Pesticides have an indispensable position in agricultural production and can improve the productivity and profitability of agricultural products (Yao et al., 2021). As a highly effective phenylpyrazole insecticide, fipronil (CAS Number 120068-37-3) was invented by May and Baker in 1987 and entered the Chinese market in 1993 (Li et al., 2014; Liu et al., 2008), and can be used to control a wide range of pests, such as leaf-cutting ant, fire ant, and Spodoptera litura (Mota et al., 2021; Hano et al., 2019; Jameel et al., 2019). Fipronil is known to target the gamma amino butyric acid (GABA) receptor, thereby blocking the chloride channels in the neurons of the central nervous system (CNS), which leads to excessive neuronal stimulation and, eventually, the death of the pests (Kumar et al., 2012; Li et al., 2007; Ikeda et al., 2004).
Due to the broad spectrum and high efficiency, fipronil has increased in popularity during the past few decades (Regan et al., 2017; Mandal et al., 2013). However, the environmental impact of fipronil has always received great attention because of its strong toxicity to some non-target organisms (Kasai et al., 2016; Morrissey et al., 2015; Pisa et al., 2015). Previous studies have reported that fipronil can significantly change the physiological and biochemical characteristics of fishes (Clasen et al., 2012; Hayasaka et al., 2012). Although the European Union has banned the use of fipronil in crops, it is still often used in crops such as sugarcane and citrus in some countries (Farder-Gomes et al., 2021). A recent study has shown that more than 480 million bees died in three months, possibly due to fipronil exposure in Brazil (Castilhos et al., 2019). It is expensive and difficult to develop a novel insecticide. Therefore, an alternative efficient strategy is to research and find ways to reduce the toxicity of fipronil to non-target organisms.
Properly modifying the structure of pesticides can change the toxicity and systemic properties of the pesticides, and the glycosylation of pesticide plays an irreplaceable role in looking for targeting carriers and reducing toxicity and side effects (Duhan et al., 2015). Early on, our group has synthesized a novel conjugate of the insecticide fipronil which containing a glucose moiety (Fig. 1). It is proved that the permeability and water solubility of glucose-fipronil is better than fipronil, and glucose-fipronil has better mobility in the sieve tubes of Ricinus communis L. seedlings (Yang et al., 2011). Subsequently, Wu et al. found that the transport mechanism of glucose-fipronil in the phloem of R. communis, their study showed that the transport of glucose-fipronil in the phloem was relate to monosaccharide transporters (Wu et al., 2021). In a recent paper, Wen et al. indicated that glucose-fipronil also has good insecticidal activity against Plutella xylostella, a target pest in cruciferous plants (Wen et al., 2018). Furthermore, the current focus of our research is to study whether fipronil could reduce its toxicity to non-target organisms after glycosylation, as this would provide important references for the application of glucose-fipronil.
Large scale use and higher doses of pesticides lead to adverse effects on the non-target organisms, pesticide residues in food, toxic effects on human beings and environmental pollution (Kumar et al, 2012). It is well recognized that there are risks attached to the consumption of pesticide-treated crops because of the presence of residues on them. Therefore, rational recommendation of a pesticide requires that it must not only provide an effective control of pests, but at the same time its residues on the other beneficial organisms and humans must be toxicologically acceptable (Kumar et al, 2013). Earthworms (Eisenia foetida) are widely distributed and frequently dominant in freshwater benthic communities (Palacios et al., 2010). As a representative organism used in the bioassay of the soil system, E. foetida plays an important role in ecological assessment, especially in the bioaccumulation of chemicals and heavy metals (Ciutat et al., 2005; Pasteris et al., 2003). In China, fipronil is mainly used as a seed-coating preparation for agricultural purposes to control soil pests (Qin et al., 2015). Like other agrochemicals, fipronil can enter into soil and aquatic system via direct spraying, rain wash and surface runoff (Chandler et al, 2010). When taking benthic organisms into consideration which use sediment and organic matter as a food resource and habitat, the increase of fipronil in sediment may bring greater risk (Chandler et al, 2010). Meanwhile benthic organisms may accumulate these sediment-associated chemicals and then pose a risk to higher trophic level organisms via food chain and help these compounds input into environment again through bioturbation (Liu et al, 2012).
In this research, methods for extraction, cleaning, and detection of fipronil and glucose-fipronil in earthworm tissue and soil were developed. In order to determine the toxic change of fipronil to worms after glycosylation, two types of uptake kinetics were examined and compared resulting from fipronil and glucose-fipronil treatment in worms and soil, respectively. And the effects of adding phlorizin on the accumulation of fipronil and glucose-fipronil in worms and soil were studied to determine whether the transport of glucose-fipronil was related to monosaccharide transporters.