approximately 27,000 ng/L. The estimation of animal health antibiotics was based upon the subtherapeutic usage in feed for growth promoting. Considerable variation in antibiotic usage exists among different animal species. Reported data on the occurrence of antibiotics in the aquatic environment confirm the persistence of certain antibiotics. Although information is limited, studies on the transformation and sorption of antibiotics indicate that these processes significantly affect the fate of mo st classes of antibiotics. By combining information on environmental fate with the predicted concentrations, we identify that antibiotics of sulfonamides and fluoroquinolones are the most likely water contaminants, followed by macrolides. Among sulfonamide and fluoroquinolone antibiotics, sulfamethoxazole and ciprofloxacin are most likely to be present in municipal wastewater effluent and sulfamethazine is most likely to be present in agricultural runoff. Azithromycin and tylosin are the most likely macrolides present in municipal wastewater effluent and in agricultural runoff respectively. An occurrence study, which is currently underway, focuses on three of the potential antibiotic contaminants, ciprofloxacin, sulfamethoxazole and sulfamethazine, identified by literature review. Solid phase extraction methods were developed. Recoveries ranged from approximately 45 to 106 percent. Analysis of the three antibiotics was conducted by liquid chromatography mass spectrometry (LC-MS). Additionally, high performance liquid chromatography (HPLC) with fluorescence detection was employed for ciprofloxacin analysis. Preliminary results indicated the presence of ciprofloxacin in secondary wastewater effluent at approximately 80 to 150 ng/L. Sulfamethoxazole was detected in one of the wastewater samples. Sulfamethazine was not detected. Concentrations of antibiotics were found to be much lower or below the detection limits in the effluent of advanced treatment processes including granular activated carbon and ozonation, indicating significant removal by those processes.