Toluene diisocyanate (TDI) is a large volume chemical used for the production of polyurethanes. It is sparingly soluble in water, but hydrolyses instantaneously liberating toluene diamine (TDA), which is highly reactive to TDI. The ecotoxicity of TDI is dominated by TDA. The hydrolysis of TDI under static and dynamic conditions was investigated previously. Previously published data on TDI hydrolysis were revisited, and based on these data a model was developed that allows a conservative and quick estimation of TDA concentrations in rivers following a major incident with TDI. As earlier published model experiments indicate, the maximum achievable TDA concentration is about 30 mg/L. Model simulations based on these experiments indicate that the TDA concentrations in a river after TDI discharge may be up to three orders of magnitude lower. (c) 2013 Elsevier B.V. All rights reserved.