This study revisits and updates the Lake Michigan Mass Balance Project (LMMBP) for polychlorinated biphenyls (PCBs) that was conducted in 1994-1995. This work uses recent concentrations of PCBs in tributary and open lake water, air, and sediment to calculate an updated mass budget. Five of the 11 LMMBP tributaries were revisited in 2015. In these five tributaries, the geometric mean concentrations of -PCBs (sum of 85 congeners) ranged from 1.52 to 22.4 ng L-1. The highest concentrations of PCBs were generally found in the Lower Fox River and in the Indiana Harbor and Ship Canal. The input flows of -PCBs from wet deposition, dry deposition, tributary loading, and air to water exchange, and the output flows due to sediment burial, volatilization from water to air, and transport to Lake Huron and through the Chicago Diversion were calculated, as well as flows related to the internal processes of settling, resuspension, and sediment-water diffusion. The net transfer of -PCBs is 1240 ± 531 kg yr-1 out of the lake. This net transfer is 46% lower than that estimated in 1994-1995. PCB concentrations in most matrices in the lake are decreasing, which drove the decline of all the individual input and output flows. Atmospheric deposition has become negligible, while volatilization from the water surface is still a major route of loss, releasing PCBs from the lake into the air. Large masses of PCBs remain in the water column and surface sediments and are likely to contribute to the future efflux of PCBs from the lake to the air.
Bibliographical noteFunding Information:
Funding for this project was provided by the U.S. Environmental Protection Agency’s Great Lakes National Program Office as part of the Great Lakes Restoration Initiative (EPA Cooperative Agreements GL-00E01422 and GL-00E00538, and USGS Cooperative Agreement G15AC00043). We thank U.S. Geological Survey hydrologic technicians Brian Heissenberger, Nathan Prokopec, and David Housner for collecting and processing the water samples. We also thank the IADN team at Indiana University Bloomington, the crew of R/V Lake Guardian, and the sediment sampling team at the University of Illinois at Chicago. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
© 2017 American Chemical Society.