title: Exploring Trends of C and N Isotope Fractionation to Trace Transformation Reactions of Diclofenac in Natural and Engineered Systems.
abstract: Although diclofenac ranks among the most frequently detected pharmaceuticals in the urban water cycle, its environmental transformation reactions remain imperfectly understood. Biodegradation-induced changes in15N/14N ratios (εN= -7.1‰ ± 0.4‰) have indicated that compound-specific isotope analysis (CSIA) may detect diclofenac degradation. This singular observation warrants exploration for further transformation reactions. The present study surveys carbon and nitrogen isotope fractionation in other environmental and engineered transformation reactions of diclofenac. While carbon isotope fractionation was generally small, observed nitrogen isotope fractionation in degradation by MnO2(εN= -7.3‰ ± 0.3‰), photolysis (εN= +1.9‰ ± 0.1‰), and ozonation (εN= +1.5‰ ± 0.2‰) revealed distinct trends for different oxidative transformation reactions. The small, secondary isotope effect associated with ozonation suggests an attack of O3in a molecular position distant from the N atom. Model reactants for outer-sphere single electron transfer generated large inverse nitrogen isotope fractionation (εN= +5.7‰ ± 0.3‰), ruling out this mechanism for biodegradation and transformation by MnO2. In a river model, isotope fractionation-derived degradation estimates agreed well with concentration mass balances, providing a proof-of-principle validation for assessing micropollutant degradation in river sediment. Our study highlights the prospect of combining CSIA with transformation product analysis for a better assessment of transformation reactions within the environmental life of diclofenac.
authors.affiliation: Helmholtz Zentrum Muenchen, German Research Center, Institute of Groundwater Ecology, Ingolstädter Landstrasse 1, Neuherberg D-85764, Germany.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Maier
authors.affiliation: German Federal Institute of Hydrology (BfG) , Am Mainzer Tor 1, 56068 Koblenz, Germany.|Department of Civil & Environmental Engineering, University of California , Berkeley, California, 94720 United States.
authors.forename: Carsten
authors.initials: C
authors.lastname: Prasse
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich , 8092 Zürich, Switzerland.
authors.forename: Sarah G
authors.initials: SG
authors.lastname: Pati
authors.affiliation: Helmholtz Zentrum Muenchen, German Research Center, Institute of Groundwater Ecology, Ingolstädter Landstrasse 1, Neuherberg D-85764, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Nitsche
authors.affiliation: Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University , 10691 Stockholm, Sweden.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University , 10691 Stockholm, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Radke
authors.affiliation: Helmholtz Zentrum Muenchen, German Research Center, Institute of Groundwater Ecology, Ingolstädter Landstrasse 1, Neuherberg D-85764, Germany.
authors.forename: Armin
authors.initials: A
authors.lastname: Meyer
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich , 8092 Zürich, Switzerland.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
authors.affiliation: German Federal Institute of Hydrology (BfG) , Am Mainzer Tor 1, 56068 Koblenz, Germany.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Ternes
authors.affiliation: Helmholtz Zentrum Muenchen, German Research Center, Institute of Groundwater Ecology, Ingolstädter Landstrasse 1, Neuherberg D-85764, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Elsner