Induction and clearance of cytochrome P4501A mRNA in Atlantic tomcod caged in bleached kraft mill effluent in the Miramichi River

Abstract

Levels of cytochrome P4501A mRNA were measured in Atlantic tomcod caged in the effluents of a bleached kraft pulp and paper mill on the Miramichi River, NB, Canada and two sites downstream, and compared to levels in fish caged upstream of the mill and in unexposed laboratory-maintained tomcod. Additionally, the rate of clearance of CYP1A mRNA in tomcod exposed at the mill and transferred to clean water was compared to that observed in tomcod treated in the laboratory with a single dose of 2,3,7,8-TCDD (0.5 μg/kg). Levels of CYP1A mRNA in tomcod caged upriver of the mill were low and comparable to those observed in untreated laboratory control fish. Levels of CYP1A mRNA were elevated up to 11-fold in tomcod caged at the mill site and a gradient in levels of gene expression was seen at the two downstream sites. Tomcod i.p. injected with a single dose of 2,3,7,8-TCDD exhibited a profile of prolonged CYP1A mRNA induction of at least 25 days. Levels of CYP1A mRNA in tomcod caged at the mill site and transferred to clean water remained significantly induced for at least 3 days post-transfer. In combination, these results suggest that CYP1A mRNA was induced in caged tomcod by constituents of the mill's effluents and that the rates of clearance of CYP1A mRNA may provide additional information concerning the identity of environmental inducers.