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Microplastic–cadmium co-contamination in agricultural soils: A critical review of interactions, transfer, and plant exposure
Summary
Tiny plastic bits in farm soil don't just sit there, they can actually change how cadmium (a toxic heavy metal) moves through soil and gets absorbed by crops, sometimes making contamination worse and sometimes better, depending on conditions we don't yet fully understand. This matters because cadmium buildup in food crops is a real health concern, and this review of existing studies shows scientists still can't reliably predict when plastic pollution will make that risk worse, meaning more research is needed before we can say how much this affects the food on your plate.
Microplastics (MPs) and cadmium (Cd) are persistent contaminants in croplands, introduced through plastic residues, organic amendments, irrigation, fertilizer impurities, and atmospheric deposition. MPs are increasingly recognized not only as passive carriers of Cd, but also as active regulators of Cd behavior across the soil–rhizosphere–plant continuum. By altering surface reactions, aggregate structure, dissolved organic matter, microbial activity, and rhizosphere conditions, MPs can reshape Cd speciation, mobility, plant uptake and translocation. However, current evidence remains highly inconsistent. Across seemingly similar studies, MPs have been reported to enhance, suppress, or exert little effect on Cd bioavailability, plant accumulation, and toxicity. This inconsistency reflects not only environmental complexity, but also the lack of a unified framework linking MP heterogeneity with Cd regulation across soil processes, rhizosphere interactions, and plant internal transport. Here, we review MP–Cd co-contamination as a coupled perturbation rather than the simple sum of two pollutants. We synthesize how MPs regulate Cd behavior in soils, how these changes are translated into biological exposure at the rhizosphere interface, and how plant uptake, redistribution, and toxicity are subsequently modified. We further evaluate whether MP-mediated Cd responses can be interpreted within conventional soil predictors of Cd phytoavailability and soil-to-plant transfer or whether they imply an additional regulatory dimension. Finally, we identify key research priorities, including standardized characterization of MP–Cd systems, direct measurement of rhizosphere pH, dissolved organic carbon, microbial activity, and Cd accessibility, improved resolution of spatiotemporal dynamics, and quantitative partitioning of soil-, rhizosphere-, and plant-level controls.