Spatial Distribution and Time Trend of Organic Pollutant Chemicals in the Sediments of Upper Great Lakes

The objective of this work is to reveal the spatial distribution and temporal trend of selected persistent bioaccumulative and toxic chemicals (PBTs) through analyzing surface grab and core sediment samples collected from Lakes Superior, Michigan, and Huron during 2010 to 2012. A laboratory procedure has been developed, including accelerated solvent extraction, silica gel / alumina chromatographic cleanup, and instrumental analyses using gas chromatography–mass spectrometry. Concentrations of nine groups of 162 individual compounds were measured. The results are reported in this thesis for three chemical groups with emerging concern, including halogenated flame retardants (XFRs), polyhalogenated carbazoles (PHCs), as well as atrazine and related compounds. In the Ponar grabs, brominated XFRs dominate eastern Lake Michigan while chlorinated XFRs were higher in southern Lake Huron and the North Channel; PHCs had significantly higher levels in central Lake Michigan, northeastern Lake Superior, and some sites in Georgian Bay of Lake Huron; and atrazine and related compounds are mostly found in Lakes Michigan and Huron. Based on the core data, the temporal profile of chemical flux to sediment showed that most XFRs increased significantly after the 1920s and decreased or levelled off after the 2000s; Dechlorane 604, Decabromodiphenylethane (DBDPE), dibromocarbazoles, tribromocarbazoles, atrazine, simazine, and atrazine degradation products are still increasing at the time of sampling; 1,3,6,8-tetrabromocarbazole and mixed halogenated carbazoles were decreasing since 1900s; carbazole, 1,3,6,8-tetrachlorocarbazole and alachlor have peaked at certain time points after the 1940s. Log surface flux and inventory are significantly correlated with latitude of the sampling sites for most compounds at 95% confidence level except some PHCs, implying the occurrence of long-range transport. Brominated biphenyl 153, syn-Dechlorane plus, and atrazine may degrade to other compounds in deep sediments. The XFRs, atrazine, and related compounds may originate from both local source and air deposition. The sources of PHCs are unclear; both natural origin and anthropogenic sources are possible, and may differ among individual PHCs. This work provides a large amount of monitoring data that is useful to the US EPA and other government agencies as well as environmental organizations for risk assessment, decision making, and pollution control.