Sulfate radical-based oxidation of the aminopyralid and picloram herbicides: The role of amino group on pyridine ring

Controllable Pyridine N-Oxidation-Nucleophilic Dechlorination Process for Enhanced Dechlorination of Chloropyridines: The Cooperation of HCO4- and HO2. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024;58:4438-4449. [PMID: 38330552 DOI: 10.1021/acs.est.3c09878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Dechlorination of chloropyridines can eliminate their detrimental environmental effects. However, traditional dechlorination technology cannot efficiently break the C-Cl bond of chloropyridines, which is restricted by the uncontrollable nonselective species. Hence, we propose the carbonate species-activated hydrogen peroxide (carbonate species/H2O2) process wherein the selective oxidant (peroxymonocarbonate ion, HCO4-) and selective reductant (hydroperoxide anion, HO2-) controllably coexist by manipulation of reaction pH. Taking 2-chloropyridine (Cl-Py) as an example, HCO4- first induces Cl-Py into pyridine N-oxidation intermediates, which then suffer from the nucleophilic dechlorination by HO2-. The obtained dechlorination efficiencies in the carbonate species/H2O2 process (32.5-84.5%) based on the cooperation of HCO4- and HO2- are significantly higher than those in the HO2--mediated sodium hydroxide/hydrogen peroxide process (0-43.8%). Theoretical calculations confirm that pyridine N-oxidation of Cl-Py can effectively lower the energy barrier of the dechlorination process. Moreover, the carbonate species/H2O2 process exhibits superior anti-interference performance and low electric energy consumption. Furthermore, Cl-Py is completely detoxified via the carbonate species/H2O2 process. More importantly, the carbonate species/H2O2 process is applicable for efficient dehalogenation of halogenated pyridines and pyrazines. This work offers a simple and useful strategy to enhance the dehalogenation efficiency of halogenated organics and sheds new insights into the application of the carbonate species/H2O2 process in practical environmental remediation.

The simultaneous degradation of prochloraz and tebuconazole in water with monitoring their degradation products using liquid chromatography-tandem mass spectrometry

Prochloraz and tebuconazole are well-known fungicides for broad applications, including medical, industrial, and agricultural. They are frequently used simultaneously which increases the probability of their co-existing in various water sources. In this study, the analysis of PCZ or TBZ in water was performed by a direct analysis using the liquid chromatography-tandem mass spectrometry technique (LC-MS/MS). The optimized method was fully validated according to the European guidelines, SANTE/11312/2021. The complete degradation of these fungicides (each of 2 mg/L) in their single presence in the water was accomplished just after 15 min using 4.2 mM persulfate at 50 °C, while a lower concentration of persulfate (1.4 mM) leads to a degradation of prochloraz and tebuconazole, in their single existence in water, at percentages of 97 % and 98 %, respectively, after 30 min at 50 °C. On the other hand, it takes a complete hour to degrade a mixture of prochloraz and tebuconazole at percentages of 99 % and 94 %, respectively, using 1.4 mM persulfate at 50 °C. Degradation products (DPds) of prochloraz and tebuconazole, either in their single or simultaneous existing in water, were also identified and monitored during the whole degradation process by LC-MS/MS using at least two mass transitions for each DPd at both positive and negative ionization modes. It was elucidated that the persulfate degradation of prochloraz was conducted by the cleavage of the imidazole ring and the subsequent formation of a trichlorophenol, while persulfate degradation of tebuconazole was mainly accomplished by the formation of a hydroxyl structure, cleavage of the tert-butyl chain, and the subsequent formation of a ketone structure. Furthermore, a new DPd of tebuconazole (m/z = 263 Da) with a diketone structure was identified and confirmed.

Formation of brominated by-products during the degradation of tetrabromobisphenol S by Co2+/peroxymonosulfate oxidation

Tetrabromobisphenol S (TBBPS), an emerging brominated flame retardant, can cause neurotoxic and cytotoxic effects to human physiology. In this study, the degradation of TBBPS in Co²⁺ activated peroxymonosulfate (PMS) oxidation process was explored. In particular, brominated by-products formed during the degradation of the TBBPS were examined. It was found that TBBPS could be effectively removed in the Co²⁺/PMS oxidation process. The pseudo-first-order rate constants were 0.13 min^-1 at 0.2 mM PMS and 0.5 μM Co²⁺ initially. It appeared that TBBPS degradation occurred via and HO attacks, but played a dominant role. The presence of natural organic matter (NOM) greatly inhibited the transformation of the TBBPS, which can be explained by the scavenging of the radical species. β-Scission, debromination, and cross-coupling were identified as the main reaction pathways of TBBPS degradation in the Co²⁺/PMS system. Further oxidation and ring-opening of the intermediates generated brominated by-products including bromoform, monobromoacetic acid, and dibromoacetic acid. The formation of the brominated by-products increased gradually in approximately 48 h. But, the presence of NOM reduced the yields of the brominated -by-products. The findings of this study indicate that organic bromine contaminants can be effectively removed but lead to brominated by-products in the activated PMS oxidation process, which should be taken into consideration when -based oxidation technology is applied.

Accelerated oxidation of the emerging brominated flame retardant tetrabromobisphenol S by unactivated peroxymonosulfate: The role of bromine catalysis and formation of disinfection byproducts

Tetrabromobisphenol S (TBBPS) is an emerging brominated flame retardant (BFR) that can cause endocrinological abnormalities in aquatic species and is neurotoxic and cytotoxic to humans. Herein, we investigated the oxidation of TBBPS by unactivated peroxymonosulfate (PMS) in aqueous solution. Results show that PMS was capable of oxidizing TBBPS without activation, and the transformation of TBBPS was pH-dependent. Interestingly, the unactivated PMS oxidation of TBBPS exhibited an autocatalytic behavior. Radical quenching experiments and electron paramagnetic resonance (EPR) analyzes ruled out the involvement of hydroxyl radical (HO•) and sulfate radical (SO₄^•‑) as reactive species. While the generation of singlet oxygen (¹O₂₎ was confirmed in PMS solution, it was also not responsible for TBBPS oxidation. The bromine substituents are believed to be responsible for the autocatalysis observed during PMS oxidation. We propose that the initial oxidation of TBBPS by PMS resulted in the release of bromide ions (Br^-) via debromination, which could be rapidly oxidized to hypobromous acid (HOBr). 3,5-Dimethyl-1H-pyrazole (DMPZ) trapping coupled with liquid chromatography-mass spectrometry (LC-MS) analysis evidenced the formation of HOBr in PMS/TBBPS system. Therefore, the presence of Br^-, albeit at trace level, could significantly accelerate the oxidation of TBBPS in PMS solution via HOBr formation. The intermediate products of TBBPS were identified by solid phase extraction (SPE) coupled with high resolution-mass spectrometry (HR-MS). The oxidation of TBBPS by unactivated PMS was likely initiated through a single electron transfer mechanism, and the transformation pathways included β-scission, debromination, and cross-coupling reactions. Further oxidation and ring-opening of the intermediates yielded three brominated disinfection byproducts (Br-DBPs), including bromoform (CHBr₃), mono-, and di-bromoacetic acids (MBAA and DBAA), as quantified by gas chromatography (GC). The presence of natural organic matter (NOM) inhibited the oxidation of TBBPS and reduced the yields of Br-DBPs. Our results indicate that unactivated PMS was efficient in the abatement of TBBPS in aqueous solution due to the accelerated oxidation by bromine catalysis; however, the formation of brominated intermediate products and Br-DBPs should be scrutinized due to their potential carcinogenicity and mutagenicity.