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The study was supported by Science Foundation for the Youth Scholars of Hubei Provincial Department of Education for Science and technology research program (No.: Q2017007).
Introduction Chlorpyrifos is an organophosphate (OP) insecticide widely used in a variety of food crops to control a great number of insects and is frequently detected in surface waters around the world (Palma et al., 2009). The values of chlorpyrifos concentrations estimated for surface waters reported by the Environmental Protection Agency range between 0.026 and 0.4μgL−1 (EPA USEPA, 2006). However, both direct and indirect applications can cause higher chlorpyrifos concentrations in small streams and wetlands adjacent to agricultural fields than those estimated by EPA (3.7–700μgL−1) as reported by Moore et al. (2002) and Wood and Starck (2002). Chlorpyrifos has a relatively persistent nature compared to other organophosphorus insecticides, with a half life in water ranging from 29 to 74 days (Racke, 1993, E.P.A. USEPA, 2006, Palma et al., 2009). OPs are thought to exert their toxicity by binding to acethylcholinesterase, which hydrolyzes the neurotransmitter acetylcholine, inhibiting the action of this enzyme. This causes the accumulation of Dp44mT in synapses and, consequently, an overstimulation of neurotransmission followed by depression or paralysis and eventual death. Cholinesterases (ChEs) are a family of enzymes that hydrolyze choline esters and belong to the B esterases groups: esterases that are inhibited by OPs (Sanchez-Hernandez, 2007). In aquatic invertebrates, it has been reported that ChEs differ in many aspects from either vertebrate acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) (Bocquené et al., 1997, Sanchez-Hernandez, 2007). The ChEs of aquatic invertebrates generally show a preference for acetylthiocholine (AcSCh) as substrate, however, there are some species that hydrolyze propionylthiocoline (PrSCh) faster than AcSCh (Basack et al., 1998, Hannam et al., 2008, Mora et al., 1999, Talesa et al., 1990, Varó et al., 2002). Assessment of ChE inhibition in wildlife population has been proposed as a general method for detecting environmental contamination from OPs, particularly since many of these chemicals have relatively short half lives in the aquatic environment and a rapid metabolism in biota (Gagnaire et al., 2008, Lacorte et al., 1995, WHO, 1986). In contrast, after being exposed to Ops, ChE recovery in organisms is very slow. Therefore, enzymatic inhibition can be detected although there is no longer pesticide in the water (Escartin and Porte, 1996, Ferrari et al., 2004, Kristoff et al., 2006, Kristoff et al., 2011, Kristoff et al., 2012, Kumar et al., 2010, Rodríguez, 2009). This may offer an advantage in monitoring OPs over the use of chemical analysis alone (Arufe et al., 2007). Carboxylesterases (CES) are another type of B-esterases. These enzymes catalyze the hydrolysis of a wide range of exogenous and endogenous esters and are assumed to play a protective role in anticholinesterase intoxication by removing a significant amount of pesticide by two main mechanisms: the detoxification by hydrolysis of ester bonds in some of these pesticides and by providing alternative sites of OP binding (Jokanovic, 2001, Sanchez-Hernandez, 2007). Glutathione S-transferase (GST) belongs to a phase II family of detoxifying enzymes. Mainly by the action of this enzyme, glutathione (GSH) can form conjugates with a wide variety of electrophilic compounds. This conjugation is essential for the detoxification of xenobiotics but also for maintaining the normal physiological metabolism (Strange et al., 2000). For this reason, GST activity can be used as a biomarker of effect. Chlorpyrifos has been used in different in vivo toxicity tests in aquatic invertebrates. It has been reported that chlorpyrifos decreases ChE activity of Artemia salina, Artemia parthenogenetica, Biomphalaria glabrata, Corbicula fluminea, Daphnia magna, Gammarus pulex, Lamellidens marginalis, Lumbriculus variegatus, Paratya australiensis, Planorbarius corneus, Potamopyrgus antipodarum, and Procambarus clarkii (Amanullah et al., 2010, Barata et al., 2004, Cacciatore et al., 2011, Cooper and Bidwell, 2006, Gagnaire et al., 2008, Kumar et al., 2010, Rodríguez, 2009, Varó et al., 2002, Vioque-Fernández et al., 2007, Xuereb et al., 2007) and CES activity of B. glabrata, L. variegatus, P. clarkii and P. corneus in vivo (Cacciatore et al., 2011, Rodríguez, 2009, Vioque-Fernández et al., 2007). However, less is known about the chronic effects of low concentrations of pesticides on more ecologically relevant endpoints such as growth and reproduction (Roex et al., 2003). Some authors have reported toxic effects due to chlorpyrifos on reproduction, survival and embryonic development in vertebrates (De Silva and Samayawardhena, 2005, Farag et al., 2010) and in invertebrates species (Jager et al., 2007, Li-Xia et al., 2009, Palma et al., 2009, Varó et al., 2006, Zaliznick and Nugegoda, 2006). In the case of crustacean, Palma et al. (2009) reported in Daphnia magna a reduction in the number of offspring produced per male and abnormalities including arrested eggs; Zaliznick and Nugegoda (2006) have studied the effect of chlorpyrifos on the next two generations of Daphnia carinata reporting that the pesticide affected survival and fecundity of animals in the first generation while in the second one, a longer time of hatching was observed. Varó et al. (2006) have studied the effect of chlorpyrifos on capsulated and decapsulated cysts of Artemia sp. showing that the pesticide caused a decrease in hatching and survival. However, little is known about the chlorpyrifos effect on the gastropods reproduction. Although gastropods in the case of Ops, are not the most sensitive group of organisms (Van Wijngaarden et al., 2005), freshwater gastropods represent about 20% of recorded mollusk extinctions (Strong et al., 2008).