3. Methods Biodegradation of Aromatic Unresolved Complex Mixtures (UCMs): A Comparative Study Using an Isolated Aromatic UCM and Synthetic Model UCM Hydrocarbons

Cyclohexylalkyltetralins, which are believed to be good model hydrocarbon compounds for components of aromatic unre olved complex mixtures (UCMs) have been synthesised in this laboratory. To validate their candidacy as components of the UCM they have been subjected to rigorous experimentation based upon known properties of the UCM (toxicity, solubility, photodegradation). This study has monitored the biodegradability of both an isolated aromatic UCM and the synthetic model compounds using the bacterium strain Pseudo onas fluorescens, a known aliphatic and aromatic hydrocarbon degrader. • Unresolved complex mixtures (UCMs) of hydrocarbons are an almost universal feature of environmental samples contaminated with weathered residues of petroleum [1]. • The UCM is considered to be relatively inert to microbial degradation [2] and, consequently, it is a dominant feature of the gas chromatograms of biodegraded crude oils (Fig. 1). • Alkyltetralins have previously been identified as important aromatic UCM components in several biodegraded and refinery feedstock oils [3,4]. • The most toxic component of the UCM is the monoaromatic fraction [5,6]. • The synthesis of proposed ‘average ’ model structures (Fig. 2, I-VI) [7,8] of monoaromatic UCM hydrocarbons has allowed a comparative toxicological evaluation to be made [5]. • Exposure of Mytilus edulis to compounds (I-III) exhibited similar toxicity effects (>70