Crude Oil

Environmental Fate

TERRESTRIAL FATE: Based on a recommended classification scheme(1), Koc values ranging from approximately 80 to greater than 100,000(2,3), indicate that the lighter weight aliphatic and aromatic components of crude oil will have high mobility in soils while the heavier molecular weight constituents will be immobile(SRC). The Henry's Law constants for constituents of crude oil ranged from 1.5X10-5 atm-cu m/mole at 25 deg C (aromatic fraction >C21-C35) to 110 atm-cu m/mole at 25 deg C (aliphatic fraction C16-C21)(2). Based on these Henry's Law constants, volatilization from moist soil surfaces is expected(SRC). However, volatilization may be attenuated for the higher molecular weight components which are expected to adsorb strongly to soil(SRC). Vapor pressures of the constituents of crude oil ranged from 3.3X10-7 mm Hg at 25 deg C (aromatic fraction >C21-C35) to 266 mm Hg (aliphatic fraction C5-C6)(2). Therefore, some components of crude oil are expected to volatilize from dry soil surfaces while others will not(SRC).

AQUATIC FATE: When released to water, initially crude oil spreads out as a film on the sea surface as a result of wind and wave action. The more volatile, lower molecular weight hydrocarbons are removed from the water surface by volatilization. Polar compounds and the mono-aromatic hydrocarbons are soluble in water and are taken into solution. A key ancillary process is that of emulsification (by oil dispersants), since crude oil has a natural tendency to form emulsions in sea water. Such emulsions are usually of the oil-in-water type, but may also be of the water-in-oil type. The latter are often of the intractable 'chocolate mousse' type. Significant amounts of crude oil, particularly the higher molecular weight compounds, sink naturally, rolling along the ocean bottom picking up sand and shells and forming tarry balls which are resistant to degradation by any method. Hydrocarbons may also reach the bottom sediments by sorption on to suspended particles which ultimately settle on the sea floor. Spilt oil also undergoes chemical changes, particularly oxidation by free radical mechanisms initiated by sunlight. The initial products of such reactions are hydroperoxides, and these in turn form compounds such as alcohols, acids and aldehydes, many of which have an appreciable water solubility. Polymerization also occurs to yield intractable tarry materials. The bulk of spilt crude oil is biodegraded by the micro-organisms present in sea water. Emulsification to form oil-in-water emulsions yields small particles of crude oil that are biodegraded by bacteria, yeasts, fungi and actinomycetes. n-Alkanes are readily degraded in sea water, since many micro-organisms can utilize them. Branched-chain or iso-alkanes are less readily biodegraded but they do ultimately biodegrade. The degradation of cycloalkanes has not been extensively studied, but the ring structure is resistant to biodegradation. Aromatic hydrocarbons are also resistant to biodegradation, but a few micro-organisms are able to utilize them. High molecular weight compounds, the tars and asphaltenes, degrade very slowly(1).

AQUATIC FATE: Use of dispersants breaks up a slick of oil on the surface into smaller droplets that can go beneath the surface(1). Oil spill dispersants do not actually reduce the total amount of oil entering the environment(2). /Dispersed oil/

AQUATIC FATE: One liter of petroleum deprives about 40 thousand liters of sea water of the oxygen that is used to sustain living inhabitants such as fish ... one ton of petroleum can pollute about 12 square kilometers surface of the ocean.

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), vapor pressure of aromatics and aliphatic fractions of hydrocarbons of crude oil range from 3.3X10-7 mm Hg at 25 deg C to 266 mm Hg(2), suggesting that many constituents of crude oil are expected to exist solely in the vapor phase in the ambient atmosphere. Vapor-phase components of crude oil are degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air was estimated to range from 0.37 to 6.5 days for typical hydrocarbon constituents of crude oil(3). Direct photolysis will not be an important environmental fate process for most of the constituents of crude oil since they do not contain chromophores that absorb light in the environmental UV spectrum; however, polyaromatic hydrocarbons in crude oil may undergo direct photolysis in the atmosphere(3).

Find more information on this substance at: Hazardous Substances Data Bank , TOXNET , PubMed