The North Carolina
Urban Water 
Consortium

New Research

More than 50 million pounds of antibiotics are produced in the United States each year. About one-half of these are prescribed for human use and one-half for agriculture. About 40 percent of the antibiotics that are produced are used for livestock (swine, poultry, and cattle), and the majority of these are given in sub-therapeutic doses as feed additives to enhance growth. Antibiotics are also used in aquaculture and sprayed on fruit trees to inhibit fungal growth.

Only a small fraction of doses of antibiotics administered to humans is metabolized, so that the vast majority of antibiotics end up in sewerage systems. Because of their bioactivity, they are likely to survive wastewater treatment and may pose a threat to the ecosystems into which the treated water is discharged. Antibiotic residues originating from animal administration may similarly be washed into streams. Drinking water plants downstream of such water sources may, therefore, be drawing raw waters containing trace levels of antibiotics and their metabolites on a daily basis, and it is unlikely that conventional drinking water treatment removes them. The presence of antibiotics in drinking water sources could be encouraging the emergence of antibiotic-resistant bacteria, which would then pose a serious human health threat.

While studies in Europe confirm the potential for antibiotic contamination of natural waters, little is known about the extent to which antibiotics may actually be found in drinking water sources in the United States let alone in North Carolina. In order to determine whether we have a major environmental problem on our hands, this new project will provide an initial screening of the prevalence of antibiotic residues in drinking water supplies across North Carolina. Sampling will be focused on susceptible drinking water supplies located downsteam from potential sources of pharmaceutical contaminants, including animal feeding operations, wastewater treatment plants serving populations likely to be large users of antibiotics, pharmaceutical manufacturers, and hospitals. At least one drinking water source that does not have any potential upstream sources of pharmaceutical contaminants will also be sampled for comparison. The investigators will collect grab samples from the intakes of the drinking water facilities during both low-flow and high-flow conditions. To determine the extent to which drinking water treatment may remove antibiotics, samples of finished drinking water will also be collected at times corresponding to sampling at water intakes.

Because concerns about the human and environmental effects of antibiotics is fairly recent, analytical methods for their measurement have only recently begun to be developed. Therefore, part of this project involves evaluating analytical techniques and developing approaches that ensure interference-free methodology. The goal is to analyze samples for 25 specific antibiotic residues.

The results of the study will provide an answer to the question “Are there antibiotics in our drinking water?” and will serve as the basis for determining whether higher priority investigations of antibiotics in drinking water sources are warranted.

Investigation of the Occurrence of Residual Antibiotics and their Metabolites in Drinking Water (50307)
Howard  Weinberg, Department of Environmental Sciences and Engineering, UNC-Chapel Hill and Michael T. Meyer, U.S. Geological Survey
September 1, 2001, to November 30, 2002
Funded by the N.C. Urban Water Consortium