![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Lake Michigan Mass Balance Study - PCBs
LMMB Study
Overview- The Issue: Are sediments, air, land, and water sources or pathways of contamination that affect the integrity of the ecosystem?
- What is the Lake Michigan Mass Balance Study?
- Sample Design and Sample Collection
Lake Michigan Polychlorinated Biphenyls (PCBs)
The Lake Michigan Mass Balance Study PCB Modeling Report is available in PDF format.
PCB concentrations in fish over the past 30 years show a downward trend from peak levels in the 1970s (Figure 4). The most recent data also exhibit a decline, however, this indicates that the rate of decline is slowing and concentrations in lake trout remain above desired levels. Similar trends are occurring for other species. Declining concentrations are also observed for other media (Figure 5). The LMMB Study was undertaken, in part, to investigate this problem in detail and to develop mathematical models that could be used to project future concentrations in water, sediment, and biota, with and without future remedial and/or regulatory efforts.
Figure 6 shows a summary of PCB loads from tributaries in 1994-1995. Total tributary loads of PCBs are approximately 400 kg/yr for the study period. The largest loads are from the Fox River, followed by the Grand Calumet and Kalamazoo Rivers.
LMMB Major Findings: PCBs
- Forecast PCB concentrations in lake trout may permit unlimited consumption as early as 2039 at Sturgeon Bay and 2044 at Saugatuck
- PCB trends indicate that concentrations are declining in all media
- Atmospheric deposition is the major source of PCBs to the lake
- Chicago urban area is a substantial atmospheric source of PCBs to Lake Michigan
- There is a dynamic interaction among water, sediments, and the atmosphere where large masses of PCBs cycle into and out of the lake via the atmosphere as vapor phase
Figure 4. Total PCB concentrations in Lake Michigan Lake Trout (more information about this image).
Figure 5. Trends of Total PCBs in Various Lake Michigan Media (more information about this image).
Figure 6. Average PCB loads (kg/year) to Lake Michigan from major monitored and unmonitored tributaries, 1994-1995 (more information about this image).