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Microplastics (PET and PVC) disrupt palygorskite-mediated cadmium stabilization in paddy soil: Polymer-specific rhizosphere mechanisms and ecological consequences
Summary
Scientists found that two common plastic pollutants (from bottles and PVC pipes) can undo soil treatments meant to lock toxic cadmium safely away in rice paddy soil—but they do it through different routes: one type makes the soil more acidic, while the other damages rice root defenses. The result in both cases was more cadmium ending up in the rice grains we eat, meaning microplastic pollution in farmland could quietly make heavy metal contamination in our food worse, even in soils that were previously treated to be safe.
Microplastics (MPs) are emerging disruptors to soil heavy metal remediation, yet how different polymer types undermine mineral-mediated in-situ immobilization remains unclear. Using a multi-omics approach (16S rRNA gene sequencing, metagenomics, transcriptomics and metabolomics), we aimed to elucidate the polymer-specific mechanisms by which polyethylene terephthalate (PET) and polyvinyl chloride (PVC) residues destabilize palygorskite-immobilized cadmium (Cd) in paddy soil, at both the soil and microbial levels. PET and PVC differentially induced the remobilization of palygorskite-immobilized Cd (F1: +132.43% and 85.52%) via distinct rhizosphere pathways. At the soil/plant level, PET enriched PETase-carrying Acidobacteriota and suppressed the ammonium transporter gene OsNRT2.3, lowering rhizosphere pH from 7.05 to 6.30. This acidification was associated with the remobilization of mineral-bound Cd and increased brown rice Cd from 0.03 to 0.06 mg/kg. PVC, in contrast, did not acidify the rhizosphere but instead induced severe root oxidative stress (MDA +78%, POD +60%), likely impairing root-barrier integrity and enhancing Cd uptake. At the microbial level, PET enriched keystone taxon Gaiella via homogeneous selection (HoS), supporting stress adaptation through branched-chain amino acid metabolism, whereas PVC redirected microbial carbon flux toward the pentose phosphate pathway and increased the genetic potential for acetate-dependent methanogenesis (acs +22.67%). These findings demonstrate that MPs compromise the durability of Cd immobilization through polymer-specific rhizosphere processes, with distinct ecological trade-offs, providing critical insights for heavy metal remediation in microplastic-polluted paddy soils.