This document provides specific guidance for test preparation, implementation, performance, analysis and reporting using the OECD TG No. 312 for testing the mobility and retention of NMs in different types of soils. The GD is likely also relevant for colloidal materials of greater size ranges, because transport of these materials occurs via the same kinetically dominated processes that determine the fate of NMs. The document informs on necessary modifications and additions to the standard test protocol including preparation and application of the test materials, analytics and data reporting. The modifications and additions proposed in the GD are included in order to generate relevant, accurate and reproducible data on NM retention and mobility in soils. Estimations of parameters such as Koc (organic carbon normalised adsorption coefficient) and Kom (organic matter normalised distribution coefficient)as presented in the parent TG No. 312 are not applicable for NMs.