Since Pb and Cd are both non-biodegradable and non–essential, they represent a serious threat for aquatic ecosystems. Metal determination in aquatic organisms such as gammarids offers encouraging perspective to monitor water quality. However, metal uptake in organisms may be influenced by water cationic composition because of competition processes on biological binding sites. The development of bioaccumulation models constitutes promising tools to quantify metal bioavailability and predict metal impact on aquatic ecosystems. In order to arise such models, it is necessary to formalize the abilities of organisms to regulate metals and water chemistry effects in controlled conditions. However, what is the environmental relevance of experimentally derived models to predict bioaccumulation in field conditions?