Figure 2. Passive-sampler deployment and fish-sampling sites, mean polychlorinated biphenyl (PCB) concentrations, and change in congener patterns along the Millers and Otter Rivers, Massachusetts. PCB concentrations increased and congener patterns changed in the downstream direction beginning at river mile O-35.2. In this study, a river mile refers to the distance from the confluence of the Millers River with the Connecticut River to the sampling station, as measured along the river channel. The sampling station is named with the first letter of the river on which the station is located and the river mile. For example, the sampling station on the Otter River that is 36.2 miles from the confluence of the Millers River with the Connecticut River is named O-36.2.