Transport and retention of engineered silver nanoparticles in carbonate-rich sediments in the presence and absence of soil organic matter

Authors: ADRIAN, YORCK - Aachen University; SCHNEIDEWIND, UWE - Aachen University; Bradford, Scott; SIMUNEK, JIRKA - University Of California; KLUMPP, ERWIN - Agrosphere Institute; AZZAM, RAFIG - Aachen University

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2019
Publication Date: 8/28/2019
Citation: Adrian, Y.F., Schneidewind, U., Bradford, S.A., Simunek, J., Klumpp, E., Azzam, R. 2019. Transport and retention of engineered silver nanoparticles in carbonate-rich sediments in the presence and absence of soil organic matter. Environmental Pollution. 255. https://doi.org/10.1016/j.envpol.2019.113124.
DOI: https://doi.org/10.1016/j.envpol.2019.113124

Interpretive Summary: Silver nanoparticles (AgNPs) in the environment pose a potential risk to ecosystem health because of their antimicrobial properties. Experiments were conducted to investigate the influence of the positively charged carbonate mineral fraction and soil organic matter on AgNP transport and fate. Our results indicate that greater AgNP retention and delay in transport occurred with increasing carbonate fraction of the soil, although only a small fraction of the carbonate surface contributed to AgNP retention due its surface roughness. The retention of AgNPs was enhanced in the presence of soil organic matter and calcium from carbonate minerals when the AgNPs were coated by a surfactant, but retention was unaffected when they were coated by a polymer due to differences in charge of the AgNPs. The results from this study will be of interest to scientists and engineers concerned with the fate and risks associated with AgNPs in natural environments with carbonate minerals and soil organic matter.

Technical Abstract: The transport and retention behavior of polymer- (PVP-AgNP) and surfactant-stabilized (AgPURE) silver nanoparticles in carbonate-dominated saturated and unconsolidated porous media was studied at the laboratory scale. Initial column experiments were conducted to investigate the influence of chemical heterogeneity (CH) and nano-scale surface roughness (NR) arising from mixtures of clean, positively charged calcium carbonate sand (CCS), and negatively charged quartz sands. Additional column experiments were performed to elucidate the impact of CH and NR arising from the presence and absence of soil organic matter (SOM) on a natural carbonate-dominated aquifer material. The role of the nanoparticle capping agent was examined under all conditions tested in the column experiments. Nanoparticle transport was well described using a numerical model that facilitated blocking on one or two retention sites. Results demonstrate that an increase in CCS content in the artificially mixed porous medium leads to delayed breakthrough of the AgNPs, although AgPURE was much less affected by the CCS content than PVP-AgNPs. Interestingly, only a small portion of the solid surface area contributed to AgNP retention, even on positively charged CCS, due to the presence of NR which weakened the adhesive interaction. The presence of SOM enhanced the retention of AgPURE on the natural carbonate-dominated aquifer material, which was attributed to cation bridging. Surprisingly, SOM had no significant impact on PVP-AgNP retention, which suggests that a reduction in electrostatic repulsion due to the presence of SOM outweighs the relative importance of cation bridging. Our findings are important for future studies related to AgNP transport in shallow unconsolidated calcareous and siliceous carbonate sands.