Toxic Effect And Mechanism Study Of Copper, Cadmium And Selenium On Daphnia Magna

The presence in the waters of heavy metals has grown because of their largeemployment in some industrial and agricultural activities. Zooplankter is among themain biological communities and is the direct heavy metals victim. Because of theeffort of food chains, metals will eventually accumulate in the body of human beingsand thus do harm to our health.In present study, the toxic effects of copper, cadmium and selenium on Daphniamagna were determined utilizing acute toxicity experiments. The individual andcombined toxic effect including the effect on antioxidant system and embryodevelopmental toxicity of these three metals were included into this study.The results of individual toxicity experiments indicated that the values of24h-EC₅₀of Cu^2﹢,Cd2+and Se^4﹢on Daphnia magna were0.16,0.28and3.20mg/L,respectively, and the24h-LC₅₀were0.22,0.38and7.32mg/L, respectively; thevalues of48h-EC₅₀of these three metals were0.13,0.16and2.22mg/L, respectively,and48h-LC₅₀were0.16,0.25and2.90mg/L, respectively. Therefore, the toxicsequence of the studied metals were: Cu^2﹢＞Cd^2﹢＞Se^4﹢.The additive index method was used to evaluate the combined toxicity.According to the results of the combined toxicity tests, complex effect wasdemonstrated in different toxic matches by ratio of concentration and toxic unit. Thetoxic effects changed over different toxic matches in the same combination of toxics.Particularly, for the combination of Cu^2﹢+Cd^2﹢by1:1ratio of LC₅₀s (toxic unit), thetoxic effect converted from antagonistic to synergistic response over exposure timewhen compared with other combinations.The effects of Cu^2﹢, Cd^2﹢and Se^4﹢on SOD, CAT and GST of the antioxidantsystem were determined in Daphnia magna. The results demonstrated that all metals had significant effects on the activity of SOD, CAT and GST. The activity of enzymesof the antioxidant system were inhibited or activated over both exposure time andconcentrations. On the reasoning above, SOD, CAT and GST could act as biologicalindicators for early warning.The normal stages of development in Daphnia magna were detected according towhich the development were divided into6stages including cleavage, gastrulation,early embryonic maturation, mid-embryonic maturation, late embryonic maturationand fully developed neonate. Meanwhile, the effects of Cu^2﹢, Cd^2﹢and Se^4﹢onembryo malformation were determined. The results indicated that Cu^2﹢was the mosttoxic when considering its teratogenic effect followed by Cd^2﹢.4teratogenic typeswere induced by Cu^2﹢and Se^4﹢, and3by Cd^2﹢. Cu^2﹢, Cd^2﹢and Se^4﹢couldsignificantly induce undeveloped second antennae and curved shell spine. Theseinductions showed evident dose-effect relationships.