Soot deposition in the Great Lakes: implications for semi-volatile hydrophobic organic pollutant deposition.

Air deposition is a dominant transport mechanism for many hydrophobic organic pollutants (HOCs) to the Great Lakes. Our previous research has shown that soot exhibits large surface areas with high organic carbon contents suggesting the potential for strong HOC partitioning. As yet, however, clear data showing the link between HOCs such as PAHs to the deposition of soot into the Lakes (a proposed transport mechanism) is primarily inferential. We measured soot carbon (SC) and organic carbon (OC) in sediments collected from each of the Laurentian Great Lakes. OC and SC levels collected from locations near urban areas were higher than in sediments collected from distant locations. By far, Lake Superior had the lowest current SC flux of any lake, and Lakes Michigan and Erie had the highest. SC flux for all lakes had the following order: Superior < Huron < Ontario < Michigan < Erie, ranging 0.02-0.89 mg (m2 yr)(-1). Differences in lake size resulted in a different order for total SC loading by lake: Superior < Ontario < Huron < Erie < Michigan, ranging 2.3-420 x 10(3) tyr(-1). SC and PAH accumulation rates reported previously for Lake Michigan sediment were highly correlated; with a SC to PAH mass ratio of 10(4) (0.01%). The importance of soot as a potential sorbent for various classes of airborne HOCs was examined using a simple octanol-air partitioning model together with our previous characterization of soot particles. The results predict that both PAHs and PBDEs should have strong partitioning to soot and suggest the need to further investigate soot as a vector for PBDE transport.