Study On Effect Of Biochar On Fraction And Bioavailablity Of Antimony In Contaminated Soil

Antimony(Sb)is a heavy metal with highly toxic.The amount of Sb in the soil is increasing due to anthropogenic activities.Excessive Sb intake could ultimately threat human health.Recently,biochar(BC)has been accepted for remediation of heavy metal contaminated soil.However,the mechanism of BC in Sb-contaminated soils is not clear.Therefore,clarifying the effect of BC on Sb behavior in soil and its mechanism,will help to provide more theoretical basis for the effective application of BC.The important content of this dissertation were summarized as follows:(1)Wheat straw-derived BC(SBC)and fruit(apple)tree-derived BC(FBC)were obtained at the pyrolysis temperatures of 500 °C,Sb-contaminated soil was incubated with/without 0.5%,5 %,10 % of SBC and FBC for 130 days.In order to investigate the effect of BC on the fraction and species of Sb,dynamic change of Sb fraction and species were assessed by the sequential chemical extraction and citric acid extraction respectively.The results showed that BC prepared from two different materials had different properties,which resulted in different mobilization effects on Sb.During the first 20 d with SBC incubation and 50 d with FBC incubation,the mobilization of Sb and the content of critic extractable Sb(III)increased.After 20 d with SBC incubation and 50 d with FBC incubation,the mobilization of Sb and the content of critic extractable Sb(III)decreased.BC affected the content of citric acid extractable Sb in different valence states,which directly affected the toxicity of Sb to plants.(2)To examine the change mechanism of Sb fraction and species induced by BC,the physicochemical properties of soils incubated for 130 days were analyzed.The soil pH,Eh,conductivity,cation exchange capacity and dissolved organic matter were measured during incubation.The elemental change of soil with 10 % SBC at different incubation time was checked.The correlation analysis and principal component analysis(PCA)were used to analyzerelationship between Sb immobilization/mobilization and change of soil properties induced by BC.The obvious change of soil properties can be observed when the soil was treated with 10 % BC instead of 5 % and 0.5 % BC.During the first 20 d with SBC incubation and 50 d with FBC incubation,Sb mobilization increased may be that electrostatic exclusion repulsion of functional group in BC,OM and functional group of BC governs the reduction reactions,and anionic competition,electrostatic repulsion and biological reduction in soil induced by BC.By contrast,after 20 d with SBC incubation and 50 d with FBC incubation,the mobilization of Sb decreased may attribute to formation of complexes between Sb and OM of BC,secondary mineral precipitation,and organic complex between Sb and humus acid in soil induced by BC.(3)In order to further explore the change mechanism of soil microbial properties on the Sb fraction and species,the biological properties of soils samples at change turning point of Sb fraction and species were analyzed.Sb-oxidizing bacteria were isolated from soil by traditional bacterial isolation method.The changes of soil microbial community structure and the expression of Sb oxidizing genes were measured.Redundancy analysis(RDA)and spearman correlation analysis were used to clarify the relationship between the changes of soil microbial community structure and Sb oxidizing genes and the changes of Sb fraction induced by BC.The results showed that BC increased the abundance of soil microorganisms and changed the relative abundance of soil microorganisms at different levels,and affected the community structure of soil microorganisms.BC increased the relative abundance of soil Sb oxidizing gene(anoA).The bacteria isolation showed that Sb oxidizing bacteria existed in soil,which might affect the redox of Sb.The results of correlation analysis showed that the change of microorganisms was correlated with the change of Sb fraction,indicating that the change of soil microorganisms induced by BC affected the mobilization of Sb in soil.(4)Sb-contaminated soil incubated with/without wheat straw-derived biochar(SBC)and fruit tree-derived biochar(FBC)were used to plant Lycopersicum esculentum.Sb fraction in soil was measured by sequential chemical extractions.The correlation between the content of Sb fraction in soil and the accumulation of Sb in Lycopersicum esculentum was analyzed.The chlorophyll content,antioxidant system and root cell morphology of Lycopersicum esculentum were checked to invest the effect of biochar(BC)on biochemical characteristic of Lycopersicum esculentum in Sb-contaminated soil.Compare to control,the accumulation of Sb decreased 66%(P<0.01)in treatment with 10% SBC and 32%(P<0.01)in treatment with 10% FBC,respectively.Sb accumulation distribution was root>leaf>stem in all treatments.Sb fraction was changed with BC,and FBC has obvious effect on Sb fraction.The correlation analysis showed that the change of Sb fraction in soil affected the phytoavailability of Sb.Biochar increased chlorophyll content and CAT enzyme activities while reduced SOD and POD of Lycopersicum esculentum.Root cell morphology stress was reduced by BC compared with the control.