Insights into the molecular interaction between poly(vinylpyrrolidone)-iodine disinfection system and polypropylene microplastics in aquatic environment

Abstract Microplastics (MPs) as emerging contaminants may not only act as an extra compartment for partitioning of disinfectant but also greatly affect the bactericidal power of disinfection agents. This is the first study to investigate the interaction of MPs with poly(vinylpyrrolidone)-iodine (PVP-I) disinfection system, particularly associated with the identification and characterization of the iodine species at molecular level. The results showed that the presence of MPs increased the loss of triiodide ion (I3−) in PVP-I system, which was even accelerated upon oxygen exposure. An obvious blue shift from 1714 to 1665 cm−1 at the vibrational band was observed for iodine-soaked MPs, which was resulted from the hydrogen bonding interaction as one of potential adsorption mechanisms. The interaction resulted in the affinity of polyiodide ions (I3− and I5−) in PVP-I system to MPs as foreign objects, thereby impairing the bactericidal power of PVP-I system. More evident loss of I3− in aged MP suspension was observed compared to pristine MP suspension, suggesting the enhanced interaction of PVP-I system with aged MPs. The interaction was weakened in aquaculture water, due to the photosensitive substances and alkaline condition. These findings confirmed that the interaction between polyiodide ions (I3− and I5−) and MPs in form of hydrogen bond reduced the bactericidal power of PVP-I disinfection system. This study provides a comprehensive insight in to the mechanisms involved in the interaction between MPs and PVP-I disinfection system, and would be helpful for evaluating the environmental behavior of MPs and the bactericidal power of the PVP-I system upon MP exposure in aquaculture environment.