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Doctoral Thesis
DOI
https://doi.org/10.11606/T.21.2016.tde-21032016-170005
Document
Author
Full name
Patricia Andrade Neves
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2015
Supervisor
Committee
Bicego, Marcia Caruso (President)
Cordeiro, Renato Campello
Figueira, Rubens Cesar Lopes
Madureira, Luiz Augusto dos Santos
Mahiques, Michel Michaelovitch de
Title in Portuguese
Histórico da Deposição de Hidrocarbonetos Policíclicos Aromáticos em um Estuário Amazônico nos Últimos Cem Anos
Keywords in Portuguese
Amazônia
Hidrocarbonetos Policíclicos Aromátcos
HPAs
Isótopos Estáveis
Abstract in Portuguese
Para determinar o histórico deposicional e as fontes dos hidrocarbonetos policíclicos aromáticos (HPAs) na região amazônica nos últimos 120 anos, três testemunhos foram coletados na Baía do Guajará - PA. Esses testemunhos também foram datados com 210Pb, e analises da razão isotópica do carbono estável (δ13C) e de n-alcanos foram efetuadas. Ao longo dos três testemunhos, os resultados do δ13C e n-alcanos indicaram a predominância de matéria orgânica terrígena, derivadas de plantas do tipo C3. Entretanto, uma variação nesses valores foi observada em 1965. As concentrações de HPAs também apresentaram uma alteração por volta de 1965. Até 1965, os HPAs alquilados foram predominantes em relação à seu composto parental (metilfenantreno> fenantreno). Esses HPAs estão geralmente associados a fontes petrogênicas, entretanto, nenhuma evidência de petróleo foi observada. A maior proporção de HPAs alquilados pode estar relacionada a processos naturais, diagenéticos ou de biossíntese. Após 1965, as concentrações de HPAs aumentaram. As razões diagnósticas indicaram a predominância de HPAs pirolíticos, provavelmente relacionadas às queimadas efetuadas para criação de pastos. A diminuição do δ13C no período também deve estar relacionada à extração de madeira, que introduz uma grande quantidade de resíduos de vegetação nos sedimentos.
Title in English
Depositional Hystory of Polycyclic Aromatic Hydrocarbons in an Amazon Estuary in the Last 100 Years
Keywords in English
Amazon
PAHs
Polycyclic Aromatic Hydrocarbons
Stable Isotopes
Abstract in English
In order to evaluate the historical deposition and sources of PAHs over the last 120 years (1890 to 2011) in the amazon region, three sediment cores were collected from Guajara Bay (state of Pará). The cores were also dated with 210Pb and n-alkanes and carbon isotopic ratios (δ13C) were measured. Throughout the cores, the δ13C and n-alkanes indicated the predominance of organic matter from terrigenous sources (C3 plants). Even though δ13C values and n-alkanes ratios remained representative of terrigenous sources, there was an abrupt variation around the middle 1960s. PAH concentrations also showed a variation around the late 1960s. Before 1960s, alkyl-PAHs concentrations were higher than those of their parental compound (methylphenanthrene > phenanthrene). These PAHs are usually associated with petrogenic inputs; however, no evidence of oil was observed. The higher proportion of alkyl-PAHs could be related to natural diagenetic and biogenic processes. After the 60s, PAH concentrations increased and diagnostic ratios showed a predominance of pyrolytic PAH, probably related to the forest fires used to create pastures. The deforestation can also be associated to the δ13C depletion found in the sediments, due to logging activities, which introduce more organic matter derived from vascular plants into the sediment.
 
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Publishing Date
2016-03-22
 
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