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. 2024 Aug;31(40):53447-53457.
doi: 10.1007/s11356-024-34767-9. Epub 2024 Aug 27.

Photodegradation of the phenylpyrazole insecticide ethiprole in aquatic environments and a comparison with fipronil

Soichiro Hirashima  1 , Tomoko Amimoto  2 , Yoko Iwamoto  1   3   4 , Kazuhiko Takeda  5   6   7
Affiliations

Photodegradation of the phenylpyrazole insecticide ethiprole in aquatic environments and a comparison with fipronil

Soichiro Hirashima et al. Environ Sci Pollut Res Int. 2024 Aug.

Abstract

Ethiprole (ETH) is a phenylpyrazole insecticide that is used worldwide as an alternative to fipronil (FIP). Research on the photodegradation of ETH in aquatic environments has been limited compared with that on FIP. In this study, to clarify the photodegradation of ETH in aquatic systems, the photodegradation pathway and products were investigated using liquid chromatography and liquid chromatography-tandem mass spectrometry. We also determined the photochemical half-lives (t1/2) of ETH and its main degradation products. The primary photodegradation pathway was cyclization/dechlorination and hydroxylation/dechlorination of ETH to form the didechlorinated products (benzimidazole of des-chloro-hydroxy-ETH). Some newly identified photodegradation products and analogs of FIP photodegradation products were also detected as minor products. We compared the photodegradation of ETH with that of FIP under the same conditions. Didechlorinated products of ETH and FIP had the highest photostability. However, although the photochemical t1/2 of EHT was 2.7 times that of FIP, the photochemical t1/2 of the didechlorinated product of ETH was approximately one-third that of the didechlorinated product of FIP. This comparison of the photochemical processes of ETH and FIP provides new insight into the persistence and characteristics of both insecticides in the environment.

Keywords: High-resolution mass spectrometry; LC–MS/MS; Pesticide; Photo-dechlorination products; Photostability.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
A UV chromatogram of 2.5 mg/L ETH in 2.5% aqueous MeOH irradiated under a solar simulator for 30 min. The UV detection wavelength was 280 nm
Fig. 2
Fig. 2
Main photodegradation process of ETH and chemical structures of the degradation products
Fig. 3
Fig. 3
Photodegradation pathways for ETH in aquatic environments. Paths indicated by bold arrows are main photodegradation processes
Fig. 4
Fig. 4
Temporal profiles of the main products of ETH photodegradation determined by LC (n = 3). The relative peak intensity indicates the ratio between the peak area at photodegradation time t and the initial ETH peak area (t = 0)
Fig. 5
Fig. 5
Simulations of the temporal profiles by the sequential degradation model
Fig. 6
Fig. 6
Comparison of the main photodegradation pathways between FIP and ETH. The photochemical half-lives (t1/2) under natural sunlight of FIP and ETH are also shown. The CF3 group (green) and the C2H5 group (blue) on the pyrazole ring are the specific substructures for FIP and ETH, respectively. The sulfinyl structure (SO, red) does not change in the main photodegradation pathway of ETH
See this image and copyright information in PMC

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