Crude Oils
Crude Oils - Light-weight Components
Light-weight components are characterised by (after Michel, 1992):
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Hydrocarbon compounds containing up to 10 carbon atoms.
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A boiling range up to 150°C.
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Rapid and complete evaporation - usually within a day.
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High water solubility - usually contributes >95% of water-soluble fraction.
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High acute toxicity because they contain the monoaromatic hydrocarbons (benzene, toluene, xylene) which are soluble and toxic.
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No potential for bioaccumulation (as they evaporate).
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Mostly composed of alkanes and cycloalkanes which have relatively low solubility (and thus low acute toxicity potential).
These components evaporate so quickly that they do not persist in the environment. However, it should be noted that one important exception is when oil is spilled in cold conditions and the dissolved fraction is rapidly mixed in to the water column.
Alkanes
Alkanes, or paraffins are saturated hydrocarbon compounds in which the carbon atoms are joined by single covalent bonds only. Alkanes have a branched-chain structure with the boiling and melting points increasing with the number of carbon atoms. At room temperature and pressure, alkanes with one to four carbons atoms are gas, five to 16 are liquid and those with more carbon atoms are solids. All alkanes are insoluble in water and usually include some of the most readily degradable components of a spilled oil.
Cycloalkanes
Cycloalkanes, also known as naphthenes, are saturated hydrocarbons whose carbon atoms have joined chain ends which form a ring structure. Their properties are similar to other alkanes, however, due to their cyclic nature they are particularly resistant to biodegradation.
