Impact of PVC microplastics on phytoremediation of As and Hg polluted soils using Betula pubescens

Arsenic (As) and mercury (Hg) contamination in the Asturias region, northern Spain, represents a significant environmental issue that has been extensively studied in recent decades. Mining and industrial activities, particularly those associated with Hg mining, as well as coal mining and iron or zinc metallurgical industries, have profoundly impacted the environment, as evidenced by paleoenvironmental records such as peat bogs. These pollution phenomena affect various environmental compartments, including soil. To mitigate the negative impact of these two highly toxic and carcinogenic pollutants in soils, phytoremediation technology has been developed using Betula pubescens (birch), including field experiments in different polluted sites along the region.

In recent years various activities in the region have also led to the release of another type of contaminant classified as emerging: microplastics. Studies conducted in the area have revealed their presence in several environmental compartments, including marine sediments. Notably, microplastics are increasingly detected in soils, but their implications remain unclear. In fact, their interaction with other contaminants in complex mixtures is even less understood.

This study aimed to evaluate the impact of polyvinyl chloride (PVC) microplastics on soils contaminated with As and Hg. PVC, one of the most abundant polymers, poses a potential risk of interaction with Hg due to its Cl content. To this end, an experimental plot was established in a polluted soil under controlled conditions, and a dose of 1% of PVC microplastics was added. Phytoremediation of the soil was then performed using birch, with a control plot set up without the presence of microplastics. After two and eight months, sampling of the roots, leaves, and soil was conducted. The samples were analyzed to determine their As and Hg content, assessing the differences in pollutants accumulation in plants. Significant differences were observed between treatments, indicating that the presence of microplastics influenced the accumulation of As and Hg in plants. The presence of Cl in PVC microplastics may be a key factor in their interaction with Hg, thus, to elucidate this interaction, thermal programmed desorption of Hg (Hg-TPD) coupled with microscopic analysis of microplastics extracted from the soil will be employed, enabling a better understanding of the interactions between these two contaminants. This information is critical for evaluating their effects on the soil-plant system and the implications for the feasibility of phytoremediation techniques.

This work was supported by the Ministerio de Economía y Competitividad (MINECO, Spain) under the project I+D+i PID2020-113558RB-C43 (MCIN/AEI/10.13039/501100011033).