Spatial Distribution Characteristics And Influencing Factors Of Heavy Metals In Soil Of Typical Areas In Changsha County

The content and spatial distribution of five elements of lead,cadmium,arsenic,chromium,and mercury in farmland soils of five typical agricultural towns in Changsha County of Hunan Province were studied by using a combination of multivariate statistics and geo-statistics;We then focus on a smaller area-in the vicinity of an abandoned factory from Beishan district of Changsha county with the objective of demonstrating how the several typical environmental factors influence the diffusion of soil Cd to the periphery.The following conclusions were obtained through the research:(1)The cadmium and lead in the farmland of 5 typical agricultural towns showed obvious accumulation trend and the average content was 1 time and 3 times of the local background value;The variation coefficient of cadmium was the largest,indicating that it was greatly affected by external factors.The average content of arsenic,chromium,and mercury is lower than the background value except for some sampling locations.The content of arsenic and chromium in soil has a high coefficient of variation,which may also be affected by external factors.Correlation analysis and principal component analysis showed that the three elements of Pb,Cd,and Hg had a strong correlation and were classified as the first principal component.It could be speculated that these elements come from a similar source;Cr and As were more relevant and were classified as the second principal component which was mainly controlled by geochemical background.The interlink between soil texture,soil pH and heavy metal content revealed different pattern for different elements.The content of Pb,Cd and Hg had negative correlation with soil pH;as for the soil texture,the content of the heavy metal get lower when the soil texture become more sticky.For As and Cr,it exhibited an opposite results.(2)Under the sampling scale of the study,the five elements showed good spatial autocorrelation in most areas,which is in line with the conditions of spatial interpolation analysis,except for Hg in BEISHAN ZHEN and As in FULIN ZHEN.Therefore,it is recommended that the sampling distance should be reduced in future studies.The accumulation and spatial distribution of heavy metals in the soils of five town in the study area have their different characteristics: the soil of LUKOU ZHEN,Cd is accumulated,and in some areas,it exceeded the risk screening range which mainly distributed in the central and northern parts of the township;Regarding Pb,it was also accumulated in soil and the highvalue area was distributed in central and northern parts of the town but it was still within the safe level.Besides,Cr,Hg and As are mainly natural variation which are in safe.The contents of Cd,As and Pb in the soil of JIANGBEI ZHEN were significantly affected by human activities indicated the obvious accumulation.Accordingly,some points exceeded the range of risk screening values,mainly in the eastern and northeastern parts of the township;The content of Cr and Hg is in a safe level and its main variation occurs among the natural factors.The soil Cd,Cr,Pb and As in Beishan Town were affected extensively by human activities,but in Cd content of some locations exceeded the risk screening value.The contents of Pb,Cr and Hg in the soil of FULIN ZHEN were all within the safe level,and Pb and Cr showed obvious accumulation.Considering soil Cd content,it exceeded the risk screening value and expressed the characteristics of structural variation.The contents of Cr,Hg and Pb in the soil of CHUNHUA ZHEN are all within the safe limit,only As content was heavily exceeded the risk screening value.(3)Focusing on an abandoned smelter in Beishan Town,the study on the distribution of Cd in surrounding soils showed that the irrigation and lateral seepage of Cd wastewater in the stream had the greatest impact on soil Cd content,followed by wind direction and utilization.The farther away from the former site of the smelter,the soil Cd content is significantly reduced;Subsequently,the farther away from the stream,the soil Cd content is also gradually declined.Furthermore,soil Cd content also lowered along the wind direction.Soil Cd contents under different land use patterns were in the order of garden > paddy field > vegetable field > bare land.