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Mechanisms of nanoplastics transport and retention in biochar-blended porous media: Role of surface interactions and hydrodynamic conditions
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Biochar is often added to soil to improve farmland and clean up pollution, but this study found that it can sometimes make tiny plastic particles (nanoplastics) move through soil more easily instead of trapping them—potentially letting them reach groundwater we may eventually drink. The effect depends heavily on the type of biochar used, water acidity, and dissolved salts and organic matter, with some biochars (like cow dung-based) blocking plastic movement while others (like wheat straw-based) let it pass through more freely. This matters because it shows that choosing the wrong soil treatment could unintentionally increase nanoplastic cont
The environmental risks posed by nanoplastics (NPs) are increasingly recognized, particularly their potential to infiltrate groundwater through subsurface transport. However, the role of biochar-a widely applied soil amendment-in modulating NPs fate remains ambiguous. Here, we systematically investigated NPs transport in porous media with different biochar blended under varied hydrogeochemical conditions using column experiments. The breakthrough curves (BTCs) and retention profiles (RPs) were simulated using a two-site kinetic retention model, while the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was employed to semi-quantitatively interpret the underlying retention mechanisms. Results showed that compared with pure quartz sand columns, the transport rate of NPs in biochar-blended sand column significantly facilitated under acidic conditions. In biochar-blended sand columns, biochar facilitated NPs migration within a specific salinity range (1 mM and 10 mM NaCl). Polyvalent cations suppressed NPs mobility more strongly than monovalent cations, with their interaction energy barriers between NPs and porous media of 10.63 KT. While the presence of humic acid (HA) markedly promoted transport through steric effect and electrostatic repulsion. Meanwhile, hydrodynamic conditions also played a key role-higher flow velocities and unsaturated conditions both promoted NPs transport, with the effluent recovery rate of > 86.89%. Importantly, the properties of the biochar itself emerged as a critical factor, in which wheat straw biochar (pyrolyzed at 500 °C, 5% w/w) facilitated NPs migration, whereas cow dung biochar (500 °C) enhanced retention due to its high ash content and greater surface roughness. The dominant retention mechanisms were attributed to heterogeneous aggregation and electrostatic interactions between NPs and the porous medium. This work provides actionable insights for mitigating NPs pollution risks through rational selection of biochar in agricultural and remediation practices.
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Tiny plastic particles (nanoplastics) can seep through soil and contaminate groundwater, but this study found that adding walnut shell biochar, a charcoal-like material, to soil can trap these particles and slow their spread significantly. This matters because groundwater is a major drinking water source, and factors like soil acidity, salt levels, and water flow speed all affect how well this plastic-trapping works, giving scientists practical clues for using biochar to help protect water supplies from plastic pollution.
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This study examined how magnetic biochar — a carbon-based material used in soil and groundwater remediation — affects the movement and retention of nanoplastics in porous soil-like media under varying water chemistry conditions. Magnetic biochar significantly increased nanoplastic retention and reduced their mobility through the porous medium, and the effect depended on the nanoplastics' surface chemistry, ionic strength, and the presence of organic matter. The findings suggest that adding biochar to contaminated soils could be a practical strategy to reduce the spread of nanoplastics through groundwater systems.
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Tiny plastic particles that build up in farm soil can make it harder for soil to hold onto nitrogen fertilizer, causing more of it to wash away into groundwater, which matters because excess nitrogen runoff can contaminate drinking water sources. The good news: adding biochar (a charcoal-like soil additive made from rice husks) helped soil trap nitrogen even when microplastics were present, suggesting a practical way to protect water quality as plastic pollution in farmland continues to rise.
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Researchers studied how biochar and plastic particles (nanoplastics and microplastics) mutually affect each other's transport through water-saturated sand, finding that small plastic particles enhanced biochar mobility while biochar consistently suppressed plastic particle transport across all sizes, due to heteroaggregation altering surface charge and steric interactions.
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Researchers tracked the individual transport, co-transport, and immobilization of microplastics in porous media, finding that plastic particle behavior differs significantly depending on surface charge and pore structure interactions. The results improve predictions of where microplastics migrate and accumulate in soils and aquifers.
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