Abstract:

The interaction between microplastics (MPs) and mercury (Hg) can cause potential risks to water environment and aquatic organisms. However, to the best of our knowledge, the systematic adsorption behavior of MPs and Hg in water environment has not been reported so far. The purpose of the article is to explore the interaction between polystyrene microplastics (PS-MPs) and Hg²⁺ widely existing in water environment as well as to evaluate their mutual behavior. Herein, the adsorption behavior of PS-MPs with Hg²⁺ and their related physicochemical properties were studied under different experimental conditions, including adsorption time, pH values, ionic levels, PS-MPs particle sizes, and environmental temperatures, using solid sampling Hg analyzer, scanning electron microscope, X-ray energy dispersive spectrometer (EDS) and Fourier transform infrared spectrometer. Results show that PS-MPs (average 60 μm particle size) can rapidly adsorb Hg²⁺ in a few minutes and then reach the adsorption equilibrium within 4 h; the adsorption kinetics of Hg²⁺ by PS-MPs conform the pseudo-second order kinetics, while the adsorption isotherm follows the Freundlich model. With the increase in Hg²⁺ content in solution, the Hg²⁺ adsorption capacity of PS-MPs becomes higher, with the maximum adsorption of 291.03 ng·mg^-1. The adsorption behavior of PS-MPs and Hg²⁺ is mainly controlled by the nonlinear multi-molecular layer absorption mechanism, consisting of multiple stages caused by the mutual role of static electricity, van der Waals force and chemical complexation adsorption, which has been proved by the results of energy spectroscopy and infrared spectroscopy. In addition, the study also found that when the pH value was 7.0, the equilibrium adsorption capacity of PS-MPs for 100 ng·g^-1 Hg²⁺ reached maximum (41.51 ng·mg^-1). The higher the temperature, the greater the equilibrium adsorption capacity of Hg²⁺ by PS-MPs with smaller particle size. With the increasing ionic level in the solution, the adsorption capacity of Hg²⁺ was reduced. This work is theoretically helpful for the further investigation of the mixed pollution of PS-MPs and mercury and their environmental remediation in the future and the biological effects between PS-MPs and Hg on aquatic organisms should be further studied.

Key words: polystyrene microplastics, mercury ion, adsorption, kinetics, isotherms

摘要：

微塑料（MPs）和重金属汞（Hg）之间的相互作用会对水环境及水生生物产生潜在危害，目前尚缺乏水环境中MPs对Hg吸附行为的系统研究。利用直接进样测汞仪、场发射扫描电镜-能谱仪和傅里叶变换红外光谱仪等手段，研究不同吸附时间、溶液pH、离子强度、PS-MPs粒径、环境温度等条件下PS-MPs对Hg²⁺的吸附行为以及相关的物化参数，探究环境中广泛存在的聚苯乙烯微塑料（PS-MPs）与水环境中Hg²⁺之间的相互作用，评价PS-MPs和Hg的环境行为。结果表明，平均粒径为60 μm的PS-MPs能在数分钟内快速吸附Hg²⁺，在4 h内达到吸附平衡；PS-MPs对Hg²⁺的吸附动力学符合准二级动力学模型，吸附等温线遵循Freundlich模型。其对Hg²⁺的最大吸附量为291.03 ng·mg^-1，在此范围内溶液中Hg²⁺含量越高，PS-MPs的吸附量越大。吸附过程存在多个吸附阶段且以非线性多分子层吸附机制为主，结合能谱和红外光谱结果证明了PS-MPs与Hg²⁺的吸附过程主要包括静电、范德华力和化学络合吸附作用。另外，该研究还发现当溶液pH为7.0时，PS-MPs对100 ng·g^-1 Hg²⁺的平衡吸附量最大，约为41.51 ng·mg^-1；温度越高，粒径更小的PS-MPs对Hg²⁺的平衡吸附量大；溶液中离子强度越高，Hg²⁺吸附量降低。该论文为实际环境中PS-MPs和重金属Hg的混合污染治理提供了一定的理论参考，今后还需进一步研究PS-MPs和Hg结合对水生生物的生物效应。

关键词: 聚苯乙烯微塑料, 汞离子, 吸附作用, 动力学, 等温线