Identification and ecotoxicity prediction of pyrisoxazole transformation products formed in soil and water using an effective HRMS workflow

https://doi.org/10.1016/j.jhazmat.2021.127223Get rights and content

Highlight

  • An effective environmental transformation product identification workflow of pesticides was proposed.

  • Fourteen transformation products of pyrisoxazole were proposed for the first time.

  • Eight transformation products were confirmed by corresponding reference standards.

  • Soil types and oxygen conditions influenced the kinds of transformation products.

Abstract

Pyrisoxazole, an isoxazoline-class fungicide, has been registered and used for approximately 19 years. However, its environmental transformation products (TPs) and corresponding ecotoxicological effects remain ambiguous. In this study, the photolysis, hydrolysis, and soil transformation behavior of pyrisoxazole were systematically investigated by indoor simulation experiments and analyzed by liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS) and UNIFI software. Transformation products in different environemnts were effectively identfied by a proposed workflow, which organically combined suspect and non-target screening strategies. In total, 17 TPs were screened out. Eight TPs were confirmed using the corresponding reference standards. Structures of another 9 compounds were tentatively proposed based on diagnostic evidence. Among them, 14 products were reported for the first time. The transformation pathways of pyrisoxazole in soil and water were proposed. Pathway analysis demonstrated that the different pH of aqueous solutions had little effect on the pathways, while the influence of different soil types and oxygen conditions was evident. Finally, the toxicity of the proposed TPs to fish and daphnids was predicted using ECOSAR software. These proposed TPs in soil and water, transformation pathways, and predicted ecotoxicity information could provide systematic insight into the fate and environmental risks of pyrisoxazole.

Introduction

Pesticides have been widely used to protect crops against pests, pathogens, and weeds, thereby increasing crop yields (Oerke and Dehne, 2004, Sparks et al., 2017). However, once applied, environmental residues of this large group of xenobiotic compounds and their transformation products (TPs) may pose a potential threat to non-targeted organisms and the environment (Cerrillo et al., 2005b, Ellgehausen et al., 1980, Franke et al., 1994, Jr, 1992; Kannan et al., 1994; Khan, 1997). Thus, every new pesticide plan on the market must undergo an environmental risk assessment (ERA) procedure based on a large set of data submitted by pesticide manufacturers and evaluated by the official authorities. Unfortunately, during the ERA procedure, the assessment of environmental TPs is usually not as thorough as that of parent compounds, such that several pesticides are registered and used, while our knowledge about their ecotoxicologically relevant TPs typically emerges 20–30 years later (Fenner et al., 2013a, Fenner et al., 2013b, Ji et al., 2020). Furthermore, it has been reported that some TPs have been detected more frequently than their corresponding parent compounds (Berton et al., 2014, Cerrillo et al., 2005a, Hernández et al., 2008b), and some other TPs could have a greater negative impact on the ecosystem than their parent compounds because of their higher environmental mobility, persistence, and toxicity (Lu et al., 2015, Sinclair and Boxall, 2003, Zhang et al., 2016). Thus, it is imperative to enhance the study of environmental TPs of pesticides to make the ERA process more comprehensive and accurate.

Pyrisoxazole,(3-[5-(4-Chlorophenyl)−2,3-dimethyl-3-isoxazolidinyl]-pyridine), also known as SYP-Z048, is a new member of the isoxazolidine-class fungicides developed by the Shenyang Research Institute of Chemical Industry (Shenyang. PR China). It has been defined by the Fungicide Resistance Action Committee as an inhibitor of fungal ergosterol biosynthesis (FRAC, 2015) and shows high efficacy against a broad range of fungal diseases caused by Ascomycetes, Basidiomycetes, and Deuteromycetes in fruits and vegetables (Liu et al., 2004, Si et al., 2004). Pyrisoxazole has been registered and approved for use in China since 2002 and has been patented in Japan, the United States, and the European Union (Liu, 2008). However, although this pesticide has been registered for some time and the scope of registration is being further expanded, there are only a few studies on its environmental fate and risks. For example, Pyrisoxazole showed an acute toxicity risk to the non-target organism D. semiclausum (An et al., 2017) and moderate bioaccumulation in zebrafish (Zhu, 2016). In addition, some researchers reported the dissipation rate of pyrisoxazole in vegetables (2.4–8.4 d), fruits (7.4–10.3 d), and soils (8.2–100.4 d) from the perspective of enantiomers or diastereomers (Pan et al., 2016; Qi et al., 2016; Yang et al., 2017). Thus far, studies on the environmental behavior of pyrisoxazole have focused on the parent compound, while research on its environmental transformation fate is scarce. To date, only one study has investigated pyrisoxazole TPs formed by photolysis using high-performance liquid chromatography/mass spectrometry (HPLC-MS) and nuclear magnetic resonance (NMR) (Liu et al., 2012).

