Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides

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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 languageEnglish (US)
Pages (from-to)12336-12346
Number of pages11
JournalEnvironmental Science and Technology
Volume56
Issue number17
DOIs
StatePublished - Sep 6 2022

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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