黄土区秸秆腐殖化溶解性有机质对土壤铅赋存形态的影响机制

摘要

重金属是土壤中最具代表性的污染物之一，重金属的赋存形态直接关系到其生理毒性和迁移行为，是重金属污染研究的重要方向。重金属形态与环境条件关系密切，鉴于土壤系统的高度复杂性，相近条件下的重金属形态转化行为也可能不尽相同。相关研究目前尚未有统一定论，成为有待验证的理论问题。在实验了解秸秆腐殖化DOM性质（紫外光谱、三维荧光光谱和红外光谱）的基础上，借助Tessier连续提取‐AAS法分析DOM作用下铅的形态转化规律，据此建立溶解性有机碳（DOC）与有机结合态铅的线性关系，并辅以FTIR明确DOM官能团对铅形态转化的贡献。结果发现：DOM紫外吸收主峰位于229 nm处，荧光组分集中于λex／em ＝250／350 nm ，λex／em ＝250／450 nm和λex／em ＝330／450 nm区域，归属为紫外区类富里酸和可见光区类腐殖酸荧光峰。DOM的官能团组成比较复杂，—OH ，CO，N— H等振动峰比较明显。DOM能够影响黄土铅的赋存形态，其存在有助于降低可交换态、铁锰氧化态和残渣态铅含量，但对碳酸盐结合态铅含量影响甚微。DOC含量与有机结合态铅含量正相关（r＝0.6918），表明DOM 可以有效络合铅离子；DOM中的—OH ，CO，—COOH等基团对铅离子的形态转化具有关键作用。%Heavy metal is regarded as one of the most representative contaminants in soil ,and the chemical speciation is greatly related to the toxicity and transformation behavior ,which attracts the attention of researchers for years .The environmental fac‐tors could change the speciation of heavy metals ,plus to the complexity of soil system ,and the transformation variation of speci‐ation might occasional existed under similar conditions .At present ,the different viewpoints of related issues are urgent to be in‐vestigated .The characteristics of DOM from straw humification were revealed with UV spectra ,3D‐EEMs spectra and FTIR spectra ,and the Tessier Sequential Extraction Procedure was used to study the speciation transformation behavior of lead affect‐ed by DOM .The linear relationship of the contents between DOC and lead bound to organic matter was indicated to further dis‐cuss the influence mechanism of lead speciation using FTIR .The results showed:the absorbance peak of DOM located in 229 nm in UV spectra ,and the fluorescence peaks appeared around the regions of λex/em =250/350 nm ,λex/em =250/450 nm and λex/em =330/450 nm ,referred as UV fulvic‐like fluorescence ,and visible humic‐like fluorescence ,respectively .The dominant functional groups of DOM included —OH , C O and N—H .The three fractions contents of lead (exchangeable ,bound to iron and manganese oxides ,residual) decreased ,while that of lead bound to carbonates varied little .The contents of DOC and lead bound to organic matter appeared positive correlation (r=0.691 8) ,indicating the effective complexation between DOM and lead ions . The functional groups of —OH , C O and —COOH played an important role for the speciation transformation of lead ,sug‐gested from the FTIR spectra .