Soil organic matter fractions govern the transformation of selenium nanoparticles: a multi-technique analytical study

Selenium is a vital trace element for human health, but its distribution in European arable soils is often deficient. Selenium nanoparticles (SeNPs) represent a promising solution for biofortification due to their slow-release properties and reduced toxicity. However, their environmental behavior is dictated by interactions with soil organic matter (SOM). This study presents a comprehensive investigation of the physicochemical behavior of green-synthesized SeNPs (using yeast and soapwort extracts, and orange juice) within complex soil matrices. Utilizing an advanced analytical toolkit, including single particle inductively coupled plasma mass spectrometry (spICP-MS/MS), asymmetric flow field-flow fractionation (AF4-DLS/MALS), and capillary electrophoresis (CE-ICP-MS/MS), we characterized nanoparticle stability, aggregation, and the formation of the "eco-corona". HPLC-ESIMS/ MS was further employed to identify specific SOM components, such as lignins, tannins, and peptides, responsible for surface interactions. Results indicate that the interaction of nanoparticles depends on their surface modification and, therefore, on the method of synthesis. SeNPs synthesized with orange juice exhibit superior stability, while specific SOM fractions and high salinity significantly drive aggregation and dissolution. This study provides critical insights into the ligand-mediated processes that govern the lifecycle of SeNPs in agricultural systems.