Potential Mechanisms of Methylparaben Sorption to Microplastic Fragments from Single-Use Products

Plastic pollution has attracted global attention because of its widespread presence in aqueous ecosystems and its toxicological risks to aquatic species. One of the major sources of microplastics (MPs) is the weathering and disintegration of discarded single-use plastic products. MPs and methylparaben (MeP), a common antimicrobial preservative and potential endocrine disruptor, have been observed to co-occur in surface waters. However, the interfacial sorption mechanism between the two contaminants must be better understood. Therefore, we investigated the sorption mechanism of MeP with two irregularly shaped MPs [polyethylene terephthalate (PET) and polystyrene (PS)] from single-use plastics via a series of batch sorption experiments, using sorption models and spectroscopic analysis. Sorption kinetics and isotherms were best described by the pseudo-second-order and the Freundlich models, respectively. Spectroscopic analysis demonstrated that while the polymer structures of the MPs remained intact after the sorption, the sorption of MeP onto the MPs (PS and PET) was predominantly governed by π-π stacking and hydrophobic interactions, with additional hydrogen bonding observed specifically between MeP and PET. The presence of surface defects in the MPs enhanced molecular interactions by increasing the accessibility of MeP to the polymer matrix.