4.8 Article

Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides

Journal

ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 56, Issue 17, Pages 12336-12346

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.est.2c04242

Keywords

photolysis; fluorine; F-19-NMR; pesticides; fluorine motifs; advanced oxidation processes; river water

Funding

  1. Minnesota Environment and Natural Resources Trust Fund
  2. University of Minnesota College of Science and Engineering
  3. Joseph T. and Rose S. Ling Professorship
  4. Office of the Vice President for Research
  5. College of Biological Science
  6. NIH
  7. NSF
  8. Minnesota Medical Foundation
  9. Medical School

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This study evaluated the formation of fluorinated products in the photolysis of pesticides with different fluorine motifs. The results showed that the formation of fluoride varied among different pesticides and under different treatment processes. The structure of fluorine motifs also influenced the generation of products.
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 x 10(10) M-1 s(-1) and, with sulfate radicals, 1.6 to 2.6 x 10(8) M-1 s(-1) for penoxsulam, florasulam, and fluroxypyr, respectively. The rate constants of sulfoxaflor were 100-fold lower. Using quantitative F-19-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 CF3 and aliphatic CF2 groups were retained in multiple fluorinated photoproducts. Aryl F and heteroaromatic F groups were readily defluorinated to fluoride. CF3 and CF2 groups formed trifluoroacetate and difluoroacetate, and yields increased under oxidizing conditions. F-19-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 F-19-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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