Kalis Erwin J J, Davis Thomas A, Town Raewyn M, Van Leeuwen Herman P
Laboratory of Physical Chemistry and Colloid Science, Wageningen University, The Netherlands.
Environ Sci Technol. 2009 Feb 15;43(4):1091-6. doi: 10.1021/es802305n.
Alginate gel is representative of polysaccharide-based components of cell walls which contain a large number of negatively charged functional groups. The structural charge gives rise to a Donnan potential in the gel, which impacts significantly on the partitioning of ions between the aqueous medium and the gel. We measured the Donnan potential and partitioning of Cd2+ in alginate gel as a function of ionic strength in the range 1-100 mM. The Cd2+ partition coefficient between gel and medium, as measured by in situ microelectrode voltammetry, reaches values between 10 and 100 in the 0.1-1 mM ionic strength range, and agrees well with Donnan partition calculations based on the charge density of the gels. The total Cd(II) concentration in the gel correlates approximately linearly with the free [Cd2+]gel. The results imply that metal ion activities in the biopolymer gel phase may generally differ drastically from those in the bulk medium to an extent that strongly depends on ionic strength. This feature must be taken into account in estimations of exposure conditions for predictions of bioavailability.
藻酸盐凝胶是细胞壁中基于多糖的成分的代表，其含有大量带负电荷的官能团。结构电荷在凝胶中产生唐南电位，这对离子在水介质和凝胶之间的分配有显著影响。我们测量了藻酸盐凝胶中Cd2+的唐南电位和分配情况，作为离子强度在1 - 100 mM范围内的函数。通过原位微电极伏安法测量，凝胶与介质之间的Cd2+分配系数在0.1 - 1 mM离子强度范围内达到10至100之间的值，并且与基于凝胶电荷密度的唐南分配计算结果非常吻合。凝胶中总Cd(II)浓度与游离[Cd2+]凝胶大致呈线性相关。结果表明，生物聚合物凝胶相中的金属离子活性通常可能与本体介质中的金属离子活性有很大差异，其程度强烈依赖于离子强度。在预测生物可利用性的暴露条件估计中必须考虑这一特征。
