Role of Natural Nanoparticles in Phosphorus Transport Processes in Ultisols

Labile P is a well‐recognized nonpoint source pollutant in agroecosystems. Predicting the fate and transport of P in watershed systems is critical in protecting water quality. In this case study, we investigated the role of soil nanoparticles in P release in South Carolina agricultural soils. Batch desorption experiments were coupled with scanning and transmission electron microscopy (EM) and x‐ray absorption spectroscopy (XAS) to better assess the reactivity of soil nanoparticles. The surface soils contained a total P concentration of 260 to 940 mg kg −1 , approximately 40 to 60% of which was ammonium oxalate extractable P. The 30‐d desorption experiments showed that P desorption was initially rapid, followed by a slow continuous release at pH 5.5 and 7. It was generally not correlated with the release of soil nanoparticles (operationally defined as 10–200 nm). Phosphorus was not readily retained on these nanoparticles at pH 4 to 7. These nanoparticles were rich in Si and S, and coated with Fe and C and trace amounts of P, Ca, Na, Mg, and Al. The EM images of nanoparticle morphology showed C‐associated globular formations as well as assembled platelets and spherical nanoparticles. The colloid‐ and nanoparticle‐facilitated P release has often been suggested as one of the important pathways for P transport in the soil‐water environment. This study presents a new aspect of nanoparticle reactivity in the soil environment, however: nanoparticles do not always contribute to P transport processes.