The current approach to ecological risk assessment of chemicals is based on the quotient of a predicted no effect concentration and a predicted exposure concentration. We have gathered knowledge supporting the prediction of the exposure concentration of nanomaterials (NMs) in the aquatic environment and have evaluated the adequacy of the current guidance documents for use with NMs and therefore have also conducted a literature review on two important environmental fate processes for NMs, sedimentation and dissolution. This resulted in an overview of the available quantitative data for sedimentation and dissolution of NMs. We have used this overview to propose a way forward in modeling the exposure concentration of NMs in the water phase. Transport to sediment seems to be of greater relative importance than advection or dissolution of NMs. Both the transport of nanomaterials from water to sediment and the dissolution of nanomaterials can be incorporated into current exposure models simply by adding first-order rate constants. Our proposed exposure model for nanomaterials can be used to improve current risk assessment for nanomaterials.