W9 PM Residual Oil and its Effects
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 339-340

(AAA-1117-571215) Predicting and Comparing the Narcotic Potential of Neat and Weathered Crude Oil: Is A New Paradigm Needed?

Di Toro, D^{1, 2}, McGrath, J², Stubblefield, W³, ¹ University of Delaware² HydroQual, Inc³ Oregon State University

ABSTRACT- The toxicity of the components of oils can be understood using the concept of narcotic potential. It is the toxicity of a solution at the water solubility of each component of the oil. Using the target lipid model (TLM) of narcotic toxicity, and the observed relationship of the solubility of oil components to log (K_OW), it is demonstrated that components with lower log (K_OW) have greater narcotic potential than those with higher log (K_OW). The total toxic unit concentration in an aqueous phase in equilibrium with the oil is shown to be weighted sum of the narcotic potentials of the components, where the weights are the component mole fraction concentrations in the oil. Weathering removes the lower log (K_OW) chemicals and the higher log (K_OW) chemicals remain. The replacement of more narcotically potent compounds with less narcotically potent compounds in the oil lowers the toxicity of the aqueous phase. The idea that weathering increases toxicity is based on the erroneous use of total petroleum hydrocarbon concentrations as though it were a single chemical compound that can be used to gauge the toxicity of a mixture, regardless of it makeup. The use of narcotic potential and toxic units eliminates this confusion, puts all the chemicals on the same footing, and allows an intuitive understanding of the effects of weathering. Case studies using laboratory and field data will demonstrate that weathered oil is less toxic than neat oil. This miss-application of total PAH concentration has lead to the proposal of a new paradigm of PAH toxicity. In fact no new paradigm is needed to explain the observed toxicity of PAH mixtures.

Key words: narcotic potential, weathering, PAHs