Toxic Effects Of Cadmium On Japanese Medaka And The Underlying Mechanism

Cadmium is a metal with no known beneficial properties that support life and is toxic to nearlyall organisms. Like all metals, cadmium can move from one environmental compartment toanother, but it dose not degrade by breaking down to a less toxic forms. Thus, it has a profoundinfluence on aquatic organisms in the long run. The environmental status of cadmium in partialmain water bodies is still far from being satisfactory in China. Therefore, to improve theenvironmental monitoring of cadmium is necessary and urgent as well.Cadmium has a significant influence on the early life stage of fish, in terms of teratogeniceffect and protein toxic, which in turn indicates the high sensitivity of fish of early life stage tocadmium. Heavy metals exist in many chemical phases most of which can affect theirbioavailability in aquatic environment. Therefore, the total content of heavy metals obtained byphysical and chemical methods can not reflect the realistic ecological and environmental effects.However, the results of biological monitoring are derived from the direct interaction betweenorganisms and metals, so they are more relevant ecologically.To establish a convenient biological monitoring model on the basis of the sensitivityabovementioned, the toxic effects of cadmium on the early life stage of Japanese medakaOryzias latipes were determined in this study. The results indicate that cadmium of lethalconcentrations could induce necrosis in embryos, which might help us imply the effect target ofcadmium in a tissue level and thus the pattern of transfer and accumulation of cadmium in thewhole embryo. Some polluted waters nearby mining areas have cadmium concentrations that arethe same or higher than the 96h LC50-value of yolk-sac larvae which thus could act as abiological indicator in these areas. The results exhibited that the protein content of embryo andyolk-sac fry were highly sensitive to cadmium. After exposed to 4μg·L-1cadmium, the contentof protein significantly decreased indicating the high sensitivity of yolk-sac fry. The EC50 valueof spinal deformity of yolk-sac fry for cadmium was less than the upper limit of cadmium for IIwater according to the water quality standard GB3838-2002. A linear relationship between theratio of spinal deformity and cadmium concentration could be used to quantitative monitoring.Further more, spinal deformity could be significantly induced by 4μg·L-1cadmium in 48 h,which made yolk-sac fry promising to be used in fast response to cadmium in water. Bothchanges of protein content and ratio of spinal deformity of yolk-sac fry could be able to monitorthe context of cadmium concentration in several main waters in China. Therefore, the embryoand yolk-sac fry could act as sensitivity models for biological monitoring low level cadmium pollution.The water used in present study is remarkably different from that in the natural environment.Long-term, chronic and mixed exposure to low concentrations of pollutants may impair thefitness and viability of organisms. Thus, it is necessary to go insight into the combined effects ofmixed metals and organic pollutants.