Atmospheric Loading of Polycyclic Aromatic Hydrocarbons to Lake Michigan as Recorded in the Sediments

Abstract

Five sediment cores from a north−south transect of Lake Michigan were collected using box cores deployed from the RV Lake Guardian and from a submersible (Johnson Sea Link II, RV Seward Johnson). The sediments, analyzed for PAHs (n = 28) and 210Pb to obtain accumulation rates and inventories of PAHs, were used to determine the role of the atmosphere in contaminant loading to Lake Michigan. The accumulation of PAHs in the sediments increased dramatically around 1900, reached a plateau around 1930−1975, and decreased slightly in recent time. Surface sediment accumulation rates and inventories for ∑PAHs (n = 17 parent), corrected for sediment focusing with 210Pb, equaled 50−70 ng cm-2 yr-1 and 5000−7000 ng cm-2, respectively. The relative abundances of individual PAH compounds from Lake Michigan sediments, PM-10 aerosol of Chicago, and a coke oven signature are statistically similar establishing a linkage between combustion sources in the south, atmospheric deposition, and sediment accumulation. Further support for this linkage is the historical PAH accumulation in lake sediments and historical coal use in Illinois over the same time period. The major source of PAHs to Lake Michigan sediments is coke and steel production found in the urban/industrial complex around Chicago, IL, and Gary, IN. These PAHs are deposited primarily in the southern basin after which they are redistributed throughout the lake as a result of in-lake integration processes (water and sediment transport).