Formation of Nitrophenolic Byproducts during Heat-Activated Peroxydisulfate Oxidation in the Presence of Natural Organic Matter and Nitrite

Abstract

Sulfate radical (SO4 •–)-based advanced oxidation is a viable in situ remediation technology for degrading organic contaminants in the subsurface. In this study, we demonstrated that SO4 •– could induce the activation of nitrite, an anion commonly present in the subsurface environment, leading to the formation of nitrophenolic byproducts. Fourier-transform infrared spectroscope and 15N nuclear magnetic resonance analysis revealed that the inorganic nitrite was incorporated into natural organic matter (NOM) to form organic nitrogen upon SO4 •– oxidation. Nitrophenolic byproducts, including 2-hydroxy-5-nitrobenzoic acid, 4-nitrophenol, and 2,4-dinitrophenol, were identified using high-resolution mass spectrometry in combination with a 15N labeling technique. Formation of nitrated byproducts was ascribed to the scavenging of SO4 •– by nitrite, which not only generated the nitrating agent NO2 • but also inhibited the degradation of organic compounds, making them more available to the reactions with NO2 •. The phenolic moieties in NOM served as the main reactive sites for NO2 • attack. The nitration begins with H abstraction on the phenoxy oxygen, followed by the addition of another NO2 • to its ortho or para site. Decarboxylation followed by NO2 • addition can also generate nitrophenolic byproducts. To the best of our knowledge, this is the first study reporting the nitration of NOM and formation of toxic nitrophenolic byproducts during SO4 •–-based oxidation. It sheds light on the potential risks of this technology in subsurface remediation practices.

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

“…The occurrence of nitrate and nitrite in water and wastewater opens up the additional possibility for nitroaromatic compounds to be formed also in the framework of photochemical processes for water treatment, where radiation is often provided by UV lamps and where the aromatic substrates may occur either as contaminants, or as components of the natural organic matter. In some cases, nitrite may even occur together with strong oxidising agents intended for pollutant degradation, yielding nitroderivatives upon oxidation to • NO 2 [ 72 , 73 , 74 , 75 ].…”

Comparative Study for Interactions of Sulfate Radical and Hydroxyl Radical with Phenol in the Presence of Nitrite

“…•−based AOP with NO 2 − : (1) nitration of phenol or 4hydroxybenzoic acid can be directly initiated by • NO 2 through hydrogen abstraction to form phenoxy radicals, which further react with another • NO 2 to generate nitro compounds; 23,24 and (2) chlorophenols are first attacked by SO 4…”

“…Previous studies have reported that nitrophenolic byproducts are significantly generated during phenolic compound degradation by thermally activated PDS oxidation in the presence of NO 2 – . − The following two pathways of nitro compound formation have been proposed during the SO 4 •– -based AOP with NO 2 – : (1) nitration of phenol or 4-hydroxybenzoic acid can be directly initiated by • NO 2 through hydrogen abstraction to form phenoxy radicals, which further react with another • NO 2 to generate nitro compounds; , and (2) chlorophenols are first attacked by SO 4 •– to form phenoxy radicals, which then combine with • NO 2 to form chloronitrophenols . However, both pathways are speculated and lack direct experimental evidence.…”

UV light irradiation combined with nitrate for degradation of bisphenol A: kinetics, transformation pathways, and acute toxicity assessment

“…In light of the reports in the literature that nitrogen-containing by-products are toxic and carcinogenic to humans, 65,66 the change regularity in the acute toxicity of BPA in the UV/NO 3 − process was investigated (Fig. 11).…”