GUAMA RIVER AND GUAJARA BAY (BELEM -PARA).Lead analyses in bottom sediments from the hydrographic system of Belem (Para) indicated low contents of this metal for the sediments from the Guama river, with no significant anthropogenic contribution.A concentration of 18.1 ± 1.5 mg kg -1 and 206 Pb/ 207 Pb isotopic signature of 1.196 ± 0.002 are assigned for Pb from natural sources.On the other hand, the significant increase of Pb contents in the sediments from the Guajará bay, together with the decrease of 206 Pb/ 207 Pb ratios (1.172 < 206 Pb/ 207 Pb < 1.188) point to an anthropogenic lead contribution, originated by the industrial and urban activities of the city of Belem.