This report includes a detailed review of main processes and equations involved on chemical behaviour at sea. These processes were implemented in MOHID modelling system, in order to generate a chemical fate and behaviour model, integrated in lagrangian module of MOHID (a public domain / open-source water modelling system – www.mohid.com). The approaches methodology and algorithms selected are also described. To unzip the file, please, send an email to arcopol@maretec.org to get the password.