Pollution Characteristics And Risk Assessment Of Heavy Metals In Sediments Of Ganjiang River

The Ganjiang River runs through the north and south of the province and is located south of the lower reaches of the Yangtze River.It is one of the main tributaries of the Yangtze River.The Ganjiang River supplies the province's industrial,agricultural,and domestic water,and is the mother river" of Jiangxi province.In the southern part of Jiangxi Province,there are abundant mineral resources.Long-term mineral mining and smelting have brought certain burdens to the aquatic system of the Ganjiang River,such as frequent eutrophication of rivers and accumulation of large amounts of heavy metals in sediments.However,relatively few investigations and investigations have been conducted on the pollution of water bodies and sediments in the Ganjiang River.This article selects the Ganjiang River system as the research object,measures its physical and chemical indicators and heavy metal content in its water bodies and sediments,analyzes the actual pollution degree of the Ganjiang River system,and evaluates the potential ecological risks of the Ganjiang River system,providing a theoretical basis for environmental safety of the Ganjiang River system.The research results are as follows:(1)the average values of pH,CODMn,total nitrogen,total phosphorus,and ammonia nitrogen in the surface water of Ganjiang river system were 7.28,4250.67?g·L-1,3812.415?g·L-1,and 30.06?g·L-1,respectively.The ammonia nitrogen and total nitrogen were significantly higher than the national surface water quality V,and the total nitrogen and ammonia nitrogen content exceeded the V water quality standard sampling points,accounting for 82.76%and 68.97%,respectively,The sampling sites of pH>7 in Ganjiang river system accounted for 68.97%,the sampling sites of CODMn content belonging to class ? water quality accounted for 62.07%,and the total phosphorus content was above class ? water quality.(2)the average contents of Ganjiang river system W,Cu,Zn,Cd,Hg and As are 1.83?g·L-1,186.14?g·L-1,112.95?g·L-1,0.05?g·L-1,1.78?·L-1and 1.99 ?g·L-1 respectively,namely,the order is Cu>Zn>As>W>Hg>Cd.Where,Pband Cr are both lower than the detected value.The content of W.Cd,and As belongs to class I water quality,Cu and Zn belongs to class ? water quality.but the average content is 2.6 times higher than the standard for class V water quality on the surface,But the average Hg content was 2.6 times higher than the surface water quality standard for class ? The average values of W?Cu?Zn?Cd?Hg and As are the highest in the upper reaches of Ganjiang river.(3)the average values of pH,CEC,organic matter and total nitrogen of sediments in Ganjiang river system were 6.56,10.73 mol·L-1,12.23g·kg-1 and 1.16 g·kg-1,respectively.In terms of spatial distribution,the average pH value of each section of Ganjiang river system is the downstream>the upstream>midstream,the average CEC and organic matter content is the upstream>and the downstream>midstream,and the average total nitrogen content is the upstream>midstream>the downstream.(4)the average content of heavy metal elements in sediments of Ganjiang river system is Mn>Zn>Cu>Pb>As>W>Cr>Cd>Hg.Heavy metals W?Cu?Pb?Zn?Cd?Cr?Hg?As and Mn in the upper reaches were 2.87,4.61,1.93,4.14,23.2,0.13,10.38,2.59,4.71 times of the soilbackground value in Jiangxi province,2.23,2.06,1.27,7.54,24.00,0.10,9.00,1.98,2.86 times of the background value in the middle reaches,and 1.03,2.79,1.20,3.93,11,0.01,4.13,1.42,2.10 times of the background value in the lower reaches.Among them and exceed bid multiple serious.By using correlation analysis and factor analysis,it was concluded that pH was not significantly correlated with the total amount of heavy metals,and was significantly positively correlated,indicating that the pollution sources were similar.(5)the main occurrence pattern of W?Cu?Zn?Cr?Hg?As and in the sediments of Ganjiangriver is residual state(B4 state),and the average proportion of B4 state is 74.99%,45.20%,40.13%,49.61%,76.28%and 86.39,respectively.The main form of occurrence of,and is reducible state(B2 state),with the average proportion of B2 state being 51.55%,63.26%and 58.24%,respectively,indicating that heavy metals Cd?Pb and Mn are more capable of transforming with environmental migration,and are prone tocause greater risks of environmental pollution.(6)the water quality of Ganjiang river was evaluated by the two evaluation methods of water pollution index and comprehensive pollution index.The results showed that the total phosphorus and CODMn both belonged to class ? or ? water quality,but the total nitrogen and ammonia nitrogen content in class ??inferior ? water accounted for 89.66%and 68.97,respectively.Therefore,the main physical and chemical pollutants in the water of Ganjiang river were nitrogen-containing compounds.Heavy metals in the middle reaches and the lower reaches of Ganjiang river belong to class ? or ? water quality,but Hg content in the upper reaches of Ganjiang river is class ??inferior? water quality.From the analysis of spatial pollution distribution,pollution degree in the upper reaches of Ganjiang river is higher than that in the middle reaches and the lower reaches.(7)Geoaccumulation index and nmeiro comprehensive pollution index evaluate the degree of sediment pollution in Ganjiang river.The results show that geoaccumulation index values are Cd>Hg>Zn>Cu>Mn>As>W>Pb>Cr.75.86%of the collected sediment samples were slightly contaminated,17.24%were moderately contaminated,and 6.90%were moderately contaminated.Among them,the heavy metals with the highest pollution level are Cd and Hg.According to the risk evaluation coding method,the ecological risk index of 9 heavy metals is Cd>Mn>Zn>Cu>Hg>Cr>Pb>As>W.The results of secondary phase and primary phase comparison showed that the secondary phase/primary phase values of heavy metals Cd,Cr and Mn were larger than those of the 6 heavy metals W,Hg,As,Cu,Pb and Zn,with mean values of 20.61,8.14 and 5.66 respectively.In conclusion,the Ganjiang river system and water bodies are seriously polluted by nitrogen pollutants and heavy metals Hg,while the sediments are seriously polluted by heavy metals Cd and Hg,and the ecological risks of heavy metals Cd,Cr and Mn are hig.