Impact of Minerals (Ferrihydrite and Goethite) and Their Organo-Mineral Complexes on Fate and Transport of Nanoplastics in the Riverine and Terrestrial Environments

Abundantly occurring minerals are detrimental in dictating nanoplastics (NPs) fate and transport in the environment. However, in natural scenarios, minerals barely exist in their pure phases. Minerals are often associated with organic matter and form organo-mineral complexes (OMCs), exhibiting different reactivity than their pure mineral phase. In this study, we investigated the impact of ferrihydrite, its weathering-originated secondary mineral goethite, and their corresponding OMCs, i.e., organo-ferrihydrite (O-Fh) and organo-goethite (O-Goe) on NPs mobility under varying environmental conditions (ionic strength, pH, and river water). Results showed higher sorption capacity of minerals compared to their respective OMCs for NPs, i.e., ferrihydrite (529.62 mg/g), O-Fh (439.08 mg/g), goethite (823.64 mg/g), and O-Goe (688.88 mg/g). Zeta potential and sedimentation kinetic studies suggested higher heteroaggregation and coagulation in the goethite-NPs bimodal system. NPs-minerals/OMCs interaction mechanisms were confirmed by FTIR and XPS analysis. Column transport experiments and DLVO analysis revealed that minerals/OMCs coated sand showed higher NPs retention than bare quartz sand under different pore water chemistry. Ferrihydrite and goethite coated sand columns have shown maximum NPs retention (>95%). Our study provides insight into how environmentally relevant mineral phases and thier corresponding OMCs impact NPs fate and transport in aqueous and terrestrial environments.