Investigação do comportamento geoquímico de metais-traços em solos e sedimentos da bacia inferior do rio jaguaribe, Nordeste do Brasil

Abstract

The extent of metal inputs to the marine environment depends on the levels these metals found in river water and the physical, chemical and biological processes which occur in estuaries and in river drainage basins. Thus, the purpose of this study is to verify the control of geochemical parameters in the dynamics of trace-metals in the soils of the lower basin and estuary of the Jaguaribe river (CE) for an assessment of metal retention capacity in the semi-arid northeastern coast of Ceara, Brazil. For this purpose, surface soil and estuarine (upper, medium and plume) surface sediments samples were collected in the lower basin of the Jaguaribe river. Soil and sediment samples were dried at 60° C, grinded and sieved through a 0,063 mm sieve to determine fine content. The physical and chemical properties selected to characterize the soil samples are: CEC, pH, percentage of bases and, organic matter (OM), following Embrapa protocols, and metal contents (by FAAS or ICP-MS) in grain size < 2 mm and <0,063 mm (fine). In sediments were determined fine content, organic matter and metal content, by the same techniques. The soils of the lower Jaguaribe were classified as slightly acid, predominately sandy and low organic matter content. The low OM content was enough to provide High CEC. Statistical correlations showed high association between the trace metals, suggesting a common source and direct associations of trace-metal and Fe and Al, suggestting the importance of Fe and Al oxy-hydroxides on metal retention in soil. The metal contents in estuarine sediments were higher than in soils, indicating autochthonous enrichment. The trace metal geochemistry in soils and sediments was different showing a greater association between metals and organic matter. Enrichment factors (EF) were higher for Pb, Zn, Cr, Cu and Ni, respectively. EF indicated natural enrichment in soils and sediments and higher metal contents obtained in the estuarine plume, characterizes the estuary such as low metal retainer.