French environmental law for nature protection requires that all the facilities, works, and development projects that may affect the environment should be the subject of an impact study to evaluate their consequences, including on human health. For this analysis, the risk assessment approach is used and the population's exposure is estimated with the aid of multimedia models. The CalTOX model is frequently used for this kind of study. Unfortunately, the analysis of these studies shows that the model is often badly understood and poorly used. The difficulties encountered by the users, the errors and the problems met in the interpretation of results, which are the most commonly found in the human exposure assessment, are listed and their consequences illustrated. CalTOX has been shown to have many advantages (adaptability, speed in carrying out calculations, transparency), but it ought not to be used as a "black box" because such a use may lead to many errors and a loss of confidence in the studies.