Untreated plant waste of the Mediterranean region as bioadsorbent of persistent organic pollutants

The excessive and/or improper use of plant protection products (PPPs) can generate alarming levels of residues in the environment, compromising both soil fertility and food safety. Various organic wastes released in large amounts by agro-industrial activity are currently studied and applied as bioadsorbents for water and soil decontamination. This study explored the capacity of untreated orange peel, olive stones and pistachio shells to adsorb the PPPs oxyfluorfen (OXY), metribuzin (MET) and imidacloprid (IMI), and the xenoestrogen bisphenol A (BPA) from water. The physicochemical, microstructural, and spectroscopic characteristics of the adsorbents were first evaluated using TXRF, SEM and FTIR-ATR techniques. Adsorption kinetics showed that each pollutant was rapidly (∼24 h) retained by all adsorbents according to a pseudo-second order model, which suggested a prevalent chemisorption. Interpretation of the sorption isotherm data with various theoretical equations showed that all molecules on all adsorbents preferentially followed the Freundlich model. Among the materials, olive stones showed the highest adsorbent capacity with K_F values equal to 713, 317, 359 and 736 mg kg^-1 for OXY, MET, IMI, and BPA, respectively. The desorption of each compound from all materials was hysteretic. Based on the overall results obtained, it appears that all three materials tested may have interesting applications for the retention of organic pollutants, especially very hydrophobic ones. This paves the way for further investigations into natural adsorbents as sustainable tools for environmental remediation.