Microplastics in Soil Increase Cadmium Toxicity: Implications for Plant Growth and Nutrient Imbalance

The increasing presence of microplastics (MPs) and cadmium (Cd) in agricultural soils represents an emerging environmental challenge, necessitating urgent investigation due to their potential synergistic effects on soil and plant health. This study investigated how polyethylene microplastics (PE-MPs) affect Cd behavior in soil, focusing on both their individual and combined impacts on soil pH, Cd bioavailability, plant growth, and nutrient dynamics. MPs can act as carriers of Cd, enhancing its mobility within the soil–plant system. To achieve this, a pot experiment was conducted using soils treated with different doses of PE MPs (0%, 1%, and 2%, w/w) and Cd (20 mg Cd kg−1). Soil pH, DTPA-extractable Cd, plant growth parameters, Cd accumulation in roots and shoots, and mineral nutrient concentrations were measured. The results indicated that while Cd alone did not significantly alter soil pH, increasing MP doses statistically reduced soil pH and enhanced Cd bioavailability, with DTPA-extractable Cd rising by 14.4% to 25.4%. The combined application of MPs and Cd resulted in a 38% reduction in root yield and a 32% decrease in above-ground biomass. The presence of MPs exacerbated Cd uptake, leading to significantly higher Cd accumulation in both roots and shoots compared to Cd application alone. Moreover, the combined presence of MPs and Cd disrupted the nutrient uptake mechanisms, as evidenced by significant reductions in nitrogen (N) and phosphorus (P) concentrations in root and shoot tissues. These results indicate that MPs and Cd together disrupt soil chemical stability and compromise plant nutritional status. Thus, our findings emphasize that MPs not only serve as physical pollutants but also as vectors that intensify heavy metal contamination risks in agricultural ecosystems.