Presentation Abstract

Fate, Attenuation, and Effects of Fluoroquinolone Antibacterials in Aquatic Systems
Charles Knapp
University of Kansas, Lawrence, KS

The objective of this research project was to assess the fate, attenuation, and ecotoxicity of selected fluoroquinolone (FQ) antibiotics on surface water quality, under both laboratory- and field-scale conditions. Further, emphasis was placed on developing new methods for quantifying FQs and degradation products and developing new molecular techniques for monitoring antibacterial resistance to FQs in microorganisms.

Early work focused on quantifying key FQs, including ciprofloxacin (cipro), enrofloxacin (enro), and their breakdown products at low environmental concentrations, using C-18 solid phase extraction followed by LC-MS analysis. ^1,2 The structure of 12 FQ photodegradation and other degradation products were elucidated, including products not previously reported in the literature.

These methods were used for monitoring of cipro and enro within the context of controlled experiments aimed at determining factors that affect their fate in the natural environment. Laboratory results indicate that particulate organic matter (POC) and light intensity and wavelength influence FQ disappearance rate. ³ Photodegradation reactions quickly destroy both cipro and enro under natural sunlight and ambient water conditions. Additionally, both FQs readily adsorb onto POC in solution, although the final fate of the FQs after adsorption has not been fully defined.

Further, fate and effects studies using outdoor 11.3 m³ aquatic mesocosms verified the laboratory data that POC and light conditions were centrally important to FQ fate in surface waters. The data also indicated that cipro was a significant degradation product of enro, especially under lower light aquatic conditions (~ 25% full light exposure [FLE]), and residual enro could be detected more than 30 days after release when light levels were low (0.5% FLE), suggesting that FQ residuals can accumulate in surface waters under low light conditions.

Associated with FQ fate work, new molecular biological methods for tracking FQ antibacterial resistance in exposed organisms were developed. ⁴ These methods use density gradient gel electrophoresis for tracking mutations in gyrA gene sequences in the region known to confer FQ resistance in bacteria (the quinolone resistance-determining region [QRDR]). Field exposure experiments indicate, however, that at the highest enro exposure levels tested (25 ppb), no major changes in QRDR region were noted. Small changes in microbial community diversity were noted, although it is not possible to state whether such variations resulted from exposure or were a consequence of natural dynamic variability in the microbial communities.

Parallel to the above, toxicity tests were performed on five aquatic organisms with seven FQs (cipro, enro, lomefloxacin, ofloxacin, levofloxacin, clinafloxacin, and flumequine). ⁵ Microcystis aeruginosa, Lemna minor, and Pseudokirchnerialla subcapitata were sensitive to FQ, whereas no observed effects were found at 10 mg/L with Daphnia magna and fathead minnows.

The results generally indicate that FQ antibacterials are short-lived in aquatic water columns; however, they can last for much longer periods in zones where light exposure is minimal. Even in those regions, however, FQs bind to POC matter, which appears to reduce the bioavailability of the compounds.

Future work on FQs should focus more on their possible transmission through the food supply and the transmission of previously resistant organisms of environmental and public health significance. Data indicate that FQ resistance does not readily develop in situ, and that the key issue is the migration of resistant pathogens away from the point of resistance development. Work on the quantitative refinement of molecular biological FQ resistance testing methods is still warranted, however, because this will allow the better tracking of resistance in all settings, including hospitals.

References

1. Cardoza L.A., Williams T.D., Drake B., and Larive C.K. LC/MS/MS and LC/NMR for the structure elucidation of ciprofloxacin transformation products in pond water solution. Mass Spectrometry, LC/MS/MS and TOF/MS: Analysis of Emerging Contaminants, ACS Symposium Volume 850. Editors: I. Ferre and E. M. Thurman. Washington, DC: Oxford University Press and American Chemical Society, 2003.
2. Cardoza L.A., Almeida V.K., Graham D.W., and Larive C.K. Separations coupled with NMR detection: emerging techniques for the study of contamination fate. Trends in Anal Chem (TRAC) 2003;22:766-775.
3. Cardoza L.A., Knapp C.W., Larive C.K., Belden J.B., Lydy M., and Graham D.W. Factors affecting the fate of ciprofloxacin in aquatic field systems. Wat Soil Air Poll 2005;165:383-398 .
4. Knapp C.W., Cardoza L.A., Hawes J., Wellington E.M.H., Larive C.K., and Graham D.W. Fate and effects of enrofloxacin in aquatic systems under different light conditions. Environ Sci Technol (submitted, 2005).
5. Robinson A.A., Belden J.B., and Lydy M.J. Toxicity of fluoroquinolone antibiotics to aquatic organisms. Environ Toxicol Chem 2005;24:423-430.

Research Opportunities | Guidance & FAQs | Grants | Fellowships | Small Business | Research Centers | Other Programs
Research Results | Science Topics
About NCER | Publications | Events | Search | Personalize

EPA Home | Privacy and Security Notice | Contact Us