2004 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, 2003 through August 26, 2004
Project Amount: $524,992
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water Quality , Water
The objective of this research project is to incorporate a multipronged approach to evaluate the fate and transport of pharmaceutically derived 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 and determining whether antimicrobial resistance traits in bacteria found in those waters are correlated to environmental levels of the compounds. In addition, because during the previous years of this research project ng/L levels of a wide range of major-use antibiotics were found in the surface waters that feed drinking water treatment plants, sensitive and reliable solid phase extraction followed by analysis with liquid chromatography and tandem mass spectrometric methods (SPE-LC-MS/MS) were developed for their analysis throughout the drinking water treatment process. An occurrence study then was begun in source and finished drinking waters. Additional objectives for this component of the research project include assessment of their removal and transformation during chlorination through identification of transformation products. To evaluate what happens to a wide range of pharmaceutical chemicals in the environment, methods are being developed to extract them from river sediments and track their fate during natural photolysis. In addition, treatment processes also are being evaluated to determine how best to remove the chemicals if they infiltrate groundwater or survive drinking water treatment.
Analytical methods were developed for analyses of 25 antibiotics, including tetracyclines, sulfonamides, macrolides, quinolones, fluoroquinolones, trimethoprim, and lincomycin in source and finished drinking waters using SPE-LC-MS/MS. 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. The coextracted natural organic matter in sample matrices caused signal suppression for most of the analytes. The method of standard addition was used for quantitation to compensate for the matrix effect on signal variation. Results of a sampling holding time study indicated that source water samples should be analyzed as soon as possible after being collected to avoid appreciable analyte loss, whereas quenched chloraminated finished water samples should be analyzed within 7 days of sample collection. A preliminary occurrence study of antibiotics in five selected drinking water treatment plants 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 few antibiotics also were detected at levels below 5 ng/L in consumers’ tap water collected at representative points in the distribution systems from the participating plants.
To determine the fate of these compounds during chlorination, bench-scale experiments are being conducted to study the reaction kinetics of chlorination of selected antibiotics, including tetracycline, doxycycline, tylosin, and roxithromycin in aqueous solutions. The transformation products are being identified by LC-MS/MS. The removal efficiencies of these antibiotics at environmentally relevant concentrations (i.e., ng/L levels) under simulated drinking water chlorination conditions also are being assessed. In evaluating the risk posed by pharmaceutical release into the environment, there could be an underestimation of pharmaceutical compounds when considering aqueous concentrations only because they will exist partially in the aqueous phase but also can be sorbed to suspended components and sediments. Indirect photolysis of these chemicals in both phases may be possible depending on shielding effects.
The effect of photolysis on the fate of antibiotics in the aquatic environment is being studied in the laboratory through the use of a constructed reactor. The lamp initially utilized to perform the controlled photolysis was a doped medium pressure mercury vapor lamp located in a quartz cooling sleeve with running water positioned 4 inches above a pyrex (borosilicate) baking pan to filter out wavelengths less than 290 nm. The distance between the lamp and the open rectangular reactor was 17 inches. The reactor was placed in a water bath consisting of a small cooler with flowing water at 21°C. The entire lamp system was enclosed in a black structure to limit stray light. Radiometer measurement of emitted light between 300-400 nm showed an intensity of 1 mW/cm2 with the pyrex filter in place at the water surface. Sulfamethoxazole was the first antibiotic to be studied because of its stability, and its average first order rate constant was calculated to be -0.237 ± 0.0155 hour-1, corresponding to an average half life of 2.93 ± 0.196 hours. The main detected byproduct was a result of ring contraction and expansion.
Subsequent changes were made to the photolysis system to better emulate environmental conditions in a stream. The lamps were changed to provide a broader spectrum, and a pump was added to create a recycling flow (chemicals are cycled in and out of the upper layer of the sediment with the flow through the pores). Two baffles were made for the reactor to distribute the flow over the entire surface area of the soils that will be added to the basin.
The evaluation of antibiotic resistance that was correlated to the environmental persistence of antibiotics initially focused on studying enteric bacteria such as Escherichia coli and Enterococci isolated from environmental samples as indicators. Making the distinction between environmentally acquired resistance induced by antibiotics introduced into the environment through wastewater treatment plant discharges and drug resistance acquired in the human gut, however, has proven difficult. Therefore, we now are studying the prevalence of antimicrobial resistance in Aeromonas hydrophila and A. caviae. We will attempt to add to the body of knowledge surrounding the particular consequences of urban effluent on antibiotic resistance profiles by sampling upstream and at various points downstream of a municipal wastewater treatment plant discharge. Fifty isolates from each sampling point are being tested for resistance to several commonly employed antibiotics. To date, 78 isolates have been confirmed as either A. hydrophila or A. caviae, with an additional 40 highly likely Aeromonas isolates soon to be confirmed for a total of 118. Of these 118, 35 have been found upstream, 26 at the point of effluent discharge, 26 at a nearby downstream point, and 31 at the furthermost sampling point downstream of the wastewater treatment plant.
