Effects of solution chemistry and humic acid on transport and deposition of aged microplastics in unsaturated porous media

Xiaoxia Wang; Yinzhu Diao; Yitong Dan; Feihong Liu; Huan Wang; Wenjing Sang; Yalei Zhang

doi:10.1016/j.chemosphere.2022.136658

Effects of solution chemistry and humic acid on transport and deposition of aged microplastics in unsaturated porous media

Chemosphere. 2022 Dec;309(Pt 2):136658. doi: 10.1016/j.chemosphere.2022.136658. Epub 2022 Sep 29.

Authors

Xiaoxia Wang¹, Yinzhu Diao¹, Yitong Dan¹, Feihong Liu¹, Huan Wang¹, Wenjing Sang², Yalei Zhang³

Affiliations

¹ Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, College of Environmental Science and Engineering, Donghua University, Shanghai, 201620, China.
² Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, College of Environmental Science and Engineering, Donghua University, Shanghai, 201620, China. Electronic address: wjsang@dhu.edu.cn.
³ College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.

PMID: 36183879
DOI: 10.1016/j.chemosphere.2022.136658

Abstract

Microplastics (MPs) are susceptible to aging in the environment, and aged MPs are highly migratory in soil due to their smaller particle size and more negative surface charge, but the effects of soil environmental factors on the fate and transport of aged MPs are still unclear. In this study, the transport behavior of pristine/aged MPs in unsaturated sandy porous media was examined under different ionic strength (IS), cationic type (Na⁺, Ca²⁺) and humic acid (HA) conditions. The results indicated that the surface charge, surface oxygen-containing functional groups and surface morphology of MPs changed significantly after aging, and that the mobility of aged MPs was significantly enhanced than the pristine MPs under all test conditions. The retention amounts of pristine/aged MPs in unsaturated porous media increased with IS, and IS had a less inhibitory effect on the transport of aged MPs than pristine MPs. The mobility of pristine/aged MPs in Ca²⁺ solutions was significantly weaker than that in Na⁺ solutions due to enhanced straining and electrostatic adsorption. HA promoted the mobility of pristine/aged MPs in unsaturated porous media under all IS Na⁺ (1, 10, and 25 mM) solutions and lower IS (1 mM) Ca²⁺ solutions, and the ability of HA to promote the transport of aged MPs was significantly stronger than that of pristine MPs due to the higher adsorption of HA on the surface of aged MPs. However, at higher IS (10 mM) Ca²⁺ solution conditions, the bridging effect of Ca²⁺ led to the formation of HA-MPs complexes, which altered the hydrophobicity of the pristine/aged MPs surface and the pristine/aged MPs were mainly retained on the air-water interface (AWI). CFT theory and two-site kinetic retention models indicated that the retention of pristine/aged MPs in unsaturated media was dominated by monolayer adsorption, straining and clogging effects. The current research findings may provide insights into the fate and transport of aged MPs in soil and their potential risk of groundwater contamination.

Keywords: Aged MPs; Cation type; Humic acid; Transport; Unsaturated media.

MeSH terms

Humic Substances* / analysis
Microplastics*
Oxygen
Plastics
Porosity
Soil / chemistry
Solutions
Water

Substances

Humic Substances
Microplastics
Plastics
Solutions
Soil
Water
Oxygen