Distribution and isotopic composition of lead in bottom sediments from the hydrographic system of Belém, Pará (western margin of Guajará Bay and Carnapijó River)

Abstract

This study first aimed to evaluate the effect of human activities on the distribution of lead within the estuarine system of Belém, Pará. This was achieved by studying the concentration and isotopic signature of Pb in bottom sediments from the western margin of Guajará Bay and from Carnapijó River, an area removed from the influence of the city of Belém. Secondly, the contribution of suspended matter in the transportation of anthropogenic Pb in Guajará Bay was evaluated. Third, the content and background isotopic signature of Pb in the hydrographic system of Belém was determined. Isotopic signatures of sediments from the western margin of Guajará Bay confirm an anthropogenic contribution of Pb throughout the entire bay. The Pb accumulation process has become more efficient over the last 10 years, and this can be attributed to the rapid population growth of Belém city. Sediments in Carnapijó River are not affected by human activities, and the average concentration values (Pb = 19.6 ± 3.7 mg kg-1) and isotopic signatures (206Pb/207Pb = 1.196 ± 0.004) confirm the background Pb values previously proposed for the river system in the Belém region. The isotopic signatures of suspended matter on the eastern (206Pb/207Pb = 1.188) and western (206Pb/207Pb = 1.174) margins of Guajará Bay show that suspended matter is an efficient Pb transportation mechanism of domestic and industrial wastewater from Belém to the western margin of the Bay due to tidal effects at the confluence with Guamá River.