<p>Dechlorane Plus (DP) is a chlorinated flame retardant used in wire coatings, furniture and hard plastic connectors in computer monitors. It is manufactured in high volumes with production facilities located in the United States and China bringing into question whether the flame retardant existed in the environment. DP was detected in Lake Ontario sediments at concentrations 60-fold greater than in Lake Erie sediments; the maximum values were 586 ng g^-1 and 8.6 ng g^-1, respectively. These data suggest there is DP source into the Niagara River, which contributed to Lake Ontario’s DP burden. Analyses of Lake Ontario sediment core slices showed that recent concentrations were two orders of magnitude less than the core’s maximum concentration of 920 ng g^-1 (1976-1980). New chemicals related to DP were also found in this core which DP’s profile, suggesting these compounds maybe impurities or side products in the manufacture of DP. The concentrations of one of the mono Diels-Alder adducts, 1,3-DPMA, was found in Lake Ontario lake trout to be two orders of magnitude greater than that of DP, suggesting the monoadduct is more bioaccumulative than DP. Analysis of a Lake Ontario food web illustrated that 1,3-DPMA was being diluted up the food chain, much like DP, while a second monoadduct, 1,5-DPMA was only detected in lower trophic species. <em>In vitro</em> lake trout liver microsomal exposures to the individual DPMA isomers showed that the depletion rate constant for 1,3- and 1,5-DPMA were 0.34 and 0.84 h^-1, respectively, with corresponding t_1/2’s of 2.02 ± 0.50 and 0.83 ± 0.18 h, respectively. The shorter 1,5-DPMA half-life was ascribed to the unsterically hindered double bond which allowed for greater enzyme attack.</p> <p>Dechlorination of DP was observed during the analysis of sediment extracts and was attributed as being an artefact of dirty injector liners; care needs to be taken to insure this dechlorination does not occur during analysis of environmental samples. This was important as dechlorinated DP products were observed in Lake Ontario sediment and core extracts.</p> <p>DP was shown to be a worldwide airborne contaminant from analysis of passive samplers over a period of one year. The maximum concentration was detected in Delhi, India (226 pg m^-3). Middle Eastern and Indo-Asian regions exhibited the greatest concentrations in the world providing likely the result of other DP manufactures and/or that the practice of open pit burning of wires and cables was adding to the regions air burden.</p> / Doctor of Philosophy (PhD)