Microplastics in Mediterranean Agricultural Soils: Effects on Soil Properties, Metal Accumulation in Plants, and Implications for Sustainable Agroecosystems

The influence of three different types of microplastics (PE, PET, and PS) on soil physicochemical properties is the main scope of the present investigation. To this end, a pot experiment has been conducted, incorporating each kind of microplastic (MP) in two different soil samples in equal portions. The soils were typical of Mediterranean areas, moderately contaminated with Pb and Zn. Furthermore, two different plants, Nicotiana tabacum L. (Burley cv.) and Cannabis sativa L. (Fedora cv.), were planted to study the influence of a multi-contaminated soil environment on plant growth, along with their ability to absorb metals in their tissues. The addition of microplastics caused stronger reactions in slightly acidic soil, where the bioavailability of zinc and lead increased by 5–20% compared to alkaline soil rich in CaCO3. Plant-to-soil indices have been calculated to monitor the plant’s capacity to transfer metals from the soil environment to plant tissues. PE induced the strongest and most consistent responses, increasing Zn and Pb bioavailability and systematically enhancing total concentration factors (TC), bioaccumulation factors (BAF), and translocation factors (TF) by up to 20%, particularly in acid soil, while PET reduced the mobility of metals on the surface while enhancing vertical transport, and PS caused moderate but stable changes. Plant responses were cultivar-dependent. Plant biomass increased by approximately 7–15% in Cannabis sativa L. (cv. Fedora 17), while Nicotiana tabacum L. (cv. Burley) showed greater sensitivity to the presence of microplastics. Even low MP inputs can subtly but persistently modify soil structure, metal dynamics, and soil–plant transfer processes without increasing total metal loads, highlighting the importance of soil chemistry and polymer type in assessing the environmental risk of microplastics for sustainable agroecosystems.