Different clean-up methods to determine isotopic composition of n-alkanes were tested. Sources of organic matter in Guanabara Bay were re-examined through the δ13C of individual n-alkanes in surface sediment samples. The n-alkanes were efficiently isolated without significant losses of the compounds of interest. The δ13C of n-alkanes (n-C17 to n-C35) ranged between -34.0 and -26.4‰. More depleted δ13C values associated to higher carbon preference index (CPI > 4) suggest prevalence of biogenic n-alkanes from terrestrial origin in the inner stations influenced by inputs from mangrove areas. Small isotopic differences between odd and even-numbered chains and 13C-enrichment in long-chain homologues indicate a petrogenic hydrocarbons contribution. Higher concentrations of short-chain compounds associated to a more 13C-enriched total organic carbon (TOC) were found near the most intense sewage discharges. Results show that δ13C of n-alkanes can be applied to a highly degraded system as the Guanabara Bay and help improve the characterization of the organic matter.

The goals were to estimate nutrients and carbon flow rates between Guanabara Bay and the adjacent coastal waters, to characterize the provenance of the exported/imported organic matter. Samples were collected from different depths over 25 h in two seasons at the bay entrance. Measurements included physicochemical parameters, nutrients, chlorophylls, dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN), carbon (δ13C) and nitrogen (δ15N) isotopic composition, sterols in suspended particulate matter (SPM) and bacterioplankton. Most variables showed higher values in ebb tide events. The flow rates calculated on daily basis and estimated on annual basis revealed the exportation to the continental shelf of 1.27 × 104 kmol year-1 dissolved inorganic nitrogen (DIN), 9.52 × 102 kmol year-1 dissolved inorganic phosphorus (DIP), 2.65 × 104 t year-1 DOC, 1.96 × 104 t year-1 POC, and 2.96 × 104 t year-1 PN. The estimates show the bay contributes with 0.01% of the total global carbon influx to the ocean.

Ethanol is a biofuel produced in Brazil through fermentation of sugarcane, requiring vast plantation areas and water availability. The present work aimed at testing isotopic markers as tools for ethanol source appointment or certification of origin. For this, oxygen and hydrogen isotopic patterns were determined in plant-water, soil-water, rainwater, and water from reservoirs and some rivers in four sugarcane crop areas. The isotopic fingerprint of carbon and hydrogen in ethanol produced in the respective mills was also determined. Samples were collected in 2011 and 2012 in crop areas of the state of Amazonas (North), Mato Grosso (Center-West), São Paulo (Southeast) and Rio Grande do Sul (South). The substantial and complex influence of the hydrological cycle on the ethanol δD and the small δ13C variations constrain the use of isotopes for the intended objectives.

As concentrações de black carbon (BC), assim como a contribuição relativa de BC para o total de carbono orgânico sedimentar, foram determinadas pela primeira vez na Baía de Guanabara. A quantificação de BC realizou-se por método térmico (CTO-375) e a de carbono orgânico por método de oxidação a seco. As concentrações de carbono orgânico apresentaram grande variabilidade entre as estações (0,82 a 10,3%), mas foi possível definir regiões distintas na Baía de acordo com parâmetros como granulometria do sedimento, localização e magnitude de fontes autóctonas e alóctonas de matéria orgânica e hidrodinamismo. As concentrações de BC foram inesperadamente baixas (0,03 a 0,31%, com média de 0,19 ± 0,07%, n = 25), levando-se em conta o largo espectro de fontes possíveis, tanto em terra como na água, para essas substâncias. No entanto, em algumas estações o BC estava presente em níveis que podem exercer influência sobre o destino de contaminantes prioritários, tais como HPA e dioxinas. Os resultados mostraram que a distribuição espacial das concentrações de BC na Baía de Guanabara é complexa e não pode ser completamente compreendida no estágio atual de conhecimento, sendo necessárias informações adicionais, tais como fontes de emissão de BC (p.ex., queima de biomassa e consumo de combustíveis) e processos de dispersão de partículas.

The concentration of black carbon (BC), as well as the relative contribution of BC to total organic carbon, was determined for the first time in sediments from Guanabara Bay. BC was quantified by a thermal oxidation method (CTO-375) and total organic carbon by dry oxidation. Sedimentary organic carbon showed a large range in concentrations (0.82 to 10.3%), but it was possible to define distinct regions of the Bay accordingly to variations in sediment grain size, location and magnitude of allochthonous and autochthonous sources of organic matter and hydrodynamic features. Low concentrations of BC were observed (0.03 to 0.31%, with a mean of 0.19 ± 0.07%, n = 25) when considering the large spectrum of possible sources on land and at sea. However, in some stations levels are sufficiently high as to influence the fate of pollutants of concern, such as PAH and dioxins. The space distribution of BC concentrations in Guanabara Bay cannot be fully understood at this stage since further information on contributions from various sources and on natural dispersion processes are required.