Arsenic and Mercury mobility in brazilian sediments from the São Francisco River Basin

Abstract

Os sedimentos possuem propriedades de acumulação de poluentes e a determinação de elementos tóxicos nessas amostras permite avaliar o seu ciclo geoquímico. Arsênio e mercúrio foram determinados em 28 amostras de sedimento da Bacia do Rio São Francisco, Minas Gerais, Brasil, por geração de hidretos acoplada à espectrometria de absorção atômica (HG AAS). Foram empregados procedimentos de digestão pseudo-total empregando HCl:HNO 3 (3:1 v/v) e extração parcial com HCl 1 mol L -1 . Realizou-se ainda a determinação de Hg nas amostras sólidas, utilizando-se um analisador direto de mercúrio. Observou-se que 46% das amostras apresentaram concentrações de As acima do limite de nível 1 estabelecido pela Resolução 344/2004 do CONAMA e que 14% excederam o limite de nível 1 para Hg. As amostras com altas concentrações de Hg foram também analisadas por termodessorção acoplada à espectrometria de absorção atômica (TDAAS) para especiação e os termogramas apontaram somente a presença da espécie Hg(II).Sediments have metal accumulation properties, then, an evaluation of their geochemistry cycle is feasible via toxic element determination of these samples. Arsenic and mercury determinations were accomplished in 28 sediment samples from the São Francisco River Basin, Minas Gerais, Brazil. For sample pretreatment were employed a pseudo-total digestion procedure with HCl:HNO 3 (3:1 v/v) and a partial extraction procedure with 1 mol L -1 HCl. Arsenic and mercury were analysed by hydride generator atomic absorption spectrometry (HG AAS). Mercury determination was realized in the solid samples by direct mercury analyzer (DMA). It was observed that 46% of the samples presented arsenic concentrations above Brazil's legal limits, and 14% of samples exceeded the established mercury limit. The samples with high mercury content were also analysed by thermodesorption coupled to atomic absorption spectrometry (TDAAS) and only Hg(II) was identified.Keywords: arsenic, mercury, sediment samples, environmental monitoring, São Francisco River IntroductionIn most aquatic environments, dissolved metal concentrations in overlying water are low due to the precipitation of solids or the adsorption of suspended particles and the deposition of these particles as sediments. 1 Sediment is a matrix comprising inorganic and organic particles. It is relatively heterogeneous in terms of its physical, chemical, and biological characteristics. Sediments have an important role in the transport and storage of contaminants, being of high relevance in the identification of contaminant sources and in the determination of dispersion pathways. Sediment quality determines the biodiversity and the ecological health in aquatic systems as well as being economically important in the environmental assessment of coastal areas. 2 São Francisco is the third largest hydrographic basin in Brazil. It is responsible for drainage of a 640.000 km² area, corresponding to 8% of land in the country of Brazil. About 40% of the basin is located in the state of Minas Gerais and it is divided ...

Arsenic and Trace Metals in Water and Sediment of the Velhas River, Southeastern Iron Quadrangle Region, Minas Gerais, Brazil

“…10,[53][54][55] Therefore, the origin of As in the surface waters of the IQ is associated with weathering and involves the natural oxidation of minerals, together with anthropic activity leading to discharges of mining wastes into drainages. 53,54 The total As values were in agreement with those reported in previous studies on As in surface waters of the Velhas River, [5][6][7][8]10,55 and were within the range found in other regions of the IQ. 3 Flowing water samples collected along the Velhas River by Borba et al 10 in April 1998 contained As, in the soluble fraction, at concentrations between 12 and 160 μg L -1 .…”

“…Furthermore, organic matter interrupt or release toxic elements to the plants, thus affecting the mobility, availability, volatility, and biodegradability of organic and inorganic molecules. 8 The X-ray diffractograms of the sediment samples ( Figure 2) revealed the presence of secondary minerals (gibbsite, goethite and hematite), which also indicated good capacity for the retention of trace elements on the surfaces of iron and aluminum oxides. 9,40 Concentrations of As and trace metals Table 2 shows the concentrations of arsenic and the trace metals for the sediment samples.…”

“…The presence of arsenic in IQ sediments has been studied during several decades. [6][7][8][9][10] Borba et al 10 reported As concentrations exceeding 1000 μg g -1 in sediments of the Velhas River between 1997 and 1998. Deschamps et al 6 studied the same area and found values up to 3300 μg g -1 between the years 1998 and 2003.…”

Distribution of Arsenic and Mercury in the Aquatic Ecosystem of the Five Chilean Reservoirs

“…Each value is the mean of six replicates; <DL =below detection limit; ‫٭‬ = no samples. 37 . In the Bortala River (China) 38 As concentration ranged from 3.27 to 10.34 mg kg -1 and Hg 0.01 to1.69 mg kg -1 in eight sites studied.…”

Seasonal variations, metal distribution and water quality in the Todos os Santos River, Southeastern Brazil: a multivariate analysis

“…Therefore, water bodies may be contaminated with complex, ill-defined mixtures of chemicals and most freshwater organisms will be exposed, to varying degrees, to this contamination (Scalon et al 2013). The toxic elements produced are relocated by the action of rain, contaminating soils and waterways that surround these areas (Ren et al 2004, Rezende et al 2011. CLÁUDIA A.F.…”