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Modeling the adsorption mechanism of 3-tertiary-butyl-4-hydroxyanisole (3BHA) on polyethylene and polypropylene microplastics
Summary
Researchers used molecular dynamics simulation and density functional theory to model how 3-tertiary-butyl-4-hydroxyanisole (3BHA) — a food packaging antioxidant with endocrine-disrupting potential already detected in human urine and serum — adsorbs onto polyethylene and polypropylene microplastics via van der Waals forces. This work demonstrates that microplastics act as carriers for 3BHA, transporting an endocrine disruptor from agricultural soils through aquatic systems and potentially into the food chain and human body.
The polyethylene (PE) and polypropylene (PP) microplastics (MPs) can act as carriers of the molecule 3-tertiary-butyl-4-hydroxyanisole (3BHA), which propose harmful impacts to aqueous ecosystems. Meanwhile, 3BHA has already been detected in several environments and human urine and serum samples. 3BHA is an antioxidant in foods, food packaging, cosmetics and pharmaceuticals. However, it raised concerns about its possible endocrine-disrupting effect in recent years. The interaction between two MPs and 3BHA could start in farmland and be maintained during transportation to the ocean. Herein, the adsorption behavior and mechanism of 3BHA by PE and PP MPs were investigated via molecular dynamics (MD) simulation, density functional theory (DFT), non-covalent interactions (NCI), the total density of states (TDOS) and frontier molecular orbital (FMO). Furthermore, the stability of 3BHA adsorbed complexes was investigated by adsorption-free energies (ΔGads), showing that the 3BHA has a significant interaction with the MPs studied, with energies of -1.31 kcal mol−1 and − 4.19 kcal mol−1 for PE and PP, respectively. Intermolecular van der Waals forces were one of the primary adsorption mechanisms of 3BHA by MPs, as evidenced by NCI calculations. It was demonstrated that the adsorption of the 3BHA in MPs decreases the energy gap (Eg) of the HOMO and LUMO orbitals; for PE MP, the Eg decreases from 12.8386 to 9.1445 eV, and from 12.7957 to 9.2092 eV for PP MP. The adsorption of the 3BHA on the MPs resulted in an increase in the TDOS distribution and a slight shift in the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states. In conclusion, this study about the mechanism of adsorption of the 3BHA in PE and PP MPs can provide new evidence and enhance our understanding of the environmental behavior of 3BHA in the environment.