Study On The Fractionation Of Exogenous Arsenic Under Intermittent Irrigation

It is a prerequisite to reasonably evaluate the risk of soil arsenic contamination to explore the fractions transformation mechanism of soil arsenic.Intermittent irrigation,seasonal precipitation and dynamic change of groundwater level can cause the alternation change of soil moisture,resulting in soil redox conditions change.Arsenic,as a variable element,is very sensitive to redox conditions.Therefore,situation of soil moisture changes the combination of exogenous arsenic form transformation mechanism needs to be clear.This study of soil arsenic combination form as the research object,mainly by soil column simulation experiment method,the use of combination form continuous extraction technology,the research of intermittent irrigation,add humic acid soil,add sponge iron access to soil and filter material containing phosphate ions in the solution of soil exogenous arsenic in combination with the influence of the dynamic change of the form,then reveal mode of soil moisture changes exogenous arsenic aging-the activation process.It provides scientific basis for ecological risk assessment of soil arsenic and risk assessment of groundwater pollution,so as to guarantee safe production of food crops and safe drinking water of groundwater resources.The main conclusions of this study are as follows:(1)Under intermittent irrigation conditions,arsenic content in soil water at different depths in the four systems was all related to the upper layer>middle layer>lower layer.In the lower layer,the content of arsenic in soil water decreases with the increase of water access time.Compared with the control group,Humic acid and sponge iron filter material can effectively inhibit the release of water-soluble arsenic in soil in the upper soil water with significantly different redox conditions,and the inhibition of sponge iron filter material was stronger than that of humic acid,while the addition of phosphoric acid promoted the release of soil arsenic.(2)Compared with the control group,the addition of humic acid and sponge iron filter was beneficial to the reduction of the percentage of arsenic in the easily transported state and the increase of arsenic in the difficult transported state in the soil under intermittent irrigation.The addition of phosphate in soil inhibited the decrease of easy arsenic and the increase of the percentage of refractory arsenic.In addition,the aging degree of arsenic in soil with different depths in the same system is related to the lower layer >middle layer>upper layer.(3)Under intermittent irrigation conditions,The aging-activation process of arsenic in soil at different depths of each system is obviously different.Compared to the other two layers,arsenic in the lower soil would be activated under intermittent irrigation.(4)Under the effect of aging,with the increase of time,the bioavailability of arsenic in soil of different depths decreases continuously,and the relationship between the bioavailability is the upper layer>middle layer>lower layer.Compared with the control group,the addition of humic acid and sponge iron filter material was beneficial to reduce the bioavailability of arsenic in soil,while the addition of phosphoric acid increased the bioavailability of arsenic in soil.