Wavelength-Dependent UV-LED Photolysis of Fluorinated Pesticides and Pharmaceuticals

Abstract

The wavelength dependence of photoproduct formation and quantum yields was evaluated for fluorinated pesticides and pharmaceuticals using UV-light emitting diodes (LEDs) with 255, 275, 308, 365, and 405 nm peak wavelengths. The fluorinated compounds chosen were saflufenacil, penoxsulam, sulfoxaflor, fluoxetine, 4-nitro-3-trifluoromethylphenol (TFM), florasulam, voriconazole, and favipiravir, covering key fluorine motifs (benzylic-CF 3 , heteroaromatic-CF 3 , aryl-F, and heteroaromatic-F). Quantum yields for the compounds were consistently higher for UV-C as compared to UV-A wavelengths and did not show the same trend as molar absorptivity. For all compounds except favipiravir and TFM, the fastest degradation was observed using 255 or 275 nm light, despite the low power of the LEDs. Using quantitative 19 F NMR, fluoride, trifluoroacetate, and additional fluorinated byproducts were tracked and quantified. Trifluoroacetate was observed for both Ar-CF 3 and Het-CF 3 motifs and increased at longer wavelengths for Het-CF 3 . Fluoride formation from Het-CF 3 was significantly lower as compared to other motifs. Ar−F and Het-F motifs readily formed fluoride at all wavelengths. For Het-CF 3 and some Ar-CF 3 motifs, 365 nm light produced either a greater number of or different major products. Aliphatic-CF 2 /CF 3 products were stable under all wavelengths. These results assist in selecting the most efficient wavelengths for UV-LED degradation and informing future design of fluorinated compounds.

Fluorinated Pharmaceutical and Pesticide Photolysis: Investigating Reactivity and Identifying Fluorinated Products by Combining Computational Chemistry,19F NMR, and Mass Spectrometry

“…Additional compounds chosen for parent compound 19 F NMR computations were hexafluorobenzene (HFB), trifluoroacetic acid (TFA), favipiravir, 2-fluorophenol (2-FP), 3-FP, 4-FP, 2,6-difluorophenol (2,6-DFP), 3,5-DFP, enrofloxacin, celecoxib, sitagliptin, broflanilide, flucarbazone, and trifluralin. Except for saflufenacil, celecoxib, and sitagliptin, all experimental shifts were obtained from previous studies. − , Sources and purities of all the chemicals used in this study are given in the Supporting Information (SI).…”

“…For example, several of the fluorinated functional groups in pesticides and pharmaceuticals remain intact during photolysis and oxidative treatment processes, forming multiple fluorinated persistent byproducts that could be long-lived in surface and drinking waters . More than 100 different fluorinated photoproducts have been identified from fluorinated pesticides and pharmaceuticals in sunlit surface waters or during photolysis-based degradation processes. − Photoproducts may arise from small structural changes with the parent compound retaining the fluorinated motif. More extensive degradation leads to formation of smaller compounds like trifluoracetic acid (TFA) or fluoride (defluorination) .…”

“…The most common method used for identification of fluorinated degradation products of pesticides and pharmaceuticals is liquid chromatography with nontargeted high resolution mass spectrometry (LC-HRMS) . It was reported that using only LC-HRMS to quantify fluorinated compounds can result in fluorine mass balances falling short, with up to 90% of fluorine being unaccounted for. − Recent studies on fluorinated product formation and identification during photolysis and advanced treatment processes have reported more complete product identification by complementing LC-HRMS with quantitative 19 F-nuclear magnetic resonance spectroscopy (NMR) analysis. − ,, An NMR spectrum contains all fluorinated product peaks, and the chemical shifts provide insight into the identity of the functional group and its chemical environment. With the broad range of fluorine NMR shifts (∼400 ppm) and the 100% abundance of 19 F isotope of fluorine in the environment, 19 F NMR has been reported to be a highly suitable method to detect fluorinated compounds and products .…”

“…Experimental studies have shown differences in the extent of defluorination from different fluorine motifs . While Aryl or Het-F groups are generally not a concern with respect to stable fluorinated byproducts via photolysis, CF 3 groups have been shown to form TFA along with persistent products retaining the CF 3 groups. − Previous studies on photolysis have reported that Het-CF 3 and Aliphatic-CF 2/3 motifs are retained in the product structures. ,− An increased application of heteroaromatic fluorine motifs in compounds due to their improved metabolic stability coupled with the environmental stability (and retention) of Het-CF 3 motifs in surface waters, drinking waters, and wastewaters upon photolysis and advanced treatment conditions could ultimately lead to an unparalleled increase in persistent and stable fluorinated byproducts in the environment. , …”

Modification of Crystal-Optimized TiO2 with Biomass-Derived Carbon Quantum Dots for Highly Efficient Degradation of Favipiravir in Water

“…Its multiple mutant strains spread rapidly, and thus far, the number of infected people worldwide has exceeded 550 million . Antiviral drugs, such as remdesivir, favipiravir, oseltamivir, and chloroquine, which have been approved for use by the Food and Drug Administration, are the most commonly recommended effective treatments for COVID-19. , Among them, favipiravir, an emerging environmental water pollutant, has a half-life of only 2.5–5 h in the human body, and the unabsorbed drug is promptly excreted by the kidney . It is highly resistant to biodegradation, and several studies have shown that typical wastewater treatment can only eliminate 20% of favipiravir and its metabolites .…”