Influence of Different Microplastic Forms on pH and Mobility of Cu2+ and Pb2+ in Soil.

Agnieszka Medyńska-Juraszek,Bhakti Jadhav

doi:10.3390/molecules27051744

Agnieszka Medyńska-Juraszek, Bhakti Jadhav

Open Access

https://doi.org/10.3390/molecules27051744

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Abstract

Microplastics, due to their surface properties, porosity and electrostatic interactions have a high affinity for cations sorption from the aqueous phase. As soil is a complex matrix, interactions between microplastics, soil constituents and heavy metals (HM) may modify the soil microenvironment for heavy metal mobilization/immobilization processes. In order to better understand the problem, three commonly found forms of microplastics in soil (fibers, fragments and microbeads) were mixed with Cu2+- or Pb2+-contaminated soil and incubated at 22 °C for 180 days. In soil samples pH and the content of water and acid exchangeable species of metals were analyzed. The results of this study showed that the presence of microplastics in HM-contaminated soil affected metal speciation, increasing the amount of easily exchangeable and potentially bioavailable forms of Cu2+ or Pb2+ in the tested soil. Soil pH also increased, confirming that microplastic particles affect soil properties relevant to the sorption/desorption process of metal cations. Overall, the smallest microplastic particles (≤1 mm), such as fibers or glitter microbeads, had a greater impact on the change in the sorption and desorption conditions of metals in tested soil than larger particles. The findings of our study show that microplastic form, shape and size should be considered as important factors that influence the soil properties and mobility of heavy metals in soil.

Highlights

Microplastics (MPs), defined as particles with a size of less than 5 mm, became a threat of global concern due to their unknown, potentially negative impacts on the environment
Our results showed that the long-term deposition of microplastic in soil increases soil pH, modifying conditions of heavy metal mobilization/immobilization processes
This study indicated a higher content of acid-exchangeable forms of tested metals in MPs-polluted soil, suggesting that MPs particles contributed to the process of Cu2+ and Pb2+ adsorption, which affected metal speciation in the soil

Summary

Introduction

Microplastics (MPs), defined as particles with a size of less than 5 mm, became a threat of global concern due to their unknown, potentially negative impacts on the environment. Due to their small particle size and very slow biodegradation rate, they can be absorbed by organisms and, subsequently, transported through food webs [1,2]. Compared with large forms of plastic, microplastics exhibit a large specific surface area, high hydrophobicity [3,4] and remarkable binding capacity [5] and may act as a vector for other organic and inorganic contaminants in environmental media [6]. Agricultural soils potentially store more microplastics than oceanic basins [13]. Primary microplastics are mainly represented by microbeads, plastic pellets or fibers manufactured in sizes smaller than 5 mm and directly incorporated into the environment as an airborne or wastewater deposition [15]

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