Polybrominated diphenyl ethers in the sediments of the Great Lakes. 4. Influencing factors, trends, and implications.

A total of 199 sediment samples were collected from 16 locations in the five Laurentian Great Lakes, and each was analyzed for 10 congeners of polybrominated diphenyl ethers (PBDEs) as well as selected polychlorinated biphenyls (PCBs). This paper presents a comprehensive analysis on previously published results for individual lakes. The total accumulation of nine tri- to hepta-PBDE congeners (sigma9BDEs) in the sediments of all the Great Lakes was estimated to be approximately 5.2+/-1.1 tonnes, and that of decabromodiphenyl ether (BDE209) was 92+/-13 tonnes, around year 2002. The inventories of sigma9BDEs and major individual PBDE congeners show strong dependence on the latitude of sampling sites, and such dependence is believed to reflect both the influence of urbanization, which shows south-to-north gradient in the region, and the general direction of long-range transport of airborne pollutants in the northern hemisphere. From the 1970s to 2002, the increases in PBDE input flux to the sediments are exponential at all locations, with doubling times (t2) ranging from 9 to 43 years for sigma9BDEs, and from 7 to >70 year for BDE209. The longer t2 values found in sediments compared with those in human and fish in the region suggest the slower response of sediment to emissions. The correlations between the concentrations of sigma9BDEs or BDE209 in surface sediments and latitude are strengthened by normalization of the concentrations with sediment contents of the organic matter or organic carbon, but not soot carbon. Multivariate linear regression equations were developed using data obtained with sediment segments deposited after 1950. All the regressions are statistically significant; and the three independent variables-year of deposition, latitude, and organic matter content of the sediments-account for 73% and 62% of the variations in the concentrations or the fluxes of S9BDEs and BDE209, respectively, in the Great Lakes sediments.