4-nitroso-sulfamethoxazole generation in soil under denitrifying conditions: Field observations versus laboratory results

Monica Brienza; Céline Duwig; Sandra Pérez; Serge Chiron

doi:10.1016/j.jhazmat.2017.04.015

4-nitroso-sulfamethoxazole generation in soil under denitrifying conditions: Field observations versus laboratory results

J Hazard Mater. 2017 Jul 15:334:185-192. doi: 10.1016/j.jhazmat.2017.04.015. Epub 2017 Apr 7.

Authors

Monica Brienza¹, Céline Duwig², Sandra Pérez³, Serge Chiron⁴

Affiliations

¹ UMR HydroSciences 5569, IRD, Montpellier University, 15 Avenue Ch. Flahault, 34093 Montpellier Cedex 5, France.
² UMR LTHE 5564, IRD, Grenoble University, 70, rue de la physique - Domaine Universitaire, 38041 Grenoble Cedex 9, France.
³ Water and Soil Quality Research Group, IDAEA-CSIC, c/Jordi Girona 18-26, 08034 Barcelona, Spain.
⁴ UMR HydroSciences 5569, IRD, Montpellier University, 15 Avenue Ch. Flahault, 34093 Montpellier Cedex 5, France. Electronic address: Serge.Chiron@msem.univ-montp2.fr.

PMID: 28412628
DOI: 10.1016/j.jhazmat.2017.04.015

Abstract

The formation of 4-nitroso-sulfamethoxazole and 4-nitro-SMX, two transformation products (TPs) of sulfamethoxazole (SMX) was investigated under batch soil slurry experiments and in a field study. Due to their low occurrence levels (ng/L) in environmental waters, a suitable analytical method based on liquid chromatography - high resolution - mass spectrometry was developed. Consequently, field observations revealed, for the first time, the occurrence of 4-nitroso-SMX in groundwater at concentrations as high as 18ng/L.Nitric oxide (NO) steady-state concentrations were determined in soil slurry experiments because this reactive specie accounted for the formation of 4-nitroso-SMX and 4-nitro-SMX. Measurements revealed that environmental SMX concentrations (0.2-2μg/L) at neutral pH induced the accumulation of nitric oxide. Under acidic conditions (pH<6), nitrous acid (HONO) was the major source of nitric oxide while under neutral/basic conditions nitric oxide release was related to the inhibition of denitrification processes. Under laboratory experiments, SMX nitration reaction appeared to be an irreversible transformation pathway, while 4-nitroso-SMX was slowly transformed over time. The occurrence of 4-nitroso-SMX conditions was therefore unexpected in the field study but could be due to its continuous input from soil and/or its relative persistence under anoxic conditions. A mechanism for 4-nitroso-SMX formation was proposed involving a nitrosative desamination pathway through a phenyl radical.

Keywords: Denitrification; Nitric oxide; Nitrosation; Soil; Sulfamethoxazole.