Polymer inclusion membrane (PIM) extraction technique for assessing metal interactions with organic pollutants and microplastics in aquatic systems

This study presents a novel approach for studying metal-contaminant interactions in aquatic environments, based on a polymer inclusion membrane (PIM) as extraction technique, for the divalent metal ions (Ni(II), Cu(II), and Zn(II)). PIMs are designed to selectively extract metal ions, offering a simple method for assessing the free fraction of metals, which is crucial for understanding their bioavailability and potential toxicity. The PIM, composed of 40 % triacetate cellulose (CTA), 30 % di-(2-ethylhexyl) phosphoric acid (D2EHPA), and 30 % tributyl phosphate (TBP), efficiently facilitates the transport of Ni(II), Cu(II), and Zn(II) into a receiving phase of 0.5 M HNO₃, with the affinity following the trend Cu(II) > Zn(II) > Ni(II). All metals exhibit a linear trend in relation to the concentration of metal in the feed phase and the amount accumulated in the receiving phase, within the studied range (0.02 to 0.08 mM). Moreover, this research explores, for the first time, the potential interactions of these metals with two sulfonamide antibiotics, sulfamethoxazole (SMX) and sulfamethazine (SMZ), and two types of microplastics: commercial PVC and a blend of waste plastics. Although a potential interaction is inferred between Cu(II), Zn(II), and sulfamethoxazole at higher concentrations, no significant interaction is observed for Ni(II). In contrast, sulfamethazine does not exhibit measurable interactions with any of the metal ions under the conditions studied. Additionally, microplastics show weak or negligible interactions with the metals, suggesting a minimal impact on metal extraction under the experimental conditions. Finally, the PIM-extraction technique was applied to measure free Zn levels in a river water sample impacted by drainage from an abandoned mine, and in the same matrix enriched with microplastics and SMX at environmentally relevant concentrations.