Why does crude oil cause blue sac disease in larval fish?

Blue sac disease (BSD) in fish exposed to crude oil has been linked to concentrations of C1-C4 alkyl-phenanthrenes (APs) but not to unsubstituted polynuclear aromatic hydrocarbons (PAH). The toxicity of APs is related to their oxygenation by cytochrome CYP1A enzymes to benzylic alcohols. In this study, larval trout was exposed to retene and to compounds that promote the cyp1A gene, inhibit CYP1A activity, or compete for glucuronide conjugation. It was determined that toxicity was not caused by excreted metabolites because treatments affecting cyp1A gene expression had little effect on retene metabolism or toxicity. Excretion rates of retene were reduced by the inhibition of CYP1A activity, as was the metabolic profile in tissues and bile. The study demonstrated that oxygenation of alkyl PAH by CYP1A enzymes play a significant role in their metabolism and toxicity. Inhibition of oxygenation causes toxicity. The toxicity of unsubstituted phenanthrene increased when metabolism and excretion were accelerated by co-exposures with an inducer. The study showed that it is necessary to consider more than just the individual components of crude oil in order to fully understand the toxicity of oils