Town Raewyn M, van Leeuwen Herman P, Blust Ronny
Systemic Physiological and Ecotoxicological Research (SPHERE), Department of Biology, University of Antwerp, Antwerp, Belgium.
Physical Chemistry and Soft Matter, Wageningen University & Research, Wageningen, Netherlands.
Front Chem. 2018 Dec 14;6:627. doi: 10.3389/fchem.2018.00627. eCollection 2018.
A simple model, based on spherical geometry, is applied to the description of release kinetics of metal species from nano- and micro-plastic particles. Compiled literature data show that the effective diffusion coefficients, , for metal species within plastic polymer bodies are many orders of magnitude lower than those applicable for metal ions in bulk aqueous media. Consequently, diffusion of metal ions in the aqueous medium is much faster than that within the body of the plastic particle. So long as the rate of dissociation of any inner-sphere metal complexes is greater than the rate of diffusion within the particle body, the latter process is the limiting step in the overall release kinetics of metal species that are sorbed within the body of the plastic particle. Metal ions that are sorbed at the very particle/medium interface and/or associated with surface-sorbed ligands do not need to traverse the particle body and thus in the diffusion-limiting case, their rate of release will correspond to the rate of diffusion in the aqueous medium. Irrespective of the intraparticulate metal speciation, for a given diffusion coefficient, the proportion of metal species released from plastic particles within a given time frame increases dramatically as the size of the particle decreases. The ensuing consequences for the chemodynamics and bioavailability of metal species associated with plastic micro- and nano-particles in aquatic systems are discussed and illustrated with practical examples.
一个基于球面几何的简单模型被用于描述金属物种从纳米和微米级塑料颗粒中的释放动力学。汇编的文献数据表明，塑料聚合物体内金属物种的有效扩散系数远低于大量水性介质中金属离子的有效扩散系数，相差多个数量级。因此，金属离子在水性介质中的扩散比在塑料颗粒体内的扩散快得多。只要任何内球金属配合物的解离速率大于颗粒体内的扩散速率，后一过程就是吸附在塑料颗粒体内的金属物种整体释放动力学的限制步骤。吸附在颗粒/介质界面处和/或与表面吸附配体相关的金属离子不需要穿过颗粒体，因此在扩散限制的情况下，它们的释放速率将与水性介质中的扩散速率相对应。无论颗粒内的金属形态如何，对于给定的扩散系数，在给定时间范围内从塑料颗粒中释放的金属物种比例会随着颗粒尺寸的减小而急剧增加。文中讨论了与水生系统中塑料微颗粒和纳米颗粒相关的金属物种的化学动力学和生物有效性的后续影响，并通过实际例子进行了说明。
