Transporte de chumbo e metais associados no Rio Ribeira do Iguape, São Paulo, Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

The objective of the present study is to clear some aspects of the transport of Lead and associated metais by suspended particulate matter along the Ribeira de Iguape River, in the southeastern region of the state of São Paulo. Literature data were taken into account, as well as findings gathered trom studies of sediments collected in stations at different sectors of the Ribeira river basin. In addition, in the region surrounding the city of Sete Barras, samples of water, suspended solids and sediments of the river were taken for study immediately after an atypical flood front had passed, causing the flooding of high and low plains. In the alluvial plains of Sete Barras, columns of sediments were also collected in lagoons, in order to verify the increase of metais with time. The behavior of concentrations of lead ranged from 347 1-19/g, in Itapeúnas,SP, to 90 1-19/g, at the entrance of Vaio Grande Channel. This behavior has been related with the dilution effect, due mainly to the contribution of the suspended material of the other tributaries which flow into the Ribeira in the stretch between these two sampling stations. Isotopic ratios of lead were determined in sediments taken at 10 sampling stations distributed from the high valley of the Ribeira down to its mouth in the estuarine lagoons system of Iguape and Cananéia , and were compared to values obtained by other authors in galenas of mines of the Perau and Panelas do deposits types, and of younger ore deposits as well. Results showed similar isotopic rates for sediments and galenas of deposits of the Panelas type, showing that extractive and beneficiation activities of its ores were the ones that most contributed to the contamination by lead verified in sediments of this river. Studies with water samples, sediments and suspended solids taken in the channel of the Ribeira River, and with sediments columns, of the marginal lagoons in Sete Barras, proved that metais are transported mainly by the solids that are suspended in water. Concentrations of metais, especially lead, in samples of the solids suspended in river waters were similar to those found in the midle of the column of sediments taken at Lagoa Nova. Therefore, the mass of this metal transported yearly by the Ribeira River could be estimated as being of 151 tons adsorbed on 840.000 tons of suspended solids.This mass of lead equals 6% of the annual production of metallic lead in the Ribeira River valley in the 80 s. Samples of the sediments profile of the lagoons, indicated as background concentrations of lead, zinc and copper respectively 33, 116 and 43 I-Ig/g. These values are two times the values found by other authors. The procedure used for the determination of background levels of metais has proved efficient, fast and by far more economic than the ones traditionally adopted in geochemical prospecting, which count on a great number of determinations in stream sediments samples

ASSUNTO(S)

chumbo geoquimica rio vale (pr e sp) geologia ambiental transporte de sedimentos - ribeira do iguape

ACESSO AO ARTIGO

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