A Preliminary Study On The Remediation Effect And Mechanism Exploration Of Amendments On Arsenic In Agricultural Soils Around High Arsenic Coal Mine

China is one of the countries more seriously affected by arsenic pollution,and according to the National Soil Pollution Survey Bulletin released in 2014,the rate of exceeding the standard for arsenic in soil points nationwide was 2.7%.Arable land around high arsenic coal mining areas in Guizhou province is contaminated to varying degrees,with soil arsenic levels ranging from 5.25mg/kg?234.14 mg/kg.With many mountains and little land in Guizhou,the land carrying load is large and the land use situation is rigorous,with many contaminated farmlands having to continue to be used for agricultural production.The use of chemical amendments to remediate or regulate arsenic-contaminated agricultural soils has been considered an effective and economical measure.In this paper,arsenic-contaminated farmland soils around a high arsenic coal mine were used as the object of study.An iron oxides(ferrihydrite)and an industrial by-products(phosphogypsum),which have the ability to immobilize arsenic,were selected as amendments.The effects of the two amendments on arsenic uptake by crops were compared.The arsenic bioavailability under different rhizosphere conditions and influence of two amendments on forms of soil arsenic were clarified.The mechanism and rhizosphere effect of soil arsenic immobilization by amendment were preliminarily explored in combination with crop physiological indexes.The main results are as follows:(1)The two amendments have better immobilization effect on arsenic in the agricultural soils around the high arsenic coal mine.It can effectively inhibit the uptake of arsenic to crops,promote the growth of crops and reduce the content of available arsenic in soil.Compared with control,the arsenic content of the above-ground part of crops could be reduced up to 24.25%,the dry weight of the crop increased by17.14%?66.66%,and the reduction rate of the soil effective arsenic state was 19.12%?24.48% under the phosphogypsum treatment.The arsenic content of the above-ground part of the crop could be reduced up to25.95%,the dry weight of the crop increased by 20.10%?433.33%,and the reduction rate of the soil effective arsenic state were 2.19%?29.26%under the ferrihydrite treatment.(2)amendments can enhance the resistance to arsenic stress in all four crops.The application of ferrihydrite can reduce the transport coefficients of arsenic to plants treated.Except for water spinach,the transport coefficients of arsenic to plants treated with ferrihydrite were lower than phosphogypsum and control.With the application of amendments,the chlorophyll content showed an increasing trend.Chlorophyll increased by 2.8%?21.2% and 15.7%?23.6% under phosphogypsum and ferrihydrite treatments,respectively.The effects of arsenic on antioxidant system enzymes in crop leaves vary with crop types.SOD was more affected by amendments,especially in phosphogypsum treatment.SOD in cabbage leaves was significantly increased,and the increase rate was up to 71.38% under the phosphogypsum treatment.Arsenic trapped in root surface cells,or accumulated in cell walls,and stored in vesicles through compartmentalization to reduce the damage of arsenic to crop root cells by amendments.(3)Amendments affect the availability of arsenic in rhizosphere,structure of soil microbial community was changed,and various microbial communities were inhibited or enhanced.The content of available arsenic in rhizosphere reduced by amendments significantly.Compared with control,the content of available arsenic in rhizosphere soil decreased by 30.42% and 38.50% under phosphogypsum and ferrihydrite treatments,and the application energy of hydropyrite increased soil p H.In addition,amendments reduced the proportion of arsenic in the highly migratory weakly acidic extractable,reducible and oxidizable states compared to the control.Amendments promoted the transformation of soil arsenic from mobile to immobile form.Amendments altered the structure of rhizosphere microbial communities of crops,improving the abundance of beneficial bacterial groups and alleviating arsenic stress on crops.At the phylum level,the relative abundance of Chloroflexi in vegetable(except rape)soils,the relative abundance of Proteobacteria and Firmicutes,and decreased the relative abundance of Acidobacteria in inter-rhizosphere soils of four crops were increased by amendments.(4)The remediation mechanism of arsenic in agricultural soils around high arsenic coal mines by amendments may be as follows: firstly,the amendments directly immobilized the unstable arsenic in the soil.Secondly,crop tolerance was improved,the abundance of beneficial microbial communities was increased,arsenic stress was reduced,and healthy crop growth was promoted,all through the synergistic action of the amendments,crop root and rhizosphere microorganisms.