Environ. Sci. Technol. 2010, 44, 962–970
Fate of Beta Blockers in Aquatic-Sediment Systems: Sorption and Biotransformation MARIA RAMIL,† TAREK EL AREF, GUIDO FINK, MARCO SCHEURER, AND THOMAS A. TERNES* Federal Institute of Hydrology (BfG), D-56068 Koblenz, Am Mainzer Tor 1, Germany
Received September 11, 2009. Revised manuscript received November 24, 2009. Accepted December 3, 2009.
The fate of beta blockers (atenolol, acebutolol, bisoprolol, celiprolol, metoprolol, nadolol, pindolol, propranolol, and sotalol) was studied in surface water-sediment systems. A new analytical method was developed to determine the beta blockers in sediments by LC-ESI-tandem MS detection. The relative recoveries in sediments ranged from 89 ( 7% (acebutolol) to 102 ( 3% (nadolol) using deuterated surrogate standards. Beta blockers were present with concentrations up to 86 ng/g (bisoprolol) in the sediments of small German streams containing an elevated percentage of treated wastewater. Biotransformation studies and sorption isotherms of the beta blockers were performed with two natural river sediments (“Burgen”, “Dausenau”) differing in organic carbon content and particle size distribution. Biotransformation of beta blockers in the surface water-sediment systems exhibited a low to high persistence with 90% disappearance (DT90) ranging from 0.4-10 d (pindolol, atenolol) to >100 d (sotalol, propranolol or celiprolol). For sorption studies neither NaN3 addition nor autoclavation led to a complete mass balance of the beta blockers, probably due to biotransformation. Isotherms at 6 h (apparent equilibrium, measuring aqueous and sediment phase) fitted by the Freundlich equation show that sorption of all beta blockers to the Burgen sediment were linear or close to it (i.e., n-values between 0.93 and 1.13), while in the Dausenau sediment the sorptions were slightly non linear (i.e., n-values 0.77-0.91). In river water the sorbed fraction is negligible in comparison to the dissolved fraction. Nevertheless, beta blockers can be detectedwithconcentrationsupto86ng/g(bisoprolol)insediments of small streams containing more than 50% treated wastewater.
Introduction During the past decade, a wide range of pharmaceuticals have been discovered ubiquitously in the aquatic environment with a potential risk for the ecosystem (1-3). Beta adrenergic antagonists (beta blockers) are one of the crucial medicinal classes. They are applied for treating cardiac arrhythmias, anxiety, hypertension, and angina as well as for cardio protection after myocardial infarction (4). In Germany alone, more than 100 tons of beta blockers are * Corresponding author phone: ++49 261 1306 5560; fax: + +49 261 1306 5363; e-mail:
[email protected]. † Present address: Department of Analytical Chemistry, Institute of Food Analysis and Research (IIAA), University of Santiago de Compostela, 15782-Santiago de Compostela, Spain. 962
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consumed per year (5, 6), with metoprolol by far the main purchased active ingredient. Beta blockers have been detected in wastewater treatment plants (WWTPs), surface waters (7-14), and hospital effluents (15) in the ng/L to the µg/L range. Sotalol has even been detected in groundwater up to 560 ng/L (16). Beta blockers have been reported to cause harmful effects on aquatic organisms. Physiological effects such as the decrease of the heart rate were observed by Dzialowski et al. (17) in Daphnia magna at concentrations in the µg/L range (propranolol: lowest observed effect concentration (LOEC) was 55 µg/L). Moreover, additive effects of different beta blockers have been reported by different authors, as they feature the same mode of action (18, 19). Regarding vertebrates, fish have beta adrenergic receptors very similar to those present in mammals and therefore cardiovascular dysfunction is one possible consequence of exposure of fish to beta blockers leading to impaired fitness (e.g., reduced growth and fecundity) (20). Huggett et al. (21) observed a decrease of fecundity for Oryias latipes (Japanese medaka) after exposure to propranolol at concentrations as low as 0.5 µg/L. Beta blockers are positively charged at neutral pH due to their amino moiety (22). Kibbey et al. (23) have recently investigated the adsorption behavior of three beta blockers (propranolol, metoprolol, and nadolol) to a natural alluvial material. They concluded that hydrophobicity of beta blockers is a good predictor of their adsorption properties. Yamamoto et al. (24) investigated the biotransformation of atenolol and propranolol in contact with river water (without sediment), the sorption on river sediments using OECD 106 (28), as well as the photodegradation by sunlight. They found no biotransformation of the beta blockers, but an increased sorption affinity to sediments even comparable to the PAH pyrene. Furthermore, propranolol underlied an enhanced photodegradation. Nevertheless, there is still a lack of information about the biotransformation and the sorption of beta blockers in contact with water and sediment. In the present work, the main objective was to study the (bio)transformation of beta blockers in contact with sediments and to distinguish it from sorption. To enable the determination in both solid and aqueous matrices, an analytical method was developed enabling the analysis of beta blockers in sediments by LCtandem MS detection.
