Toxicity and metabolism of alkyl-polycyclic aromatic hydrocarbons in fish
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Alkyl-polycyclic aromatic hydrocarbons (alkyl-PAHs) constitute more than 90% of the total PAHs in crude oil and are the main constituents toxic to fish. Little characterization of alkyl-PAHs has been reported and is needed to predict the effects of crude oil following spills. The objectives of this thesis were: (1) to evaluate the toxicity of alkyl-phenanthrenes and alkyl-anthracenes to the early life-stages of medaka (Oryzias latipes) using the partition controlled delivery of toxicants (PCD); (2) to investigate the effect of light on alkyl-anthracene toxicity; (3) to further characterize the PCD method; (4) to better understand alkyl-PAH mechanisms of toxicity; and (5) to identify the major phase I and phase II alkyl-PAH metabolites in rainbow trout (Oncorhynchus mykiss) and in medaka by both in vitro and in vivo methods. It was determined that the toxicity of both series of alkyl-PAHs increased with the number of carbon substituents on the rings. Some alkyl-PAHs had EC50 values lower than the value from conventional semi-static exposure methods. These values were below the water solubility limit, consistent with the ability of PCD to correct for values from nominal concentrations above solubility. PCD provided stable concentrations for up to 17 days but could not always compensate for losses of alkyl-anthracenes by photodegradation. Both series of alkyl-PAHs were toxic through different mechanisms that resulted from their physical and chemical properties. Alkyl-phenanthrenes such as 7-isopropyl-1-methylphenanthrene (retene) were more toxic to medaka embryos than phenanthrene. The appearance of blue sac disease suggested toxicity enhancement through the aryl hydrocarbon receptor pathway. Alkyl-anthracenes were toxic by narcosis in the absence of light and by phototoxicity in the presence of light. The photoproducts of alkyl-anthracenes were not toxic to fish. The in vitro phase I metabolism by rainbow trout CYP1a enzymes and in vivo phase II metabolism in rainbow trout produced alkyl-anthracenes metabolites substituted mainly on the ring system. The phase II in vivo metabolites of alkyl-phenanthrenes in medaka larvae were substituted mainly on their alkyl chains. For all alkyl-PAHs, a predominance of glucuronide conjugates was identified in the phase II metabolites. This characterization of the toxicity of alkyl-PAHs may contribute to predicting the toxicity of crude oil based on its composition.