2003 Progress Report: Impact of Residual Pharmaceutical Agents and their Metabolites in Wastewater Effluents on Downstream Drinking Water Treatment FacilitiesEPA Grant Number: R829014
Title: Impact of Residual Pharmaceutical Agents and their Metabolites in Wastewater Effluents on Downstream Drinking Water Treatment Facilities
Investigators: Weinberg, Howard S.
Current Investigators: Weinberg, Howard S. , Meyer, M. T. , Singer, Philip C. , Sobsey, Mark D.
Institution: University of North Carolina at Chapel Hill
Current Institution: University of North Carolina at Chapel Hill , United States Geological Survey [USGS]
EPA Project Officer: Page, Angela
Project Period: August 27, 2001 through August 26, 2004 (Extended to August 26, 2006)
Project Period Covered by this Report: August 27, 2002 through August 26, 2003
Project Amount: $524,992
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water Quality , Water
The results of the U.S. Geological Survey's reconnaissance studies of pharmaceutical agents in the aquatic environment are being used to focus a study on the occurrence, fate, and transport of these chemicals from the point of discharge from wastewater treatment plants to the finished product in drinking water treatment. The objective of this research project is to answer the following questions:
1. Can models, such as Estimation Program Interface (EPI) suite, efficiently predict the environmental fate and toxic effects of pharmaceutical compounds? We will investigate various model predictions after evaluation against the known effects of other environmental triggers (such as pesticides) with the goal of prioritizing compounds by their health endpoints and determining which of them can be expected to persist and be present in the different matrix environments.
2. Where the models predict significant partitioning out of the aqueous phase, can approaches be developed to obtain a mass balance on target compounds as they transport through watersheds?
3. What is the fate of these agents during treatment of drinking water (such as ozonation and chlorination), and if byproducts are not changed significantly in structure, do they possess the same potential environmental impacts as their parent compounds?
4. As a major use group of pharmaceutical products, can antibiotics or their environmental degradates contribute to the evolution of antimicrobially resistant bacteria?
Antibiotics, which are widely used in human and veterinary medicine and as growth promoters in animal production, can enter the environment via various pathways. As micropollutants, antibiotics potentially can be transported to drinking water supplies. The occurrence, fate, and transformation of these and other pharmaceutical residues in drinking water treatment are of concern because of their uncertain long-term health effects.
Methods have been developed for the extraction and analysis of 22 antibiotics in source and finished (chlorinated) drinking water samples and applied to a preliminary occurrence study in several drinking water treatment plants. Fluoroquinolones were the most frequently detected antibiotics in source waters, followed by sulfonamides, lincomycin, tetracyclines, and macrolides. In most of the drinking water treatment plants, the finished water showed either no detectable antibiotic residues or very much reduced levels. Laboratory chlorination experiments showed that tetracyclines and sulfonamides were highly reactive towards free chlorine, with the type of byproduct depending on the contact time.
The low concentrations of antibiotics found in wastewater treatment plant effluent resulting from human use may exert selective pressure on native bacterial populations, engendering resistant pockets of pathenogenic and nonpathenogenic strains. The preliminary development of methods and the identification of appropriate sampling sites, where such resistance may be found, have been the major tasks accomplished during Year 2 of the project. We have begun to examine sediment samples for a ubiquitous environmental organism, Aeromonas spp., at points upstream, at the point of discharge, and downstream from a wastewater treatment plant that has demonstrated antibiotic concentrations in its effluent. The changing distribution of resistance patterns, with respect to distance from the effluent discharge, are being determined. Coupled with the isolation and antibiotic resistance testing of these bacteria, the sediment will be analyzed for antibiotics to better correlate the presence of resistant bacteria to the drugs suffused in the solid phase.
In addition to antibiotics, the following agents have been targeted for a study of their occurrence and fate during drinking water treatment: the x-ray contrast agent iohexol, the antiepileptic drug carbamazepine, and the acidic compounds clofibric acid, ibuprofen, naproxen, ketoprofen, and diclofenac. The EPI suite was used to predict physical-chemical properties of these compounds, their biodegradation timeframe, a wastewater mass balance prediction, and their fate in the environment. The results show that the compounds have low vapor pressure (i.e., high fugacity in the gas phase), relatively high water solubility, and, therefore, low Henry's law constants. The predicted octanol-water partition coefficients favorably agree with experimental values from the literature, giving the research team a very useful predictive tool. The extremely low values predicted and obtained experimentally for iohexol show that the hydrophilic compound can be expected to partition considerably into the aqueous phase. The soil adsorption coefficient predicted for the different compounds is indicative of the expected partition between solid and solution phases in soil, or between water and sediment in aquatic systems. The high value predicted for carbamazepine indicates that the compound is expected to partition considerably into soil. According to the predicted physical-chemical properties, the selected compounds are expected to partition mainly between soil and water. In concurrence with the predicted properties and sewage treatment plant fugacity model of iohexol, x-ray contrast media have been found to be ubiquitously distributed in sewage effluents and the aquatic environment. The predicted iohexol biodegradation and sewage fugacity results agreed very well with experimental results obtained when studying the biodegradation of compounds with similar structures to iohexol such as diatrizoate and iopromide.
The initial study of the degradation of carbamazepine using direct photolysis demonstrates effective transformation in the presence of hydrogen peroxide. First order rate constants and quantum yields have been calculated and we will examine the byproducts of these and other treatment processes using liquid chromatography with tandem mass spectrometric analysis.
Kinetic studies of chlorination of antibiotics will be accompanied by an investigation of the structures of the byproducts formed during the preparation of drinking water. Field studies will be performed to determine whether antibiotics present in source waters survive drinking water treatment and persist into the tap. Antimicrobial resistance testing will begin using identified sources of wastewater discharges and samples collected up- and downstream from these points to determine when and how such resistance, if found, is acquired and, if possible, correlated to the levels and types of antibiotics discharged into the stream. Photodegradation and advanced oxidation processes also will continue to be explored to understand their effectiveness in reducing exposure to pharmaceutical products in drinking water.