Estudo de hidrocarbonetos e metais em sedimentos de fundo do Rio Negro na orla urbana de Manaus

Abstract

The waters of the Rio Negro, in the border city of Manaus, receives large amounts of domestic and industrial waste from its main tributaries (Tarumã-Acu, Sao Raimundo, Pupils and Puraquequara) that may be compromising their natural features (water, plants, sediments and etc.). Due the ability to accumulate organic and inorganic compounds, the bottom sediments are used to assess the contamination levels of aquatic environments. As a result, we determined the concentrations of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAH) and potentially toxic metals (MPT) in ten samples of bottom sediments collected in March 2009 in the confluence between the Rio Negro and major watersheds the city of Manaus. The aim of study was to classify the origin and level of contamination of these compounds. In the determination of hydrocarbons, sediments were freeze dried, extracted with hexane, fractionated by open column liquid chromatography. The determination of aliphatic hydrocarbons was performed by GC-FID and the PAH by GC-MS. After digestion with aqua regia the MPT (Al, Fe, Zn, Cu, Ni, Cr, Pb, Cd and Mn) in total fraction of sediments were determined by ICP-OES. The results showed that concentrations of total aliphatic hydrocarbons were 13.4 to 448 mg g-1, and the sum of 38 PAHs was 58.8 to 6832 ng g-1. These values are considered high for natural aquatic environments that have not suffered oil spill accidents. Among the metals determined Al (32 091 mg kg-1) and Fe (35 474 mg kg-1) were those with the highest concentrations.The sediments that received the largest anthropogenic contribution were those collected at the entrance of the basin of the streams São Raimundo and Educandos. The diagnosis index hydrocarbons the origin of in sediments showed a predominance of mixed sources and petrogenic sources in most seasons