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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 into crops, sometimes making it worse, sometimes better, depending on conditions we don't fully understand yet. This matters because cadmium buildup in food crops is a real health concern, and this review of existing research shows scientists still don't have a clear picture of when plastic pollution might make heavy metal contamination in our food more likely. More consistent research is needed before we can predict, or prevent, this risk.
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. Diagram showing pathways of microplastics and cadmium contamination in an agricultural setting.This diagram illustrates co-contamination pathways of microplastics (MPs) and cadmium (Cd) in an agricultural landscape. The top section highlights contamination sources such as tire abrasion, wastewater irrigation, fertilizer, plastic mulch residues, and atmospheric deposition. Yellow arrows indicate the migration of MPs while dashed blue arrows show Cd mobility. Below, bioaccumulation is depicted in soil and plants, emphasizing their complex interactions and transport to deeper soils, with microorganisms playing a key role in this process. Elements like a river, farmland, and a greenhouse contextualize the scene.