The Sorption of Amoxicillin on Engineered Polyethylene Terephthalate Microplastics

The adsorption studies of contaminants on microplastics (MPs) collected from the marine environment are very hard to carry out mainly due to the difficulties associated with both to filtration of MPs and separation from biofilm and organic matrices. In this work, MPs were produced by a top-down protocol from polyethylene terephthalate (PET) bottles collected on the beach, thus already aged in the natural environment, and compared with engineered MPs obtained from PET pellets. Both types of MPs (size < 150 μm) were used to study the adsorption of amoxicillin, which is one of the most widely consumed antibiotics in the world and is found unchanged in the aquatic environment. The results of sorption kinetics and isotherm tests indicated that aged MPs absorbed a higher antibiotic content than unaged ones since the two kinds of microplastics had different specific surface areas. The experimental results were explained by analysing the thermodynamic affinity among amoxicillin and PET MPs and comparing it with several pharmaceuticals and other microplastics by evaluating Hansen’s solubility parameters (HSPs), which account for dispersive, polarizable and hydrogen bonding contributions to the overall cohesive energy of a compound. The possible interaction mechanism among amoxicillin and PET MPs, based on hydrogen bond interactions among the antibiotic and the ester groups of the polymer, was hypothesised. The results of adsorption tests demonstrated that PET MPs can be pollutant carriers with potential long-range transport in the aquatic environment.