A Mesocosm Study on the Fate of Iranian Heavy Crude Oil in Water Column

Abstract

We studied the environmental fate of the water-soluble fraction of Iranian Heavy crude oil using experimental 980 liters of in situ mesocosm bags (0.5 m in diameter and 5 m in depth) that mimic natural ecosystems. Mesocosm facilites composed of nine experimental bags (‘control’ x 3, ‘oil’ x 3, ‘oil+dispersant’ x 3). Mesocosm experiment was conducted from April 17 to July 2, 2009. The fate of artificially spilled crude oil in water column and the effect of dispersant application were monitored by measuring total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs) and their compositional changes with time. Much faster increase of oil concentration in water column was observed in dispersant treated oiled mesocosm (313 ppb/day) than in non-treated oiled one (3.47 ppb/day) within eight days after oil addition. Oil concentrations in water column remained relatively stable thereafter and the TPH levels in ‘oil+dispersant’ mesocosms were about two orders of magnitude higher than those in ‘oil’ mesocosm. TPH levels are relatively high according to water depth in order of surface (0.5 m) > middle (2.5 m) > bottom (4.5 m) within several folds. The difference decreased according to time. Depuration rates of oil were also 6 times higher at ‘oil+dispersant’ mesocosm compared to ‘oil’ group.