Developing Non-lethal Biomarkers to Detect Exposure to Organic Contaminants in Aquatic Habitats

Biomarkers have become essential tools to monitor organism responses to contaminant exposure and are continuously developed as new anthropogenic chemicals are released into the environment. Biomarkers can be used to determine if an organism has come into contact with and is responding to a contaminant and allows researchers to obtain information on the organism\u27s ambient environment. The cytochrome P4501A (CYPIA) enzyme is a commonly used biomarker to determine if animals have been exposed to contaminants such as: polyaromatic hydrocarbons (PAHs), dioxin-like compounds, and polychlorinated biphenyls (PCBs, Melancon et al., 1992). As aquatic environments have become more infiltrated with contaminants due to run-off, effluents, and leaching, there has been greater emphasis on monitoring for CYPIA induction in fish and other aquatic organisms. Cytochrome P4501A induction is typically measured lethally through the ethoxyresorufin-o-deethylase (EROD) activity assay which measures the induction of CYP1A in the liver (Whyte et al., 2000); however, ERODs have also been measured using gills (Jonsson et al., 2002) and kidneys (Oriz-Delgado et al., 2008). Non-lethal methods are needed for endangered species when lethal sampling is prohibited, but would benefit all organisms that are exposed to contaminants. Gill filaments have been used in a lethal method to perform the EROD activity assay in various salmonids (Jonsson et al., 2002, 2003, and 2006); however, we were interested in using this assay in a non-lethal manner. We also had interest in using scales to measure EROD activity as it has been published that scales express CYP1A mRNA (Quiros et al., 2007). The experiments addressed in this thesis include utilizing Atlantic salmon (Salmo salar) parr and smolts to determine if a reliable, sensitive biomarker could be developed using gill filaments and scales in a non-lethal manner for the EROD activity assay. Atlantic salmon were chosen due to their endangered status and importance in Maine and their anadromous life history that causes them to encounter a variety of contaminants in the aquatic environment. Our hypothesis was that gill and scale samples could be sampled non-lethally and be used to detect CYP1A induction through EROD activity after Atlantic salmon parr were exposed to a waterborne contaminant. Our experimental design consisted of exposing Atlantic salmon to untreated water, vehicle (acetone - 32.25 ppm), 0.01 uM PCB-126, or 0.001 uM PCB-126 for 24 hr (n=50 fish per exposure). Gill, scale, and liver samples were taken at 6 and 24 hr during exposure and 2, 14, and 34 d post exposure to monitor EROD induction over time. Our results indicated that liver ERODs show the fastest induction to waterborne contaminants within 6 hr for both PCB-126 concentrations, but gill ERODs showed the highest fold change between the three tissues at 24 hr for the 0.01 uM PCB-126 concentration. Scale ERODs showed significant induction at 0.01 uM PCB-126 concentration at all time points. High variability; however, indicated that further optimization was needed. Optimization of scale techniques resulted in a decline in variability, but further experimentation is necessary for eventual use in the field