Influence of inorganic nano-fertilizer on the transport and release of nano- and micro-plastics in saturated quartz sand†

The use of fertilizer is a routine method of soil improvement, and thereby fertilizer is considered as an emerging factor affecting the transport of plastic particles in agricultural soils. Nano-CaCO₃ was selected as a representative nano-fertilizer to investigate its effect on the transport and release of nano- and micro-plastics (NPs and MPs) in saturated porous media. The effect of 200 mg L⁻¹ nano-CaCO₃ on the transport of nano- (0.51 μm, PS NPs) and micro- (1.1 μm, PS MPs) polystyrene particles (5 mg L⁻¹) in saturated quartz sand was investigated. Nano-CaCO₃ facilitated both the transport and release of PS NPs and MPs in examined 0.1–10 mM NaCl and 0.1–1 mM CaCl₂ solutions. In addition, it was believed that the remaining deposition of PS NPs and MPs after copresent nano-CaCO₃ and release treatment was solid and stable, as evidenced by the negligible detachment of PS NPs and MPs with deionized water washing. Further investigation indicated that the competition for deposition sites on quartz sand surfaces by nano-CaCO₃ copresent in solutions was the major factor dominating the enhanced transport of both PS NPs and MPs. This was verified by the transport of single nano-CaCO₃, the increased transport of PS NPs and MPs in quartz sand that was subjected to pre-equilibration with nano-CaCO₃ and also the SEM images of quartz sand covered with nano-CaCO₃. Meanwhile, the sweeping effects induced by nano-CaCO₃ were found to be responsible for the enhanced release of PS NPs and MPs during the transport process. This was further confirmed by the relatively high surface area and roughness of nano-CaCO₃ and the fluorescence microscopy imaging of the detached particles in effluents of column experiments of PS NPs and MPs induced by nano-CaCO₃. The findings of this study give insights into assessing the ecological risks of plastic particles with agrochemicals.