Geochemical markers as a tool to assess sedimentary organic matter sources of the Laguna Estuarine System, south Brazil: aliphatic and polycyclic aromatic hydrocarbons

Abstract

Amostras de sedimentos superficiais do Sistema Estuarino de Laguna foram analisadas objetivando a identificação das fontes de matéria orgânica. Razões entre n-alcanos selecionados, elevados teores de hidrocarbonetos alifáticos (HA) (média de 9.168 µg g -1 de carbono orgânico, CO) e policíclicos aromáticos (HPA) (média total de 426.593 ng g -1 CO), e a distribuição de hopanos com estereoquímica αβ detectados nas amostras da Lagoa de Santo Antônio foram evidências de que o aporte de hidrocarbonetos petrogênicos prevalece sobre os de fontes naturais. Nas demais amostras estudadas, a distribuição de HA (de 38 até 2.749 µg g -1 CO), a detecção de hopenos e hopanos-ββ sugerem hidrocarbonetos de fontes mistas. Todavia, o teor de HPA em todas as amostras (de 7.731 até 786.469 ng g -1 CO, sendo que os aromáticos alquilados representaram > 92% do total) revelou contaminação petrogênica crítica. As atividades pesqueira e urbana são fontes potenciais dos hidrocarbonetos petrogênicos detectados nas amostras sedimentares.Surface sediment samples from the Laguna Estuarine System were analyzed to identify organic matter sources. The ratios between selected n-alkanes, high concentrations of aliphatic hydrocarbons (AH) (average of 9,168 µg g -1 of organic carbon, OC) and polycyclic aromatic hydrocarbons (PAH) (total average of 426,593 ng g -1 OC), and the hopanes distribution with αβ stereochemistry found in the Santo Antônio Lagoon samples were evidence that hydrocarbon inputs from petrogenic sources predominate over natural sources. In the other samples studied, the AH distribution (from 38 to 2,749 µg g -1 OC), and detection of hopenes and hopanes-ββ suggest mixed sources of hydrocarbons. Nevertheless, PAH concentrations in all samples (from 7,731 to 786,469 ng g -1 OC, whereof alkyl naphthalenes accounted for > 92% of the total) indicated critical petrogenic contamination. Fishing and urban activities are potential sources to the petrogenic hydrocarbons detected in these sediment samples. Keywords: hydrocarbons, hopanes, PAH, sediment, chromatography IntroductionEstuaries are important areas of world's coastal zones. In general, they are highly productive and provide spawning and nursery grounds for migratory species, besides playing a significant role in the global carbon cycle.1,2 Furthermore, an overwhelming majority of the human populations is concentrated along or near coasts, which inevitably leads to complex problems concerning environmental quality due to the residues generated by miscellaneous human activities.Along with various other organic and inorganic contaminants, the study of sedimentary aliphatic hydrocarbons (AH) (e.g., n-alkanes and hopanes) provides an important tool to assess organic matter sources and pollution levels in aquatic ecosystems. [3][4][5] This class of organic compounds has biogenic and anthropogenic sources. Natural inputs are comprised mostly of vascular plants, algae, microorganisms and early diagenesis of natural products, whereas petroleum and its derivatives are generally examples of hu...

Aliphatic hydrocarbon profiles in sediments of the Forcados River, Niger Delta, Nigeria

“…The total concentrations of n-alkanes in sediments of Colony Z3 (Pelotas, RS, Brazil) were found to be 337.6 to 5,868.9 mg/kg (Sanches Filho et al, 2013). The concentrations of aliphatic hydrocarbons found in the Forcados River sediment were comparable to levels reported for Red Sea sediments but they were very much lower than those previously reported for some river sediments in the Niger Delta Fubara et al, 2012Fubara et al, , 2014Eguvbe et al, 2015) and in sediment systems of some other regions with high anthropogenic activities (Jeng and Huh, 2006;Gao et al, 2007;Jeng, 2007;Sakari et al, 2008aSakari et al, , 2008bCompanioni Damas et al, 2009;Tarozo et al, 2010;Bouzid et al, 2012;Sakari et al, 2012;Yusoff et al, 2012;Zrafi et al, 2013). n-C 11 had the highest concentration in the study area, as shown in Figure 2.…”

“…In this study, the ratio of n-C 17 /pristane and n-C 18 /phytane ranged from 0.62 to 2.11 and 0.13 to 2.74 respectively. Since microorganisms generally utilize n-alkanes before isoprenoids as an energy source during biodegradation, low values for these ratios (less than 1) indicate biodegraded oils, while recent input may yield values greater than 1 (Tarozo et al, 2010). The n-C 17 /pristane and n-C 18 / phytane ratios of our sediment samples correspond to non-heavily degraded petroleum, i.e., recent inputs (Companioni Damas et al, 2009).…”

Geochemical Study of Weathered Coal, a Co-Substrate for Bioremediation of South African Coal Discard Dumps

“…Variations within the weathered coal samples were evident, such as a hopene series present only in sample 6, and esters of palmitic (C16:0) and stearic (C18:0) acids in five of the samples (1, 4, 5, 7, and 9). The presence in sample 6 of 17α(H),21β(H)-homohopanes might indicate a high degree of geochemical maturity of this weathered coal [37,38]. However, since these indicator compounds typically originate from bacterial membrane lipids and were predominantly in the R,S-or α,βstereochemical configuration, any bacterial activity most likely occurred prior to transformation of hard coal to weathered coal.…”

Evaluation of the Analytical Method Applied to Geochemical Biomarkers in a Paleoenvironmental Study of Coastal Barrier Associated to Conceição Lagoon (Florianópolis / SC)

“…6,7 Eles podem ser utilizados na caracterização da fonte e distribuição de MO, além fornecer informações a respeito de mudanças em paleoambientes marinho e continental. [8][9][10][11] A determinação de biomarcadores em amostras de perfis sedimentares envolve uma série de etapas, entre elas a extração com solvente, cleanup, fracionamento dos compostos, derivatização e concentração dos analitos para posterior analise cromatográfica. Em função do grande número de etapas envolvidas, é preciso garantir que as concentrações determinadas sejam representativas do sedimento, de forma a não comprometer os dados das análises.…”