MFO ACTIVITY IN CARP (CYPRINUS-CARPIO) EXPOSED TO TREATED PULP AND PAPER-MILL EFFLUENT IN LAKE COLEMAN, VICTORIA, AUSTRALIA, IN RELATION TOAOX, EOX, AND MUSCLE PCDD PCDF

European carp (Cyprinus carpio) ''posed to highly treated pulp mill ef fluent in Lake Coleman, a shallow-water lake in southern Victoria, Aus tralia, had significantly elevated hepatic microsomal EROD levels rela tive to reference fish from a nearby unexposed water body (Dowds and H eart morasses). Mean hepatic microsomal EROD activity appeared to be c orrelated with site adsorbable organic halogen (AOX) levels, with a si mple linear regression yielding the equation Y = 0.059X + 1.415 (r2 = 0.93, n = 5), where Y is mean EROD activity in nanomoles per minute pe r milligram and X is mean AOX concentration in micrograms per liter. M ean liver EROD activity was poorly related with fish muscle-tissue ext ractable organic halogen (EOX) and sediment EOX concentrations. Hepati c microsomal EROD activity also appeared to be correlated with the low levels of PCDD/PCDFs measured in carp muscle (1.0-4.0 ppt TCDD intern ational toxic equivalents (TEs) in effluent-exposed fish muscle compar ed to 0.48-0.64 ppt TEs in reference fish muscle). Simple linear regre ssion of mean EROD activity in carp liver with the mean fish muscle di oxin content yielded the equation Y = 6.514X + 5.754 (n = 4, r2 = 0.88 ), where Y is mean EROD activity in nanomoles per minute per milligram and X is mean dioxin concentration in ppt of TCDD TEs. Hepatic micros omal ECOD activity, however, was not significantly different at any ex posure site from the reference sites. Overall, Lake Coleman contained between 4.5 and 9.3 times the water AOX levels, 0.8 and 13.7 times the sediment EOX levels, 1.5 and 2.2 times the carp muscle-fat EOX levels , 5.0 and 5.3 times the carp whole-muscle TCDD toxic equivalents, and 6.5 times the carp fat TCDD toxic equivalents, compared to the Dowds a nd Heart morass reference samples. Within Lake Coleman, mean liver mic rosomal EROD activity levels were 2.3 to 6.3 times higher than the Dow ds and Heart reference sites, respectively. Tissue concentrations of P CDD/PCDF and water AOX levels reduced with increasing distance from th e ef fluent point source. Carp liver microsomal EROD represented a goo d biomarker of exposure to low levels of organochlorine contaminants f rom well-treated pulp mill effluent.