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Environmental context. The dwindling fossil fuel sources have led to a major interest in expanding the use of bioenergy. While biodiesel is moving towards the mainstream as an alternative source of energy, a thorough understanding of the potential impact and risk posed by spills of biodiesel and biodiesel fuel mixtures should be obtained. We present new data here that will allow the prediction of biodiesel behaviour and the extent of contamination in soils and groundwater in the event of such a spill.Abstract. Partition coefficients of polynuclear aromatic hydrocarbons (PAHs) between biodiesel fuel mixtures (i.e. B1, B5, and B20) and water were determined by the frequently applied estimation method of Raoult's law. The experimental partition coefficients were compared with calculation by polyparameter linear free energy relationship (PP-LFER) approaches. Deviations from poor recovery of PAHs from the aqueous phase in partition experiments and parameters in the PP-LFER equation are discussed. The results suggest that the extent of deviation from ideal behaviour for biodieselwater partitioning is relatively small (i.e. errors remain within a factor of two). The concentrations of PAHs in water in equilibrium with these biodiesel fuel mixtures, estimated from the model presented, may be considered as a reasonable approximation for most field-scale applications.Additional keywords: polyparameter linear free energy relationship, Raoult's law.

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