Plasma B-esterase and glutathione S-transferase activity in the toad Chaunus schneideri (Amphibia, Anura) inhabiting rice agroecosystems of Argentina.

B-esterase (BChE: butyrylcholinesterase and CbE: carboxylesterase) and glutathione S-transferase (GST) activity were measured in the plasma of Chaunus schneideri collected in rice fields and surrounding environments and in a reference pristine forest. The chemical criterion based on in-vitro reactivation of BChE activity using pyridine-2-aldoxime methochloride (2-PAM) was also determined. Mean values of plasma BchE, CbE, and GST activity for samples from agricultural areas were different from those for samples from pristine forest. Plasma samples from the two agricultural areas showed positive reactivation of BChE activity after incubation with 2-PAM. Based on our experimental evidence we suggest B-esterases and gluthatione S-transferases can be used in field monitoring as biomarkers of exposure of wildlife to pesticides, because the analysis in non-destructive and is sensitive to anti-ChE agrochemicals. Chemical reactivation of BChE is also a complementary method for assessing the effects of pesticides on toads inhabiting rice fields. Further studies are urgently needed to investigate adverse effects of massive exposure to pesticides experienced by native populations of anurans.