Weight-of-evidence on environmental impact assessment of metal contaminated sediments in the São Francisco river (Três Marias - Minas Gerais - Brazil): a case study

Abstract

The weight-of-evidence -WOE approach was used to assess the environmental impact of sediments contaminated by metals in the São Francisco river and one of its tributaries, Consciência creek, both affected by anthropic activities, in the region of Três Marias (Minas Gerais/Brazil). The assessment provided support to a risk management decision. The WOE was based on bulk metal analysis, AVS-SEM assays, elutriate tests, ecotoxicity assays, benthic community assessment and a comparison for the reference area. Brazilian legislation and other available literature were used as criteria to evaluate the lines of evidence. All samples, except for the reference area, presented some contamination. However, geochemical testing for bioavailability studies showed that toxicity is unlikely as suggested by the chemical results. Ecotoxicity and benthic structure studies provided further information to support decision making. Metal acid volatile sulfide formation mechanisms were identified, which can eventually attenuate metal toxicity observed. The removal of active sources of contamination (for example, from tailings dumps) associated with Monitoring Natural Recovery could be sufficient to eventually lessen the risk of the biota in São Francisco river sediments.Keywords: weight of evidence, contamination, sediments, São Francisco river. Balanço das evidências na avaliação do impacto ambiental por sedimentos contaminados por metais no Rio São Francisco (Três marias -Minas Gerais -Brasil) -um estudo de caso ResumoEsse artigo teve como objetivo avaliar o impacto da contaminação por metais dos sedimentos de corrente do Rio São Francisco e de um de seus tributários, Córrego Consciência, na região de Três Marias (Minas Gerais/Brasil), ambos impactados por atividades antrópicas, a partir da metodologia de Balanço das Evidências -BDE, e, dessa forma, prover embasamento para uma decisão de gerenciamento de risco. Para o BDE se utilizou resultados de: concentração de metal nos sedimentos, ensaios de SVA-MES, ensaios de elutriação, ensaios de ecotoxicidade, estudo da comunidade bentônica. Legislação nacional e outras literaturas disponíveis foram utilizadas como critério de avaliação das linhas de evidências. Todas as amostras, exceto pela área de referência, apresentou alguma contaminação. Entretanto, ensaios geoquímicos para estudo da biodisponibilidade demonstraram que a toxicidade não é provável como sugeriram os resultados químicos. Estudos de ecotoxicidade e de estrutura da comunidade bentônica forneceram informações complementares importantes para embasar a tomada de decisão quanto ao gerenciamento ambiental dos sedimentos. Mecanismos de formação de metais volatilizáveis por acidificação foram identificados, podendo atenuar a toxicidade eventualmente verificada. A remoção de fontes ativas de contaminação associada ao Monitoramento da Recuperação Natural pode, portanto, ser suficiente para diminuir o risco à biota, eventualmente identificado nos sedimentos do Rio São Francisco.Palavras-chave: balanço das evidências, contamina...

Investigation into River Sediments Toxicity as a Result of Inappropriate Waste Disposal

“…Similar results were reported in the literature for that region [3,4,15]. Geochemical, toxicity test, and bioavailability studies showed that some sediments collected near the old effluent discharge are most likely to present adverse effects on biota, associated with elevated contents of zinc, lead, and cadmium [4,15]. In a study of sediments collected in the vicinity of the new dam, which corresponds to the point 6 Journal of Waste Management PLV01, the levels of metals in sediments determined through AVS-SEM are not high enough as to cause deleterious effects to the biota, as discussed elsewhere [3].…”

“…So, they should be prioritized during the remediation, monitoring, and controlling actions. Similar results were reported in the literature for that region [3,4,15]. Geochemical, toxicity test, and bioavailability studies showed that some sediments collected near the old effluent discharge are most likely to present adverse effects on biota, associated with elevated contents of zinc, lead, and cadmium [4,15].…”

Seasonal study of concentration of heavy metals in waters from lower São Francisco River basin, Brazil

“…Good correlations between a few elements like Fe and Cr and nickel can also be observed, thus showing the mineralogical affinities with existing mineral assemblages in the river, where, according to Landrigan et al (2007), opaque minerals (magnetite, ilmenite, hydrated oxides), hornblende, hypersthene, augite, and others can be found; these are easily degraded by the intense physical processes in the region. Almeida et al (2011), reported that the coarser sediments of São Francisco River are characterized by being immature, subarkosic and by having a high content of unstable heavy minerals (1 to 8%).…”

“…The high levels of Zn, Mn and Pb observed in the shallow water of the stream highlight the need for periodically monitoring this body of water, considering the toxic and bio accumulative effects of these metals. Almeida et al (2011), conducted a study on heavy metals and water quality in the river segment between San Francisco Três Marias and Pirapora -MG, found clearly the influence of metals on the health of coastal fishermen, who used the river water without any treatment for consumption.…”

Caracterização Exploratória-Espacial Da Bacia Hidrográfica Do Ribeirão João Leite/Goiás

“…Segundo Simpson et al (2005), Mozeto e Zagatto (2008), e Almeida et al (2011) existe correlação entre a granulometria do sedimento e os contaminantes, sendo positiva a presença de semimetais e metais pesados em frações mais finas (silte e argila) e negativa a presença destes em frações mais grossas (areias), do sedimento.…”