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Impact of ManganeseMineral Transformations on NanoplasticTransport and Sedimentation in Surface and Subsurface Aqueous Systems
Summary
Tiny plastic particles (nanoplastics) can travel through soil and water, potentially reaching drinking water sources—but this study found that a common natural mineral called manganese oxide can trap these particles, especially in one form called manganite, which grabbed onto plastic particles far more effectively than other mineral forms. This matters because it suggests that certain soils and sediments naturally rich in manganese oxides might act as filters, slowing the spread of nanoplastics into groundwater and reducing human exposure through drinking water.
The fate and transport of nanoplastics (NPs) are strongly governed by interactions with ubiquitous mineral particles in natural environments. While Fe/Al/Si mineral phases have been extensively investigated, the role of manganese oxide minerals (MnOx), a dominant and highly reactive mineral fraction, has received comparatively little attention. This study systematically examines interactions between polystyrene NPs and primary MnOx (manganite) as well as its subsequent transformed phases, i.e., pyrolusite and bixbyite, under environmentally relevant pH, ionic strength, and humic acid conditions. The results show that the higher density of surface hydroxyl groups and positive surface charge of manganite resulted in the maximum NP sorption capacity (1071.4 mg/g) compared to pyrolusite and bixbyite. Manganite promoted rapid and strong heteroaggregation with NPs in aqueous systems, as confirmed by zeta potential measurements and sedimentation kinetics. Spectroscopic analysis (FTIR and XPS) confirmed that surface functional groups play a vital role in NPs–MnOx interactions. Column transport experiments in saturated porous media further demonstrated that MnOx and pore-water chemistry influence NP mobility. Manganite-coated sand exhibited maximum NP retention relative to pyrolusite and bixbyite, indicating restricted NP transport under subsurface conditions. Overall, these findings highlight the importance of MnOx in controlling NP mobility in aqueous environments.