On February 25, 2021, the Organization for Economic Cooperation and Development (OECD) will hold a webinar on “Assessing the dispersion stability and dissolution (rate) of nanomaterials in the environment” to discuss the scope, content, and use of Test Guideline No. 318: Dispersion Stability of Nanomaterials in Simulated Environmental Media and its accompanying guidance document. According to OECD, “[t]he increased production and wide usage of manufactured nanomaterials suggest a higher probability of finding them in the environment. Therefore, testing the dissolution rate and dispersion stability for toxicity assessment are of paramount importance for adequate hazard assessment.” Test Guideline No. 318 describes a test procedure to obtain information on dispersion stability of nanomaterials in simulated environmental media. The accompanying guidance document provides additional recommendations on dispersion stability measurements. OECD states that it is developing a Test Guideline to determine the solubility and dissolution rate of nanomaterials in the aqueous environmental media and that the webinar will include discussion of this Test Guideline.