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Updated polychlorinated biphenyl mass budget for Lake Michigan
Citation:
Guo, J., K. Romanak, S. Westenbroek, A. Li, R. Kreis, R. Hites, AND M. Venier. Updated polychlorinated biphenyl mass budget for Lake Michigan. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 51(21):12455-12465, (2017).
Impact/Purpose:
In the mid-1990s, EPA scientists conducted research and published results describing a mass balance model quantifying the sources and fate of PCBs in Lake Michigan. Mass balance models were used to describe the relationship between the levels of PCBs found in Lake Michigan at the time and identify the addition and removal of those PCBs through various environmental inputs and outputs such as streams, atmospheric deposition/volitization or uptake by fish or other organisms. The approach was used to prioritize and target areas for clean-up of sources of contamination into the system and subsequently track the effectiveness of management decisions. This current publication uses the same mass balance model used in the mid-1990s, but with updated environmental data from 2015 to describe current potential sources of PCBs and their movement within Lake Michigan. The results discuss how total PCBs and their individual congeners have been decreasing since the 1970s and updates the understanding of the flow of PCBs into and out of Lake Michigan and its major tributaries.
Description:
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.
