Cytochrome P450 induction in Ictalurus punctatus following exposure to wastewater treatment plant effluent

Abstract

Induction of the cytochrome P450 enzymes in fish, measured as ethoxyresorufin-O-deethylase (EROD) activity, has been extensively used as a biomarker in assessing exposures and responses of aquatic organisms to contaminants. This study focused on whether exposure to Troy (Alabama) wastewater treatment plant (TWWTP) effluent at the Walnut Creek mixing zone, induced transcription of mRNA for cytochrome P4501A1 enzyme production and increased EROD activity in channel catfish (Ictalurus punctatus). Water from Big Creek (Barbour County, AL), regarded as least impacted by pollutants, was used as a reference source for administration of a positive control chemical (PCB – Aroclor 1254). All water samples were transported from field sites to the Troy University laboratory for conducting the study. Reverse transcriptase-polymerase chain reaction (RT-PCR) indicated the presence of compounds capable of inducing transcription of CYP1A1 mRNA in catfish liver. Increased transcription of mRNA for cytochrome P4501A1 enzyme production, confirmed by a 3-fold induction of EROD activity, was found in catfish exposed to water from the TWWTP mixing zone on Walnut Creek compared to catfish exposed to Walnut Creek Upstream. Catfish exposed to water from Big Creek treated with PCBs were found to have only slightly higher enzyme activities than those exposed to water from Big Creek Control, but a 2.7-fold EROD level was found in catfish exposed to Big Creek Control compared to Walnut Creek Upstream. Determining the induction of cytochrome P450 and subsequent enzymatic activity in catfish and other fish species common to this region could be useful early molecular warnings of possible pollution effects, beyond those methods typically used to characterize water quality.

Keywords :

• EROD
• molecular biomarkers
• channel catfish
• liver monooxygenases

Acknowledgements

This study was supported by a faculty development grant from Troy University (Troy, Alabama).