High-resolution mass spectrometry (HRMS) has become a prominent platform for the detection and structural elucidation of pesticide environmental TPs (Botitsi et al., 2011, Hernández et al., 2008a). The current research methodology for TP identification using HRMS could generally be classified into three types: “target screening,” “suspect screening,” and “non-target screening” (Schymanski et al., 2015). (1) Target screening is conducted by the in-house measurement of corresponding reference standards under the same analytical conditions. The retention time and fragmentation spectra of the targeted compounds are compared with those of the standard. Target screening is the most confirmative method; however, its application is often limited owing to the lack of reference standards. (2) Suspect screening is performed to identify known unknowns. Possible TPs could be collected from literature review, chemical databases, or in silico transformation prediction (Seema et al., 2014, Wickert et al., 2016, Latino et al., 2017, Sivakumar et al., 2017, Pan et al., 2018). Once the prior information is available, the accurate m/z ions calculated by adding or subtracting the expected adduct (s) according to the molecular formula can be used to screen the suspect substance in the sample. Suspect screening is highly effective and time-saving, but TPs not in the suspect list are easily omitted. (3) Non-target screening is conducted to identify the unknown unknowns. Because no prior information is available in advance, the non-target screening type is usually operated through filtering out the chromatographic peaks of interest, and then elucidate them into possible structures according to their mass spectrum information (Liu et al., 2012, Gonzalez-Marino et al., 2018). Non-target screening is the most comprehensive approach, but it is also a time-intensive process. A complementary combination of suspect and non-target screening is now an effective way to identify the TPs of pesticides in the environmental matrix (Beretsou et al., 2016).

The present study aims to contribute to the existing knowledge on the fate of environmental transformation and the corresponding risk of pyrisoxazole after its application. For this purpose, indoor simulated batch experiments were conducted, including photolysis, hydrolysis in different pH buffers, and soil transformation under aerobic and anaerobic conditions. The experimental samples were detected by liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS). First, the transformation kinetics of pyrisoxazole under different environmental conditions were investigated. Subsequently, an effective HRMS workflow, using both suspect and non-target screening strategies, was used to identify the TPs formed. Finally, the ecotoxicities of the proposed TPs were evaluated using ECOSAR software.

Section snippets

Chemicals and reagents

Pyrisoxazole (99.3% purity) was obtained from the Shenyang Research Institute of Chemical Industry. Chromatography-grade acetonitrile was purchased from Sigma-Aldrich (Steinheim, Germany). Analytical grade sodium chloride (NaCl), potassium chloride (KCl), sodium hydroxide (NaOH), anhydrous magnesium sulfate (MgSO4), potassium acid phthalate (C8H5NaO), monopotassium phosphate (KH2PO4), boric acid, and formic acid were purchased from Beijing Chemical Company (Beijing, China). Analytical grade

Soil transformation

The transformation behavior of pyrisoxazole varied significantly with different soil types and oxygen conditions. The transformation kinetics of pyrisoxazole in the five types of soils follow first-order kinetics (Section S4, Fig. S3). The half-lives of pyrisoxazole in red, black, paddy, fluvo-aquic, and cinnamon soils were 346.0, 48.7, 19.8, 15.9, and 21.7 d under aerobic conditions, and 246.1,25.2,7.8,6.8 d and 26.8 d under anaerobic conditions, respectively. In our study, we found that the

Conclusions

In this study, we systematically investigated the transformation kinetics and products of pyrisoxazole in different environments and evaluated their ecotoxicity. Pyrisoxazole is prone to degradation under anaerobic and alkaline conditions and is difficult to degrade in soils with low pH, organic matter content and high clay content. The proposed workflow for the identification and confirmation of TPs proved to be an effective tool. In total, 17 TPs were tentatively identified, 8 of which were

CRediT authorship contribution statement

Bin Jiao: Conceptualization, Methodology, Formal analysis, Writing – original draft, Preparation. Yuxiao Zhu: Formal analysis. Jun Xu: Resources, Writing – review & editing, Supervision, Funding acquisition. Fengshou Dong: Writing – review & editing. Xiaohu Wu: Supervision. Xingang Liu: Supervision, Yongquan Zheng: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (32072467).

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