Distribution And Contamination Status On Radioactive And Heavy Metal Elements Of Surface Sediments Around Uranium-Mine In Northern Guangdong Province

A uranium mine in northern Guangdong is located in the mountainous area of northern Guangdong,which is a typical granite-type uranium deposit.This subject takes the sediments of a uranium mine in northern Guangdong as the research object,analyses the content of heavy metals in the sediments and the occurrence characteristics of heavy metals.The occurrence of heavy metals Cu,Zn,Pb,Cd,Cr and U in 18 surface sediment samples from the study area was analyzed by BCR continuous extraction method.The enrichment factor evaluation method,the ground accumulation index evaluation method,the potential ecological hazard index evaluation method and the secondary phase and the original value comparison method have analyzed the pollution status and potential ecological risks of six heavy metals in the study area.The main conclusions drawn are as follows:Firstly,the analysis of the radioactive and heavy metal elements in the surface sediments of 18 sampling points in the study area shows that the content of Cd in surface sediments exceeds the standard value of soil environment III in both water-I and water-II.And its natural background value is higher than the soil environmental standard value,which may be caused by the study area located in the metallogenic zone;the mean values of Cu,Zn,Pb and Cr do not exceed the soil environment III standard;the average content ratio of U element The background value of the sediment is more than three times.Except for the U element,the content of other heavy metal elements in the surface sediments of water-Iand water-II is not much different.At the same time,principal component analysis(PCA)was used to analyze the load factor of heavy metal elements in all sampling points in the study area.The variance of the first principal component F1 was 48.8%,mainly showing that Cu,Pb and Cd had higher positive loads.That is,F1 has a strong correlation with Cu,Pb and Cd,indicating that these heavy metals have good covariance;the variance of the second principal component F2 is 24.5%,and the Zn and U elements have a high positive load,ie F2 and Zn and U have a strong correlation.The higher content of Zn and U appeared in the vicinity of water-I,close to the tailings pond,indicating that U in the environment may be mainly derived from uranium mining and slag leaching.The variance of the third principal component F3 is 14.1.%,expressed as Zn,Pb element has a high positive load.According to the spatial distribution and size,Zn,Pb content is higher in the downstream of water-II,and there are more farmland nearby.Therefore,the sources of the second and third principal components may be mostly agricultural and industrial pollution emissions.Secondly,the analysis of the occurrence and distribution characteristics of heavy metals in the surface sediments of the study area shows that Pb,Cr,Cu and Zn mainly exist in the residual state,and U and Cd are mainly distributed in the exchangeable state,and the biological validity is the highest.The proportion of shares is 52.39% and 56.34%respectively,which is the most active in the environment,showing high biological activity and easy to be released into the environment to cause secondary pollution.Thirdly,the results of enrichment factor evaluation and geoaccumulation index show that Cu,Cr and Pb are mainly affected by natural sources in the study area,and Cd,U and Zn are affected by different degrees of human activities;potential ecological risk assessmentThe results show that the potential ecological hazard of each heavy metal is Cd>Pb>Zn>Cu>Cr,and the average ecological risk index of single heavy metal of Cd is 344.8.The pollution level is strong pollution,Cu,Pb,Cr and Zn.The potential ecological risk index is much lower than 40,and the pollution type is non-polluting.The results of the secondary phase and the original value evaluation method show that the order of the RSP mean values of each heavy metal element is: Cd>U>Pb>Zn>Cu>Cr,wherein the RSP average values of Pb,U,Cd and Zn are in the range of 1-2,it showed mild pollution;the RSP of Cu and Cr were all less than 1,indicating that the two groups of heavy metal elements were not polluted in the study area.