title: Biodegradation of sulfamethoxazole photo-transformation products in a water/sediment test.
abstract: Occurrence of the antibiotic sulfamethoxazole (SMX) in the aquatic environment is of concern due to its potential to induce antibiotic resistance in pathogenic bacteria. While degradation of SMX can occur by numerous processes, the environmental fate of its transformation products (TPs) remains poorly understood. In the present work, biodegradation of SMX photo-TPs was investigated in a water/sediment system. Photo-TPs were produced by exposing SMX to artificial sunlight for 48 h. The resulting mixture of 8 photo-TPs was characterized using a combination of ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry and tandem mass spectrometry, and then used in biodegradation experiments. Significant differences in transformation among SMX photo-TPs were observed in the water/sediment system, with four photo-TPs displaying evidence of biodegradation (dissipation half-lives [DT50] of 39.7 d for 3-amino-5-methylisoxazole, 12.7 d for 4-nitro-sulfamethxoazole, 7.6 d for an SMX isomer and 2.4 d for [C10H13N3O4S]), two displaying primarily abiotic degradation (DT50 of 31 d for sulfanilic acid and 74.9 d for 5-methylisoxazol-3-yl-sulfamate), and two photo-TPs behaving largely recalcitrantly. Remarkably, TPs previously reported to be photo-stable also were persistent in biodegradation experiments. The most surprising observation was an increase in SMX concentrations when the irradiated solution was incubated, which we attribute to back-transformation of certain photo-TPs by sediment bacteria (85% from 4-nitro-sulfamethoxazole). This process could contribute to exposure to SMX in the aquatic environment that is higher than one would expect based on the fate of SMX alone. The results highlight the importance of considering TPs along with their parent compounds when characterizing environmental risks of emerging contaminants.
authors: College of Environmental Science and Engineering, Tongji University, Siping Road 1239, 200092 Shanghai, PR China; Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden.
authors: Tong
authors: T
authors: Su
authors: College of Environmental Science and Engineering, Tongji University, Siping Road 1239, 200092 Shanghai, PR China.
authors: Huiping
authors: H
authors: Deng
authors: Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden.
authors: Jonathan P
authors: JP
authors: Benskin
authors: Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, Svante Arrhenius väg 8, SE-114 18 Stockholm, Sweden; Institute for Hygiene and Environment, Marckmannstraße 129b, 20539 Hamburg, Germany. Electronic address: michael.radke@hu.hamburg.de.
authors: Michael
authors: M
authors: Radke
mesh_terms: D000900:Anti-Bacterial Agents / Q000528:radiation effects*; D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D002851:Chromatography, High Pressure Liquid; D019015:Geologic Sediments / Q000382:microbiology; D013420:Sulfamethoxazole / Q000528:radiation effects*; D013472:Sunlight; D053719:Tandem Mass Spectrometry; D014867:Water; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D000900:Anti-Bacterial Agents; D014874:Water Pollutants, Chemical; D014867:Water; D013420:Sulfamethoxazole
keywords: Back-transformation; Biodegradation; Phototransformation products; Sulfamethoxazole