Responses of Fishes Following Developmental Exposure to Complex Hydrocarbon Mixtures

Abstract

The continuing use of crude oil and development of the oil industry have resulted in complex hydrocarbon mixtures becoming common environmental contaminants. These contaminants, such as oil sands process affected water (OSPW) and crude oil, are especially of concern in aquatic ecosystems. OSPW is a complex alkaline and saline mixture with both organic and inorganic components. Naphthenic acids (NAs) are currently considered to be the primary toxic component, though other components of OSPW such as metals and salts likely contribute to its toxicity as well. Polycyclic aromatic hydrocarbons (PAHs) are considered the main source of toxicity in crude oil, though other aromatic hydrocarbons may also be responsible for some of its toxicity. Both of these complex hydrocarbon mixtures have been shown to cause many adverse effects in fishes. My thesis focuses on the effects of developmental exposures to OSPW in zebrafish and crude oil in both zebrafish and sheepshead minnow. Zebrafish were developmentally exposed to either raw or ozonated OSPW from 0-7 days post fertilization (dpf). Survival from 1-7dpf was not affected by exposure to either type of OSPW. However, otolith area was slightly smaller in exposed zebrafish at 7dpf, potentially indicating a slight physiological change due to exposure. The expression of cardiac development genes was also affected by exposure but heart rate and cardiac area were not adversely affected. The expression of biotransformation enzymes cytochrome P450 1A (cyp1a) and cyp1b were induced by exposure to raw OSPW, with cyp1b more highly expressed than cyp1a. The expression of CYP enzymes returned to levels similar to that of the control within 2 days after exposure ended, indicating the fish were likely capable of excreting or metabolizing compounds present in OSPW relatively quickly. Exposure to neither raw nor ozonated OSPW affected overall fish length, yolk sac absorption, jaw morphology, apoptosis, or the expression of neurodevelopment genes and vitellogenin, a marker of estrogenicity. Overall, the OSPW exposures were not overtly toxic to embryonic zebrafish and very few endpoints were affected. For the crude oil studies, zebrafish and sheepshead minnow were exposed to water accommodated fractions (WAFs) of three types of crude oil (source, moderately weathered, and heavily weathered) plus dispersant. The chemical composition of these WAFs was compared and contrasted between freshwater and saltwater and responses to these WAFs were compared between zebrafish, a model freshwater species, and sheepshead minnow, an ecologically relevant saltwater species. WAFs varied little between freshwater and saltwater except for the source oil plus dispersant treatment group. Dispersant increased amount of PAHs in both the saltwater and freshwater source oil WAFs but lead to a much greater amount in saltwater compared to freshwater (~10 fold). The source oil plus dispersant WAF was the only treatment group to significantly decrease survival in both zebrafish and sheepshead minnow. Species-species differences in responses were found in cardiotoxicity and estrogenicity endpoints. Overall, saltwater and freshwater WAFs were considerably different when dispersant was present with source oil; furthermore, their impacts differed between species, indicating that freshwater systems and species may not be reliable for studying marine oil spills. The study of complex hydrocarbon mixtures can be challenging due to the large variability in environmental samples and the differences in species’ sensitivities.