Approximately 15% of the world's population endures disorders linked to selenium deficiency. Selenium-fortified food from suitable fertilizers is crucial for addressing a micronutrient deficiency. Inorganic Se fertilizers are increasingly being replaced by selenium nanoparticles (SeNPs) as a slow releasing additive. Selenium from nanoparticles' surfaces is released as selenium oxides for uptake by plants from the soil solution at the oxidation stage [1]. SeNPs mobility and stability in soil is greatly impacted by soil organic matter (SOM) promoting or reducing aggregation. The study aimed to evaluate the effect of SOM and soil salinity on SeNPs’ physicochemical characteristics, including their concentration and size distribution, demonstrating their stability and potential function in soil.
Three microwave-assisted methods, utilizing yeast and saponin extracts, and orange juice as reducing/stabilizing agents, were employed to synthesize SeNPs. Chernozem soils with varying humus content were fortified with inorganic salts to investigate their influence on solubility of SOM. Soil compositions were extracted using various methods to yield in separated fractions hydrophilic, polar organic, inorganic, low and high-molecular-weight compounds differently associated with soil insoluble components [2-4]. SeNPs were incubated for 1, 2, and 7 days with soil extracts. The size, particle concentration, and dissolved Se concentrations were determined using SP-ICP-MS/MS and confirmed with CE-ICP-MS/MS. The extracts’ composition was analysed by non-targeted LC-UV-ESI-MS/MS.
The particle diameter in the synthesis of SeNPs varied around 300 nm with yeast, 190 nm with saponin, and 70 nm with orange extracts. 50 nm and 55 nm SeNPs form a secondary cluster in yeast and saponin extracts. An increase in salinity enhances the aggregation of SeNPs. At high ionic strength and charge neutralization, the electrical double layer is compressed and van der Waals forces become dominant. The choice of solvent significantly influences the solubility of SeNPs during fractionation. Addition of humic acid to the soil enhanced SeNPs stability via interactions with the chemicaly active components of SOM. The physicochemical properties of SeNPs can be investigated using SP/CE-ICP-MS/MS techniques in relation to the impact of specific soil components. The LC-UV-ESI-MS/MS provides molecular structure details of SOM extracts.

References
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Research was funded by the Warsaw University of Technology within the Excellence Initiative: Research University (IDUB) programme Young PW II.