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Levels of heavy metals in sediments of the Puyango River basin, Ecuador

Abstract:

In this study the concentrations of Al, Co, Cu, Fe, Hg, Mn, Ni, Pb and Zn were determined in bottom sediment samples of the Puyango River and its tributaries with the goal to know the enrichment factors of these elements in the sediments. Bulk sediment samples were digested using the EPA method 3050B and then analyzed by atomic absorption spectrometry. The samples for Hg determinations were digested with a mixture of HNO3, HCl y KMNO4and then analyzed by the cold-vapor generation technique. The highest concentrations of heavy metals in sediments were found in the sector located after the Calera-Amarillo rivers confluence. The high levels of heavy metals and the low concentrations of Al in the bottom sediments of this sector indicate that these riverine sediments are mainly composed by polymetallic mineral, which has been discharged from the ore processing plants after the gold extraction process. Sediments from the middle and lower Puyango River showed a severe contamination for Hg, Cu, Pb, Zn and Mn, and a moderate contamination for Co and Fe. The high concentrations of Hg, Cu, Pb, Zn, Mn and Fe in the sediments of these rivers can have adverse effects on aquatic biota, according to international guidelines.