Synergistic modulation of Lead (II) bioavailability by polyethylene terephthalate microplastics and insights into assimilation kinetics in Canna indica

The proliferation of microplastics (MPs) in terrestrial ecosystems has introduced a novel variable into the biogeochemical cycling of heavy metals. This study elucidates the role of Polyethylene Terephthalate (PET) microplastics in modulating the bioavailability and assimilation kinetics of Lead(II) ions Pb2+ in Canna indica. Through a 35-day microcosm experiment, we investigated the interplay between PET dosage (0.5–2.5 g), initialPb2+concentration (5–45 mg/L), and soil pH (4.0–7.0). Our findings reveal a significant "vector effect," where PET amendment increased Pb uptake by up to 250% compared to MP-free controls. Assimilation was highest under acidic conditions (pH 4.0), reaching 4.529 mg g-1, suggesting that pH-mediated desorption from PET surfaces governs metal mobility. The uptake behavior conformed to the Freundlich isotherm (R2 > 0.98), indicating a multi-layer, heterogeneous sorption process, while pseudo-first-order kinetics highlighted a time-dependent saturation of plant tissues. These results underscore the potential for microplastics to exacerbate heavy metal bioaccumulation in phytoremediation-relevant species, necessitating a re-evaluation of soil safety standards in plastic-contaminated agricultural zones.