A framework to measure the availability of engineered nanoparticles in soils: Trends in soil tests and analytical tools

In this study, the reactions of engineered nanoparticles (ENPs) in soils, with respect to their nanospecific properties, and observed effects of key soil properties (e.g. pH, ionic strength and natural colloids) on their stability in pore water are discussed. Key processes include aggregation and dissolution of ENPs, straining of ENPs in the solid matrix, stabilization of ENPs in pore water due to binding of molecules from dissolved organic matter (DOM) and inorganic colloids and the effect of artificial coatings. In view of these processes, this study provides guidance in the development of a framework to measure available and total soil contents of ENPs, via a set of extraction methods and advanced analytical tools. Particularly, the lack of effective extraction methods is thoroughly discussed regarding the identification of most relevant research gaps preventing an effective assessment of the availability, mobility and risks of exposure of sensitive receptors to ENPs in soils.