No abstract

In this 10 year study, Brazilian gasoline (100 L, containing 24% ethanol by volume) was released to a sandy aquifer to evaluate the natural attenuation of benzene, toluene, ethylbenzene, and total xylenes (BTEX) in the presence of ethanol. Groundwater concentrations of BTEX, ethanol, and degradation products (e.g., acetate and methane) were measured over the entire plume using an array of monitoring well clusters, to quantify changes in plume mass and region of influence. Ethanol biodegradation coincided with the development of methanogenic conditions while acetate (a common anaerobic metabolite) accumulated. The benzene plume expanded beyond the 30 m long monitored area and began to recede after 2.7 years, when ethanol had disappeared. Theoretical calculations suggest that the transient accumulation of acetate (up to 166 mg L(-1)) may have hindered the thermodynamic feasibility of benzene degradation under methanogenic conditions. Yet, benzene removal proceeded relatively fast compared to literature values (and faster than the alkylbenzenes present at this site) after acetate concentrations had decreased below inhibitory levels. Thus, site investigations of ethanol blend releases should consider monitoring acetate concentrations. Overall, this study shows that inhibitory effects of ethanol and acetate are relatively short-lived, and demonstrates that monitored natural attenuation can be a viable option to deal with ethanol blend releases.

No abstract

ResumoNesse trabalho, 14 dos hidrocarbonetos policíclicos aromáticos (HPA) incluídos pelo Environmental Protection Agency (EPA) na lista de poluentes prioritários foram analisados através de cromatografi a gasosa com espectrometria de massas acoplada (GC-MS). A amostragem das águas superfi ciais foi realizada no estuário do rio Paraguaçu e do rio Jaguaripe (Bahia), nordeste do Brasil. Concentrações totais de HPAs variaram de 0,0029 a 0,1079 ng/L em águas superfi ciais (rios principais, afl uentes), com valor médio de 0,0344 ng/L. Tais concentrações podem ser tomadas como valores-base para a região estudada. Os perfi s de HPAs foram dominados por HPAs de baixo peso molecular (dois ou três anéis de componentes) em amostras de água superfi cial. Isto é indicativo de sua origem a partir de óleo ou contaminação residual (entrada petrogênica). Os dados recolhidos mostram que entrada petrogênica foi predominante em quase todas as estações investigadas. Para discriminar diferenças e semelhanças entre as amostras, a análise de componente principal (ACP) foi realizada utilizando uma matriz de correlação. A ACP revelou as relações entre todas as águas superfi ciais das estações investigadas. Palavras-chave:Hidrocarbonetos policíclicos aromáticos (HPA), água superfi cial, fonte, cromatografia à gás-espectrometria de massas (CG-EM), análise da componente principal (ACP). Abstract Fourteen polycyclic aromatic hydrocarbons (PAHs) included in the US Environmental Protection Agency's (EPA) priority pollutant list were analyzed using gas chromatography-mass spectrometry (GC-MS

Persistent toxic substances (PTSs) such as polycyclic aromatic hydrocarbons (PAHs) are of great concern due to their persistence, bioaccumulation and toxic effects. In this work, 14 PAHs included in the US Environmental Protection Agency's (EPA) priority pollutant list were analysed using gas chromatography-mass spectrometry (GC-MS). Surface water sampling was undertaken in Todos os Santos Bay, northern Brazil. Total PAH concentrations varied from 0.0029 to 0.1079 ng/L in surface waters (main rivers, tributaries, etc.) with mean value of 0.0344 ng/L. Such concentrations can be taken as background values for the studied region and show that PAHs are within or lower than levels reported in certain other areas. The PAH profiles were dominated by high molecular weight PAHs (four-and five-ring components) in surface water samples. It indicated that PAHs in surface water have its origin from oil or sewage contamination (petrogenic input). The collected data, based on indices among phenanthrene versus anthracene, showed that petrogenic input was predominant at almost all the stations investigated. Principal component analysis (PCA), using a correlation matrix, revealed the latent relationships among all the surface water stations investigated and confirmed our analytical results.