Study On The Toxic Effects Of U And Cd In The Effluent Of A Uranium Mining Area On Ctenopharyngodon Idellus

Uranium and cadmium are typical contaminants of uranium mining process,which are potential threats to ecological environment and human health.As an important part of aquatic organisms,few studies have been reported on the toxicity of mixed exposure to uranium and cadmium in fish.Therefore,this paper used Ctenopharyngodon idellus as the test organism and uranium,cadmium as the target toxicants for the experiment,which was divided into two parts,the first part was an indoor toxicity experiment containing acute toxicity and subacute toxicity experiments,and the second part was a toxicity experiment simulating the effluent from a uranium mining area in Guangdong.The acute toxicity experiment used 96 h exposure experiment,and the measured index was 96 h LC₅₀;the subacute toxicity experiment and simulated sewage toxicity experiment used 14 d semi-static experiment,and the changes of SOD,MDA and CAT in liver,kidney,muscle,gill,and the accumulated growth rate of each tissue element were used as biological indexes to study the toxic effects of uranium and cadmium on Ctenopharyngodon idellus juveniles.The main conclusions obtained from the paper are as follows:（1）The chemical toxicity of heavy metals on Ctenopharyngodon idellus juveniles was related to the type of heavy metals,and the 96 h LC₅₀of uranium and cadmium on juveniles were 28.5 mg/L and 3.455 mg/L,so cadmium was more chemically toxic.（2）Sub-acute toxicity experiments showed that SOD,MDA and CAT of each tissue could respond to exogenous pollutants and changed significantly at the end of exposure,so SOD,CAT and MDA could be used as sensitive biomarkers.At low concentrations and short time of heavy metal exposure,CAT and SOD produced induced effects,and showed significant inhibition with increasing exposure duration and concentration,with obvious time-effect and dose-effect relationships.Comparing the biological indicators of oxidative stress（SOD,CAT,MDA）in each tissue of juvenile fish,it was found that kidney and liver were more sensitive to uranium and cadmium.The maximum inhibition rate of SOD and CAT and the induction rate of MDA were higher for exposure to the mixed solution of uranium and cadmium than for the single solution of uranium and cadmium,indicating that the biological toxicity was enhanced by the coexistence of uranium and cadmium in the same environment. All tissues of the fish were enriched with heavy metals,and the increase of uranium and cadmium accumulation in all tissues of the experimental group with very high concentration was significantly higher than that of the group with low concentration,and there was a significant concentration-effect relationship.uranium was mainly enriched in liver and kidney,and cadmium was mainly enriched in kidney,while the accumulation growth of both in muscle was the smallest,reflecting the different absorption capacity of different tissues for uranium and cadmium.（3）The radioactive element uranium was highest at the pit mouth K1,and the heavy metal element cadmium was highest at the tailing pond W1,and the response of each tissue oxidative stress index was also most significant at the two sampling sites.With the increase of the distance from the sampling point to the pit entrance,the content of radionuclide U gradually decreased and the biotoxic effect was significantly reduced,and the same pattern existed in the tailings pond compared with the pit entrance.