INDUCTION AND CLEARANCE OF CYTOCHROME P4501A MESSENGER-RNA IN ATLANTIC TOMCOD CAGED IN BLEACHED KRAFT MILL EFFLUENT IN THE MIRAMICHI RIVER

Levels of cytochrome P4501A mRNA were measured in Atlantic tomcod cage d in the effluents of a bleached kraft pulp and paper mill on the Mira michi River, NB, Canada and two sites downstream, and compared to leve ls in fish caged upstream of the mill and in unexposed laboratory-main tained tomcod. Additionally, the rate of clearance of CYP1A mRNA in to mcod exposed at the mill and transferred to clean water was compared t o that observed in tomcod treated in the laboratory with a single dose of 2, 3, 7, 8-TCDD (0.5 mu g/kg). Levels of CYP1A mRNA in tomcod cage d upriver of the mill were low and comparable to those observed in unt reated 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 o f gene expression was seen at the two downstream sites. Tomcod i.p. in jected with a single dose of 2, 3, 7, 8-TCDD exhibited a profile of pr olonged CYP1A mRNA induction of at least 25 days. Levels of CYP1A mRNA in tomcod caged at the mill site and transferred to clean water remai ned significantly induced for at least 3 days post-transfer. In combin ation, these results suggest that CYP1A mRNA was induced in caged tomc od by constituents of the mill's effluents and that the rates of clear ance of CYP1A mRNA may provide additional information concerning the i dentity of environmental inducers.