Key Laboratory of Water and Sediment Sciences of Ministry of Education, State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, PR China.
Key Laboratory of Water and Sediment Sciences of Ministry of Education, State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, PR China.
Environ Pollut. 2024 Feb 1;342:123061. doi: 10.1016/j.envpol.2023.123061. Epub 2023 Nov 30.
The widespread promotion attempt of biodegradable plastics is considered as an effective solution to address conventional plastic pollution. However, the interaction of microplastics (MPs) easily broken down from biodegradable plastics with the coexisting pollutants in aquatic environments has gained less attention. Herein, we investigated the effects of the aging process and environmental factors on copper (Cu(II)) adsorption behavior by biodegradable polylactic acid and conventional polystyrene MPs. Results demonstrated that the aging process significantly altered physicochemical properties of both types of MPs, and PLA showed less resistance to aging. The aged polylactic acid MPs (aged-PLA) exhibited the far highest Cu(II) maximum adsorption capacity (7.13 mg/g) mainly due to its abundant oxygen-containing functional groups (OCFGs), followed by pristine polylactic acid (PLA, 6.08 mg/g), aged polystyrene (aged-PS, 0.489 mg/g) and pristine polystyrene (PS, 0.365 mg/g). The adsorption kinetics of Cu(II) on PLA MPs were controlled by film and intraparticle diffusion, while film diffusion governed the Cu(II) adsorption onto PS MPs. In addition to roles of rougher surface structure, greater surface area and pore filling, the complexation of OCFGs and electrostatic interaction were critical to the adsorption mechanism of aged-PLA and aged-PS, and cation-π interaction was associated with adsorption of aged-PS. Moreover, the adsorption capacity of Cu(II) on aged MPs gradually grew with the increasing pH from 4 to 7. Besides, humic acid significantly promoted the adsorption of Cu(II) at a low concentration (0-20 mg/L) due to the formation of binary mixtures of MPs-HA but inhibited the adsorption at a high concentration (50 mg/L) because of its competitive effect, suggesting the dual roles of humic acid in the adsorption process. Overall, our findings provide a better understanding of the adsorption behavior of metals on biodegradable MPs and emphasize their non-negligible risk as carriers of contaminant.
可生物降解塑料的广泛推广被认为是解决传统塑料污染的有效方法。然而，可生物降解塑料中容易分解成微塑料（MPs）与水生环境中共存污染物的相互作用却较少受到关注。在此，我们研究了老化过程和环境因素对可生物降解聚乳酸和传统聚苯乙烯 MPs 吸附铜（Cu(II)）行为的影响。结果表明，老化过程显著改变了两种类型 MPs 的物理化学性质，且 PLA 对老化的抵抗力较弱。老化后的聚乳酸 MPs（老化-PLA）表现出最高的 Cu(II)最大吸附容量（7.13mg/g），主要是由于其丰富的含氧官能团（OCFGs），其次是原始聚乳酸（PLA，6.08mg/g）、老化聚苯乙烯（老化-PS，0.489mg/g）和原始聚苯乙烯（PS，0.365mg/g）。Cu(II)在 PLA MPs 上的吸附动力学受膜扩散和内扩散控制，而 PS MPs 上的 Cu(II)吸附则受膜扩散控制。除了粗糙的表面结构、更大的表面积和孔填充作用外，OCFGs 的络合作用和静电相互作用是老化-PLA 和老化-PS 吸附机制的关键，而阳离子-π 相互作用与老化-PS 的吸附有关。此外，Cu(II)在老化 MPs 上的吸附容量随着 pH 值从 4 增加到 7 而逐渐增加。此外，腐殖酸在低浓度（0-20mg/L）下因 MPs-HA 二元混合物的形成而显著促进了 Cu(II)的吸附，但在高浓度（50mg/L）下由于其竞争作用而抑制了吸附，表明腐殖酸在吸附过程中具有双重作用。总的来说，我们的研究结果提供了对金属在可生物降解 MPs 上吸附行为的更好理解，并强调了它们作为污染物载体的不可忽视的风险。
