Adsorption of copper by naturally and artificially aged polystyrene microplastics and subsequent release in simulated gastrointestinal fluid

Microplastics, especially aged microplastics can become vectors of metals from environment to organisms with potential negative effects on food chain. However, a few studies focused on the bioavailability of adsorbed metals and most studies related to aged microplastics used artificial method that cannot entirely reflect actual aging processes. In this study, virgin polystyrene was aged by ozone (PS-O₃), solar simulator (PS-SS) and lake (PS-lake) to investigate adsorption of Cu by virgin, artificially and naturally aged microplastics and subsequent release in simulated gastrointestinal fluids (SGF). Characterization results show carbonyl was formed in PS-O₃ and PS-SS, and the oxidation degree was PS-O₃ > PS-SS > PS-lake. However, Cu adsorption capacity followed this order PS-lake (158 μg g^-1) > PS-SS (117 μg g^-1) > PS-O₃ (65 μg g^-1) > PS-virgin (0). PS-O₃ showed highest Cu adsorption capacity at 0.5 h (71 μg g^-1), but it dropped dramatically later (10 μg g^-1, 120 h), because PS-O₃ could break up and the adsorbed Cu released in solutions subsequently. For PS-lake, precipitation of metallic oxides contributes to the accumulation of Cu. The addition of dissolved organic matter (DOM) could occupy adsorption sites on PS and compete with Cu, but also can attach PS and adsorb Cu due to its rich functional groups. The simultaneous ingestion of microplastics with food suggested that adsorbed Cu is solubilized mostly from aged PS to SGF.