Biodegradation studies of unresolved complex mixtures of hydrocarbons: model UCM hydrocarbons and the aliphatic UCM

Determination of aliphatic hydrocarbons in urban runoff samples from the “Le Marais” experimental catchment in Paris centre

“…Several studies using gas chromatographic analysis of hydrocarbons show the same pattern, called unresolved complex mixture (UCM). The UCM is a common feature of the gas chromatograms of crude oils and certain refined products such as lubricating oils, and it is especially marked for weathered and biodegraded oils [14,15]. The UCM is a complex mixture, extremely resistant to biodegradation, composed of many structurally complex isomers and homologous of branched and cyclic alkanes [13].…”

Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

“…The use of oxidative degradation followed by GC enables the release of additional compounds, which led to the notion that UCMs might be mixtures of fairly simple compounds comprising unsubstituted alkyl chains such as isometric monoalkyl substituted "T"-branched alkanes (Gough et al, 1992;Warton et al, 2000). "T"-branched alkanes were shown to be resistant to biodegradation (Gough et al, 1992). Warton et al (1997) demonstrated that 3% of the alkanes from a biodegraded crude oil were "T" branched alkanes.…”

“…These attempts have led to the initial belief that UCMs were composed of hydrocarbons with similar chemical properties that include large numbers of branched and cyclic aliphatic and aromatic isomers (Eglinton et al, 1975;Payzant et al, 1979;Alexander et al, 1982;Sanders and Tibbetts, 1987;Killops and Al-Juboori, 1990). The use of oxidative degradation followed by GC enables the release of additional compounds, which led to the notion that UCMs might be mixtures of fairly simple compounds comprising unsubstituted alkyl chains such as isometric monoalkyl substituted "T"-branched alkanes (Gough et al, 1992;Warton et al, 2000). "T"-branched alkanes were shown to be resistant to biodegradation (Gough et al, 1992).…”

Further Paleogene and Cretaceous sediment cores from the Kilwa area of coastal Tanzania: Tanzania Drilling Project Sites 6–10

“…The saturated hydrocarbon fraction of this sample has a very different composition compared to all the other saturated hydrocarbon fractions analysed from this site. It contains a relatively large Unresolved Complex Mixture (UCM; "hump"), typical of heavily biodegraded organic material, including petroleum (Magoon and Claypool, 1985;Rowland, 1990, 1991;Gough et al, 1992;van Dongen et al, 2003). In addition, the hopanes/hopenes and steranes have a thermally mature distribution distinct from the other samples analysed.…”