Microplastic sorption of personal care products in aquatic environments: mechanisms and key factors

Microplastics (MPs) have emerged as dynamic vectors for personal care product (PCP) contaminants, including triclosan, methyl-triclosan, synthetic musks, organic and inorganic UV filters, parabens, caffeine, and other preservatives. Sorption behaviors of MPs are strongly influenced by polymer type, particle size, surface chemistry, aging, and environmental conditions, including pH, salinity, ionic strength, and natural organic matter. Hydrophobicity, hydrogen bonding, π–π interactions, van der Waals forces, and electrostatic effects govern adsorption. Aging and surface oxidation generally enhance MP sorption capacities. For triclosan and methyl-triclosan, hydrophobicity enhances adsorption (24.8–70.8 l g−1 adsorption affinity for methyl-triclosan versus 0.14–0.77 l g−1 for triclosan), while competition/cooperation between compounds alters their individual uptake (antagonist effects on triclosan). Synthetic musks exhibit size- and temperature-dependent adsorption, with polyvinyl chloride generally outperforming polyethylene and polypropylene due to higher surface area and pore volume (0.88–1.60 µg g−1 adsorption capacity for polyvinyl chloride versus 0.860–1.0 µg g−1 for polyethylene). Organic UV filters show multilayer adsorption (5–9100 µg g−1), influenced by polymer type, hydrophobicity, and co-occurring contaminants. Inorganic UV nanoparticles (ZnO, TiO2) interact with MPs via aggregation, dissolution, and reactive oxygen species generation. TiO2 generally shows greater adsorption (up to 72%) than ZnO (16% on polyethylene). Paraben adsorption increases with ester chain length. It is affected by MP polarity, particle size, and aging. Caffeine adsorption is enhanced on aged or humic-acid-enriched MPs (362 µg g−1 on aged polyethylene microplastics versus 237 µg g−1 on pristine ones). It demonstrates limited desorption under pH changes, indicating low bioavailability. Surfactants (anionic, cationic, nonionic) significantly alter MP transport and pollutant uptake by modifying surface charge, adhesion, and hydrophilicity. Adsorption kinetics generally fit pseudo-first- or second-order models, and isotherms align with Freundlich, Langmuir, or Temkin models, reflecting heterogeneous surface interactions. Overall, MPs act as carriers for diverse PCPs, modulating their mobility, persistence, and ecological risk in aquatic systems. Future studies should focus on the combined effects of mixed MPs, surfactants, and co-existing contaminants under realistic environmental conditions to better predict the fate and transport of PCPs.