| In recent years,due to the rapid development of China's industry,agriculture and animal husbandry,a large amount of arsenic has entered the farmland,causing serious soil arsenic pollution.The arsenic-contaminated soil phytoremediation technology is economical and environmentally friendly,and is especially suitable for the repair and treatment of large-scale arsenic-contaminated soil,and is widely used in the repair of production.P.vittata L.is an arsenic hyperaccumulator.However,the activity of arsenic in arsenic-contaminated soil is low.In addition,the growth of P.vittata L.is slow and the biomass is low.The efficiency of P.vittata L.to repair soil arsenic pollution needs to be improved.This study selected two different types of soil(brown red soil,Jiaotian Village,Daye City,Hubei Province;yellow brown soil,Hushan Village,Jingmen City,Hubei Province)and 45 activator materials,soil and arsenic extraction by activator to remove the test and soil constant temperature and humidity culture experiments were carried out to select activators which can effectively improve the bioavailability of arsenic in soil,and the effect of activator on soil arsenic activation and arsenic pollution repair was investigated by using potted soil pot experiment.The main findings are as follows:1.The batch treatment experiment soil was carried out,to study the arsenic extracting effects of 45 kinds of materials on Jiaotian soil and Hushan soil was studied.The results showed that the five materials of phytic acid,metaphosphoric acid,oxalic acid,phosphoric acid and aminotriacetic acid(NTA)had better extraction effects on the two soils,and the extraction rate was 19%-48%(Jiaotian soil),66%-87%.(Hushan soil);followed by sodium phytate,silicic material,sodium dihydrogen phosphate,sodium pyrophosphate,citric acid,extraction rate of 13%-18%(Jiaotian soil),33%-56%(Hushan soil).Among them,phytic acid and oxalic acid had the best arsenic extraction effect on Jiaotian soil and Hushan soil,and the extraction rates were 48.2% and 37%,87% and 84%,respectively.2.Based on the results of soil solution test,considering the physical and chemical properties and agronomic properties of the material,alkaline activator materials(silicic material,sodium carbonate,biochar),chelating agent activator materials(NTA,phytic acid,oxalic acid,citric acid)and phosphoric acid activator materials(pyrophosphate,metaphosphoric acid,sodium dihydrogen phosphate)10 kinds of activators,were tested in the laboratory for 90 days of soil constant temperature and humidity culture to investigate the dynamic effect of the agent on soil arsenic activation.The results showed that the highest effective arsenic concentration of various activator Jiaotian soils was highest in sodium carbonate,sodium dihydrogen phosphate and phytic acid,which was 269%,209% and 141% higher than that of the original soil,followed by metaphosphoric acid,pyrophosphoric acid and oxalic acid,increased by 119%,112% and 102%,the effect of biochar,silicic material,citric acid and NTA is lower,from 76% to 98%;the highest effective arsenic concentration of sodium sulphate,NTA and silicic material is the highest in Hushan soil,compared with the original soil by 327%,256% and 194%,followed by citric acid,oxalic acid and biochar,increased by 179%,149% and 131%,phytic acid,pyrophosphoric acid,dihydrogen phosphate,sodium dihydrogen phosphate and metaphosphoric acid activation effects are low,ranging from 103% to 119%.In summary,sodium carbonate has a good effect on the activation of arsenic in both soils.3.The effects of different activators on the transformation of arsenic species in soil were studied by soil constant temperature and humidity culture experiments.The results showed that the addition of biochar,oxalic acid and NTA to Jiaotian soil could continuously reduce O-As content and increase Al-As and Fe-As content,silicic material,sodium carbonate,phytic acid,citric acid,metaphosphoric acid,pyrophosphoric acid and sodium dihydrogen phosphate can reduce O-As content in the soil for 20 days,increase the bioavailable arsenic content in soil,90-day the organism available arsenic content is reduced.The addition of medium and high concentration(0.5%,1% and 2%)activator to Hushan soil can reduce the content of Ca-As in soil and increase the content of A-As and Al-As.Among them,NTA,sodium carbonate and silicic material have the best activation effect,sodium dihydrogen phosphate,pyrophosphoric acid,and metaphosphoric acid are the second most effective,and phytic acid,citric acid,oxalic acid,and biochar are the least effective.4.The soil constant temperature and humidity culture experiment was carried out to study the effect of different activators on soil pH.The results showed that the alkaline activator materials could increase the pH of the two soils,and the effect of activator on the pH of Hushan soil was greater than that of the Jiaotian soil,sodium carbonate has the best effect on pH improvement,and biochar is the worst.The chelating agent activator material can reduce the soil pH,and the effect on the pH of the Jiaotian soil is greater than that of the Hushan soil.The phosphoric acid activator materials,pyrophosphoric acid and metaphosphoric acid treatment can reduce the pH of the two soils,and the effect on the pH of the Jiaotian soil is greater than that of the Hushan soil.After the treatment with sodium dihydrogen phosphate,the soil pH and CK are not much different.5.Five kinds of activators of silicic material,oxalic acid,phytic acid,fulvic acid and pyrophosphate were used in the P.vittata L.pot experiment.The results showed that 0.25 g/kg silicic material treatment had the highest recovery efficiency of arsenic by 10% and 8%,and the above-ground biomass respectively increased by 145% and 173%,and arsenic absorption increased by 174% and 128%,respectively.Silicic material treatment can improve the photosynthesis and antioxidant enzyme activities of Pteris vittata L.leaves,improve soil pH,promote the transformation arsenic of soil O-As to Al-As and Fe-As,and activate soil.Different activators improve the efficiency of valerian repair: silicic material > oxalic acid > pyrophosphate > phytic acid > fulvic acid.6.Hydrogen culture experiments were conducted to study the root exudates and the type of organic acid in the leaves of arsenic-sensitive plant P.nervosa Thunb.,arsenicenriched plant Nephrolepis exaltata L.and P.vittata L.The results showed that only oxalic acid was detected in the root exudates of Boston fern.Oxalic acid and tartaric acid were detected in N.exaltata L.Oxalic acid was detected in the P.vittata L.,and the tartaric acid was detected only under the stress of 50 mg/kg arsenic.The organic acids detected in the water extract of Boston fern leaves were oxalic acid and acetic acid;the organic acids detected in the water extracts of N.exaltata L.and P.vittata L.leaves were oxalic acid,acetic acid,malic acid and citric acid. |
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