HR: 0800h
AN: V51A-0518    [Abstracts]
TI: Hg Isotope Ratios of a Sediment Core from Plastic Lake, Ontario: Implications for Hg Cycle in Aquatic Environment
AU: * Xie, Q
EM: qianlixie@trentu.ca
AF: Water Quality Centre/ERS Program Trent University , 1600 West Bank Dr., Peterborough, ON K9J 7B8 Canada
AU: Dillon, P
EM: pdillon@trentu.ca
AF: Water Quality Centre/ERS Program Trent University , 1600 West Bank Dr., Peterborough, ON K9J 7B8 Canada
AU: Evans, D
EM: devans@trentu.ca
AF: Water Quality Centre/ERS Program Trent University , 1600 West Bank Dr., Peterborough, ON K9J 7B8 Canada
AU: Lu, S
EM: sylu@trentu.ca
AF: Water Quality Centre/ERS Program Trent University , 1600 West Bank Dr., Peterborough, ON K9J 7B8 Canada
AU: Lu, S
EM: sylu@trentu.ca
AF: Activation Laboratories Ltd., 1336 Sandhill Dr., Ancaster, ON L9G 4V5 Canada
AB: Hg isotope ratios in a sediment core obtained in Plastic Lake, Ontario, Canada, have been measured by coupling a gold trap with an MC-ICP-MS. The core is about 30 cm in depth and corresponds to a time period of about 250 years, based on 210Pb dating. The samples were combusted at high temperature and the Hg collected onto a gold trap. The gold trap was subsequently heated to release Hg directly into the MC-ICP-MS. An in-house sample introduction system was employed to extend Hg signal duration in order to obtain high precision in isotope ratio measurement. The instrumental mass bias was corrected using Tl introduced simultaneously via an Aridus membrane desolvation nebulizer. Based on long term measurement of a NIST-2225 elemental Hg standard (over 120 measurements since Oct. 2002), the external reproducibility ranges from 45 ppm for 201Hg/202Hg to 100 ppm for 199Hg/202Hg (2 sigma relative standard error). Hg in the sediments shows an increase in light isotope enrichment at about 10 cm depth. The total Hg also displays an increase at the same depth. The depth corresponds to approximately the 1920s, a time period when there was a major increase in coal-burning power generation. Limited Hg isotope data for other terrestrial samples appears to indicate that Hg bound to organic carbon is enriched in light isotopes relative to elemental Hg. For example, the DOLT-3, a dogfish liver standard reference material with half of its Hg as MeHg, has the lightest Hg isotope composition among measured terrestrial samples. It is not clear at this stage whether the increase in total Hg and light Hg isotope enrichment in recent years represent a change in methylation rate of the lake, or an increase in atmospheric deposition of Hg combined with a change in source. Discussions based on available Hg isotope data of terrestrial samples together with other chemical data for the lake will be presented.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1094 Instruments and techniques
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting