POLYCHLORINATED DIBENZO-P-DIOXINS, DIBENZOFURANS, BIPHENYLS AND 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN EQUIVALENTS IN FISHES FROM SAGINAW BAY,MICHIGAN

Concentrations of polychlorinated biphenyls (PCBs), polychlorinated di benzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polych lorinated naphthalenes (PCNs), polychlorinated dibenzothiophenes (PCDT s), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) equivalents were measured in composite samples of forage fishes and several sizes of walleyes (Stizostedion vitreum) and common carp (Cyprinus carpio) collected from Saginaw Bay, Michigan, USA. The concentrations of 2,3,7 ,8-TCDD equivalents determined from the use of TCDD equivalency factor s (TEFs) and instrumentally determined concentrations of individual co ngeners were designated TEq. The 2,3,7,8-TCDD equivalents determined o n the same extracts with the H4IIE bioassay were defined as TCDD-EQ. C oncentrations of TCDD-EQ and TEq were significantly, but poorly correl ated (R-2 = 0.44). Concentrations of TCDD-EQ and TEq ranged from 10.6 to 348 and 13.5 to 69.5 ng/kg, wet weight, respectively. The ratio of TCDD-EQ to TEq ranged from 0.5 to 5.0, with the greatest ratio observe d in common carp but the average ratio between TEq and TCDD-EQ was app roximately 1.0. In common carp, larger walleye, and medium-sized alewi fe (Alosa pseudoharengus) there were significant concentrations of TCD D-EQ that could not be accounted for by TEq calculated from an additiv e model of PCBs, PCDDs, or PCDFs. As much as 75% of the TCDD-EQ in som e samples could not be accounted for by TEqs. It is unlikely that PCNs , PCDTs, or polychlorinated diphenyl ethers (PCDEs) occurred at concen trations that were, based on their relative potencies, great enough to contribute significant quantities of TCDD-EQ. The discrepency between TCDD-EQs and TEqs was not due to antagonisms among congeners or extra ction efficiencies.