Investigation of Factors Affecting Metal Ion Desorption from the Surface of Microplastics

MicroPlastics (MPs) are plastic materials of micro-size dimension, often between the ranges of 1μm to 5mm. MPs are potential carriers that can adsorb metal ions in aquatic environments due to their specific surface areas. MPs and their associated contaminants can reach humans in many ways and are found in drinking water sources, foods, and beverages. The metal ions associated with MPs on their surfaces can desorb into the food materials and enter humans. The current research investigates the physicochemical parameters (pH, temperature, time, and type of plastic) affecting the desorption of metal ions from MPs into aqueous solutions using Inductively Coupled Plasma-Mass-Spectrometry (ICPMS). The MP surface characterization was studied using Fourier Transform Infrared (FT-IR) spectroscopy, X-Ray Diffraction (XRD), and The Brunauer-Emmett-Teller (BET) analysis. An experiment was conducted on three metal ions Lead, Cadmium, and Chromium on PET (polyethylene terephthalate), PP (polypropylene), PS (polystyrene), and PVC (polyvinyl chloride). In this work, PP showed the highest desorption efficiency, while PVC was the lowest one. Acidic pH 3.0 favored the desorption process and with an increase in temperature and time of contact with metal ions, the desorption efficiency also increased. The Scanning Electron Microscopic (SEM) characterization of MPs disclosed the presence of wrinkles and pits which encouraged both adsorption and desorption. The BET analysis revealed the role of high specific surface area (10.6±0.3 m2/g) and higher total pore volume (Vtotal) 1.58±0.09 cm3/g in significant adsorption and desorption of metal ions on PP.  The study findings provide a better perception of the desorbing efficiency of metal ions in the surrounding environment and the optimal conditions favoring this process.