Study On Spatial Distribution Of Mercury In Agrarian Soil And Its Absorption In Wheat Of Baiyin City's Suburb

The content and chemical speciation distribution characteristics of mercury in surface and profile cropland of Baiyin suburb,and the migration and distribution characteristics of mercury in soil-wheat system were studied through field investigation and laboratory analysis.The mercury pollution levels in soil and wheat grain was evaluated,and the relationships between mercury content in soil and wheat and soil physicochemical property were analyzed.The results indicated that:(1)The range of mercury contents were 0.0449-4.2978mg/kg,and the average content of mercury was 1.3946mg/kg in surface soil.The average contents of mercury of topsoil in different sampling in ranking were Sha Pogang>Minqin three team,Yi Duqiang and Temporary two pumping stations>Ya Qushui>Liang Jiayao>Lee counter>Su Jiadun>Hao Jiachuan,Fluoride salt factory>Guan Yinya.57.5%of the samples exceeded the ? grade standard soil environmental quality standards.Slight pollution,middle pollution and serious pollution points were 27.5%?20%and 10%,respectively.(2)In profile soils,the contents of mercury were mainly enriched in the topsoil,and the migration was weak in vertical direction.Mercury contents in topsoil(0-20cm)were much higher than the subsoil.Mercury contents decreased with soil depth,and it decreased drastically between the layers of 0-20cm and 20-40cm,then droped slowly as the depth increased.The differences of mercury contents were not significant under 40cm soil layers,meanwhile,the contents of mercury showed a significant negative power variation from topsoil to subsoil.(3)Based on analysis of mercury speciation,the contents of different mercury species reduced,along with the reduction of total mercury contents in selected eight soil profile sample points.The percentages of hydrochloric acid soluble mercury,nitric acid soluble mercury and sulfide mercury were higher in surface and profile soil samples,furthermore,the proportion of nitric acid soluble mercury tended to rise as depth increasing.While the average partition coefficient of mercury species in wheat rhizosphere soil samples was as follows in sequence:sulfide mercury(Hg)>hydrochloric acid soluble Hg>organic matter bound Hg>nitric acid soluble Hg>residual Hg>humus acid bound Hg>exchangeable Hg.It turned out that Hg was dominantly associated with sulfide Hg,hydrochloric acid soluble Hg and organic matter bound Hg.The content of stable state Hg was majority,and its bioavailability was lower comparatively.(4)The average contents of mercury in wheat in ranking were root>leaf>stem>chaff>grain.The contents of mercury were mainly accumulated in the roots,with its low migration.The assessment of single factor pollution index for wheat grain showed that the average content of mercury in grain was 0.0181mg/kg,which was lower than the tolerance limit of mercury in foods,and 34.62%of the samples exceeded the limit.The assessment of health risk showed that almost the entire grain samples were security,and there was little health risk for human body to eat the wheat which produced in the study area.(5)The content of each form of mercury was significantly and positively correlated with the total content of mercury.The total content of mercury in topsoil and pH values showed strong negative correlations.The organic matter had remarkably affect on the content of totalmercury and species in profile soils.The contents of mercury in root,leaf and chaff of wheat had significant relationships with the content of total mercury and active state mercury.Conversely,the contents of mercury in stem and grain were not significant relationships with the content of total mercury and species.In addition,the contents of mercury in root,stem,leaf and chaff of wheat was significantly and negatively correlated with the pH values.