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Effect of NaNO3, NH4Cl and urea on the fate and transformation of various typical microplastics in porous media
Summary
Column experiments showed that nitrogen compounds commonly found in soil and groundwater—nitrate, ammonium, and urea—reduced the mobility of four types of microplastics (PVC, PMMA, PET, PP) in porous media, with effects varying by plastic polymer properties. This finding is important for predicting how microplastics spread through soils and into groundwater under real agricultural conditions where nitrogen fertilizers are routinely applied.
Understanding the transport behaviors of microplastics (MPs) in porous media is crucial in controlling MPs pollution. Given nitrogen is one of the most important nutrients in soil and groundwater systems, unclearness of the transport behaviors of microplastics (MPs) under various nitrogen conditions may inhibit the acknowledgment of MPs fate. For this reason, this study innovatively investigates the transport characteristics of four kinds of typical MPs (PVC MPs, PMMA MPs, PET MPs, and PP MPs) under various NaNO, NHCl and urea conditions via column experiments numerical models. The FTIR and XPS analysis were conducted to excavate the transform of MPs. The MPs mobility was generally reduced with the increasing nitrogen concentrations. The polarity and density properties of different MPs played combined roles in transport under similar conditions. Compared to NO, NH may neutralize the negative charge of MPs and then restrain their transport in porous media. Urea may coat the surface of MPs and promote the mobility, however, increasing concentrations of urea may result in the interattraction between MPs and porous media via hydrogen-bond and π-π interaction. PET MPs and PP MPs showed barely transform during transport under the tested conditions. Particularly, the chlorines on PVC MPs could react with the amide on urea and produce amidogen, which may improve PVC MPs transport. The N-H and C-N bond also generated on PMMA MPs in presence of urea also may enhance the mobility.