Noninvasive\nInvestigation of Gold Nanoparticle Transport\nand Fate in Soil

This work uses spectral-induced polarization (SIP) to\nmonitor the\ntransport of citrate-coated gold nanoparticles (AuNPs) in soil. The\nexperimental setup includes batch experiments with different NP-to-soil\nratios, designed to determine the NP concentration at which electrodic\npolarization is significant, as well as a flow-through experiment\nin a natural soil column. The analyzed SIP measurements allow not\nonly the noninvasive monitoring of NP progression through the soil\nbut also the deduction of NP–soil interactions through combination\nwith elemental analysis. The real conductivity increased in a breakthrough\npattern in response to the AuNP transport due to CaCO<sub>3</sub> dissolution\nand subsequent Ca<sup>2+</sup> release. The imaginary conductivity\npresented a more complex pattern and reflected a combination of NP–soil\ninteractions (NP retention and accumulation, CaCO<sub>3</sub> dissolution\nwith subsequent Ca<sup>2+</sup> release, and exchange processes).\nOverall, we show that the progression of NPs through soil can be tracked\nusing SIP even at low concentrations due to their effect on pore water,\nsediments, and NP–soil and NP–CaCO<sub>3</sub> interactions.\nNevertheless, many parts of the observed phenomena require further\nresearch to gain better understanding and quantification.