Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides

Akash P. Bhat; William C.K. Pomerantz; William A. Arnold

doi:10.1021/acs.est.2c04242

Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides

Akash P. Bhat, William C.K. Pomerantz, William A. Arnold

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Abstract

The photolysis of pesticides with different fluorine motifs was evaluated to quantify the formation of fluorinated products in buffered aqueous systems, advanced oxidation (AOP) and reduction processes (ARP), and river water. Simulated sunlight quantum yields at pH 7 were 0.0033, 0.0025, 0.0015, and 0.00012 for penoxsulam, florasulam, sulfoxaflor, and fluroxypyr, respectively. The bimolecular rate constants with hydroxyl radicals were 2 to 5.7 × 10¹⁰M^-1s^-1and, with sulfate radicals, 1.6 to 2.6 × 10⁸M^-1s^-1for penoxsulam, florasulam, and fluroxypyr, respectively. The rate constants of sulfoxaflor were 100-fold lower. Using quantitative ¹⁹F-NMR, complete fluorine mass balances were obtained. The maximum fluoride formation was 53.4 and 87.4% for penoxsulam and florasulam under ARP conditions, and 6.1 and 100% for sulfoxaflor and fluroxypyr under AOP conditions. Heteroaromatic CF₃and aliphatic CF₂groups were retained in multiple fluorinated photoproducts. Aryl F and heteroaromatic F groups were readily defluorinated to fluoride. CF₃and CF₂groups formed trifluoroacetate and difluoroacetate, and yields increased under oxidizing conditions. ¹⁹F-NMR chemical shifts and coupling analysis provided information on hydrogen loss on adjacent bonds or changes in chirality. Mass spectrometry results were consistent with the observed ¹⁹F-NMR products. These results will assist in selecting treatment processes for specific fluorine motifs and in the design of agrochemicals to reduce byproduct formation.

Original language	English (US)
Pages (from-to)	12336-12346
Number of pages	11
Journal	Environmental Science and Technology
Volume	56
Issue number	17
DOIs	https://doi.org/10.1021/acs.est.2c04242
State	Published - Sep 6 2022
Externally published	Yes

Bibliographical note

Funding Information:
Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative Citizen Commission on Minnesota Resources (LCCMR), a graduate fellowship to A.B. from the University of Minnesota College of Science and Engineering, and the Joseph T. and Rose S. Ling Professorship. Thanks to Thomas Mundhenke and Jiaqian Li for help with the NMR. We thank the Minnesota NMR Center for access to instrumentation. Funding for NMR instrumentation was provided by the Office of the Vice President for Research, the Medical School, the College of Biological Science, NIH, NSF, and the Minnesota Medical Foundation. Thanks to Peter Villalta, Yingchun Zhao, and Jingfang Huang at the Analytical Biochemistry Mass Spectrometry Services Shared Resource at the Masonic Cancer Center, University of Minnesota for help with LC–MS/MS instrumentation.

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

Keywords

F-NMR
advanced oxidation processes
fluorine
fluorine motifs
pesticides
photolysis
river water

PubMed: MeSH publication types

Journal Article
Research Support, Non-U.S. Gov't

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abstract = "The photolysis of pesticides with different fluorine motifs was evaluated to quantify the formation of fluorinated products in buffered aqueous systems, advanced oxidation (AOP) and reduction processes (ARP), and river water. Simulated sunlight quantum yields at pH 7 were 0.0033, 0.0025, 0.0015, and 0.00012 for penoxsulam, florasulam, sulfoxaflor, and fluroxypyr, respectively. The bimolecular rate constants with hydroxyl radicals were 2 to 5.7 × 1010M-1s-1and, with sulfate radicals, 1.6 to 2.6 × 108M-1s-1for penoxsulam, florasulam, and fluroxypyr, respectively. The rate constants of sulfoxaflor were 100-fold lower. Using quantitative 19F-NMR, complete fluorine mass balances were obtained. The maximum fluoride formation was 53.4 and 87.4% for penoxsulam and florasulam under ARP conditions, and 6.1 and 100% for sulfoxaflor and fluroxypyr under AOP conditions. Heteroaromatic CF3and aliphatic CF2groups were retained in multiple fluorinated photoproducts. Aryl F and heteroaromatic F groups were readily defluorinated to fluoride. CF3and CF2groups formed trifluoroacetate and difluoroacetate, and yields increased under oxidizing conditions. 19F-NMR chemical shifts and coupling analysis provided information on hydrogen loss on adjacent bonds or changes in chirality. Mass spectrometry results were consistent with the observed 19F-NMR products. These results will assist in selecting treatment processes for specific fluorine motifs and in the design of agrochemicals to reduce byproduct formation.",

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author = "Bhat, {Akash P.} and Pomerantz, {William C.K.} and Arnold, {William A.}",

note = "Funding Information: Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative Citizen Commission on Minnesota Resources (LCCMR), a graduate fellowship to A.B. from the University of Minnesota College of Science and Engineering, and the Joseph T. and Rose S. Ling Professorship. Thanks to Thomas Mundhenke and Jiaqian Li for help with the NMR. We thank the Minnesota NMR Center for access to instrumentation. Funding for NMR instrumentation was provided by the Office of the Vice President for Research, the Medical School, the College of Biological Science, NIH, NSF, and the Minnesota Medical Foundation. Thanks to Peter Villalta, Yingchun Zhao, and Jingfang Huang at the Analytical Biochemistry Mass Spectrometry Services Shared Resource at the Masonic Cancer Center, University of Minnesota for help with LC–MS/MS instrumentation. Publisher Copyright: {\textcopyright} 2022 American Chemical Society. All rights reserved.",

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AB - The photolysis of pesticides with different fluorine motifs was evaluated to quantify the formation of fluorinated products in buffered aqueous systems, advanced oxidation (AOP) and reduction processes (ARP), and river water. Simulated sunlight quantum yields at pH 7 were 0.0033, 0.0025, 0.0015, and 0.00012 for penoxsulam, florasulam, sulfoxaflor, and fluroxypyr, respectively. The bimolecular rate constants with hydroxyl radicals were 2 to 5.7 × 1010M-1s-1and, with sulfate radicals, 1.6 to 2.6 × 108M-1s-1for penoxsulam, florasulam, and fluroxypyr, respectively. The rate constants of sulfoxaflor were 100-fold lower. Using quantitative 19F-NMR, complete fluorine mass balances were obtained. The maximum fluoride formation was 53.4 and 87.4% for penoxsulam and florasulam under ARP conditions, and 6.1 and 100% for sulfoxaflor and fluroxypyr under AOP conditions. Heteroaromatic CF3and aliphatic CF2groups were retained in multiple fluorinated photoproducts. Aryl F and heteroaromatic F groups were readily defluorinated to fluoride. CF3and CF2groups formed trifluoroacetate and difluoroacetate, and yields increased under oxidizing conditions. 19F-NMR chemical shifts and coupling analysis provided information on hydrogen loss on adjacent bonds or changes in chirality. Mass spectrometry results were consistent with the observed 19F-NMR products. These results will assist in selecting treatment processes for specific fluorine motifs and in the design of agrochemicals to reduce byproduct formation.

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Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides

Abstract

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Keywords

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