Exposure of northern leopard frogs in the Green Bay ecosystem to polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans is measured by direct chemistry but not hepatic ethoxyresorufin-O-deethylase activity

We measured concentrations of polychlorinated biphenyls (PCBs), polychlorin ated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) i n northern leopard frogs collected from the Green Bay ecosystem and explore d the catalytic activity of hepatic cytochrome P450-associated monooxygenas e (P450 enzyme) as a biomarker for exposure to aryl hydrocarbon receptor (A hR) agonists. The two hypotheses tested were PCH concentrations in northern leopard frogs would be positively correlated with sediment polychlorinated hydrocarbon (PCH) levels in wetland habitats along a contamination gradien t and hepatic ethoxy-resorufin-O-deethylase (EROD) activity of northern leo pard frogs, which is presumably mediated by aryl hydrocarbon receptor (AhR) , would be positively correlated with PCH concentrations in frog carcasses (whole body minus liver) from different collection sites. In 1994 to 1995, frogs from seven sites along the lower Fox River and Green Bay, USA, were a ssayed for hepatic EROD activities and whole carcass concentrations of PCBs , PCDDs, and PCDFs. Tissue total PCB concentrations ranging from 3 to 154 n g/g were significantly correlated with sediment PCB levels. Only one PCDD a nd two PCDFs at concentrations of 6 to 8 pg/g were found in the frogs colle cted from one of the sites. The EROD activity in frogs ranging from 186 to 270 pmol/min/mg protein was not significantly correlated with frog body wei ght and was similar among sites except for Peter's Marsh. No significant co rrelation was found between EROD activity and carcass PCB concentration. Th is result was consistent with the fact that the frogs collected from the Gr een Bay ecosystem had relatively low PCB concentrations compared with what was required for induction in the laboratory (ED50 for EROD is between 700 and 2,300 ng/g).