Toxicity of the unresolved complex material (UCM) of in-reservoir biodegraded oils

Figure 1. Gas chromatographic diagram of a typical UCM-rich oil

Many oils contain large fractions of poorly characterized mixtures of unresolved complex materials (UCM), also called “the hump” due to their characteristic chromatographic profile (see Figure 1). The UCM contain mixtures of aromatic hydrocarbons and polar compounds which are toxicologically important, e.g. compounds containing oxygen-, nitrogen-, or sulphur-molecules. Experimental data also show that UCM compounds are recalcitrant to biodegradation in the environment and may therefore persist after oil spills or produced water discharges.

In a project sponsored by the Norwegian Research Council we have focused on the toxicity of UCM separated from water-soluble fractions (WSFs) of selected oils. The project is a cooperation between SINTEF, NIVA (Oslo), and the University of Plymouth.

In phase 1 of the project (2005) UCM in the WSFs were separated by polarity in several fractions by high-pressure liquid chromatography (HPLC), and the toxicities of individual fractions were assessed by several bioassays at NIVA. Preliminary results have so far shown that UCM-related fractions are associated  with sub-lethal effects like metabolic inhibition, estrogenicity, induction of CYP1A activity, and DNA damage. Acute toxicity (cytotoxicity) was observed in crude extracts, but not in individual fractions.

In phase 2  (2006) we will focus on the comparison of the toxicities of UCM-related compounds and well-characterized compounds like polycyclic aromatic hydrocarbons (PAH), alkylated phenols (AP) and NPD (naphthalenes, phenanthrenes, dibenzothiophenes). Some toxic UCM-rich fractions will also be analysed by high-resolution chromatography methods. In this way selected compounds representative for toxic UCM-groups may be identified and used for toxicity screening.

For further information contact: 

Odd Gunnar Brakstad or Alf Glein Melbye