Weathering characteristics of Iranian Heavy crude oil with and without dispersants using a mesocosm

Abstract

The environmental fate of Iranian Heavy crude oil with and without an oil spill dispersant (OSD) has been studied using a 1,000 kL capacity in situ mesocosm. Physical weathering and chemical composition changes of the oil were monitored for 77 days. The OSD significantly changed the chemical fingerprint of the oil. Compound-specific effects of the OSD could be observed as changes over time in the content of the TPH, unresolved complex mixture (UCM), alkanes, PAHs, hopanes and steranes in the oil. As oil weathers, most hydrocarbons showed a rapidly decreasing phase followed by a slowdown and stabilization. Recalcitrant biomarkers, however, showed an opposite trend. An additional ca. 10% increase in hydrocarbon formation in the form of UCM occurred after OSD treatment. This change, in effect, increased the half-life of the TPH in the oil with the dispersant (OD), while the enhanced solubility of the low molecular weight PAHs by the OSD decrease the half-life of alkylated PAHs in the OD. The mass balance of the weathered oil was calculated using laboratory and mesocosm data and the results demonstrate the importance of using a mesocosm for the production of environmentally realistic data. for 77 days. The OSD significantly changed the chemical fingerprint of the oil. Compound-specific effects of the OSD could be observed as changes over time in the content of the TPH, unresolved complex mixture (UCM), alkanes, PAHs, hopanes and steranes in the oil. As oil weathers, most hydrocarbons showed a rapidly decreasing phase followed by a slowdown and stabilization. Recalcitrant biomarkers, however, showed an opposite trend. An additional ca. 10% increase in hydrocarbon formation in the form of UCM occurred after OSD treatment. This change, in effect, increased the half-life of the TPH in the oil with the dispersant (OD), while the enhanced solubility of the low molecular weight PAHs by the OSD decrease the half-life of alkylated PAHs in the OD. The mass balance of the weat