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Influence of aging on the affinity between microplastics and organic contaminants
Summary
Researchers investigated how UV and UV+H2O2 aging affects the capacity of polystyrene microplastics to adsorb and release pesticides and other organic contaminants, finding that aging-induced surface changes significantly altered adsorption affinity and desorption behavior compared to unaged controls.
This dissertation investigated how aging affects the affinity between microplastics (MPs) and organic contaminants in liquid media, focusing on the adsorption, desorption, and leaching of various organic compounds. The first project evaluated the adsorption capacities of three commonly used pesticides—alachlor, lindane, and methomyl—onto polystyrene (PS) MPs subjected to different aging treatments, including UV-aged, UV+H2O2-aged, and non-aged control groups. Aging modified the surface morphology and chemistry of PS MPs by generating surface defects and introducing oxygen-containing functional groups, which increased hydrophilicity and reduce zeta potential. The PS MPs exhibited adsorption capacities in the order lindane > alachlor > methomyl, suggesting that hydrophobic interactions were the primary driving force. The second project investigated the release of plasticizer additives from polyvinyl chloride (PVC) MPs derived from commercial wire insulation in synthetic freshwater, seawater, and a fish in vitro digestion system. Hexane extraction identified di(2-ethylhexyl) adipate (DOA), di(2-ethylhexyl) phthalate (DEHP), and di(2-ethylhexyl) terephthalate (DOTP), with DEHP selected as the target compound for leaching studies. UV-aged PVC MPs leached more DEHP than non-aged MPs across all media, and most of the DEHP leached from the MPs occurs during the instantaneous leaching stage. In the digestive system, digestive secretions drove re-equilibration and enhanced DEHP leaching, while food particles acted as a sorptive matrix that reduced DEHP bio-accessibility. The third project investigated the adsorption and desorption of benzalkonium chlorides (BACs, C8-C14), a class of cationic surfactants, on PVC MPs. Hydrophobic and electrostatic interactions were the primary adsorption mechanisms. For the same PVC MPs, longer-chain BAC homologues exhibited higher adsorption capacities than shorter chains. while for the same BAC homologue, UV-aged PVC MPs showed higher adsorption capacities than non-aged MPs. Desorption experiments in the fish digestion system showed increased release from aged MPs under with-food conditions than in deionized water, implying the potential ecological risks of MPs as contaminant carriers for BACs.