Abstract
The objectives of this study were as follows: 1) to establish a baseline ethoxyresorufin-O-deethylase (EROD) activity level in channel catfish (Ictalurus punctatus), 2) to assess changes in induction of cytochrome P450 enzyme in channel catfish following exposure to creek water at the discharge point from the Troy (Alabama) Wastewater Treatment Plant (TWWTP) compared to upstream samples from Walnut Creek, 3) to compare EROD activity in populations maintained in laboratory and field settings, and 4) to quantify cytochrome P450 gene expression. Enzyme activity was measured fluorometrically and CYP1 gene expression was analyzed by quantitative real-time reverse transcription polymerase chain reaction. A mean EROD baseline was established at 0.03 nmol/min/µg of protein. The overall mean field effluent (TF) EROD had a significant 5-fold increase over field upstream (UF) exposed catfish; and overall mean laboratory effluent (TL) exposed catfish EROD had a significant 1.8-fold increase over laboratory upstream (UL) exposed catfish. Field exposures generally showed more robust enzyme induction over laboratory exposures on all sampling days. Ex- pression of the CYP1B gene following TF exposure was 6-fold over UF. Results suggested that in situ exposure to wastewater pollutants using caged test organisms provided a much more sensitive local monitor of pollutant exposure and biological impact than ex situ toxicological studies.
Highlights
Measurements of molecular biomarkers are useful for determining the impact of water-borne contaminants on living organisms in the aquatic environment
This study suggested that establishing a baseline EROD level in catfish, as well as doing a controlled comparison of laboratory versus field exposures were necessary for adequate interpretation of future studies involving impact of Troy (Alabama) Wastewater Treatment Plant (TWWTP) effluent on channel catfish [12]
Forty-liter polypropylene tanks were used for ex situ exposures (Troy University Laboratory), with three replicates used for each exposure condition – Walnut Creek upstream (UL), TWWTP effluent mixing zone (TL), and dechlorinated tap water (TP) – for a total of nine tanks
Summary
Measurements of molecular biomarkers are useful for determining the impact of water-borne contaminants on living organisms in the aquatic environment. The problem with mixtures may be addressed through use of bioassessments, these studies primarily examine a single end point, such as reproduction, lethality (as LC50), and behavioral changes; and while these are clearly defined and frequently used, they may be inadequate in terms of sensitivity, duration, and accuracy [3]. Because of their focus on the toxicity of pollutants [4], bioassessments may miss subtle metabolic changes that can be picked up by molecular biomarkers. One important and useful molecular biomarker is induction of cytochrome P450 (CYP1) enzyme, measured as ethoxyresorufin-O-deethylase (EROD) activity, which is involved in metabolism of a variety of drugs and xenobiotics, such as polycyclic chlorinated biphenyls (PCBs) [5] and polycyclic aromatic hydrocarbons (PAHs)
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