Environmental Impacts of Microplastics in Contaminated Soils: Potential Implications for Cu, Mn, and Sr Phytoremediation

Abstract

Microplastics (MPs) are widespread environmental pollutants and have emerged as a growing global concern. In soil ecosystems, MPs frequently coexist with potentially toxic elements (PTEs), yet their combined effects on soil–plant interactions and phytoremediation processes remain insufficiently explored. This field-based study investigated the occurrence of MPs in urban soils from four Serbian cities and assessed their influence on the uptake of PTEs - copper (Cu), manganese (Mn), and strontium (Sr) - by Capsella bursa-pastoris (L.) Medik. MPs were extracted from soil using an optimized density separation method, while total (aqua regia) and phytoavailable (EDTA-extractable) fractions of PTEs were quantified in both soils and plant tissues. Maximum MPs abundance was recorded in Bor — 500 ± 100 MPs kg^-1.The highest total concentrations of Cu (516.14 µg g⁻¹), Mn (553.46 µg g⁻¹), and Sr (173.69 µg g⁻¹) were detected in soils from Bor. The geoaccumulation index (I_geo) indicated moderate to heavy contamination levels. Cu_EDTA accounted for UP to 50.7% of Cu_AR, Mn_EDTA for 34.4% of Mn_AR, and Sr_EDTA 27.3% of Sr_AR. After the uptake, C. bursa-pastoris primarily translocated the elements to the aerial parts, indicating shoot accumulation as the dominant strategy. Principal component analysis (PCA) revealed distinct clustering of samples by city, while Spearman correlation analysis highlighted significant associations between MPs and PTEs mobility in the soil-plant system. Strongest correlations were found between MPs phytoavailable Cu fraction (ρ =+0.49) and Cu content in shoots (ρ =+0.56). The highest BCF values were determined for Sr, ranging from 2,40 (SM) to 5,41 (BO). PTEs were mainly transferred to the shoots. TF range for Cu was 0.54 (BO) – 1.48 (VR), 0,68 (BO) to 1,42 (VR) for Mn, and 0,76 (BO) to 1,34 (VR) for Sr. Strong correlations among MPs abundance and Cu mobility and accumulation in shoots (ρ = +0.56), and Sr bioaccumulation potential (BCF up to 5.41), highlight the role of MPs in modifying element transfer within urban soil–plant systems and consequent phytoremediation potential.