Properties of Oil & Dispersant

Chen, J. and M.S. Denison.  2011.  The Deepwater Horizon Oil Spill:  Environmental Fate of the Oil and the Toxicological Effects on Marine Organisms.  Journal of Young Investigators 21(6):  84-95.  Find it Online*
Lighter components of crude oil evaporate more easily than heavier components.  After volatilization (i.e., evaporation), the remaining, heavier components of oil are weathered, emulsified (i.e., dispersion in liquid) and eventually fall through the water column where they may attach to other organic particles to form larger aggregates.  Oil contamination occurs through direct contact, inhalation, or indigestion and can induce hypothermia, drowning, and suffocation.  Hydrocarbons (e.g., oil) are either aliphatic or aromatic and crude oil is composed of four hydrocarbons (i.e., naphthenes, paraffins, aromatics, asphaltics).  Light crude oil is low density oil that has a higher hydrocarbon to metals/organics ratio.  Heavy crude oil is a high density oil that has a lower hydrocarbon to metals/organics ratio.  Sweet crude oil has low concentrations of sulfur and sour crude oil has high concentrations of sulfur.  Oil pollution comes from natural seeps (46%) and anthropogenic impacts (53%).

Zuijdgeest A, Huettel M. 2012. Dispersants as Used in Response to the MC252-Spill Lead to Higher Mobility of Polycyclic Aromatic Hydrocarbons in Oil-Contaminated Gulf of Mexico Sand. PLoS ONE 7(11):e50549. Find it Online*
Polycyclic aromatic hydrocarbons (PAHs) are the carcinogenic portions of crude oil.  PAHs have a low volatility and resistance to decomposition, but surfactants (e.g., emulsifiers, dispersants) solubilize PAHs in soils.  The matrix of soil increases diffusivity of the PAHs; this is a threat to groundwater and benthic soil contamination.  The coating of dispersed oil reduces sorption to sand grains by increasing the adsorption of dispersant to sand, increased by saltwater, thus facilitating PAH mobility.  PAHs are broken down to fit through interstitial (i.e., pores) space in sediment.  The hypothetical penetration depth is 50-80 cm, but tidal & wave flushing drives the oil deeper into the sand.  Photolysis, or chemical decomposition by sunlight, degrades oil, but also increases toxicity for organisms by a multiple of 5-8.  The exclusion of oxygen reduces degradation and PAHs will linger. 

Kujawinski EB, Kido Soule MC, Valentine DL, Boysen AK, Longnecker K, Redmond MC. 2011. Fate of Dispersants Associated with the Deepwater Horizon Oil Spill. Environmental Science & Technology 45(4):1298-1306. Find it Online*
Dioctyl sodium sulfosuccinate (DOSS) is the tracer element found in the 2 types of Corexit (i.e., 9527a [surface] and 9500 [bottom]) used in the Deepwater Horizon oil spill.  The majority of DOSS was diluted rather than biodegraded (this was opposite of freshwater applications).  DOSS remained in deepwater plume longer than expected.  The question has been raised if the dispersants were successful or did they increase the sequestration of oil in deepwater.  The dispersant was either dissolved or diluted in ascension, from the blown oil well, to approximately 1100 meters.  Organisms were subject to dispersant (10-100 µg/L) for 1-10 km from the point of application. 

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