| Recently, water pollution has been a serious influence on the stability ofaquatic ecosystem and human security. Using the behavior change of aquaticorganism, can carry out real-time and rapid water quality monitoring. Aquaticorganisms exposed to the environmental pollution would produce the toxiceffects of performance in five levels, respectively molecular level, cellular level,organizational level, the individual level and the group level. Usually aquaticanimals in individual performance level display various kinds of behaviorchange such as swimming ability, avoidance behavior, reflex ability and so on.The behavior change of aquatic organism which exposed to pollutants has beenrelativity with contaminant concentration and exposure time on the individuallevel. This kind of behavior change is directly related to environmentalpressure, under certain environmental pressure, the trend of behavior changecorresponds with Stepwise Stress Model. Contaminants have a primordiallyeffect on biological indicator of organisms like enzymes or proteins. Therefore,with the biological indicator change, biological behaviors will also make acorresponding reaction.In this study, the inhibitory effects of three insecticides, dichlorvos,methomyl and deltamethrin, on acetylcholinesterase of Daphnia magna wereinvestigated in the laboratory. The concentrations of insecticides are 2 TU and5 TU, and 1 TU is defined as the 24 h-LC50 of insecticides. Combined withStepwise Stress Model, to analyze the trend on cholinesterase activity ofDaphnia magna exposed to pollutants and explore the response mechanism.The results show that the AChE activity has obviously relationship withthe relative concentration of insecticides based on 24 h-LC50 and the exposure time, hereinto, there is obviously relationship between AChE activity andtoxicological mechanism of pesticides in vitro.Firstly, the results of acute toxicity indicated that different pollutants havedifferent virulence to Daphnia magna and the 24h-LC50 of insecticides, DDVP,methomyl and deltamethrin, were 0.746μg/L, 9.829μg/L and 6.680μg/L.Meanwhile, an obvious positive relationship was observed between themortality rate of Daphnia magna and the concentration of insecticides. Underthe stimulation of different types of environmental pollutants, Daphnia magnawere showing significant behavioral changes.Secondly, in vivo, dichlorvos, methomyl and deltamethrin had obviousinhibition on AChE activity of Daphnia magna. Overall, along with theincrease of the exposure time, AChE activities of experimental groups dropsignificantly lower than blank control groups. The inhibition rates of threeinsecticides on AChE were increasing gradually with time, and the 5 TUgroups were more serious influence on AChE activity than the 2 TU groups.The result indicated that metabolism maybe had an effect on the insecticidesinhibit AChE activity, sometimes; the back sampling’s AChE activity maybeappears higher than the previous one with time.Finally, in vitro, just dichlorvos and methomyl had important influence onAChE activity of Daphnia magna. Within the scope of a certain time, theinhibition on AChE activity of Daphnia magna would go up with the increaseof exposure time exposed to dichlorvos or methomyl. However, deltamethrinhad less impact in AChE activity, because AChE was not the target position.In conclusion, AChE activity was indeterminacy at different time, mayappear raise or lower, but total trend is downward trend with time in pollutantscontinued exposure. The trend is consistent with the rule of biologicalbehaviors, which accorded with Stepwise Stress Model (SSM). Comparing theresults between the inhibition on AChE activity of Daphnia magna in vitro andin vivo, concluded that the same insecticides caused different inhibition rate onthe activity of AChE. |
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