Because studies have shown that pharmaceutically active chemicals can be resistant to conventional treatment in both wastewater and drinking water, we investigated whether direct and indirect photolysis using low-pressure (LP) and medium-pressure (MP) lamps could be used effectively to remove a suite of compounds. Ultraviolet (UV) radiation is used widely for drinking water disinfection in Europe and currently is gaining importance in the United States because of its effectiveness against Cryptosporidium parvum. Its use also can reduce the chlorine dose applied for final disinfection, and therefore lower the levels of disinfection byproducts formed. Advanced oxidation processes (AOPs) using UV/hydrogen peroxide (H2O2) have been shown to reduce the levels of numerous environmental contaminants such as methyl tertiary butyl ether, n-nitrosodimethylamine, some endocrine disrupting compounds, and pharmaceuticals that are resistant to conventional treatment. Few studies have described degradation of pharmaceuticals by UV treatment, and in combination with H2O2, this process could be very effective in mineralizing or transforming the parent compounds. Experiments were conducted to compare the efficiency of UV and UV/H2O2 for the photodegradation of compounds that belong to different therapeutic classes (analgesics, lipid regulators, antiepileptics, antibiotics, and x-ray contrast media). Batch-scale experiments employing direct photolysis with LP and MP lamps at different UV fluences (ranging from 40 to 1,700 mJ/cm2) in consort with AOP (by addition of 10 mg/L H2O2 to form the highly reactive and unselective OH radical species upon photolysis) were conducted in laboratory-grade water (LGW) and surface water.
To follow the removal of the selected analytes in the different water matrices, analytical methods were developed using high-pressure LC with UV detection and LC-MS/MS for the detection of ketoprofen, naproxen, carbamazepine, clofibric acid, iohexol, and ciprofloxacin. Outcomes of this research project included the experimental determination of the fundamental reaction rate constants for all of these contaminants via direct photolysis and OH radical pathways. A summary of the practical implications of this research for water treatment plants includes:
- Some pharmaceuticals such as ketoprofen and ciprofloxacin were significantly removed from LGW by direct photolysis using a UV fluence that typically can be used during drinking water treatment (100 mJ/cm2). These results need to be validated in surface water because of the matrix competition for UV light that decreased the removal of some of the other pharmaceuticals examined in this study.
- Carbamazepine does not appear to be amenable to photodegradation in surface water at the UV fluences typically used for drinking water treatment (in the range 30 to 140 mJ/cm2). A significant reduction could be obtained if a high UV fluence (such as 1,700 mJ/cm2) was used in combination with 10 mg/L of H2O2. If higher H2O2 concentrations were used with lower UV fluences, the compounds’ removal also might be improved as a result of higher OH radical formation.
- MP lamps performed better for the removal of some pharmaceuticals such as naproxen, clofibric acid, and carbamazepine than LP lamps, and this outcome could be predicted by determination of the compounds’ absorbance spectra.
- The generation of OH radicals in an AOP in surface water does not seem to enhance removal of all pharmaceuticals, as was observed for clofibric acid and iohexol.
- All the pharmaceuticals tested in surface water (carbabazepine, naproxen, clofibric acid, and iohexol) were reduced to levels below detection using LP or MP lamps with a UV fluence of 1,700 mJ/cm2 and 10 mg/L H2O2. Economic studies should, therefore, determine whether using such high UV fluence is feasible and competitive when compared to other treatment processes (such as ozonation and membranes).
- For some of the pharmaceuticals studied (e.g., naproxen and ketoprofen) the formation of photolysis products was observed. Further studies are being conducted to address the identity, treatability, and environmental and human impacts of those products.
We will refine methods to analyze antibiotics in aquatic and sediment media that will permit more practical sample collection and handling prior to analysis. Disinfection kinetics will be studied and attempts will be made to identify the byproducts of chlorination. The National Committee for Clinical Laboratory Standards protocol for antibiotic resistance testing using the microdilution method will be employed on the collected bacterial isolates. The bacteria isolated from the downstream points should have markedly increased and perhaps multiple antibiotic resistant tendencies, as compared to those upstream of the wastewater treatment plant outfall. Because of the proximity of the sampling points to a documented source of subtherapeutic concentrations of antibiotics, correlations will be drawn between urban effluent and its impact on resistance trends in bacteria.
For the photolysis investigations, the new lamp will be monitored with actinometry as it ages and its output intensity diminishes, soils will be physically and chemically characterized, and a suitable ratio of water to soil will be determined for the laboratory reactor experiments. High aqueous concentrations (1 mg/L) of pharmaceutical compounds in LGW will be used to determine the dynamics between photolysis and sorption to the soils. The entire recycling system will run in the dark as a control. In more advanced stages, natural waters will be spiked with high concentrations of targeted pharmaceutical compounds to run through the system. A method currently is being developed to extract a wide range of pharmaceutical compounds from sediments and soils to facilitate the complete fate and transport study described in this report.