Distribution Characteristics And Risk Assessment Of Heavy Metals In Soil Of Agricultural Land

Heavy metal pollution in soil can damage the ecological environment,and then threaten human health.The harm of heavy metals can be known by soil heavy metals distribution characteristics and ecological risk and human health risk,therefore it is of great significance.This study collected the surface soil samples and rice seed samples within the whole reseacch area,got Cd,Hg,As,Pb and Cr contents in soil and rice.Then,use the traditional statistics and geostatistics methods to study the spatial distribution of heavy metals in soil.And Hakanson potential ecological risk index method and the USEPA human health risk assessment method were used to evaluate the ecological risk and human health risk.The main conclusions are as follows:(1)Descriptive statistical analysis showed that the contents of the average of Cd,Pb and Cr in the soil were higher than soil background values,Hg and As were the opposite.It indicated that the accumulation of Cd,Pb and Cr was obvious.The variation coefficient of Cd,Hg,As and Cr is large,which shows that the change in space is large and has local difference.(2)Spatial variability of heavy metals in five kinds of soils in the study area was analyzed by geostatistics.Cd was mainly composed of random variation,and the spatial correlation was weak,which was mainly influenced by human factors.Cr had moderate spatial correlation,and spatial variation was controlled by random factors and structural factors.Pb,As and Hg were dominated by structural variability,and the spatial correlation was strong,which was mainly affected by natural factors.The results of Kriging interpolation showed that the high content of Cd and Pb is mainly distributed in the southeastern part of the study area.,and the content of Hg in east was higher than west,and the content of As in high value areas are mainly distributed in the south,and the content of Cr in the high value areas are mainly distributed in the southwest.(3)The ecological risk assessment results showed that the proportion of the comprehensive ecological risk of five kinds of heavy metals which is higher than moderate risk was accounted for 24.35%,which was harmful to ecology.The risk of Cd was high,and the risk was the highest in the five kinds of heavy metals.This should cause the attention of the relevant departments.As a result of the town statistics showed that As,Pb and Cr were low risk in every town,the ecological harm was relatively small;while Cd and Hg had different degrees of risk,the difference between each town was obvious;the comprehensive risk was different between each town.Overall,the central and southern ecological risk is higher than other regions.(4)The results of human health risk assessment showed that the daily intake of food intake was the highest among the three exposure pathways and was much higher than that of soil oral intake and soil through skin contact pathway.The daily daily intake combined three exposure routes ranked Cr> Pb> Hg> As> Cd.The risk of Cd varied greatly,and there were various levels of risk in each region.It was also the most risky among several heavy metal elements.Hg was more risky in the southwest of the study area than in other places.Cr was only risky in a southern town,and other areas were low risk.The combined risk of non-carcinogenic risk was higher in the southeastern region,and the carcinogenic risk wass mainly affected by Cd,which made the overall risk larger,and the southeast and middle's were higher than other regions.