School of Environment and Energy, South China University of Technology, Guangzhou, Guangdong 510006, People's Republic of China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou, Guangdong 510006, People's Republic of China.
School of Environment and Energy, South China University of Technology, Guangzhou, Guangdong 510006, People's Republic of China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou, Guangdong 510006, People's Republic of China.
Sci Total Environ. 2022 Oct 15;843:156996. doi: 10.1016/j.scitotenv.2022.156996. Epub 2022 Jun 27.
Dissolved organic matter (DOM), a ubiquitous ligand for heavy metals, plays a crucial role in regulating the bioavailability and fate of heavy metals in the environment. However, owing to complex structure and heterogeneity of DOM, it is still challenging to develop kinetics models to predict the rates of heavy metal reactions with DOM. In this study, we investigated the kinetics of Cd, Ni, and Pb release from a typical fulvic acid (FA) under a wide range of experimental conditions using a competing ligand exchange (CLE) method. Among three metals, Cd showed the fastest release from FA while Ni and Pb had slower release rates. Reaction pH also had different impact on the release rates of the three metals, presumably attributed to different proton/metal exchange ratios for the metal ion complexation with FA. We formulated a kinetics model for Cd, Ni, and Pb release from FA by considering metal ions dissociation from FA, re-association of metal ions with FA, and metal ion uptake by the resin in the CLE experiments. The chemical speciation model WHAM 7 was used to predict the local equilibrium status that the kinetic reactions were away from, which help to derive the kinetic parameters based on the equilibrium parameters. For both Cd and Pb, model calculations were sensitive to the re-association rates, especially at high pH, while for Ni, the impact of the re-association rates was less significant. Based on the model parameters obtained in this study, our model simulations have also demonstrated that metal-FA complexes may undergo different rates of dissociation in the environment, affecting the dynamic speciation and transfer of metals to other biological processes. This work has provided a quantitative tool for predicting metal release from DOM, which would be useful for predicting the bioavailability and fate of heavy metals in the environment.
溶解有机质（DOM）是重金属的普遍配体，在调节重金属在环境中的生物有效性和归宿方面起着至关重要的作用。然而，由于 DOM 结构复杂且具有异质性，因此仍然难以开发动力学模型来预测重金属与 DOM 反应的速率。在这项研究中，我们使用竞争配体交换（CLE）方法，在广泛的实验条件下研究了典型富里酸（FA）中 Cd、Ni 和 Pb 的释放动力学。在这三种金属中，Cd 从 FA 中的释放最快，而 Ni 和 Pb 的释放速率较慢。反应 pH 对三种金属的释放速率也有不同的影响，这可能归因于 FA 与金属离子络合的质子/金属交换比不同。我们通过考虑 FA 中金属离子的离解、金属离子与 FA 的再络合以及 CLE 实验中树脂对金属离子的吸附，为 FA 中 Cd、Ni 和 Pb 的释放制定了一个动力学模型。化学形态平衡模型 WHAM 7 用于预测动力学反应偏离的局部平衡状态，从而帮助根据平衡参数推导出动力学参数。对于 Cd 和 Pb，模型计算对再络合速率敏感，尤其是在高 pH 下，而对于 Ni，再络合速率的影响则不那么显著。基于本研究中获得的模型参数，我们的模型模拟还表明，金属-FA 配合物在环境中可能经历不同的离解速率，从而影响金属的动态形态和向其他生物过程的转移。这项工作为预测 DOM 中金属的释放提供了一种定量工具，这对于预测重金属在环境中的生物有效性和归宿非常有用。
