The Impact of Chicago on Lake Michigan: Results of the Lake Michigan Mass Balance Study

As part of the U.S. EPA’s Lake Michigan Mass Balance Study, a predictive model for gas-phase persistent organic compounds over Lake Michigan has been constructed. Using air temperature, wind direction and atmospheric PCB concentration collected around and over the lake, the model predicts the concentration of PCB congeners (~100) and trans-nonachlor over the lake and gas exchange fluxes. The model shows that gas-phase PCB and trans-nonachlor concentrations over Lake Michigan vary considerably as a function of temperature, wind direction, and distance from the urban-industrial region of southwest Lake Michigan. The combined effects of southerly winds and high temperatures cause a large 'plume' of gas-phase PCBs from Chicago. The Chicago urban air toxics plume can impact the whole lake when warm southerly winds are strong. In this paper, we examine the magnitude of the Chicago plume on gas deposition of these potentially toxic compounds to the lake. Findings-PCBs 1. The LMMB atmospheric modeling shows that Chicago is a source of gas-phase PCBs. The Chicago region contributes 2 to 20% of the total deposition of PCB to the lake, depending on the congener and time of year. For an annual year the total gas-phase depositon of ΣPCBs is ~3200 kg and the Chicago contribution is ~330 kg. 2. The Chicago source behaves like a non-point release by volatilization from contaminated sites open to the atmosphere and subject to the same temperature fluctuations as the air temperature. Recommendations – PCBs 1. Reduce the deposition of PCBs to Lake Michigan by: a. Covering land surfaces contaminated with PCBs b. Removing structures contaminated with PCBs c. Conduct remediation activities in cool weather Findings – trans-nonachlor 1. The Chicago source of trans-nonachlor is most important in the winter. During the summertime, the source of trans-nonchlor is more diffuse. 2. The trans-nonachlor signal is not consistent with current use of the pesticide or of seasonal application. 3. Sources of trans-nonachlor are associated with high temperatures and southern winds. This model cannot identify the range of transport. Recommendations – trans-nonachlor 1.Reduce the deposition of trans-nonachlor to Lake Michigan: a. Prevent new application of trans-nonachlor inside and outside the Great Lakes basin b. Conduct remediation activities in cool weather. Hornbuckle and Green, 10/23/00