Geochemistry and Organic Contaminants in the Sediments of Great Slave Lake, Northwest Territories, Canada
A study was carried out in the summer of 1987 to determine the geochemistry and distribution of trace elements, PCBs and 16 other chlorinated hydrocarbons in sediments from selected areas in Great Slave Lake, Northwest Territories, Canada. Sediment cores were collected at three sampling stations in the west basin of the lake on a transect from the Slave River delta to the outlet of the Mackenzie River. The geotechnical composition of the sediments showed the deposition of similar material at all sampling stations. Sediment dating indicated a very high sedimentation rate (46.6 g/cm²/year) at a 110 m water depth in the vicinity of the Slave River delta and mixing of bottom sediments at the southwestern part of the lake. The concentrations of trace elements (Cu, Ni, Co, Cr, V, Pb and Zn) were uniform in all sediment profiles. However, surficial sediments were enriched by arsenic, Canadian standard CLB-1 containing 51 PCB congeners was used in the determination of PCBs in the sediment. Thirty-three PCB congeners were detected and their concentrations determined in selected sections of sediment cores. The most abundant congeners were 15 and 18, 44, 49, 52 and 101 (IUPAC numbering) with maximum concentrations 3.52, 2.68, 2.44, 6.20 and 2.44, 6.20 and 2.13 ng/g respectively. The concentration pattern of PCBs in Great Slave Lake sediments indicated considerably greater quantities of lower than higher chlorinated biphenyls. Several congeners, particularly those having 7-10 chlorine atoms, were determined in concentrations smaller than 0.20 ng/g only at one sediment depth. Hexachlorobutadiene, 1, 2, 3, 4-tetrachlorobenzene, pentachlorobenzene, alpha-HCH, hexachlorobenzene, pentachloroanisol and alpha-chlordane were present at all stations at different sediment depths. Maximum concentrations of the 16 chlorinated hydrocarbons analyzed in Great Slave Lake sediments were between 0.08 and 1.04 ng/g. The concentrations of PCBs and other chlorinated hydrocarbons were about two orders of magnitude lower than those in Lake Ontario sediments.
Key words: Great Slave Lake, sediments, geochemistry, PCBs, chlorinated hydrocarbons