Other types of oil include fuel oils, weathered oils and refinery and petrochemical products. Some of these also contain another group of hydrocarbon - Alkenes.
Alkenes, or olefins, are unsaturated non-cyclic hydrocarbon compounds. Although these are not found in crude oil, they do occur in many refined products such as gasoline. They have either branched or straight-chained structures and are more reactive than alkanes having a slightly lower melting and boiling point. Many alkenes are gases at room temperature and pressure but alkenes with between five and 15 carbon atoms are liquids, and those with fifteen or more carbon atoms are solids. They have poor solubility in water.
The chemical structure of the individual hydrocarbons which make up petroleum possess unique characteristics of solubility and toxicity and therefore behave differently when released into the environment.
It can generally be said that:
Water-soluble components (or the water soluble fraction (WSF)) of the oil are easily dispersed, although solubility increases their toxicity to marine plants and animals either by direct contact or in dilute solutions.
Low molecular weight constituents are the most volatile and toxic although as they weather quickly, for example through evaporation, they usually have little impact on marine life.
As molecules increase in size, their physical properties of the compounds change. In general the boiling and melting points of molecules increase with the number of carbon atoms and therefore become more stable.
Their ease of uptake (bioavailability) relies on affinity for lipids and ease of passage into tissues.
