Enhanced immobilization of trace nickel by nanoplastic-Fe-Mn oxide complexes in sedimentary systems

Fe/Mn oxides are widely distributed mineral components in marine sediments and act as significant scavengers of trace metals. The emergence of plastic-rock complexes has led to an increasing recognition that plastics may influence the environmental behavior of minerals. Plastics, especially nanoplastics, can affect the formation of Fe/Mn oxides and their ability to immobilize heavy metals. In this study, the role of polystyrene nanoplastics (PS NPs) in the mineralization of FeMn oxides and their effects on the immobilization of heavy metals (using Ni(II) as an example) at the trace concentrations in the environment were investigated. Characterization analysis indicated that PS NPs not only adsorb Fe and Mn ions from the environment through electrostatic attraction (the force that draws together objects with opposite electrical charges) but also serve as a substrate for the heterogeneous nucleation and growth of FeMn oxides. The large specific surface area of the PS NPs provides a site for the growth of FeMn. This results in smaller particle sizes and larger specific surface areas for the generated FeMn oxides. Consequently, Fe-PS-Mn@SiO₂ exhibits significantly greater adsorption efficiency for Ni(II) under various environmental conditions (such as different pH and salinity) compared to Fe-Mn@SiO₂. Additionally, Fe-PS-Mn@SiO₂ remained stable under sunlight at 60 °C over 1.5 years. These findings presented new insights into the impact of NPs on mineral formation and environmental behavior, expanding our understanding of the actual fate of NPs in sediment environments.