This test guideline describes a test procedure to gain information on dispersion stability of manufactured nanomaterials in simulated environmental media. The main purpose of this guideline is to assess the ability of a nanomaterial to attain a colloidal dispersion and to conserve this dispersion under environmentally relevant conditions. The test procedure involves a dispersion of the nanomaterial with the aid of a calibrated sonication procedure and the determination of the mass concentration of the nanomaterial in a set of test vials while the particles undergo homoagglomeration and settling in environments of different hydrochemistry