Retention of sterically and electrosterically stabilized silver nanoparticles in soils

The current study investigated the interaction of sterically stabilized OECD standard Ag ENP (AgNM-300k) and silver ions (Ag+) in 25 German arable soils with varying properties (organic carbon concentration of 0.4-25 mg g(-1) and clay content of <0.1-392 mg g(-1)) in 24 h batch retention experiments. A soil subset (n=8) was investigated to test the soil interactions with citrate-stabilized Ag ENP (AgCN30). The adsorption of Ag+ was consistent with the Freundlich model with high KF values (mean KF=2553 L kg(-1), n=25), which suggested a high retention of Ag+. The retention of AgNM-300k followed a linear partitioning model and generally exhibited a low retention for the majority of the investigated soils (group 1, mean Kr, linear=3.7 L kg(-1), n=19), and was correlated with the clay content (relation to log10(Kr, linear), r2=0.40, n=19). Soils showing a high retention of AgNM-300k (group 2, mean Kr, linear=1048 L kg(-1), n=6) either had a low (<5.1) or high pH (>7.0) and generally contained >200 mg g(-1) clay. For the sample subset tested, AgCN30 and AgNM-300k were retained in similar dimensions regarding the same soils. The results suggest that the highest risk of long-term ENP mobilization exists when Ag ENP are applied to agricultural soils with low clay contents (<130 mg g(-1)) and slightly acidic conditions.