Occurrence Of Heavy Metals In Water Of The Yitong River,Changchun And Their Bioaccumulation And Toxicity In Fish

In this study,the Yitong River basin in Changchun City was selected as the primary representative urban water body.Water samples were collected in the summer,autumn,and winter respectively,and the contents of 6 major heavy metals（Cu,Cd,Zn,As,Pb and Cr）in the water were determined to investigate the distribution status of several major heavy metals.The ecological risk of 6 heavy metals in Yitong River basin was evaluated by Nemerow comprehensive pollution index method and ecological risk index.Secondly,a simulated exposure experiment was carried out to investigate the bioaccumulation of two typical heavy metals,Cd and Cu,in carps.And the effects of the two heavy metals on liver enzyme activities and intestinal microbial community diversity were discussed.The effect of dissolved organic matter on the bioavailability of heavy metals was also investigated.The main research results are as follows:（1）The average concentrations of Cu,Cd,Zn,As,Pb and Cr in Yitong River Basin（urban section）in Changchun range from 0.0003 to 0.0618 mg·L^-1.The detected values of the 6 heavy metals at each sampling point were all lower than the classⅤwater quality standard in the GB 3838-2002,and the reaching rate was 100%.The concentrations of Cu,Cr and Cd in summer and autumn were higher than those in winter,while the concentrations of Zn,As and Pb in winter were higher than those in summer and autumn.The comprehensive analysis shows that the water quality of Yitong River basin in summer is better than that in autumn and winter.Nemero index evaluation results showed that 6 heavy metals in each sampling site of Yitong River were pollution-free.The potential ecological risk assessment results showed that the potential ecological risk of the four sampling sites was in the order of Yitong River Bridge>Saide Bridge>Sihua Bridge>Yanhe tun,and the heavy metal contribution was in the order of Cu>Pb>As>Zn>Cr>Cd.On the whole,the risk of heavy metals in Yitong River basin（urban section）in Changchun is negligible ecological risk in summer,autumn and winter.At present,the water quality of Yitong River is generally good.（2）Cd and Cu were enriched in various tissues of carp by water exposure pathway.However,the distribution of heavy metals in different tissues varies greatly.After 28 days exposure,the order of Cd concentration in tissues of carp was intestinal>liver>gill>muscle.The concentration of Cu in the tissues of fish was in the order of liver>intestinal>muscle>gill.Intestinal and liver were the main bioconcentration tissues of two heavy metals.The BCF of Cu in carp tissues was higher than that of Cd.When humic acid and fulvic acid were added to the exposure system,both organic matters promoted the uptake of Cd and Cu in carp to varying degrees,and the Cu and Cd absorption rate constants K₁in muscle,liver,intestine and gills increased to varying degrees.DOM has a significant promoting effect on Cu absorption.Although DOM significantly promoted Cu absorption in carp,BCF in muscle and liver decreased,which may be related to the rapid purification rate.（3）After 28 days exposure to Cd and Cu,the SOD activity in the liver of carp decreased significantly.The addition of fulvic acid reduced the inhibition degree of Cd on SOD activity.The content of MDA and the activity of GST in liver of fish exposed to Cd and Cu were significantly higher than those of the control group.After adding humic acid and fulvic acid,the content of MDA in liver of fish was still higher than that of the control group,but it was slightly decreased compared with that of the group without DOM.The results showed that the presence of DOM may reduce the lipid peroxidation of fish liver by heavy metals.The Alpha diversity analysis of intestinal microflora showed that the addition of Cu and Cd seriously damaged the diversity of intestinal microflora,while the addition of humic acid was beneficial to restore the diversity of intestinal microflora damaged by Cu and Cd.At the genus level,Cetobacterium are the dominant bacteria in the bacterial colonies of the intestinal contents of the 7 groups of fish in this experiment.