Effect of microplastics on bioaccumulation of tetrabromobisphenol A (TBBPA) and tetrabromobisphenol S (TBBPS) and their analogues in earthworms: Types of microplastics and aging

Microplastics (MPs) are pervasive vectors for hydrophobic organic contaminants in soil ecosystems, yet their ecological impacts under environmentally relevant conditions remain insufficiently characterized. This study investigated effects of ultraviolet aging on polyethylene (PE) and polyvinyl chloride (PVC) MPs, focusing on changes in their physico- chemical properties, the associated effect on adsorption of Tetrabromobisphenol A (TBBPA) and tetrabromobisphenol S (TBBPS), and bioaccumulation of TBBPA/S in earthworms. Aging increased the surface roughness and abundance of oxygen-containing surface functional groups on PE MPs, and significantly increased the adsorption of TBBPA (24.9%) and TBBPS (10.6%). In contrast, only limited enhancement in TBBPA/S adsorption was observed for PVC MPs, while the time to reach adsorption equilibrium for TBBPA was shortened significantly due to the optimized pore connectivity brought by aging. The bioaccumulation of TBBPA/S in earthworms was strongly influenced by the type of MPs, aging status, and exposure conditions. Results of biokinetic modeling show that the inherent polymer properties of MPs play a dominant role in the uptake of TBBPA/S by earthworms. With high free volume, PE MPs mainly promoted TBBPA/S bioaccumulation through MP intake (up to 97%), while bioaccumulation of TBBPA/S mainly occurred through skin adsorption in the presence of the rigid-chained PVC MPs (up to 99.8%). The pollutant's hydrophobicity also impact its bioaccumulation pathways, with the MP-affiliated uptake playing a more important role in the case of pollutant with higher Kow. These findings help better understand the ecological and toxicological implications of combined microplastic and organic pollutant contamination in soil systems.