Trace level nitrite sensitized photolysis of the antimicrobial agents parachlormetaxylenol and chlorophene in water

Abstract

Nitrite (NO 2− )-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 NO 2 − still remain largely unknown. Herein, we report that NO 2 − -sensitized photolysis of the antimicrobial agents parachlormetaxylenol (PCMX) and chlorophene (CP) in aqueous solution under ultraviolet 365 nm (UV 365 ) radiation. A nonlinear increase in photolysis rate constants of PCMX and CP was observed with increasing NO 2 − concentration. Radical quenching studies and kinetic modeling revealed that hydroxyl radical (HO •) and nitrogen dioxide radicals (NO 2• ) 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 ( 15 NO 2 − ) 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 NO 2 − -sensitized photolysis of PCMX and CP are elucidated. Deoxygenation partially inhibited the formation of 4-chloro-3,5dimethyl-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 NO 2 − -rich wastewater effluents or effluent-impacted surface waters under solar radiation.

Reactive Nitrogen Species Mediated Inactivation of Pathogenic Microorganisms during UVA Photolysis of Nitrite at Surface Water Levels

“…However, the signal of HO • in the EPR spectrum was rather weak (Figure S6), likely because the concentration of HO • was low under the experimental conditions. Nonetheless, the result was consistent with previous reports that ROS was not the dominant species for pollutant degradation in the UV 365 /NO 2 – process. , RNS was anticipated to be the dominant species contributing to the microorganism inactivation. It should be noted that the robust methods for identifying RNS (e.g., NO 2 • and ONOOH/ONOO – ) using EPR are currently unavailable .…”

“…The second-order rate constant of NOM toward NO 2 • and ONOO – /HOONO are unavailable in the literature, while the value of NOM toward HO • is well known (2.5 × 10 4 (mg/L) −1 s –1 ) . Previous reports also suggested that RNS is more selective than HO • toward organic compounds. , Since NO 2 • and ONOO – /HOONO contributed more than HO • to the bacterial inactivation by UV 365 photolysis of NO 2 – , this process (UV 365 /NO 2 – ) might be less affected by NOM compared to the processes in which HO • is dominating.…”

“…Nonetheless, the result was consistent with previous reports that ROS was not the dominant species for pollutant degradation in the UV 365 / NO 2 − process. 15,16 RNS was anticipated to be the dominant species contributing to the microorganism inactivation. It should be noted that the robust methods for identifying RNS (e.g., NO 2…”

“…Apart from ROS and RCS, reactive nitrogen species (RNS, e.g., nitrogen oxide radical (NO • ), nitrogen dioxide radical (NO 2 • ), peroxynitrite (ONOO – ), and amino radical (NH 2 • )) are another group of reactive species that can be generated during water and wastewater treatment. For example, RNS has been reported to be generated from UV or solar photolysis of nitrate (NO 3 – ), nitrite (NO 2 – ), monochloramine, dichloramine, and in other AOPs in the presence of NO 3 – or NO 2 – . − The role of RNS in organic pollutant degradation has been reported by a few previous studies. − These studies demonstrated that RNS is more selective than the ROS in organic pollutant degradation and plays a critical role in pollutant transformation (e.g., formation of nitrated products) in the natural and engineered aquatic systems. − Previous studies elucidated redox properties and selectivity of RNS toward organic pollutant degradation, but the role of RNS in microorganism inactivation remains unexplored and unclear.…”

“…19 Previous reports also suggested that RNS is more selective than HO • toward organic compounds. 16,43 Since NO 2…”