Remobilization of sterically stabilized silver nanoparticles from farmland soils determined by column leaching

Abstract

SummaryThe increasing application of silver (Ag)‐engineered nanoparticles (ENP) will enhance their release to the aquatic and terrestrial environments. Hence, the retention potential of the sterically stabilized Ag ENP (AgNM‐300k, Organisation for Economic Cooperation and Development (OECD)) standard material was tested in a sandy Cambisol and in a clay‐ and silt‐rich Luvisol. In addition, the remobilization potential of the same soils spiked with AgNM‐300k was investigated in columns after 3 and 92 days of incubation. The AgNM‐300k dispersion and the soil solutions were examined with dynamic light scattering (DLS). Inductively coupled plasma optical emission spectroscopy (ICP‐OES) and inductively coupled plasma mass spectrometry (ICP‐MS) were used to analyse soils and soil solutions subjected to different digestion and extraction techniques (aqua regia, nitric acid (HNO3) and EDTA (ethylenediamninetetraacetate)). The 24‐hour batch test showed a 10‐fold greater retention coefficient for AgNM‐300k in the silt‐ and clay‐rich Luvisol than in the sandy Cambisol. In addition, all applied extraction techniques indicate a greater potential for mobility of Ag ENP for the sandy Cambisol. However, a small release from the column of AgHNO3 (measured Ag content in the fraction < 0.45 µm after HNO3 digestion) was observed after 3 as well as after 92 days of incubation for both soils. The largest amount of Ag was released from the Cambisol during the first percolation step (water:soil ratio = 1 l kg−1) after the soil was incubated for 3 days. This AgHNO3 release corresponded to approximately 1% of the total amount of Ag in the soil column. The correlation obtained between released AgHNO3 and AlHNO3 suggests that even the Ag released at small concentrations is associated with soil colloids. Thus, hetero‐aggregation is a potentially important process controlling retention.