ACI Avances en Ciencias e Ingenierías (Dec 2015)
Análisis of major cations in bottom sediments from oil impacted Rivers, in the Ecuadorian Amazon
Abstract
Heavy metal pollution is one of the biggest problems of great concern at the global, regional and local levels due to mining and oil activities, because those elements constitute a threat to aquatic biota and human health. The major elements and heavy metals tend to accumulate in sediments, which act as secondary sources of contamination, and this process is closely related to the redox conditions, the particle size distribution of the sediments and the amount of sedimentary organic matter. Therefore, the aim of this work conducted in the frame of the MONOIL Research Program between France and Ecuador, is to determine the concentration of major elements (K, Mg, Na, Fe, Mn and Al) in the fine fraction of sediments, particles <4/μm, collected in the basins of the Aguarico, Napo and Esmeraldas Rivers, which are areas affected by the oil industry in Ecuador. Concentrations of major elements in the fine fraction are then compared to concentrations in the bulk, which was determined in the same sampling points in a previous work. Environmental parameters in surface waters such as temperature, dissolved oxygen (DO), pH, conductivity and oxide reduction potential (ORP) were determined in situ in each sampling point. The isolation of the fine fraction was carried out based on Stokes’ law after a homogenization, quartering and dissolution of the sediment in distilled water. Mineralization in sediments was performed by a triacid attack with HCl, HNO3 and HF. The major elements were determined by atomic absorption spectrophotometry (AAS). The ranges of major elements in the fine fraction of sediments were: Fe: 18-49, Al: 26-59, K: 3-15, Mg: 3-13, Na: 1-11 and Mn: 0.38-0.89 mg g-1; while concentrations in the bulk sediment concentrations were: Fe: 25-49, Al: 45-82, K: 5-20 Mg: 4-16, Na: 3-24 and Mn: 0.43-1.28 mg g-1. In the sediment samples of the Northern Ecuadorian Amazon rivers, 43% Na, 93% Fe, 70% Mg, 62% Mn and 94% K are associated with the fine fraction. The concentrations of Mg, Na and Mn in bottom sediments are influenced by oil activities, while Fe, K and Al concentrations depend on the natural origin of sediments. However, downstream up to the border with Peru, no significant increase in the concentrations of major elements in relation to the control points, upstream of the ZIL, the Local Area of influence of oil activities, was observed.
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