Predicting environmental concentrations of carbamazepine and oxcarbazepine and their main metabolites in a coastal system Predicting of environmental concentrations of pharmaceuticals is commonly done for risk assessment at a regional level. The difficulties appear for the prediction at a local level, where data available is scarce. This work developed a model to predict the behavior of carbamazepine (CBZ), oxcarbazepine (OxCz) and their main metabolites in a regional environmental system : a coastal zone with a WWTP submarine outfall. The model takes into account the initial CBZ and OxCz prescriptions, metabolisms and partial transformations of CBZ and OxCz into their metabolites, their fate in wastewater treatment plants and their flow to the coastal zone through the submarine outfall. Regional data on CBZ and OxCz prescription were obtained from the medical care system. CBZ and OxCz prescribed amounts have been studied over 6 months in view to calculate concentrations in wastewater treatment plant effluents and so allow for Predicted Environmental Concentrations (PECs) estimation. The human metabolic pathways of CBZ and OxCz required to include in the model the contribution of the major urinary metabolites: carbamazepine-10,11-epoxide, 10,11-dihydro-10,11-trans-dihydroxycarbamazepine, 10-hydroxy-carbamazepine and other hydroxylated derivatives. PECs lie in the ng/L level in the wastewater effluents and were compared to the measured concentrations (MECs). The diffusion in the coastal zone was estimated with an hydrodynamic numeric model (MARS 3D). The behavior in the coastal zone was qualitatively compared to measured concentrations obtained with POCIS passive samplers. Data on pharmaceuticals in the coastal zone are scare and PECs and diffusion model might therefore be useful for studying pharmaceutical transfer and fate in the coastal environment