Article pubs.acs.org/est
Degradation Kinetics and Metabolites of Carbamazepine in Soil Juying Li,†,‡ Laurel Dodgen,† Qingfu Ye,‡ and Jay Gan*,† †
Department of Environmental Sciences, University of CaliforniaRiverside, Riverside, California 92521, United States Institute of Nuclear Agricultural Sciences, Zhejiang University, Hangzhou 310029, China
‡
S Supporting Information *
ABSTRACT: The antiepileptic drug carbamazepine (CBZ) is one of the most frequently detected human pharmaceuticals in wastewater effluents and biosolids. Soil is a primary environmental compartment receiving CBZ through wastewater irrigation and biosolid application. In this study, we explored the transformation of CBZ to biologically active intermediates in soil. Both 14C labeling and liquid chromatography−tandem mass spectrometry (LC−MS/MS) were used to track transformation kinetics and identify major degradation intermediates. Through 120 days of incubation under aerobic conditions, mineralization of CBZ did not exceed 2% of the spiked rate in different soils. Amendment of biosolids further suppressed mineralization. The fraction of non-extractable (i.e., bound) residue also remained negligible ( 99%; 20 mCi/mmol; see Figure S1 of the Supporting Information for structure and 14C-labeling position) was purchased from American Radiolabeled Chemicals (St. Louis, MO). Nonlabeled CBZ was obtained from Sigma-Aldrich (St. Louis, MO). Acridine was purchased from Santa Cruz Biotechnology (Santa Cruz, CA). Carbamazepine-10,11-epoxide was purchased from Sigma-Aldrich (St. Louis, MO). 10,11Dihydro-10-hydroxycarbamazepine was purchased from Tocris Bioscience (Bristol, U.K.). A stock solution of 14C−CBZ was prepared by mixing the labeled and nonlabeled CBZ in methanol at 2000 mg/L with a final specific activity of 0.591 mCi/mmol. All organic solvents and other chemicals used were of high-performance liquid chromatography (HPLC) grade. Soils and Biosolids. Three arable soils with different physicochemical properties were taken from the top 10 cm at locations in California. San Emigdio fine sandy clay loam (University of California Research and Education Center, Irvine, CA), Grangeville loam (Scott Brother’s Dairy Farms, Moreno Valley, CA), and Salinas silty clay (University of California Hansen Agricultural Center, Ventura County, CA) are abbreviated herein as soils A, B, and C, correspondingly. The soils were air-dried, homogenized by sieving (120
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