Roberta Lourenço Ziolli

Photochemical transformations of water-soluble fraction (WSF) of crude oil in marine waters: A comparison between photolysis and accelerated degradation with TiO2 using GC–MS and UVF

Changes in the chemical nature of the water-soluble fraction (WSF) of crude oils caused by photolysis and heterogeneous photocatalysis using TiO2 were investigated by gas chromatography–mass spectrometry (GC–MS) and ultraviolet fluorescence spectrophotometry (UVF). Two Brazilian crude oil samples with different concentrations of WSF (45 and 15 mg C l −1 ) were studied. Photochemical driven reactions were investigated under UV-Vis irradiation in the absence and in the presence of the photocatalyst. The presence of aromatic hydrocarbon in the WSF before irradiation, resulting from crude oil slick solubilization on seawater, was confirmed by chromatograms that showed a series of low molecular weight aromatic hydrocarbons together with a unresolved complex mixture (UCM). However, in the irradiated WSF these compounds were not detected. After 6 days photolysis period, WSF from both crude oils did not show peaks of aromatic compounds, whereas the presence of long chains unsaturated hydrocarbons as well as sulfur compounds were detected. In contrast, when TiO2 was employed, complete photodegradation of both crude oil samples in the WSF occurred after very short light exposure periods (1–2 days). Quantitative data were also obtained and discussed here. The results reinforce photodegradation as an effective weathering process for the transformation of dissolved crude oil fraction, particularly in high solar radiation environments. Complete degradation in a short period of time was only made possible by heterogeneous photocatalysis.

Operational problems related to the preparation of the seawater soluble fraction of crude oil.

Owing to the importance of dissolution and weathering processes following oil spills, this work focused on the operational (quantitative) aspects related to the dissolution of petroleum-derived products, as well as the influence of solar light on both dissolution and the photoproduction of hydrogen peroxide. Four Brazilian crude oil samples were used to study the transfer process of organic compounds from the crude oil film to the aqueous phase (natural seawater) over a period of up to 45 days. Dissolved organic carbon (DOC), measured by non-dispersive infrared spectroscopy followed by high temperature catalytic combustion, was used to follow the partitioning between the two phases. Aqueous DOC values increased as a function of time (up to 15 days) until equilibrium was reached at concentrations ranging from 5 to 45 mg C L(-1). The final DOC concentration as well as the rate of dissolution depends on the nature of the crude oil. When exposed to sunlight, the dissolution was enhanced by up to 67.3%, and inorganic peroxides were generated in the concentration range from 4.5 up to 8.0 micromol L(-1) after 7.3 h irradiation. These results indicate that there is a need for a standard procedure for the production of the WSF in order to generate a more reliable tool to assess the impact of oil spills on the marine environment.

Uncertainties associated with signal measurements from solutions and from solid substrates using luminescence based methods

A careful study was performed to evaluate and compare uncertainties associated with the measurement of luminescence from chrysene by using fluorimetry in solution and by using solid surface room-temperature phosphorimetry (SSRTP). Chrysene was chosen as the luminescent analyte (measurand) for this study because it is a substance of environmental interest and also because it presents strong natural fluorescence and phosphorescence that is easily induced by the external heavy atom effect. The most common approach for uncertainty calculation is the one indicated in the Guide to the Expression of Uncertainty in Measurement which is recognized worldwide. The most relevant sources of uncertainty were identified. The expanded uncertainty (k = 2; 95%) for SSRTP was 3.27 × 10−6 mol L−1 (3.7 ng of chrysene) with relevant contributions from the internal reproducibility, preparation of solutions and from the analytical curve. This value is equivalent to 28% of the reference analyte value. For fluorimetry, an acceptable value for the expanded uncertainty was achieved by preparing solutions by weighing masses of analyte and solvent. In this case, the huge contribution from the preparation of solutions by adjusting volume is minimized and the uncertainty magnitude was 2.12 × 10−9 mol L−1 (21.2% of the chrysene reference concentration). In this case, relevant contributions were from the repeatability, the internal reproducibility and from the analytical curve. The preparation of solutions by weighing does not have a relevant impact in improving the quality of the signal measurements by SSRTP.

Synchronous scanning phosphorimetry for the selective determination of chrysene: a metrological study

Room-temperature phosphorimetry was used to quantify trace levels of chrysene in sugar-cane spirits and in fish bile. A selective phosphorescence enhancer (AgNO3) and synchronous scanning allowed the detection of ng amounts of chrysene. Accuracy (113 ± 17%) and selectivity was evaluated using the CRM-NIST-1647d - Priority Pollutant Polycyclic Aromatic Hydrocarbons in acetonitrile. Analysis of sugar-cane spirit samples enabled recovery of 108 ± 18% which agreed with the one achieved using HPLC. Methods uncertainty was equivalent to 3.4 ng of the analyte, however, the analyte pre-concentration (SPE) improved sensibility and minimized the relative uncertainty. Characterization and homogeneity studies in fish bile were also performed.