Metais pesados (Cr, Ni, Pb, e Zn) em sedimentos da Barragem de Massingir e seus impactos ambientais

Abstract

The present work intends to evaluate the environmental impact of heavy metals (Cr, Ni, Pb and Zn) in sediments from the Massingir dam, collected at five stations. Due to the high degree of toxicity of heavy metals to the aquatic ecosystem and the health of populations that use the waters and consume fish from the dam, it is important to assess the content of these metals in sediments that can contaminate the waters through various exchange mechanisms; This work is part of the "Massingir Dam and Smallholder Agricultural Rehabilitation" (MDSAR) project, carried out by ARA-Sul, financed by the African Development Bank (AfDB) and coordinated by the Department of Biological Sciences, Faculdade de Ciências-Universidade Eduardo Mondlane. These metals are analyzed by "FAAS" after optimizing the instrumental and analytical conditions to validate the method of analysis. Accuracy was determined using SARM 46 and SARM 52 reference materials provided by MINTEK South Africa. According to the recommended values ​​for the reference materials, very good values ​​of relative error were obtained for Cr, Ni, Pb and Zn of 0.30%, 3.8%, 0.4% and 0.1%, respectively. The RSD values ​​for the determination of all elements were good and ranged from 0.2-5.3% for Cr, Ni and Zn and for Pb between 1.0 and 6.1%. The results obtained experimentally by "FAAS" were compared with those obtained by "XRF" in the laboratories of SETPOINT in South Africa. Applying the paired t-test at a confidence level of 95%, the values ​​obtained by the two methods are not significantly different (Cr, Ni and Zn), with the exception of the Pb values. The levels of Cr, Ni, Pb and Zn determined in this study ranged from 393 to 545ug/g, 153 to 184ug/g, 59 to 75ug/g and 85 to 112ug/g respectively. The levels of As and Hg are less than 1ug/g, they were determined by "ICP-MS" in the laboratories of SET POINT. Since in Mozambique there is no legislation that regulates the maximum amounts of heavy metals in river sediments, the levels obtained are compared with those found in other studies carried out in several countries and with the maximum levels allowed in some countries. The Zn content in the sediments of the Massingirm dam, comparing with the values ​​of sediments in the rivers of several countries, especially those in South Africa, are mostly lower and, for Cr, exceeds almost all the values ​​found in the literature. For Ni and Zn the contents found in the sediments of the Massingir dam are higher than most rivers in other countries. The Cr content is higher than the Canadian and Dutch standards, the Pb content is higher than the Canadian, Queensland-Australia and Netherlands EPA standards, it is lower than the Canadian standards and by approx. ten times the PSAG of South Africa. The Zn content is higher than Canada's EPA standards and is lower than the Netherlands, Queensland-Australia, USA< UK, Germany, Switzerland and by about seven times the PSAG of South Africa. In the consulted literature, few data on Hg and As were found (TRADUÇÃO NOSSA)