| OBJECTIVE:To analyze the content and distribution of Pb and Cd in benthic Bellamya aeruginosa in the sediments of the middle reaches of Xiangjiang River,and to analyze the contents and distribution of Pb and Cd in Bellamya aeruginosa and sediments.The correlation between Pb and Cd content was studied.The Pb and Cd stress tests were carried out on Bellamya aeruginosa.The changes of catalase and superoxide dismutase in Bellamya aeruginosa under heavy metal stress were also studied.At the same time,the intestinal tract of Bellamya aeruginosa was isolated and purified.Resistant to Pb and Cd microorganisms,explored the tolerance and detoxification mechanism of Bellamya aeruginosa to heavy metals,and revealed the adaptation mechanism of Bellamya aeruginosa to Pb and Cd,in order to provide theoretical basis and technical support for bioremediation and treatment of heavy metal pollution in Xiangjiang River.Method:In the field part of the experiment,the sediments and Bellamya aeruginosa were collected at the sampling point at a position below the water surface;after the sediment was dried,pulverized and sieved,the total amount of heavy metals was extracted by wet digestion,and the improved BCR was used.The three-step continuous extraction method extracts the different forms of heavy metals in the sediment;Bellamya aeruginosa is domesticated by pure water for 3 days,spits out the sediment,and after the shell is cleaned,it is decomposed into shell,mantle,visceral mass and foot.Low temperature drying,crushing,using wet digestion to extract heavy metals;graphite liquid atomic absorption spectrometry to determine the concentration of heavy metals in the solution,and then the concentration of heavy metals in sediments and Bellamya aeruginosa;stress experiments are divided into Pb stress,Cd Three groups of stress and Pb-Cd combined stress,each group was divided into 4 groups,and pure water was used to raise Bellamya aeruginosa as a blank control group,at 0d,2d,4d,6d,8d,from each of the three groups.The concentration of CAT and SOD was determined in the concentration of Bellamya aeruginosa.At the 0d,2d,4d,6d and 8d,the maximum concentration of Pb and Cd in the single factor stress group?Pb is concentrated?.Take 5-8?about 20g?of Bellamya aeruginosa in the concentration of 0.4 mg/L and Cd concentration of 0.04 mg·L-1,and extract the heavy metal from the soft part.On the 8th day,the Pb and Cd single factor stress group The remaining Bellamya aeruginosa in the maximum concentration?Pb concentration 0.4 mg·L-1,Cd concentration0.04 mg·L-1?was transferred to pure water for breeding,and on the 10th,12d,14d,16d,and 18d,5-Eight?about 20g?of Bellamya aeruginosa were extracted to determine the heavy metal content of the soft part,and the biological half-life of Bellamya aeruginosa against Pb and Cd was calculated.result:1.The Pb and Cd in the sediments of the middle reaches of the Xiangjiang River have a certain accumulation.The concentration of Pb in the sediments of the seven sampling points is 29.105-94.675 mg·kg-1,and the concentration of Cd is 2.988-13.245 mg·kg-1,7 samples.The distribution of Pb and Cd was significantly correlated?p<0.01?,indicating that the pollution of Pb and Cd at the sampling points was consistent.Compare the“Control Standards for Soil Pollution Risk of Agricultural Environment in Agricultural Environment?Trial?”?GB 15618-2018?,the concentration of Pb has been lower than the screening value of soil pollution risk in agricultural land,and its impact can be neglected.The concentration of Cd at 7 sampling points far exceeds the screening value of soil pollution risk in agricultural land,and 6 except for Chejiang Town.The concentration of Cd at the sampling point exceeds the control value of soil pollution risk of agricultural land,which is 1.16-3.31 times of the risk control value,and the risk of soil pollution is extremely serious.2.The main forms of Pb and Cd in sediments are different.Pb is mainly present in the sedimentary state of Fe-Mn oxide.The proportion of this form is 53.29%-79.80%at seven sampling points.Cd mainly exists in sediments in exchangeable state and carbonate-bound state,accounting for 51.28%-66.25%.It is generally believed that exchanged state and carbonate-bound state have more direct harm to the environment,so Cd pollution is far away.It is much higher than Pb pollution;although Pb and Cd mainly have different forms in sediments,it