Retention of sterically and electrosterically stabilized silver nanoparticles by soil minerals

Engineered silver nanoparticles ( A g ENP ) enter the environment and lead to concerns about their environmental effects. Clay‐sized particles are assumed to govern the environmental mobility and bioavailability of ENP , although little is known about their interaction with pedogenic minerals. The interactions of sterically ( AgNM –300k, OECD standard) and electrosterically ( AgCN30 ) stabilized A g ENP with iron and clay minerals were investigated at a range of pH values from 4 to 7. The A g ENP were separated from mineral suspensions by filtration at <7 and <0.45 µm and by ultracentrifugation at <0.003 µm. The colloidal stable A g ENP were analysed by dynamic light scattering ( DLS ). The retention of AgNM –300k ( pH adjusted to 6, A g content ≈ 8 mg l −1 ) was greater than 85% for all minerals except silica and showed the tendency to increase in the following order: ferrihydrite, smectite, illite, kaolinite, goethite and allophane. The retention of AgCN30 ( A g content ≈ 8 mg l −1 ) was less than for AgNM –300k, except for silica at pH 6, and showed the tendency to increase in the following order: goethite, smectite, allophane, kaolinite, illite and silica. The zeta potential in the fraction <0.45 µm was not sufficient to explain the difference in stability of colloidal A g ENP in the A g ENP –mineral suspensions. However, the retention increased for A g ENP with decreasing pH , most probably because of homo‐ and hetero‐aggregation, but it was not necessarily related to dissolution of the A g ENP . In general, iron and clay minerals showed clearly the potential to retain A g ENP under relevant environmental conditions even though the retention was incomplete. Highlights Interaction of different A g ENP with soil minerals was tested in short‐term batch experiments. Ag ENP showed hetero‐aggregation with minerals, but the retention was incomplete. Hetero‐aggregation between minerals and A g ENP was favoured by acidic conditions ( pH  ≤ 5). Iron and clay minerals showed the potential to retain A g ENP in the environment.