Effect of microplastics on the binding properties of Pb(ii) onto dissolved organic matter: insights from fluorescence spectra and FTIR combined with two-dimensional correlation spectroscopy

Heavy metal cations are a typical type of inorganic pollutant that has persistent distribution characteristics in aquatic environments and are easily adsorbed on carriers, posing serious threats to ecological safety and human health. Some studies have shown that the coexistence of dissolved organic matter (DOM) and microplastics (MPs) promotes the adsorption of heavy metal cations, but the mechanism of promoting the adsorption process has not been thoroughly studied. In this study, the effect of polystyrene microplastics (PSMPs) on the binding properties of Pb2+ onto humic acid (HA) in aquatic environments was investigated by spectral analysis and two-dimensional correlation (2D-COS) analysis. When PSMPs co-existed with HA, the adsorption capacity of Pb2+ increased. On the one hand, Pb2+ is directly adsorbed on HA through the mechanism of complexation reaction, ion exchange and electrostatic interaction. On the other hand, Pb2+ is first adsorbed on PSMPs by electrostatic action and indirectly adsorbed on HA in the form of PSMPs-Pb2+ owing to the interaction between HA and PSMPs, which increases the adsorption amount of Pb2+ on HA. This study is significant for studying the migration and regression of heavy metal cation contaminants when PSMPs co-exist with DOM in an aqueous environment.

Automated summary

Heavy metal cations are persistent inorganic pollutants in aquatic environments, posing serious threats to ecological safety and human health. The coexistence of dissolved organic matter (DOM) and microplastics (MPs) has been found to promote the adsorption of heavy metal cations, but the underlying mechanism remains unclear. This study investigated the effect of polystyrene microplastics (PSMPs) on the binding properties of Pb2+ onto humic acid (HA) in aquatic environments using spectral analysis and two-dimensional correlation (2D-COS) analysis. The findings suggest that the presence of PSMPs enhances the adsorption capacity of Pb2+ on HA through both direct and indirect mechanisms.