Navegando por Assunto "Metal traço"

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Acesso aberto (Open Access)
Distribuição de metais pesados e isótopos de Pb em sedimentos de fundo do rio Murucupi-Barcarena-Pará
(Universidade Federal do Pará, 2013-08-29) OLIVEIRA, Diomar Cavalcante; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
The preoccupation with environmental contamination by trace metals by urban and industrial activities has led to studies with the purpose of measuring the impacts and incorporation of these substances on aquatic biota. This study aimed to identify by determining the levels of trace metals and Pb isotopic signatures a possible involvement of effluents coming from the urban areas and industrial wastes as sources of pollution of the Murucupi river, Barcarena region, Pará. It is intended to point out the potential of Pb isotopic signatures to detect future impacts of anthropogenic contamination with trace metals. In addition, reference values of natural metal concentrations and Pb isotopic composition were identified for this sector of the Pará river estuary system values. Eighteen samples were collected from the bottom sediment surface along rivers Murucupi (8 samples), Arrozal Channel (6 samples) and Pará river (4 samples) and two drill cores in the Murucupi river. Surface samples and sediment cores were collected with Van Veen dredge type and Russian Peat Borer, respectively. A granulometric analysis was performed with laser granulometer to quantify the percentage of sand, silt and clay. The mineralogical composition was determined by X-ray diffraction. The partial and total concentrations of the metals and Lead isotopic compositions were determined by ICP-MS. The organic matter contents were determined by volumetric redox by the Walkley Black method. Granulometric analyses showed that there was a predominance of silt over sand and clay. Mineralogical analyses performed on the total sample and in the clay fraction showed the presence of quartz, albite muscovite and clay minerals smectite, illite and kaolinite. In all three drainage study, the results indicate that the levels of Pb, Cu, Zn and Ni did not show significant differences and when exist, they may be related to natural variations in the sediment. The correlation matrices indicate that the contents of trace metals are not controlled by the organic matter and that these metals are predominantly associated with structures of clay minerals in Pará river and Arrozal Channel sediments and oxy-hydroxides of Fe and Mn in Murucupi river sediments, respectively. High correlations between the trace metals indicate that the concentrations of metals in the sediments are governed by similar chemical processes in the three drainages, excepting for Pb in the Murucupi river, which is not correlated with others metals and may have been introduced into the environment by different processes. Most of the enrichment factors, using the Pará river sediments as reference value, showed values lower than 1, indicating no evidence of anthropic influence on the trace metals concentrations. Sediments from Arrozal Channel displayed contents of trace metals slightly lower than those of Murucupi river. However, the similarity of their EF values point to natural geochemical variations. The levels of Pb, Cr, Cu, Zn and Ni were lower than TEL reference value for all the trace metals studied. Therefore the sediments of the Murucupi river and Arrozal Channel, although in contact with domestic sewage, do not represent, at the moment, no risk to aquatic organisms. The bottom sediments of Pará river exhibit a homogeneous isotopic signature (206Pb/207Pbmean = 1.204 ± 0.001), considered as geogenic, establishing a background value of 206Pb/207Pb isotopic ratio for the area. Lower values found in the Murucupi river (206Pb/207Pbmean = 1.186 ± 0.003) and Arrozal Channel (206Pb/207Pbmean = 1.193 ± 0.002) are interpreted as reflecting the influence of effluents from the urban areas (Vila dos Cabanos and Laranjal) and from Barcarena river, respectively. Through 206Pb/207Pb vs. 206Pb/204Pb and 208Pb/206Pb vs. 206Pb/207Pbdiagrams, it is possible to discard a contribution of red mud tailings as a source of pollution of the Murucupi river. The decrease in 206Pb/207Pb isotopic ratios from bottom to top in sediments of the Murucupi river corroborate the existence of a recent Pb anthropogenic contribution to the sediments in this river.
Acesso aberto (Open Access)
Mineralogia e geoquímica de sedimentos de manguezais da costa amazônica: o exemplo do estuário do rio Marapanim (Pará)
(2008-03) BERRÊDO, José Francisco; COSTA, Marcondes Lima da; VILHENA, Maria do Perpétuo Socorro Progene; SANTOS, Josiana Torres dos
The mangroves of the Para state represents an important segment of the Brazilian north coast on the ones which little it is known of the geological characteristics and it relationships with source areas. This research was accomplished in the Marapanim river estuary, in the Para coast, to demonstrate the contribution of continental sediments for the constititution of the mangrove's sediments. The mangrove's sediments and the Barreiras Formation sediments and soils (main continental sources) were collected. In the mangrove's sediments grain size, determination of the carbon (C%), pH and Eh measures and interstitial salinity was made. The mineralogical determination and the multi-elementary geochemistry was made in the sediments muddy and terrigenous adjacents sediments for comparisons. The mangrove's sediments are clayey silty (> 90%), with the carbon values among 0,75 to 3,5%. The main mineralogy is composed by quartz, goethita, hematite, kaolinite, illite, besides zircon, tourmaline, staurolite and cianite as accessories, what indicates contribution of the Barreiras Formation sediments and sediments muddy. It is common the occurrence in these mangroves the neoformated minerals as: smectite, K-felspars, pyrite, halite, gipsum and jarosite. The enrichment in SiO2, Al2O3, Fe2O3 and TiO2 in the mangroves and the low tenors in trace metals reflects the tropical climate and the mineralogical composition of the source area, enriched in quartz and caulinite, with low tenors in K2O, Na2O, MgO and CaO. The chemical composition associated to the organic matter, abundant diatoms besides Fe, S and the marine contributions of Cl-, Na+, K+, Ca++ and Mg++, identify the deposicional ambient and the autigenics minerals. The concentrations and the geochemical behaviour of the trace metals in the mangroves corroborates the outstanding contribution of the continental source area. Those sediments presents the prevalence of the Light Rare Earth Elements (LREE) on the Heavy Rare Earth Elements (HREE) with high reasons of Th/Co; La/Th; La/Sc; La/Co and Zr/Sc and Th/Sc and Ba/Co, elements present in the felsic igneous rocks that originated the continental sediments.