Trace level nitrite sensitized photolysis of the antimicrobial agents parachlormetaxylenol and chlorophene in water
Résumé
Nitrite (NO2−)-sensitized photolysis plays an important role in the attenuation of effluent-derived trace organic contaminants (e.g., anilines, phenolic compounds, etc.) in surface waters. However, the kinetics, mechanisms, and influencing factors of photolysis of many emerging contaminants sensitized by NO2− still remain largely unknown. Herein, we report that NO2−-sensitized photolysis of the antimicrobial agents parachlormetaxylenol (PCMX) and chlorophene (CP) in aqueous solution under ultraviolet 365 nm (UV365) radiation. A nonlinear increase in photolysis rate constants of PCMX and CP was observed with increasing NO2− concentration. Radical quenching studies and kinetic modeling revealed that hydroxyl radical (HO•) and nitrogen dioxide radicals (NO2•) contributed dominantly to the removal of PCMX and CP. Solid phase extraction (SPE) combined with high resolution-mass spectrometry (HR-MS) analysis identified a series of intermediate products including hydroxylated, nitrated, nitrosated, and dimerized derivatives. Experiments with isotopically labelled nitrite (15NO2−) showed that the nitro- and nitroso-substituents of intermediate products were derived from the nitrite nitrogen. Based on the identified products and theoretical computations, the mechanisms and pathways of NO2−-sensitized photolysis of PCMX and CP are elucidated. Deoxygenation partially inhibited the formation of 4-chloro-3,5-dimethyl-2-nitrophenol (nitro-PCMX) while the presence of HO• scavenger such as isopropanol (i-PrOH) suppressed the further transformation of nitro-PCMX. The presence of Mississippi River natural organic matter (MRNOM) inhibited the removal of PCMX and CP, likely due to light screening and radical quenching. However, appreciable degradation of PCMX and CP was still observed in wastewater and wetland water matrices. Results of this study shed some light on the transformation and fate of PCMX and CP in NO2−-rich wastewater effluents or effluent-impacted surface waters under solar radiation.
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