Influence of sulfur fertilization on CuO nanoparticles migration and transformation in soil pore water from the rice (Oryza sativa L.) rhizosphere.

The biogeochemical cycling of sulfur in soil is closely associated with the mobility and bioavailability of heavy metals; however the influence of sulfur on the behavior of metal-based nanoparticles has not yet been studied. The influence of S fertilizer (S ⁰ and Na ₂ SO ₄ ) applied in paddy soils on CuO NPs behavior in soil pore water was explored in the present study. Synchrotron-based techniques were applied to investigate the migration and speciation transformation of CuO NPs in soil pore water colloids. The application of sulfur fertilizer increased the zeta potential of soil colloids from the rice rhizosphere region and reduced the size of the colloids. Sulfur fertilization decreased the concentration of Cu in soil pore water in the rice rhizosphere region. S ⁰ fertilizer reduced the Cu concentration in soil colloids (by 55.8%-73.5%), while Na ₂ SO ₄ increased the Cu concentration in soil colloids (by 173.8%-265.1%). Sulfur fertilization changed the spatial distribution of Fe ³⁺ and Cu ²⁺ in colloids, making these ions more likely to be aggregated on the edges of soil colloids. Speciation transformation of CuO NPs happened during the process of migration. The main Cu speciation in the soil colloids were CuO NPs, Cu-Cysteine, Cu ₂ S and Cu-Citrate. Sulfur fertilization increased the proportion of Cu ₂ S (by 40.5%) in soil pore water colloids from the rice rhizosphere region, while the proportion of CuO NPs was reduced (by 18.4%). Sulfur fertilization changed the morphology and elementary composition of colloids in soil pore water, thus influencing the migration of CuO NPs in the soil column through soil colloids.
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