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    • Concerning GST we could appreciate that when

    2022-07-01

    Concerning GST, we could appreciate that when snails were exposed to the chosen concentrations of chlorpyrifos, the activity was not modified. According to this result, Kristoff et al. (2008) and Domingues et al. (2007) showed no effects on GST in B. glabrata and L. variegatus exposed to azinphos-methyl for 2 days and in 4th instar larvae of two chironomid species exposed for 2 days to the OP dimethoate, respectively. In these cases, the conjugation of the OP with the glutathione mediated by GST would not be acting as a mechanism of detoxification of the pesticides. In accordance with the obtained results, we could suggest that the most sensitive biomarker in adults snails of P. corneus exposed to chlorpyrifos for 14 days was CES activity measured with p-NPB. Regarding the results obtained in total homogenate and gonads, we did not observe differences in the responses of the B-esterases in both tissues; therefore, the use of the whole Evans Blue tetrasodium salt receptor soft tissue is recommended because it requires a smaller number of snails. The reproduction alterations can be one of the causes of the decline in the number of specimens of a species (van der Oost et al., 2003). Some authors have described that chlorpyrifos causes toxic effects on the reproduction of other aquatic invertebrates. In agreement with our results, Zaliznick and Nugegoda (2006) and Varó et al. (2006) reported a decrease in hatching and survival in adult organisms of D. carinata and cysts of Artemia sp., respectively. However, in these works, biochemical responses were not studied. Only a few amounts of works can be found that show comparisons between the effect in reproduction and biochemical responses to anticholinesterase pesticides exposure. Tripathi and Singh (2004) and Kristoff et al. (2011) compared ChE inhibition with reproductive alterations in the freshwater snails L. acuminate and B. glabrata exposed to carbaryl and azinphos-methyl, respectively. In both cases, authors found ChE inhibition greater than 45% and no eggs hatched. With a lower inhibition of ChE, they found a decrease in the number of egg masses and in the offspring. In the present work, when there was no inhibition of ChE in gonads, no significant alterations in reproduction were observed. Moreover, the high inhibition of ChE sustained over time, was accompanied by severe alterations in the Evans Blue tetrasodium salt receptor reproduction. On the other hand, some authors have investigated possible relationships between CES and the reproduction of organisms. Mikhailov et al. (1997) found in a mollusc a carboxylesterase whose expression increased in the reproductive stage. Other authors have reported the presence of a carboxylesterase in the seminal fluid of the Drosophila insect which is involved in sperm protection and activation (Korochkin, 1980, Kubli, 1992). These authors have described that these enzymes are over-expressed in their respective male reproductive systems and that polypeptides with CES activity may play a role in the detoxifying process in male reproductive systems (Korochkin, 1980, Kubli, 1992, Mikhailov et al., 1997). However, new studies should be performed to achieve better understanding of the relationship between CES and reproduction. Acute laboratory toxicity data for various groups of aquatic organisms exposed to Ops, showed that arthropods and a lesser extend of fish, are the most sensitive groups, followed by algae and non-arthropods (Van Wijngaarden et al., 2005). In particular, representatives of crustaceans, insects and fish can be considered particularly sensitive to chlorpyrifos (Barron and Woodburn, 1995, Van Wijngaarden et al., 1993). With the chlorpyrifos concentrations that were used in this work, more severe effects may be caused in these groups of aquatic organisms. It should also be taken into account that subchronic and chronic exposures to low Ops concentrations can produce more severe effects in gastropods than acute exposures, mainly related to reproduction (Kristoff et al., 2011). With regards to P. corneus, it has been reported that this species declines constantly (Jopp, 2006). For this reason, it is very important to investigate the effect of different contaminants on the reproduction of this species. Disturbances in the reproductive performance of P. corneus after subchronic and chronic exposures to sewage treatment work (STW) effluents containing natural hormones, synthetics steroids, pesticides, surfactants and plasticizers have been reported (Clarke et al., 2009). In this study, we have confirmed that the subchronic exposure to chlorpyrifos is able to cause alterations in the reproduction of P. corneus and in the survival of the offspring. Unpublished results of our group show that the subchronic exposure to environmental concentrations of azinphos-methyl also causes a decrease on hatching and survival of P. corneus. These suggest that OPs may contribute to the decline in the number of organisms of this species.