Metal type and aggregate microenvironment govern the response sequence of speciation transformation of different heavy metals to microplastics in soil

Hong Yu; Zheng Zhang; Ying Zhang; Ping Fan; Beidou Xi; Wenbing Tan

doi:10.1016/j.scitotenv.2020.141956

Metal type and aggregate microenvironment govern the response sequence of speciation transformation of different heavy metals to microplastics in soil

Sci Total Environ. 2021 Jan 15:752:141956. doi: 10.1016/j.scitotenv.2020.141956. Epub 2020 Aug 25.

Authors

Hong Yu¹, Zheng Zhang², Ying Zhang³, Ping Fan⁴, Beidou Xi⁵, Wenbing Tan³

Affiliations

¹ State Key Laboratory of Environmental Criteria and Risk Assessment, and State Environmental Protection Key Laboratory of Simulation and Control of Groundwater Pollution, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; College of Water Sciences, Beijing Normal University, Beijing 100875, China.
² Center for Soil Environmental Protection, Chinese Academy of Environmental Planning, Beijing 100012, China.
³ State Key Laboratory of Environmental Criteria and Risk Assessment, and State Environmental Protection Key Laboratory of Simulation and Control of Groundwater Pollution, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
⁴ College of Environmental and Chemical Engineering, Nanchang University, Nanchang 330031, China.
⁵ State Key Laboratory of Environmental Criteria and Risk Assessment, and State Environmental Protection Key Laboratory of Simulation and Control of Groundwater Pollution, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; College of Water Sciences, Beijing Normal University, Beijing 100875, China. Electronic address: xibeidou@yeah.net.

PMID: 32890822
DOI: 10.1016/j.scitotenv.2020.141956

Abstract

Microplastics change the physical, chemical, and biological processes in soil, and these changes further affect the transformations of heavy metal speciation in soil. Whether this influence mechanism differs between heavy metals is unknown on the soil aggregates level. In this study, 5 months incubation experiments and soil fractionation were conducted to evaluate the effect of microplastic addition on the chemical speciation of seven heavy metals (Zn, Cu, Ni, Cd, Cr, As, and Pb) in the three soil aggregate fractions. The results show that 28% concentration of polyethylene microplastics with size 100 μm reduces and increases the heavy metal content in the bioavailable and organic-bound fractions, respectively, indicating that microplastics promote the transformation from bioavailable to organic-bound species. The transformation in the larger-sized aggregate fractions is more dramatic than that of smaller-sized aggregate fractions within the incubation period. This indicates that the extent of the response of the different heavy metals to microplastics is significantly different in the three aggregate-size fractions. Soil physicochemical factors affected different heavy metals in different pathways, and microplastics have different adsorption or complexation effects on different heavy metals. These processes result in heterogeneous responses of different heavy metals to microplastic addition. In addition, the microplastics have different extents of influence on the different chemical speciation of the heavy metals, having the greatest influence on the exchangeable and carbonate-bound of Cu and Zn, FeMn oxide-bound of As, and organic-bound of Cr, Ni, Cd, and Pb. This phenomenon is relatively consistent among the three aggregate-size fractions. Our findings provide more accurate management information for soil environmental quality management with different heavy metal pollution and different soil types.

Keywords: Chemical speciation transformation; Different heavy metals; Diverse impact; Diverse microenvironments; Microplastics.