Water & Soil Environment Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan.
J Environ Sci Health A Tox Hazard Subst Environ Eng. 2010;45(6):746-53. doi: 10.1080/10934521003651465.
The present study was performed to examine the effects of soluble organic matter and pH on the solubility of Bi in relation to inference with the behavior of metallic Bi dispersed in soil and water environments using EDTA, citric acid, tartaric acid, L-cysteine, soil humic acids (HA), and dissolved organic matter (DOM) derived from the soil organic horizon. The solubility of Bi by citric acid, tartaric acid, L-cysteine, HA, and DOM showed pH dependence, while that by EDTA did not. Bi solubility by HA seemed to be related to the distribution of pKa (acid dissociation constant) values of acidic functional groups in their molecules. That is, HA extracted at pH 3.2 solubilized Bi preferentially in the acidic range, while HA extracted at pH 8.4 showed preferential solubilization at neutral and alkaline pH. This was related to the dissociation characteristics of functional groups, their binding capacity with Bi, and precipitation of Bi carbonate or hydroxides. In addition to the dissociation characteristics of functional groups, the unique structural configuration of the HA could also contribute to Bi-HA complex formation. The solubility of Bi by naturally occurring DOM derived from the soil organic horizon (Oi) and its pH dependence were different from those associated with HA and varied among tree species.
本研究旨在考察土壤和水环境中分散的金属 Bi 的行为受可溶性有机物（SOM）和 pH 值影响的情况，所用 SOM 为 EDTA、柠檬酸、酒石酸、L-半胱氨酸、土壤腐殖酸（HA）和土壤有机层中提取的溶解性有机质（DOM）。柠檬酸、酒石酸、L-半胱氨酸、HA 和 DOM 对 Bi 的溶解度具有 pH 依赖性，而 EDTA 则没有。HA 对 Bi 的溶解度似乎与其分子中酸性功能团的 pKa（酸离解常数）分布有关。也就是说，在 pH 3.2 下提取的 HA 优先在酸性范围内溶解 Bi，而在 pH 8.4 下提取的 HA 则在中性和碱性 pH 下优先溶解 Bi。这与功能团的离解特性、它们与 Bi 的结合能力以及 Bi 碳酸盐或氢氧化物的沉淀有关。除了功能团的离解特性外，HA 的独特结构构型也可能有助于 Bi-HA 络合物的形成。来源于土壤有机层（Oi）的天然 DOM 对 Bi 的溶解度及其 pH 依赖性与 HA 不同，且在树种间存在差异。
