CONTAMINANTS IN FISHES FROM GREAT LAKES-INFLUENCED SECTIONS AND ABOVEDAMS OF 3 MICHIGAN RIVERS .2. IMPLICATIONS FOR HEALTH OF MINK

Populations of mink (Mustela vison) have declined in many areas of the world. Such declines have been linked to exposures to synthetic, halo genated hydrocarbons. In the Great Lakes region, mink are fewer in are as along the shore of the Great Lakes and their tributaries where mink have access to fish from the Great Lakes. Recently, there has been di scussion of the relative merits of passage of fishes around hydroelect ric dams on rivers in Michigan. A hazard assessment was conducted to d etermine the potential for adverse effects on mink, which could consum e such fishes from above or below dams on the rivers. Concentrations o f organochlorine insecticides, poly-chlorinated biphenyls (PCBs), 2,3, 7,8-tetrachlordibenzo-p-dioxin equivalents (TCDD-EQ), and total mercur y were measured in composite samples of fishes from above or below hyd roelectric dams on the Manistee and Muskegon Rivers, which flow into L ake Michigan, and the Au Sable River, which flows into Lake Huron. Con centrations of organochlorine insecticides, PCBs, and TCDD-EQ were all greater in fishes from below the dams than those from above. Concentr ations of neither organochlorine insecticides nor mercury in fishes ar e currently a risk to mink above or below the dams. All of the species of fishes collected from downstream of the dams contained concentrati ons of PCBs and TCDD-EQ, which represent a hazard to mink. The hazard index for PCBs was less than one for the average of all species from t he upstream reaches of the Manistee and Au Sable Rivers, but not the M uskegon. The hazard index (concentration in fish/NOAEC) was greater th an 1 for all of the species collected from below the dams, in all thre e rivers. The greatest hazard index was observed for carp (Cyprinus ca rpio) downstream on the Muskegon River. Because the concentrations of PCBs used in the hazard assessment were corrected for relative toxic p otencies, the hazard ratios based on PCBs should be similar to those b ased on TCDD-EQ. This was found to be true. Thus, either total PCBs or TCDD-EQ could be used as the critical toxicant in the hazard assessme nt. However, if uncorrected concentrations of PCBs, expressed as Arocl ors(R), were used in the hazard assessment, the toxicity of the weathe red mixture would have been underestimated by approximately five-fold, and, in that instance, TCDD-EQ would be the critical contaminant for the hazard assessment. The average maximum allowable percentage of fis h from above the dams, which would result in no observable adverse eff ects of TCDD-EQ, was 70%. Based on the average TCDD-EQ concentrations in the fishes, an average of 8.6% of the diet could be made up of fish es from below dams on the rivers. The most restrictive daily allowable intakes were for carp on the Muskegon and steelhead trout (Onchorhync us mykiss) on the Manistee Rivers. Only 2.7% of the diet could be made up of these two species from below dams without exceeding the no-effe ct concentration. This would represent approximately 15 days of food i ntake. Currently, consumption of all species of fish from below the da ms would pose some risk to mink. The concentrations of PCBs and TCDD-E Q in fishes from below the dams were 10-20 times more hazardous, on av erage, than those from above the dams.