Bioassessment of mercury, cadmium, polychlorinated biphenyls, and pesticides in the upper Mississippi river with zebra mussels (Dreissena polymorpha)

Zebra mussels (Dreissena polymorpha) were sampled from artificial substrate s deployed from May 30 to October 19, 1995, at 19 locks and dams from Minne apolis, MN, to Muscatine, IA. Analyses of composite tissue samples of zebra mussels (10-20-mm length) revealed accumulation of mercury(Hg), cadmium (C d), and polychlorinated biphenyls (PCBs) during a 143-d exposure period. Co ncentrations of total Hg ranged from 2.6 to 6.1 ng/g wet weight and methylm ercury (CH3Hg) from 1.0 to 3.3 ng/g wet weight. About 50% (range 30-70%) of the mean total Hg in zebra mussels was CH3Hg. Cadmium ranged from 76 to 21 3 ng/g wet weight. Concentrations of total PCBs (Aroclor 1254) in zebra mus sels varied longitudinally (range 1000-7330 ng/g lipid weight), but the com position of PCB congeners (total of 21 measured) was similar throughout the river. Chlordane and dieldrin were the only two pesticides detected of the 15 analyzed. Zebra mussels are sentinels of contaminant bioavailability in the Upper Mississippi River and may be an important link in the trophic tr ansfer of contaminants in the river because of their increasing importance in the diets of certain fish and waterfowl.