Improving exposure assessment of complex hydrocarbon mixtures in the aquatic environment

Polycyclic Aromatic Hydrocarbons (PAHs) and oil are complex organic mixtures which are ubiquitously present in the aquatic environment. To prevent adverse effects on organisms exposed to these contaminants adequate risk assessment is of vital importance. However, current available methods are initially developed for exposure to single compounds only. Risk assessment of mixtures requires a different approach. One approach might be the assessment of bioaccumulation, the amount of chemicals that is taken up from the environment by organisms, and compare this with internal effect concentrations which are available for mixtures. Current approaches based on equilibrium partitioning of chemicals between water, sediment, and organisms, however, often overestimate bioaccumulation as it is assumed that the fraction that is available for uptake is exclusively controlled by the amount of organic carbon in sediments. It was previously demonstrated that direct measurements of the available fraction improves risk assessment, because all factors that influences the contaminants' availability are included. These techniques were so far successfully applied for simple mixtures such as PAHs were compounds are individually detectable. No experiences with such methods was, however, not gained for complex mixtures such as oil that consist of thousands compounds. The aim of these thesis was therefore to contribute to the improvement of risk assessment of complex organic mixtures in sediments by improving exposure assessment. This thesis resulted in an improvement of the current approach to assess bioaccumulation of PAHs using techniques to extract the available fraction only by incorporating the effects on temperature. Therefore, the available method is now also applicable to assess risks of exposure to PAHs in the field. Many advances in the risk assessment of oil were made. Firstly, a method was developed to remove interfering compounds from oil extracts from biota and sediments. Therefore, by applying this methods measured oil concentrations are truly related to petroleum and not to interfering compounds such as lipids and organics. Insight was also gained in bioaccumulation of oil in aquatic worms. It was demonstrated that the uptake of oil by organisms is complex and not assessable from the oil concentration in sediments. Therefore, a new method was developed to estimate bioaccumulation of oil in organisms by extracting the available fraction only, which successfully assessed internal exposure concentration in worms exposed to oil-contaminated sediments both in the laboratory and the field. In conclusion, the research described in this thesis can contribute substantially to an improved risk assessment procedure of organic contaminants. Some practical and regulatory challenges are, however, still lying ahead, but at least the road to implementation of the technique may be considered paved.