[en] In order that a geochemical balance be as complete as possible and thus, reach predictive values for toxic chemical dispersion, an understanding of the hydrological, sedimentological and geological contexts is fundamental. The dispersion of a polluent (in this case radionuclides) is dependent, in part, on its chemical properties and its interaction by sorption and desorption from solid particles (in particular, sediments). This interaction needs to be incorporated in dispersion models and can influence the passage of a pollutant along the food chain. In the case of Ribeira Bay, near the nuclear power center of Angra I, it was observed, through the analysis of sedimentological and geochemical parameters (TOC, TSS, chemical and mineralogical compositions, and granularity): an increase in absorption capacity of surface sediments owing to a homogeneous grain size distribution and a varying clay composition; a possibility of remobilization and transfer of particulate material to areas outside the bay. (Author)