Materials and Methods Chemicals and Standards. Standard compounds and deuterated surrogates were provided by the following suppliers: atenolol, acebutolol, metoprolol, nadolol, and pindolol (Sigma, St. Louis, MO), bisoprolol (Merck, Darmstadt, Germany), celiprolol (Mikromol, Luckenwalde, Germany), propranolol (Sigma-Aldrich, Steinheim, Germany), sotalol (Dr. Ehrenstorfer, Augsburg, Germany), and atenolol-d7, propranolol-d7, sotalol-d6 (CDN, Pointe-Claire, Canada). Individual solutions of the analytes and surrogate standards were all prepared in a concentration of 1 mg/mL in methanol. Stock mix solutions of all analytes (100 µg/mL) and of all surrogate standards (1 µg/mL) were separately prepared in methanol by dilution of the individual solutions and were stored at 4 °C in the darkness. Structures of the studied substances are displayed in Table 1. Sampling of Water and Sediments. The sediment samples were randomly taken from the sediment surface by a van Veen grab sampler at depths up to 5 cm. Sediments from streams and rivers (Bieber, Rodau, Landgraben, Schwarzbach, Emscher, Wupper, Lippe, Lech, Schmutter, Isar, and Danube) 10.1021/es9027452
2010 American Chemical Society
Published on Web 12/23/2009
TABLE 1. Name, CAS Number, Abbreviation, and Chemical Structure for the Investigated Beta Blockers
were analyzed for nine beta blockers. All samples were wetsieved, freeze-dried, homogenized, and ground by a ball mill. Additionally, grab samples of the water were taken from the small streams Bieber, Rodau, Landgraben, and Schwarzbach. The cooled water samples (4 °C) were filtered and analyzed within 3 d. Figure S1 displays the sampling locations and Table S1 (see Supporting Information) provides the texture and organic carbon content of the sediments. Analysis of Water Samples. The analysis of beta blockers in the aqueous phase was based on the method described by Ternes et al. and Scheurer et al. (25, 26). Aqueous samples from the sorption experiments were directly measured by LC-ESI tandem MS after centrifugation without solid phase extraction (SPE), while water samples for the biotransformation tests were filtered through glass fiber filters 99.5%) at the ambient pH 6.5/6.6 of the water/sediment-systems, due to the protonation of the amino moiety of the side chain. Depending on the pH, sotalol (97.4% is positively charged at pH 6.6 and 97.9 at pH 6.5) can even occur in 4 different species (positively charged, zwitter ion, neutral, and negatively charged) because it possesses a second amine group in the vicinity of the SO2 moiety. Considering the statistical uncertainties only very minor differences were found for the sorption properties of the nine beta blockers in contact with the two sediments, because all beta blockers are predominantly positively charged at pH 6.5/6.6. Hence it can be assumed the positive charge is dominating the sorption affinity, either to negatively charged sites in the NOM or to clay minerals with negative charges due to isomorphic substitution in the mineral structure. Sanches-Camazano et al. (35) reported that sotalol is adsorbed into the interlayer space of the clay mineral montmorillonite probably due to cation ion exchange and ion-dipole interactions. They found a maximum of sorption at around pH 7 ( 1. In any case, as already noted in Stein et al. (33) further experiments are crucial to determine the influence of single organic and mineral constituents on the overall sorption phenomena as well as to model these processes considering several terms such as electrostatic interactions, specific H-donor-acceptor interactions, or cavity effects in water. Desorption. Sorption of beta blockers was clearly hysteretic (quantity desorbed is smaller than the quantity sorbed) on Burgen sediment. The observed hysteresis could be artificial (i.e., due to experimental artifact) or truly thermodynamic (i.e., involvement of metastable states during sorption and/or desorption). Probably slow desorption kinetics of organic compounds (36) were responsible for the observed hysteresis, but the extension of this type of experiment over a period longer than 6 h would accomplish a considerable (bio)transformation. For a more profound discussion see Stein et al. (33). Environmental Relevance. Experimentally determined distribution coefficients Kd allow estimating the particleassociated fraction of beta blockers in the water of rivers and streams. This fraction is estimated according to fS ) (CSS · Kd)/ (1 + CSS · Kd), where CSS (mg/L) is the concentration of suspended solids. With an average value of 25 mg/L suspended solids in rivers (37) beta blockers are sorbed to suspended solids with less than 0.1% (maximum: propranolol with 0.03% in contact with Dausenau sediment). Hence, considering only the distribution of beta blockers in river water, the sorbed fraction is negligible in comparison to the dissolved fraction. Nevertheless, beta blockers can be detected in sediments of small streams containing an elevated percentage of treated wastewater (>50%) with concentrations up to 86 ng/g (bisoprolol) (Table S2). Dissolved concentrations as high as
2.1 µg/L (bisoprolol) were detected in these streams. Consistent with the sorption and transformation studies atenolol was only found in the water phase due to its low sorption affinity and elevated biodegradability. Nadolol and pindolol were not present at all. Comparing the concentrations measured in the water phase and the sediment phase with the sorption coefficients, it became obvious that in addition to sorption other processes such as biotransformation and/ or photodegradation as reported for propranolol (24) are occurring in the aquatic environment.
Acknowledgments This study was funded by the European Union under the 6th framework program in the STREP ERAPharm (SSPI-CT-2003511135). We thank the Hessische Landesamt fu ¨ r Umwelt und Geologie and the North Rhine Westphalia State Agency for Nature, Environment and Consumer Protection (LANUV) for providing sediment samples. We also thank Dirk Lo¨ffler and Jennifer Kormos, BfG, for the internal review of the manuscript.
Supporting Information Available This information is available free of charge via the Internet at http://pubs.acs.org/.
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