Bioavailability And Long-term Stability Assessment After Arsenic-contaminated Soil Stabilization

Arsenic is one of the main types of heavy metal pollution in soil.Stabilization has become one of the main techniques for the repair of heavy metal contaminated soil in China due to its fast repairing speed,low cost and convenient implementation.At present,the leaching toxicity test used for soil stabilization only reflects the change of heavy metal leaching concentration under simulated conditions,and cannot accurately reflect the bioavailability,toxicity characteristics and long-term stability of heavy metals after soil stabilization treatment.In this study,arsenic-contaminated soil was used as the research object,and alfalfa and soil microbes were used as indicator organisms to study the bioavailability of arsenic before and after soil stabilization,and compared with the effective state content obtained by different chemical extractants.At the same time,the soil was exposed to the freeze-thaw cycle and the drying-wetting conditions,the leaching concentration and fractionation of arsenic after long-term natural stress were studied before and after the stabilization.Provide scientific basis for bioavailability assessment and long-term stability study after soil stabilization.(1)The leaching toxicity and fractional distribution of arsenic in soil before and after stabilization were studied.The results showed that the leaching concentration of arsenic in the soil decreased from 2.03 mg·L-1 to 0.11 mg·L-1,and the stabilization efficiency was 94.6%.After the soil is stabilized,the fractionation of arsenic in the soil is transformed from the ion exchange state and the carbonate bound state to the iron-manganese oxide bound state,the organic matter bound state and the residual state which are more closely combined with the soil matrix.(2)The effects of soil stabilization on earthworms and the accumulation of arsenic in earthworms were investigated.The results showed that exposure to soil for 28 days,the mortality and relative weight loss rate of earthworms decreased by 63.3%and 6.11%after stabilization.The contents of total arsenic and As(?)in the earthworm tissue increased with the prolongation of exposure time before and after soil stabilization.The mortality and weight loss of earthworm were significantly correlated with the content of As(?)in earthworm.The accumulation of arsenic in the earthworm before and after soil stabilization was the highest correlation with the available content of 0.43 mol·L-1 HO Ac solution as extractant.The 0.43 mol·L-1 HO Ac solution was used as the extractant to accurately reflect the bioavailability of arsenic to earthworms.(3)Then,study the effects of soil stabilization on microbes.The results showed that stabilization reduced the luminescence inhibition effect of Vibrio fischeri,but the soil was toxic to Vibrio fischeri after stabilization.After stabilization,the inhibition rate of Vibrio fischeri was still as high as 43.05%.The abundance and diversity of community distribution were slightly lower than before stabilization.(4)The effects of wetting-deying and freezing-thawing on soil pH,leaching toxicity and fractional distribution of Arsenic were finally studied.After the soil freeze-thaw cycle,the leaching concentration of arsenic in the soil increased,the soil pH decreased.After 200 freeze-thaw cycles,the ion exchange state and carbonate bound state of arsenic in stabilized soil increased by 6.39%and 3.81%,the Fe-Mn oxide bound state,the organic matter bound state and the residual state of arsenic in stabilized soil were reduced by 2.45%,2.73%and 5.01%,respectively.The drying-wetting did not change the soil pH,the arsenic leaching concentration in the soil decreased.After 15 drying-wetting cycles,the ion exchange state and carbonate binding state of arsenic in stabilized soil decreased by 3.75%and 3.26%,while the organic bound state and residual state of arsenic in stabilized soil increased by 2.83%and 4.41%,respectively.