Geoquímica do arsênio, dos elementos terras raras e dos metais pesados Cr, Zn, Ni e Pb nas plataformas continentais do Rio Doce (ES) e de Abrolhos (BA)

• Ano de defesa: 2018
• Autor(a) principal: Cagnin, Renata Caiado
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Doutorado em Oceanografia Ambiental; UFES; Programa de Pós-Graduação em Oceanografia Ambiental
• Palavras-chave em Português: Arsênio; Elementos terras raras; Metais pesados; Background geoquímico; Plataforma continental; Arsenic; Rare earth elements; Geochemical background; Continental shelf; Ciências Ambientais; 55
• Link de acesso: http://repositorio.ufes.br/handle/10/9152

Aiming to know the different geochemical aspects of the brazilian east continental shelf, which includes the Doce River Continental Shelf (RDCS) and Abrolhos Continental Shelf (ACS), this thesis investigates, through the analysis of four sediment cores (± 3 m ), the sources and carrier phases that leads to the enrichment of arsenic (As); the occurrence of rare earth elements (ETRs) and their relationship to depositional processes; and the enrichment and background of heavy metals of potencial environmental risk Cr, Zn, Ni, Pb in both continental shelves. The PCRD sediment deposited in recent centuries is highly contaminated by As (FE = 15 and Igeo = 4), moderately contaminated with Cr, Ni, Zn and Pb (Igeo = 2) and enriched in ETR (FE = 5). This feature is due to the strong influence of the sediment brought by the Doce River, which originates a differentiated pattern of sedimentation in relation to PCA. The core most enriched in As, ETRs and heavy metals is on the south of the DRCS, due to the current influence of fluvial discharge. The PCA is not contaminated by the analyzed metals and only a slight enrichment is observed in the superficial sediment of the inner shelf (T06) that comes from the recent urbanization in the region. It is proposed that one of the main sources of sediment enriched by the chemical elements, especially As, in the PCRD is the input of the river and the impacts caused by the mining of the river basin. The geochemical background shows natural enrichment of all elements analyzed on both continental shelves. In general, the same factors determine the natural contribution of As, ETR and Cr, Zn, Ni, Pb in the continental shelves studied, where the increment is related to the exogenous processes, the remobilization of the sediment and the occurrence of Fe and Mn oxides. One of the main natural sources of the chemical elements is the Barreiras Group, due to the similar geochemical signature to this formation found in the region of study. The increase of ETR and heavy metals in the deeper samples on the north of the Doce River and in the Abrolhos depression may be related to the higher deposition of enriched detrital material due to the greater influence of the continental drainage in the period of lower sea level. In the case of PCRD, this enrichment may also indicate past positioning of the mouth of the Rio Doce to the north. Sediment enrichment in As, Cr, Ni, Zn and Pb provides environmental risks associated with the bioavailability of these elements to the water column. This thesis provides important unpublished data on the geochemistry of a stretch of the Brazilian East continental shelf recently hit by the iron ore tailings in the Mariana Disaster, making the geochemical background present in this work extremely important for the understanding of the real impacts caused in this region.