Kalis Erwin J J, Weng Liping, Dousma Freerk, Temminghoff Erwin J M, Van Riemsdijk Willem H
Wageningen University, Department of Soil Quality, P.O. Box 8005, 6700 EC, Wageningen, The Netherlands.
Environ Sci Technol. 2006 Feb 1;40(3):955-61. doi: 10.1021/es051435v.
Metal toxicity is not related to the total but rather to the free or labile metal ion concentration. One of the techniques that can be used to measure several free metal ion concentrations simultaneously is the Donnan Membrane Technique (DMT) in combination with the inductively coupled plasma-mass spectrometer (ICP-MS). However, free metal ion concentrations in natural waters are commonly below the detection limit of ICP-MS. We decreased the detection limit by making use of a ligand, and we developed a field DMT cell that can be applied in situ in natural waters. A kinetic approach can be used to calculate free metal ion concentrations when the equilibrium time becomes too large. The field DMT measured in situ in natural waters a free metal ion concentration ranging from 0.015% (Cu) to 13% (Zn) of a total metal concentration ranging from 0.06 nM (Cd) to 237 nM (Zn). The free metal ion concentrations were difficult to predict using an equilibrium speciation model, probably due to the uncertainty in the nature of the dissolved organic matter or the presence of other reactive colloids. It is shown that DMT can follow changes in the free metal ion concentration on times scales less than a day under certain conditions.
金属毒性并非与总金属浓度相关，而是与游离或不稳定的金属离子浓度有关。可用于同时测量多种游离金属离子浓度的技术之一是唐南膜技术（DMT）与电感耦合等离子体质谱仪（ICP-MS）联用。然而，天然水中的游离金属离子浓度通常低于ICP-MS的检测限。我们通过使用一种配体降低了检测限，并开发了一种可原位应用于天然水的现场DMT装置。当平衡时间过长时，可采用动力学方法来计算游离金属离子浓度。现场DMT对天然水中的原位测量表明，游离金属离子浓度占总金属浓度的0.015%（铜）至13%（锌），总金属浓度范围为0.06 nM（镉）至237 nM（锌）。使用平衡形态模型很难预测游离金属离子浓度，这可能是由于溶解有机物性质的不确定性或其他活性胶体的存在。结果表明，在某些条件下，DMT能够在小于一天的时间尺度上跟踪游离金属离子浓度的变化。
