老化微塑料对水体中重金属铜和锌的吸附行为研究

Adsorption of heavy metal ions Cu^(2+) and Zn^(2+) onto UV-aged microplastics in aquatic system

微塑料(Microplastics, MPs)在水环境中可以作为重金属载体,对金属离子的迁移和毒性效应产生较大影响.本文开展了紫外光老化后的聚丙烯(Polypropylene, PP)和聚乙烯(Polyethylene, PE)对两种重金属离子Cu^(2+)和Zn^(2+)在单一和二元复合体系中的吸附行为研究.通过拟一级和拟二级动力学模型研究发现,微塑料对重金属离子的吸附过程更符合拟二级动力学过程,利用Langmuir模型和Freundlich模型对吸附等温线结果进行拟合,结果表明,在单一体系中,相同老化条件下的PP相比PE对金属离子的平衡吸附量更高,且对Cu^(2+)的吸附量均大于对Zn^(2+);在二元复合体系中,由于竞争吸附作用,MPs对重金属离子的吸附量小于在单一体系中的吸附量,且MPs对重金属离子的吸附过程更符合Freundlich模型,即吸附主要以多层吸附为主.吸附热力学研究表明,老化PP和PE微塑料对Cu^(2+)和Zn^(2+)的吸附行为属于自发吸热过程.微塑料PP和PE吸附前后对莱茵衣藻的毒性试验结果表明,微塑料存在均对藻类的生长有抑制作用,但吸附重金属后的微塑料对藻的生长抑制率有所降低.通过藻的酶活性(包括超氧化歧化酶(SOD),丙二醛(MDA)和过氧化氢酶(CAT))的测定结果表明,微塑料对藻造成一定的氧化损伤,而吸附重金属后的微塑料的毒性作用下降.本论文可以为环境中微塑料存在下复合污染物的竞争吸附行为和联合生态效应研究提供理论依据.

Microplastics(MPs)can act as metal vectors that strongly influence the migration and toxicity of metal ions in aquatic environment.Adsorption affinity of UV-aged polypropylene(PP)and polyethylene(PE)MPs to Cu^(2+) and Zn^(2+) were investigated in both single and binary system.Results of adsorption kinetics study found that Pseudo second-order kinetic models can well fit the adsorption process.Freundlich isotherm and the Langmuir isotherm were used to stimulate the adsorption behavior of these two MPs.The results showed that the aged PP had the higher equilibrium absorption capacity than the aged PE.Meanwhile,the adsorption amount of Cu^(2+) was larger than Zn^(2+) on MPs in both single and binary system.Due to the competition absorption in binary system,MPs presented lower adsorption capability on heavy metals than in the single ion system.The well fitting by Freundlich model implied that the metal ion adsorption mechanism on MPs was dominated by multilayer adsorption.The adsorption thermodynamic process of aging PP and PE MPs showed that the adsorption behavior of Cu^(2+) and Zn^(2+) was spontaneous endothermic process.Toxicity experiments of combined system of MPs and metal ions indicated that all the MPs treatment had the inhibition effect on the growth of Chlamydomonas reinhardtii,while the inhibition ratio decreased in the presence of MPs with Cu^(2+) or/and Zn^(2+) .With the prolonged exposure time,the inhibition effect was decreased obviously due to the acclimation of algae.Based on the enhancement of superoxide dismutase(SOD),malondialdehyde(MDA)and catalase(CAT),we can also conclude that the existence of MPs could induce oxidative damage of algae,while the toxicity was reduced in the binary system.This study provides valuable insight into the competitive behavior of the sorption sites on the aged MPs and the combined ecological effect of MPs in the aquatic system containing multiple metal ions.