How does organic material get converted into aliphatic hydrocarbons in sediment?
Hydrocarbons are derived from wood, petroleum distillates or other sources. Polycyclic aromatic hydrocarbons are derived form crude oil or from one by-product of carbonized coal, called coal tar.
Burning process of organic materials or natural processes, such as volcanos' eruptions or forest fires create polycyclic aromatic hydrocarbons.
The presence or absence of alternating single and double bonds in hydrocarbon rings classifies them as aromatic or aliphatic hydrocarbons. The characteristic of aliphatic hydrocarbons can be saturated or unsaturated, based on the number of double with respect to single bonds.
The solubility of aliphatic hydrocarbons is decreased in comparison with aromatic hydrocarbons having comparable molecular weight and the tendency of larger hydrocarbons to bioaccumulate because of the increased sorption potential.
Usually, longer-chain aliphatic hydrocarbons have decreased water solubility and volatility and they will sorb into rorganic matter, while aliphatic hydrocarbons having smaller chain lengths will more likely move out and volatilize from soils. Hence, aliphatic hydrocarbons having longer chain length remain to sorbed sediments, while aliphatic hydrocarbons having shorter chain length will volatilize to air.