Determinação de Hidrocarbonetos Alifáticos e Aromáticos na Matéria Orgânica Sedimentar do Rio Amazonas e de Igarapés que Entrecortam Parintins (AM).

Abstract

Fires in the Amazon are closely linked to deforestation, which negatively impacts biodiversity and the climate. Additionally, the particulate matter generated during vegetation burning contains various compounds harmful to human health, such as polycyclic aromatic hydrocarbons (PAHs). These compounds are also generated during the combustion of fossil fuels and/or the use of petroleum-derived products. In this context, this project aims to evaluate the chemical composition of the sedimentary organic matter (OM) of water bodies in the municipality of Parintins (AM) to investigate the contribution of pyrogenic and pyrolytic sources. For this purpose, twenty-four surface sediment samples were collected from the following water bodies: Amazon River, Lagoa da Francesa, Macurany Lake, Lagoa Azul, Areal Lake, Parananema Lake, and Aninga Lake. Through the lyophilization of the sediment, OM extraction, and open-column fractionation, individual fractions containing aliphatic hydrocarbons (n-alkanes and hopanes) or PAHs were obtained. These compounds were quantitatively determined by gas chromatography-mass spectrometry using the selective ion monitoring method. The quantification of n-alkanes and PAHs was performed using the internal standardization method with deuterated homologs. A series of n-alkanes from n-C17 to n-C37 was identified, with distribution profiles indicative of different OM sources, including aquatic and terrestrial plants. The total n-alkane concentrations were similar for sediment samples from water bodies intersecting Parintins (2.11 to 11.07 µg g-1) and the Amazon River (3.37 to 9.64 µg g-1). Diagnostic ratio values indicate a predominance of biogenic n-alkanes from terrestrial vegetation; however, the values were low for an area surrounded by forest, suggesting a significant contribution of OM from fossil products and combustion and/or cycling by microorganisms. The presence of hopanes with a predominance of the more thermodynamically stable 17α(H),21β(H), and 22S configurations confirms the input of fossil-derived OM in the studied environments. Overall, total PAH concentrations were higher in samples from water bodies intersecting Parintins (4.37 to 1312.25 ng g-1) compared to those from the Amazon River (30.40 to 425.17 ng g-1). The predominance of four- and five-ring PAHs, along with diagnostic ratios, indicates a strong contribution of OM from biomass burning and fossil products. Keywords: n-Alkanes, Hopanes, PAHs, Fires, Amazon.