Polychlorinated biphenyl congeners in emergent mayflies from the upper Mississippi river

We determined polychlorinated biphenyls (PCBs) in emergent mayflies (Hexagenia bilineata) from a 1250-km reach of the upper Mississippi River (UMR). Total PCB concentrations (sum of 125 congeners) ranged from 0.21 to 4.1 μg/g of dry weight (1.2-29 μg/g of lipid weight). Concentrations were highest in pools near the Twin Cities and the Quad Cities metropolitan areas. Longitudinal movement of PCBs was extensive downstream from the Twin Cities (175-320 K) but was not apparent downstream from the Quad Cities. The PCB composition of mayflies was relatively homogeneous throughout most of the river. However, the congener composition in mayflies from two distant locations differed markedly from the other samples and contained a greater abundance of lower molecular weight congeners