A bridge between the lead release from masterbatch microplastics and ecological effects: From surface release to...

Masterbatches, as concentrated pigment carriers used pervasively in plastic products, represent potential sources of heavy metals during microplastics aging process. Understanding how polymers aging regulates heavy metal release and toxicity is critical for long-term environmental risk assessment. In this study, polyethylene (PE) and lead chromate (PbCrO₄) masterbatch microplastics were investigated to elucidate the polarity-release-toxicity framework. This framework was verified through aging induced polar groups, release kinetics experiments, combined DFT calculations, and wheatgrass toxicological experiments. The results showed that aging-induced oxygen changed the lead (Pb²⁺) release kinetics from Fickian diffusion to Super Case-II diffusion. The maximum Pb²⁺ release reached 5.27 ± 0.04 mg/g under acidic conditions. DFT results revealed that the surface polarization is aging-induced, which becomes more negative, increasing the binding energy between PE and PbCrO₄ from -1.40 eV to -1.64 eV, promoting the Pb²⁺ release. Furthermore, Pb²⁺ release was regulated in real environmental waters (e.g., tap, lake, and river water) rather than uniformly suppressed, reflecting the combined effects of pH, dissolved organic matter, and inorganic ions. Additionally, the toxicological experiments revealed that MMPs could generate oxidative stress in wheatgrass and inhibit growth. This study reveals surface polarization induced as a key factor amplifying heavy metal release and associated toxicity from pigmented microplastics. These findings provide mechanistic insights for the environmental risk assessment and management of plastic materials containing toxic metal additives.