Release and Transformation of Polymer-Associated Chemicals from Aged Polypropylene and Polyurethane Microplastics in Freshwater Laboratory and Mesocosm Studies

Microplastics (MPs) release polymer-associated chemicals (PACs) into aquatic environments, yet their environmental release, transformation, and persistence remain poorly understood. We applied nontargeted liquid chromatography high-resolution mass spectrometry to characterize PACs released from polypropylene (PP) and polyurethane (PU) MPs in complementary 12-month freshwater wetland mesocosm and 3-month laboratory photolysis and leaching experiments. More leachable compounds were detected from PP (128) than PU (34), reflecting differences in polymer formulations and physicochemical properties. Laboratory studies identified readily mobilized and transformable PACs, including the PP additive bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (BTMS) and the PU monomer 4-(4-formamidobenzyl)phenyl formamide. Laboratory experiments using higher MP concentrations (10,000 mg L–1) prioritized target PACs for monitoring in lower-concentration mesocosms (50 mg L–1), where ricinine was quantified in PU treatments and BTMS and 2,2,6,6-tetramethyl-4-piperidinol (TMPO) were quantified in PP treatments. PAC concentrations increased over time under simplified laboratory conditions but declined in environmentally complex mesocosms, suggesting environmental attenuation through processes such as sorption, sedimentation, and microbial degradation that require further confirmation in future studies. UV exposure minimally affected BTMS hydrolysis but promoted ricinine photodegradation and the formation of additional PU-derived transformation products. These findings identified environmentally relevant PACs and demonstrated the value of integrating simplified laboratory studies with environmentally realistic mesocosms to improve PAC identification and evaluate environmental fate.