The importance of the earthworms in the agricultural practices is well known. The increasing applications of pesticides and chemicals in the agricultural farms have adversely influenced the flora and fauna of the soil. Earthworms which immensely contribute in increasing the quality and fertility of agricultural soil are reported be worst hit organisms under such conditions. Recent reports have indicated growing interests among researchers to explore biochemical and molecular markers as indicators of accumulation of pollutants in the soil in general and pesticides in particular. The varying levels of several biomolecules in different parts of the earthworm have been reported which are indicative of sensitivity of the organisms to different xenobiotics. However, the existing information lacks the literature displaying stock of information regarding the impact of pesticides on the levels of some key enzymes regulating many crucial functions in the earthworm at one place. Keeping in view this issue, it was envisaged to bring out a mini review which illustrates updated information available on the impact of pesticides on the activities of certain key enzymes reported to be responsible for catalysing metabolic pathways concerning the neurotransmission system, energy metabolism, oxidative stress and amino acids metabolism in different body parts of the earthworms, a prospective bioindicators of pesticides contamination in the soil.
In the present study, the acute toxicity of chlorpyrifos (an organophosphate, OP) and cypermethrin (a pyrethroid) pesticides was estimated for 96 h in Heteropneustes fossilis. The LC for chlorpyrifos (CPF) and cypermethrin was found to be 1.90 mg/L and 0.085 mg/L, respectively. The acetylcholinesterase (AChE, EC 3.1.1.7) activity in Heteropneustes fossilis exposed to both the insecticides was assayed in brain, muscle and gills. In general, tissue specific as well as dose-dependent decrease in the AChE activity was exhibited by both pesticides. In response to the increasing concentrations of chlorpyrifos and cypermethrin as well, a significant decrease in the activity of AChE was found in brain while muscle and gills exhibited lesser inhibition. Thus, the brain was the main target organ for both insecticides, followed by muscle and gills. Between the two pesticides chlorpyrifos acted as more potent AChE inhibitor than cypermethrin since more intense changes in behavioral pattern was observed with the chlorpyrifos. These changes indicate that the effects of these pesticides are at neural as well as neuromuscular level.
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