is found that the three forms of B1,B2 and B3 of Pb and Cd are related by correlation analysis of four forms?p<0.05?.3.The distribution of Pb and Cd in Bellamya aeruginosa is very different.Pb is only detected in the shell,but not in other tissues and organs.Cd is mainly distributed in the visceral mass,and Cd in the viscera of seven sampling points in Bellamya aeruginosa.The concentration reached 12.825-34.375 mg·kg-1,accounting for more than40%,indicating that Pb is easily metabolized into the shell and in vitro in the body of Bellamya aeruginosa,so that the soft part is protected from the accumulation of Pb,and Cd can also enter through metabolism.The shell is neutralized and excreted,but due to its high intake,it cannot be completely discharged by metabolism,resulting in a high concentration of accumulation in the soft part.Analysis of the content of heavy metals in Bellamya aeruginosa,and the correlation between the total amount of heavy metals in the sediments and the occurrence of heavy metals,found that there was no correlation between Pb and Cd in the rusted snails and the total amount and morphology of Pb and Cd in the sediments.?p>0.05?,indicating that there is a difference in the content of heavy metals between Bellamya aeruginosa and sediment.4.Under the combined stress of Pb,Cd and Pb-Cd,the activity of CAT and SOD in Bellamya aeruginosa increased significantly.With the increase of time,the enzyme activity increased,and the corresponding low,medium and Among the four concentrations of medium and high,the changes of CAT and SOD were basically consistent?p<0.05?.As the concentration of Pb and Cd in the solution increased,the enzyme activity also increased.As a whole,the enzyme The rate of activity increase Pb-Cd combined stress>Cd stress>Pb stress indicated that Cd toxicity was higher than Pb,but the enzyme activity decreased under high concentration of heavy metal stress in each stress group.It shows that within a certain range,the activity of protective enzymes of CAT and SOD can be improved to alleviate the biological toxicity of Pb and Cd on snails;under too high concentration of Pb and Cd stress,the enzyme activity decreases,indicating protective enzyme activity.The mitigation of heavy metal toxicity is limited.5.Under the experimental conditions,the expression of Pb from Bellamya aeruginosa was CPb=e-0.0006t+1.0303,and the expression of Cd from Bellamya aeruginosa was CCd=e-0.0005t-1.0985,which was discharged from Bellamya aeruginosa.The biological half-life?B1/2?of Pb was1155.245h,which was about 48.14d,and the biological half-life?B1/2?of Cd excreted was 13862.294h,which was about 57.76d.The biological half-life of Pb was 9d less than that of Cd by Bellamya aeruginosa.It is indicated that Bellamya aeruginosa has a faster metabolic rate for Pb than Cd,and Cd is more likely to accumulate in Bellamya aeruginosa than Pb.6.Bellamya aeruginosa can survive normally in high concentrations of Cd2+and Pb2+.In addition to its own metabolism and tolerance mechanism,intestinal flora is also involved.Microorganisms in the intestinal tract can absorb some of the Pb and Cd ingested into the digestive tract.Thereby reducing the absorption of Pb and Cd by the organism.In addition,the microorganisms can change the valence state of heavy metals through their own metabolism,so that the toxicity of Pb and Cd is greatly reduced,and the toxicity caused by biological absorption of heavy metals is reduced,thereby protecting Biological health.Conclusion:1.The heavy metal pollution of Pb and Cd in the sediments of the middle reaches of the Xiangjiang River still has certain ecological risks.The pollution degree of Cd heavy metals is much higher than that of Pb heavy metals.2.Bellamya aeruginosa has enrichment and tolerance to both Pb and Cd,and the enrichment ability of Cd is much higher than that of Pb.3.Bellamya aeruginosa increased the activity of CAT and SOD in the body when exposed to a certain concentration of Pb and Cd to reduce the toxic effects of Pb and Cd in vivo.4.Bellamya aeruginosa In the metabolism of Pb and Cd,the biological half-life of Cd is longer than that of Pb,and Cd is more likely to accumulate in Bellamya aeruginosa.5.There are many Pb and Cd-tolerant flora in the intestinal flora of Bellamya aeruginosa,which can reduce the toxicity of Bellamya aeruginosa under Pb and Cd stress. |
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