The present work is an evaluation of the ecological risk, associated with the concentrations of mercury, zinc, copper, lead, nickel, chromium, arsenic and cadmium in bottom sediments of the Rodrigo de Freitas lagoon (RJ). Sediment samples were collected from 16 stations within the lagoon, and metals concentrations, organic carbon, total phosphorus, pH and grain size were determined. The contamination was evaluated by the application of the Enrichment Factor (EF), as established by the ratio between the metal contents and the background value, normalized by the aluminum content, which indicate the anthropic contribution. The Potential Ecologic Risk Index (PERI), which integrates metallic concentrations and their toxicology was also applied as a tool for the diagnosis of the quality of the aquatic ecosystems. The application of the PERI shows that the ecological risk to the aquatic biota in the lagoon is low. In general, the metals presented a strong correlation with organic matter, fine grained fraction, iron and aluminum. Data also indicate a common source of the contaminants Zn, Cu, Pb and Hg, possibly associated with the runoff of the neighboring urbanized environs, or the disposal of domestic sewages.
