Toxic Effect Of Chromium On Rana Chensiensis Tadpole

The growth and development of amphibian tadpoles were susceptive to the chemical pollutions and the variation of the environments. In order to investigate the acute toxic mechanism of chromium on Rana chensiensis tadpoles, the 26-28 development stage tadpoles were exposed to the tap water which was added in various concentrations of Cr6+ and Cr3+. The death rates of tadpoles were determined in various concentrations of Cr6+ and Cr3+, and the LC50 and SC for 24h, 48h, 72h and 96h were calculated, in order to analyze the acute toxic effect of Cr6+ and Cr3+. In order to investigate the effect of Cr6+ and Cr3+ on growth and development of R chensiensis tadpoles, the tadpoles were exposed to sublethal concentrations of Cr6+ and Cr3+, then fully metamorphism. The weights and lengths of tadpoles were measured, and abnormality rate and the fully metamorphism time were counted. In order to discuss the mechanism of Cr6+ and Cr3+toxicity, damnification of the liver and kidney, which were caused by the Cr6+ and Cr3+, were observed in microscope. The metallothionein (MT) levels in frog livers were assessed by the immunohistochemistry, and the enzyme activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) were sssessed by enzyme histochemistry. The results of this paper are following:1. The results of the acute toxic test as follows: When tadpoles exposed to Cr3+ and Cr6+ for 24h ~ 72h, the LC50 of Cr3+ on tadpoles were 34.09+1.06 ~ 32.58±0.11mgCr3+/L, and the LC50 of Cr6+ were 91.97±5.32~35.79±1.40mgCr6+/L. It is obvious that Cr3+ was more toxic than Cr6+ within 72h. When exposed for 96h, the LC50 of Cr3+ on tadpoles was 32.05+0.20 mgCr3+/L, higher than 28.81±1.87 mgCr6+/L of Cr6+. It indicated that Cr6+ showed more toxic for long time exposure. The lethal concentration range of Cr3+ was narrower than that of Cr6+, which showed the tadpoles were more susceptive to Cr3+ than to Cr6+.2. The weights and lengths of tadpoles were measured, after the tadpoles were exposed to the Cr3+ and Cr6+ for 21d and 35d. The results showed that the growth of tadpoles which exposed to the Cr3+ and Cr6+ for 21d, were retard compared with control. It indicated that Cr3+ and Cr6+ restrained the growth of the tadpoles. Especially, the growth of tadpoles which exposed to 0.75 and 1.00mgCr6+/L, were remarkable difference with control. After the tadpoles were exposed to the low concentration of Cr3+ and Cr6+ for 35h, restraining effect of Cr3+ and Cr6+ on the growth of the tadpolesbecome weaken. With the growth of the tadpoles, the resistance of the tadpoles to the Cr3+ and Cr6* enhanced. With the growth of the tadpoles, the low concentration of Cr3* and Cr6+ approach the available dose. Sublethal concentration of Cr3+ and Cr6+ affected the time of holometabolism and abnormality poorly.3. Cr3+ and Cr6* could cause hepatic impairment by the section observation. Cr3+ and Cr6+ can produce toxic effect, such as disrepair of cell membrane, loosen of cytoplasm and fatty degeneratiaon appeared in the hepatocytes. MT, as a kind of heavy metal detoxification protein, could express highly in hapatocytes of tadpoles exposed to the Cr3* and Cr6* by immunohistochemistry. Exposed to the higher concentration of Cr3*, the MT expressed stronger in order to chelated Cr3*, and to lessen the toxicity of Cr3*. Exposed in the 0.25 ~ 0.75mgCr6+/L of Cr6*, the MT expressed stronger with the concentration rising;but in 1.00mgCr6*/L> the MT expression dropped. It could conclude that the high concentration of Cr6* can do harm to the hepatocytes and suppress the expression of MT.4. Cr3* and Cr6* could cause renal impairment by the section observation. With the concentration of Cr3* and Cr6* rising, renal impairment aggravated. In iow concentration of Cr3*, Cr3* do harm to kidney tubules epithelium;with the concentration of Cr3* rising, Cr3* do harm to kidney glomerulus. Exposed to the 0.25 ^ 0.50mgCr6+/L Cr6*, kidney glomerulus atrophied and kidney tubules epithelium can produce the fatty degeneratiaon . The examination with enzyme histochemistry showed that Cr3* and Cr6* could inhibit the enzyme activities of ALP and ACP, and it indicated that Cr3* and Cr6* could affect the phosphorylation and dephosphorylation in cell, then affected the metabolism of organism.