Effects of weathering on the toxicity of three offshore australian crude oils and a diesel fuel to marine animals

Abstract

Abstract The evaporative weathering properties, chemical composition, and toxicity of three Australian Northwest Shelf crude oils and an Australian diesel fuel were evaluated. The crude oils include one each of a condensate, a light, and a medium crude oil. Between 23 and 100% of the mass of the oils is lost during evaporative weathering equivalent to about 1 week on the sea surface. During weathering, the oils lose most of their monocyclic aromatic hydrocarbons (MAHs) and phenols; concentrations increase of less volatile phenols and polycyclic aromatic hydrocarbons (PAHs). The acute toxicity of water-accommodated fractions (WAFs) of the fresh and weathered oils to six species of temperate and tropical marine animals ranges from > 100% to about 11% WAF. The MAHs are the most important contributors to the acute toxicity of the WAFs of the fresh oils. The contribution of PAHs to WAF toxicity increases with weathering. About 58% of the hazard indices (HI: exposure concentration/acutely toxic concentration) for the WAFs of the two light oils weathered for the equivalent of 1 d are attributable to PAHs. The toxicity of the WAFs of the condensate and light crude oil can be accounted for by MAHs, PAHs, and phenols; WAFs of the middle-weight crude oil and diesel fuel are higher than predicted based on their concentrations of total MAHs, PAHs, and phenols, indicating that other components of the WAFs are contributing to their toxicity. These components may include the unresolved complex mixture and polar compounds (resins).