Hiradate Syuntaro, Furubayashi Akihiro, Uchida Natsuyo, Fujii Yoshiharu
Biodiversity Division, National Institute for Agro-Environmental Sciences (NIAES), 3-1-3 Kan-nondai, Tsukuba, Ibaraki 305-8604, Japan.
J Environ Qual. 2007 Jan 9;36(1):101-9. doi: 10.2134/jeq2005.0415. Print 2007 Jan-Feb.
To identify the important soil components involved in 2,4-dichlorophenoxyacetic acid (2,4-D) adsorption on Andosols, 2,4-D adsorption on a surface horizon of an Andosol was compared with that on hydrogen peroxide (H2O2)-treated (soil organic matter [SOM] was removed), acid-oxalate (OX)-treated (active metal hydroxides and SOM were removed), and dithionite-citrate-bicarbonate (DCB)-treated (free and active metal [hydr]oxides and SOM were removed) soil samples at equilibrium pHs ranging from 4 to 8. Although the untreated soil contained a large amount of organic C (71.9 g kg-1), removal of SOM had little effect on 2,4-D adsorption. Active surface hydroxyls, which were attached to the active and free metal (hydr)oxides and metal SOM complexes, were identified as the most important soil functional group for 2,4-D adsorption. The dominant mechanism of the 2,4-D adsorption was a ligand exchange reaction in which the carboxylic group of 2,4-D displaced the active surface hydroxyl associated with metals and formed a strong coordination bond between the 2,4-D molecule and soil solid phase. The ligand exchange reaction reasonably accounted for the selective adsorption of 2,4-D over Cl-, competitive adsorption of phosphate over 2,4-D, reduction in plant-growth-inhibitory activity of soil-adsorbed 2,4-D, and the high 2,4-D adsorption ability of Andosols. Although a humic acid purified from the soil did not adsorb 2,4-D, the presence of the humic acid increased 2,4-D adsorption on Al and Fe, probably by inhibiting the hydrolysis and polymerization of Al and Fe resulting in the preservation of available adsorption sites on these metals. The adsorption behavior of 2,4-D on soils could be a good index for predicting the adsorption behavior of other organic acids in soils.
为了确定参与2,4-二氯苯氧乙酸（2,4-D）在安山土上吸附的重要土壤成分，将2,4-D在安山土表层的吸附与在过氧化氢（H2O2）处理（去除土壤有机质[SOM]）、酸-草酸盐（OX）处理（去除活性金属氢氧化物和SOM）以及连二亚硫酸盐-柠檬酸盐-碳酸氢盐（DCB）处理（去除游离和活性金属[氢]氧化物以及SOM）的土壤样品在pH值为4至8的平衡条件下的吸附情况进行了比较。尽管未处理的土壤含有大量有机碳（71.9 g kg-1），但去除SOM对2,4-D吸附影响不大。附着在活性和游离金属（氢）氧化物以及金属SOM络合物上的活性表面羟基被确定为2,4-D吸附最重要的土壤官能团。2,4-D吸附的主要机制是配体交换反应，其中2,4-D的羧基取代与金属相关的活性表面羟基，并在2,4-D分子与土壤固相之间形成强配位键。配体交换反应合理地解释了2,4-D相对于Cl-的选择性吸附、磷酸盐对2,4-D的竞争性吸附、土壤吸附的2,4-D植物生长抑制活性的降低以及安山土对2,4-D的高吸附能力。尽管从土壤中纯化的腐殖酸不吸附2,4-D，但腐殖酸的存在增加了2,4-D在Al和Fe上的吸附，可能是通过抑制Al和Fe的水解和聚合，从而保留了这些金属上的可用吸附位点。2,4-D在土壤上的吸附行为可能是预测其他有机酸在土壤中吸附行为的良好指标。
