Silver nanoparticles in soil: Aqueous extraction combined with single-particle ICP-MS for detection and characterization

- Developing an extraction and analysis method for AgNPs in soil.
- Single-particle inductively coupled plasma mass spectrometry (spICP-MS) was chosen as the analytical technique.
- The method developed in several steps and validated for the recovery.

Silver nanoparticles (AgNPs) are used in a growing number of applications and products. Previous studies showed AgNPs can leach from these products to the environment. As a result of AgNPs leaching, sediment, soil and sludge-treated soils may be contaminated with AgNPs. Methods to detect, quantify and characterize AgNPs in soil are urgently needed. This study describes the development and validation of a method for the extraction, quantification and particle size determination of AgNPs in soils. The final method consists of pre-wetting the sample followed by an aqueous extraction, using sonication to re-suspend adsorbed AgNPs, and analysis of the aqueous extract with single particle ICP-MS. Validation of the method showed that the recovery of AgNPs spiked to soil was 44% for sandy soil and 42% for clayey soil. Although this recovery is relatively low, the repeatability and reproducibility values of the particle concentration were within the limits of Horwitz ratio, which makes the method suitable for its purpose. Further, the method concentration detection limit, LODc., is 5 μg kg−1 soil. The developed method can be applied in eco-toxicological and risk-assessments studies for AgNP in the soil environment.