| The parent material types of Hunan rock minerals are complex and diverse,and the soil types are numerous.For the purpose of understanding the As,Hg,Cr,Pb content and distribution of heavy metals in paddy soil,guiding the prevention and control of heavy metals in farmland,establishing and perfecting the database of heavy metals,based on the soil classification,60 typical sections and 339 soil samples were excavated from the paddy soils in Hunan region of typical parent material distribution area,namely purple clayey soil,reddish yellow clayey soil,grey clayey soil,alluvial sand soil,yellow clayey soil and granitic sandy soil.The physical and chemical properties of soil As,Hg,Cr,Pb,p H,organic matter,free iron oxide and particle classification composition were detected and analyzed to investigate content and distribution characteristics of paddy soil As,Hg,Cr,Pb with different parent material development,assess the percentage of heavy metals in the bottom layer as a percentage of the surface soil,explore the influence of parent material type and soil physicochemical properties on the heavy metal content in the soil.The conclusions are as follows:(1)Analysis of the total content of As,Hg,Cr,Pb in surface layer of 60 paddy soil sections shows that the average content of each element is 12.51±7.78mg/kg,0.22±0.23mg/kg,88.05±22.45mg/kg,30.93±15.48mg/kg,respectively.The average content of the six parent material paddy soils is As6.83～17.54mg/kg,Hg0.137～0.394mg/kg,Cr54.41～99.22mg/kg,Pb23.35～40.01mg/kg,respectively.The content of most elements in alluvial sand soil,yellow clayey soil and grey clayey soil is in the middle and high level,purple clayey soil and reddish yellow clayey soil are in the middle and low level,and the four elements of granitic sandy soil are different,two elements are high,the other two are low.The highest element content ranged from 1 to 3 times of the lowest,in which the whole As,Cr of alluvial sand soil was 2.57 times and 1.82 times of that of granitic sandy soil,total Hg of grey clayey soil is 2.88 times of that of reddish yellow clayey soil,and total Pb of granitic sandy soil is 1.71 times of that of purple clayey soil.All the average contents of total As,Hg,Cr,Pb in surface layer of 60 paddy soil profiles were lower than those of the pollution screening values(As30mg/kg,Hg0.5mg/kg,Cr250mg/kg,Pb100mg/kg).Comparing the cumulative changes of soil background values of each parent rice in Hunan,the accumulation of total As,Pb in the surface layer of most paddy soil is not obvious and the Hg,Cr content is accumulated.The paddy soil samples with heavy metal content greater than the background value were distributed in the east,west and south of the province.(2)Analysis of the effective content of As,Hg,Cr,Pb in surface layer of 60 paddy soil sections shows that the average content of each element is 0.26±0.16mg/kg,0.028±0.033mg/kg,2.44±0.86mg/kg,10.37±4.79mg/kg,respectively.The average content of the six parent material paddy soils is effective As0.09～0.49mg/kg,effective Hg0.015～0.058mg/kg,effective Cr1.78～2.77mg/kg,effective Pb 8.47～11.39mg/kg.The effective content of 4 elements in granitic sandy soil and purple clayey soil is on the middle low level,and the remaining paddy soil is on the upper middle level.(3)In most paddy soils,the effective content of Hg,Cr is basically consistent with the change law of its corresponding total content,As,Pb are different.There was a significant positive correlation between the effective state content and its total content.Except for Cr element,the other elements extraction percentage of different parent paddy paddy rice soil(percentage of effective state content in total content)all differ greatly,generally grey clayey soil and yellow clayey soil is higher,granitic sandy soil is lower.The average extraction percentage of element is Pb>Hg>As≈Cr.(4)The heavy metal content in the bottom of paddy soil divided by the surface content indicate that the proportion of total As,Hg,Cr,Pb is between 47～122%.The proportion of total Hg,Pb is in the upper middle,and the proportion of the total As,Cr is higher.With the exception of higher effective Hg(100～200%),the proportion of effective states of other elements is between 31～95%.The proportion of effective As,Cr is medium upper,and the proportion of effective Pb is medium lower.Except for the Hg element,the total proportion of each parent paddy soil bottom / surface As,Cr,Pb is higher than that of the effective state,and alluvial sand soil is higher in different parent material.(5)Correlation analysis show that the correlation degree between the content of each element and the physical and chemical properties of soil is different.The content of total As,Hg,Pb in soil is significantly correlated with the content of organic matter(among which only As is negatively correlated),and the content of total As,Cr is positively correlated with free iron oxide in soil.Effective As,Cr content of soil was significantly correlated with organic matter and particle content at all levels(only sand grains are negatively correlated).Free iron oxide content is the main soil factor affecting total As,Cr content.Organic matter content is the main influencing factors affecting the content of total Hg,Pb and the content of effective As,Cr,Pb. |
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