Unresolved complex mixtures of aromatic hydrocarbons in the marine environment : toxicity, solubility and photodegradation studies
Unresolved complex mixtures (UCMs) of aromatic hydrocarbons have been found in a wide range of environmental matrices at high concentrations. However, limited consideration has been given to the potential detrimental effects of the accumulation of these compounds in the marine environment. In particular, there is a need to evaluate these compounds in the light of recent evidence that points to the long term effects of oil in the marine environment. The overall aim of this work was therefore to investigate unresolved complex mixtures of aromatic hydrocarbons in the marine environment with particular emphasis on assessment of toxicity, aqueous solubility and photodegradation behaviour. A previously established link between the reduced Scope for Growth (SFG) of mussels with the concentration of 2-3 ringed aromatic hydrocarbons in mussels from petroleum impacted sites was found also to correlate well with concentrations of aromatic hydrocarbon UCMs in mussel tissues found at the same sites. This suggests that aromatic hydrocarbon UCMs or components within may be responsible for the observed effects. To determine whether an aromatic hydrocarbon UCM was capable of eliciting a toxic response in mussels, a monoaromatic UCM was isolated from a Gullfaks (North Sea) produced crude oil. At the highest nominal aqueous concentration tested, mussel feeding rate was reduced by -40 % in the 24 hour exposure period, during which the mussels accumulated a body burden similar to the body burden of monoaromatic UCM hydrocarbons in wild mussel populations, previously shown to exhibit reduced SFG. Recent studies of hydrocarbon UCM composition using chemical degradation methods have led to the proposition of alkylcyclohexyltetralins as 'average' structures for some monoaromatic UCM hydrocarbons. The aromatic hydrocarbon 7-cyclohexyl-lmethyltetralin was synthesised herein in good yield and purity. This compound reduced mussel feeding rate by 50% during the 24-hour exposure period. The aqueous solubility of a compound is an important physicochemical parameter that influences behaviour within the marine environment and is thought to be a limiting factor in the onset of measurable toxicological response. The aqueous solubilities of three 'model' aromatic UCM hydrocarbons were determined in distilled water at 25°C using a generator column set-up. The effects of salinity and temperature on aqueous solubility were also investigated. An aqueous solution comprising an aromatic UCM was also generated. Another influence on the fate of aromatic hydrocarbons in the environment is the action of sunlight (phototransformation). Therefore aqueous solutions of three model aromatic UCM hydrocarbons were exposed to light simulated under environmental conditions. The halflives of these compounds suggested that if these compounds are indeed representative of the aromatic UCM phototransformation may influence its fate in the marine environment. The results of this study have furthered knowledge on the environmental behaviour of unresolved aromatic hydrocarbons, and suggest that these compounds should be considered in the long term impacts of oil in the environment and also warrant further study. Parts of this work have been published and the author (Smith, E. L. ) was awarded the Procter and Gamble Eurorcar prize at the 3'd World Congress of the Society of Environmental Toxicology and Chemistry, 21-25 May 2000, Brighton, for the best presentation by a young scientist.