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Release mechanisms of decabromodiphenyl ether from typical e-waste microplastics into water: Insights from molecular dynamics simulations
Summary
This study used molecular dynamics simulations to understand how a flame retardant chemical called BDE-209 — commonly added to plastics in electronic waste — leaks out of polystyrene microplastics and into water. The simulations revealed that the chemical moves very slowly inside the plastic, more freely at the plastic-water boundary, and fastest once dissolved in bulk water. This three-stage release process explains why microplastics from e-waste can act as slow-release sources of toxic flame retardants in aquatic environments. The findings help predict how such chemical pollution behaves over time and can be adapted to study other plastic additives.
E-waste-derived microplastics (MPs) serve as a significant source, have been releasing decabromodiphenyl ether (BDE-209) into aquatic environment. Conventional release kinetics experiments fail to effectively distinguish the three-stage release process, which includes internal diffusion, interfacial mass transfer, and diffusion in the environment. Herein, we took typical flame-retardant plastic (polystyrene, PS) as a paradigm to construct diffusion and release models corresponding to the three-stage release process, with large-scale all-atom molecular dynamics (MD) simulations providing insights into the release process. The level of BDE-209's self-diffusion coefficients (D) was calculated at different release stages: 10 (PS matrix), 10 (PS-water interface), and 10 m s (bulk water). BDE-209 exhibits a confined diffusion mode within the PS matrix, significantly diminishing its release capability. At the interface, the strength of dispersion attraction between BDE-209 and the PS surface determines the ease of its release and the partition equilibrium between the two phases. Our findings elucidated the molecular-scale dynamic and thermodynamic mechanisms governing BDE-209 release from MPs into water, expanding the understanding of polybrominated diphenyl ether release from e-waste-derived MPs. Moreover, our established MD simulation methods can be adapted to explore the release or adsorption mechanisms of various additives in different kinds of MPs.