Presentation Abstract

Occurrence and Fate of Antibiotics and Other Pharmaceutically Active Compounds During Transport to and During Drinking Water Treatment
Howard S. Weinberg, Mark D. Sobsey, Philip C. Singer, Embrey L. Bronstad, Vanessa J. Pereira, Katherine M. Stauffenberg, Zhengqi Ye, and Joshua D. Huneycutt
University of North Carolina, Chapel Hill, NC

This research project incorporates a multipronged approach to evaluate the fate and transport of pharmaceutically active chemicals in the aquatic environment. Because of their high end-use, antibiotics were singled out for a major investigation that includes isolating them from surface waters impacted by wastewater treatment plant effluent, determining whether antimicrobial resistance traits in bacteria found in those waters are correlated to environmental levels of those compounds, and the fate of such compounds during transport to and through drinking water treatment plants. Appropriate disinfectant quenching—solid phase extraction followed by analysis with liquid chromatography and tandem mass spectrometric methods—was applied to determine occurrence levels for 25 antibiotics, including tetracyclines, sulfonamides, macrolides, quinolones, fluoroquinolones, trimethoprim, and lincomycin in source and finished drinking waters. The method detection limits of the target analytes are generally below 10 ng/L in source water and below 5 ng/L in finished water, but because co-extracted natural organic matter in sample matrices caused signal suppression for most of the analytes, the method of standard addition was used for quantitation. A preliminary occurrence study revealed the presence of a variety of antibiotics in source drinking waters at ng/L levels whose concentrations were somewhat reduced during treatment but in some cases were found, albeit at lower levels, in the finished drinking waters. A kinetic study revealed major differences in the potential for reaction and the fate of antibiotics with disinfectants. Furthermore, it appears that an increase in the levels of antibiotic resistance among naturally occurring microbes downstream of wastewater treatment plant discharges is correlated to the levels of antibiotics in that discharge. Once these chemicals enter “natural systems,” they can partition into sediments or undergo some degree of photodegradation with resulting byproducts that might be missed by the techniques used to target individual compounds at environmental levels. A case study with sulfamethoxazole is presented.

It appears that some of the chemical species targeted in this study survive conventional wastewater treatment depositing levels, sometimes exceeding 1µg/L in the receiving stream. This study also has shown that ultraviolet (UV) treatment, which is a technology with increasing deployment for both wastewater disinfection and remediation of water supplies, can remove a variety of compounds including iohexol (a widely used X-ray contrast medium), carbamazepine (an antiepileptic), and analgesics. The effect of using UV together with hydrogen peroxide to enhance oxidation also is demonstrated. Some pharmaceuticals, such as ketoprofen and ciprofloxacin, were significantly removed from synthetic water by direct photolysis using a UV energy that is typically used during drinking water treatment (100 mJ/cm²), and these results were replicated in contaminated surface waters.

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