Evidence on enhanced transport and release of silver nanoparticles by colloids in soil due to modification of grain surface morphology and co-transport

Authors: LIANG, YAN - Guangxi University; LUO, YONGLU - Guangxi University; LU, ZHIWEI - Guangxi University; KLUMPP, ERWIN - Forschungszentrum Juelich Gmbh; SHEN, CHONGYANG - China Agricultural University; Bradford, Scott

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2021
Publication Date: 2/4/2021
Citation: Liang, Y., Luo, Y., Lu, Z., Klumpp, E., Shen, C., Bradford, S.A. 2021. Evidence on enhanced transport and release of silver nanoparticles by colloids in soil due to modification of grain surface morphology and co-transport. Environmental Pollution. 276. Article 116661. https://doi.org/10.1016/j.envpol.2021.116661.
DOI: https://doi.org/10.1016/j.envpol.2021.116661

Interpretive Summary: Nanoparticles (NPs) are increasingly used in a variety of industrial applications and may eventually contaminate the environment. This research showed that natural soil colloids can facilitate NP transport and release by alteration of the soil grain surface roughness. Grain surface roughness was found to have a larger influence on NP fate than charge heterogeneity. These findings provide valuable insight into mechanisms and interactions of NPs and the natural porous media. This research will be of interest to scientist, engineers, and public health officials concerned about predicting the fate and risks of NPs in the environment.

Technical Abstract: Natural soils have frequently been considered to decrease the mobility of engineered nanoparticles (NPs) in comparison to quartz sand due to the presence of colloids that provide additional retention sites. In contrast, this study demonstrates that the transport and release of silver nanoparticles (AgNPs) in sandy clay loam and loamy sand soils were enhanced in the presence of soil colloids that altered soil grain surface roughness. In particular, we found that the retention of AgNPs in purified soils (colloid-free and acid-treated) was more pronounced than in raw (untreated) soils or soils treated to remove organic matter (H2O2 or 600 °C treated). Chemical analysis and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy demonstrated that the grain surfaces of raw and organic matter-removed soils were abundant with metal oxides and colloids compared to purified soil. Column transport and release experimental results, SEM images, and interaction energy calculations revealed that a significant amount of concave locations on purified soils hindered AgNP release by diffusion or ionic strength (IS) reduction due to deep primary energy minima. Conversely, AgNPs that were retained in soils in the presence of soil colloids were more susceptible to release under IS reduction because the primary minimum was shallow on the tops of convex locations created by attached soil colloids. Additionally, a considerable fraction of retained AgNPs in raw soil was released after cation exchange followed by IS reduction, while no release occurred for purified soil under the same conditions. The AgNP release was highly associated with soil colloids and co-transport of AgNPs and soil colloids was observed. Our work is the first to show that the presence of soil colloids can inhibit deposition and facilitate the release and co-transport of NPs in soil by alteration of the soil grain surface morphology and shallow primary minimum interactions.