Environmental Sciences Group, Department of Chemistry and Chemical Engineering, Royal Military College, Kingston, P.O. Box 17000, Station Forces, Ontario, Canada K7K 7B4.
Chemosphere. 2011 Sep;84(10):1378-85. doi: 10.1016/j.chemosphere.2011.05.019. Epub 2011 Jun 23.
Dissolution kinetics of arsenic from soils and tailings were studied under simulated gastrointestinal conditions to determine the effects of residence time, pH and soil composition on the bioaccessibility of arsenic. The samples were sieved to four particle size fractions from bulk to <45 μm, and included arsenic minerals, soils and tailings with total arsenic concentrations ranging from 19 to 42000 mg kg(-1). The bioaccessible arsenic concentrations varied from 2.8 to 10000 mg kg(-1), and the highest concentrations were associated with the smallest particle size fractions. Kinetic parameters were determined for each sample extracted under gastric conditions (pH=1.8) followed by intestinal conditions (pH=7.0). Under gastric pH conditions, dissolution appeared to be diffusion-controlled and followed an exponential curve, whereas a logarithmic or linear model was used to describe the mixed dissolution mechanisms observed under intestinal conditions. Nine of the 13 samples tested reached a steady state bioaccessible arsenic concentration within the 5-h physiologically-based extraction test (PBET). However the bioaccessible arsenic concentrations in four tailings samples increased significantly (p=0.034) between the 5-h and the extended 24-h extraction under intestinal conditions. Since arsenic absorption may occur along the entire digestive tract, assessments based on the standard 5-h PBET extraction may not adequately estimate the risks associated with arsenic absorption in such cases. The slow dissolution kinetics associated with secondary arsenic minerals in some tailings samples may require extending the PBET extractions to longer periods, or extrapolating using the proposed kinetic models, to reach steady state concentrations in simulated gastrointestinal fluids.
在模拟胃肠道条件下研究了土壤和尾矿中砷的溶解动力学，以确定停留时间、pH 值和土壤成分对砷生物可给性的影响。将样品筛分至四个粒径范围，从大块至 <45 μm，包括砷矿物、土壤和总砷浓度范围为 19 至 42000 mg kg(-1)的尾矿。生物可利用的砷浓度变化范围为 2.8 至 10000 mg kg(-1)，最高浓度与最小粒径范围相关。在胃条件（pH=1.8）下提取每个样品后，确定动力学参数，然后在肠条件（pH=7.0）下提取。在胃 pH 条件下，溶解似乎是扩散控制的，遵循指数曲线，而对数或线性模型用于描述在肠条件下观察到的混合溶解机制。在 5 小时生理相关提取试验（PBET）中，测试的 13 个样品中有 9 个达到了稳定的生物可利用砷浓度。然而，在肠条件下，4 个尾矿样品中的生物可利用砷浓度在 5 小时和延长至 24 小时的提取之间显著增加（p=0.034）。由于砷吸收可能沿着整个消化道发生，因此基于标准 5 小时 PBET 提取的评估可能不能充分估计在这种情况下与砷吸收相关的风险。一些尾矿样品中次生砷矿物的缓慢溶解动力学可能需要将 PBET 提取延长至更长时间，或者使用提出的动力学模型进行推断，以在模拟胃肠道液体中达到稳定状态浓度。
