Recent and (mainly) former anthropogenic activities have among other factors contributed to an accumulation of contaminants in aquatic sediments. As these pollutants are not permanently stored in these sediments, they form a real 'time bomb'. Under certain conditions these pollutants may be released into the water column and counteract measurements actually undertaken to improve the quality of river- and seawater. The objective of this project is to assess the risks of a planned or unforeseen modification of the sedimentary environment (increased supply of oxygen to the water column and sediments as a result of the actual measures for waste water treatment or through activities such as bioturbation, dredging and the management of banks ) in the northern part of France, the south of Belgium and the coastal zone. This problem can only be the object of a study in the framework of a cross-border programme and a common policy in both regions. Only a multidisciplinary group with sufficient critical mass and know-how can conduct a project with such a geographic interest. To fulfil these criteria therefore it is necessary to join skills and resources from both regions in order to develop new techniques applicable to a wide range of pollutants, to refine and further explore the techniques, and to thus be able to determine the bioavailability of pollutants in water and sediments, to validate the methodology on the field and through modelling techniques to develop a predictable instrument. In a second stage, the project aims to develop a policy for the exchange of students and scientists in order to create a cross-border research network for water quality. The first three years of the project will be dedicated to: development of a common policy for methodology and an improvement of existing but yet incomplete techniques (each participant must make their know-how available to the others) the application of this methodology on both French and Belgian pilot sites (fresh- and seawater) creation of a research network and experimental models. In later stages, the project aims to widen the geographical reach and to develop a cross-border research network for water quality. A biochemical sediment model will permit a better understanding and quantification of the sediment as well as the flux from and to the sediment.