DEVELOPING NON-LETHAL BIOMARKERS FOR WATERBORNE ORGANIC CONTAMINANTS

Expression of cytochrome P4501A (CYP1A) in the liver is a well-established, but lethal biomarker for organic contaminant exposure in vertebrate species. A non-lethal biomarker using scales and gill filaments to measure CYP1A enzyme activity (measured as ethoxyresorufin o-deethylase, EROD) would present an alternative method for detection of water-borne contaminant exposure in endangered or threatened fish species. This analysis would also provide an inexpensive technique (compared to whole body chemical analysis) to determine acute organic contaminant exposure and help identify specific geographical areas for chemical analysis to aid in implementing restoration plans for contaminated sites.

We are evaluating the sensitivity, reliability, and time course of the induction and duration of CYP1A activity in gills, scales, and livers in Atlantic salmon (Salmo salar). Atlantic salmon are indigenous to Maine and are currently listed as an endangered species. We exposed salmon parr to two aqueous concentrations of PCB-126 (0.01 µM & 0.001 µM, static exposure), acetone (32.25 ppm, vehicle), and untreated water for 24 h before transferring the fish to clean, flow-through water. Throughout several time points (during and post exposure) we collected gill filaments and scales (non-lethally) and whole livers (lethally).

Gill EROD activities in fish treated with 0.01 µM PCB-126 were elevated at 6 h during exposure and remained significantly elevated (compared to untreated and acetone controls) throughout the experiment. The 0.001 µM PCB-126 treated fish showed an elevated gill EROD activity at 6 h which declined at 24 h exposure before reaching untreated activity levels by 48 h post exposure. Scale EROD activities were elevated for 0.001 µM PCB-126 treated fish at 6 h, but not significantly elevated in the 0.01 µM PCB-126 treated fish until 24 h. After 48 h post exposure, scale EROD activities became highly variable in all groups.

Gill and scale CYP1A activity show encouraging results as non-lethal biomarkers of contaminant exposure and response for use with endangered fish species. Liver EROD activities are currently undergoing analysis. Future investigations include optimizing scale and gill EROD protocols to reduce variability.