| Gold nanoparticles (AuNPs) are extensively used in a number of applications including molecular detection through surface-enhanced Raman scattering, multifunctional nanocarriers for drug delivery, cancer diagnosis and treatment, catalysis and photonic/plasmonic devices. However, environmental fate and toxicity of AuNPs are not well understood or characterized. In this work, AuNPs of different concentrations were introduced and allowed to filter through various soil matrices in an effort to determine the physico-chemical interactions between the AuNPs and the aqueous porous soil medium. AuNPs deposition onto the soil particles and the mechanisms of their transport and release into the soil matrix are key factors that influence the leaching of nutrients, i.e., ionic species of various elements such as sodium (Na), magnesium (Mg), aluminum (Al), phosphorous (P), potassium (K), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu) and gold (Au). Simultaneously, soil matrix composition and properties also greatly influence the transport, reactivity and fate of AuNPs in a porous environment. The surface electrical charge of a soil matrix can affect the transport of gold nanoparticles by electrostatic repulsion or attraction, thus increasing mobility or hindering movement. In this study I utilize a saturated filtering column to explore the soil-AuNPs interaction and to illustrate its effect of ten environmentally important elemental species using ICP-MS analysis of the effluent of each soil matrix. Natural soil-AuNPs matrix retained 99.9% of the total AuNPs introduced. Sandy soil, though very porous and negatively charged, retained 85% of the gold nanoparticles added. A mixture of clay and clean sand ranging from 10%-40% of clay retained gold particles between 99.43%, and 99.52% respectively. However, results show that aggregation, grain size distribution and electrostatic forces are contributors to such high retention rates. Further experiment was conducted to exam the outcome of precipitation as a mean to evaluate the fate gold nanoparticles after deposition. |
