Acumulação e transporte de mercúrio devido à atividade garimpeira em sistemas fluviais no Quadrilátero Ferrífero, Minas Gerais , Brasil

• Ano de defesa: 1997
• Autor(a) principal: Zeferino, Jane
• Orientador(a): Tobschall, Heinz Jürgen
• Banca de defesa: Rossner, Reinhold
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: ger
• Instituição de defesa: Naturwissenschaftlichen Fakultäten der Friedrich-Alexander-Universität Erlangen-Nürnberg; Doutorado; Geowissenschaften Fakultäten; Doutorado em Ciências Nauturais; Acadêmico; Instituição pública; Doutorado em Ciências Naturais por pesquisa; Universidade
• País: Alemanha
• Palavras-chave em Português: Mercúrio em garimpos; especiação de mercúrio; contaminação por mercúrio; Quadrilátero Ferrífero
• Link de acesso: https://deposita.ibict.br/handle/deposita/835; http://www.fau.eu; http://ror.org/00f7hpc57

The elevated price of gold in the world market in late 1970s and early 1980s triggered a gold rush all over in Brazil. Mercury is used by gold prospectors (garimpeiros) for the separation and purification of fine gold particles. As a result, mercury is lost directly by washing and by volatilization during amalgam burning. In order to investigate the level of pollution and the seasonal mercury distribution, two sampling campaigns were performed (during summer/rainy season 1992/93 and during winter/dry season 1994). Sediment samples and suspended material were collected from five tributaries of he Doce river in the eastern region of Quadrilatero Ferrifero. The samples were fractionated in four grain size classes: < 2 um, 2 - 6.3 um, 6.3 - 20 um and 20 - 63 um. All these fractions were analysed for total mercury by a Hg-analyser AMA254. Major and trace elements were determined by ICP-OES. Organic carbon was determined by a titration method. Total mercury of suspended matter, metallic mercury and mercury bound to iron minerals were determined by a cold vapour method using AAS with Hg enrichment at a gold net. The sediments contain total mercury concentrations upto 55 ug/g (Fraction <63 um). This concentration is 550 times higher than that of the natural regional background value of about 0.1 ug/g. The finer fractions ofthe river sediments, especially the fraction of<2 um, show high concentrations ofmercury as compared to those ofcoarser fractions. These fine fractions contain mainly clay minerals (mostly kaolinite), Fe- and Mn-oxy-hydroxides. This fraction also shows high contents oforganic carbon whose contents are positively correlated with the total contents of mercury. High contents of Fe- ( upto 70 wt. %) and Mn-oxide minerals (upto 4 wt. %) of the river sediments stem from the pre-Cambrian deposits of BIFs. Upto 70 % ofthe total mercury contents are bound to iron minerals which are mostly present in all size fractions of the sediments. A high percentage ofthe total mercury contents (upto 98 wt. %) is metallic mercury in river sediments which are very close to gold processing sites. The percentage of metallic Hg in total Hg is low in sediments far from the gold processing sites. This indicates that discharged Hg is oxidized in the water-sediment system and then is subjected to a transformation to other organic or inorganic Hg-species. Suspended matter ofthe surface water in the study area is highly polluted with Hg (upto 10 ug/g during winter time) which is transported further downstream from the gold mining site. The results of this analysis illustrate that mercury pollution is more intensive in winter as compared to summer. Storm floods during rainy time enhance the erosion and remobilization offiner fractions ofthe sediments. The high redox potential and the low pH ofthe surface water during the rainy season are the cause ofthe low concentrations ofHg in river sediments. During high water level of the rainy season suspended load which is highly polluted with Hg is deposited near to the flood plain areas in which the mercury contents increase substantially. During the dry season, a time of intensive mining activities, the river sediments and suspended matter show higher mercury contents as compared to those ofthe rainy season. Contrary to it, the mercury concentrations ofsediments of the flood plain decrease considerably during the dry season which is due to the loss of elemental mercury by evaporation.