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Anita Thapalia 1 , David M. Borrok 1 , Peter Van Metre 2 , and MaryLynn Musgrove 2

APPLICATION OF ZN ISOTOPES TO RESOLVE METAL SOURCES IN A SEDIMENT CORE FROM AN URBAN LAKE IN SEATTLE, WASHINGTON. 1 Department of Geological Sciences, University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968 2 U.S. Geological Survey, 8027 Exchange Drive, Austin, TX 78754.

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Anita Thapalia 1 , David M. Borrok 1 , Peter Van Metre 2 , and MaryLynn Musgrove 2

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  1. APPLICATION OF ZN ISOTOPES TO RESOLVE METAL SOURCES IN A SEDIMENT CORE FROM AN URBAN LAKE IN SEATTLE, WASHINGTON • 1 Department of Geological Sciences, University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968 • 2 U.S. Geological Survey, 8027 Exchange Drive, Austin, TX 78754 Anita Thapalia1, David M. Borrok1, Peter Van Metre2, and MaryLynn Musgrove2

  2. Presentation Outline • Location of Lake Ballinger and history of metal inputs • Results of bulk chemical analysis including selective sequential dissolution • Isotopic results • Discussion • Conclusions Sediment Cores

  3. Location of Lake Ballinger WA Tacoma Smelter Highway 99 Interstate 5 Hall Creek Image From Google Earth

  4. Tacoma smelter – Pb and Cu smelting and a major domestic supplier of As. Urbanization, including tire wear, highway runoff, industrial inputs, storm water, etc. Possible Metal Inputs Tacoma Smelter (closed 1985) Mahler et al. (2006) Trends in metals in urban and reference lake sediments across the United States, 1970 to 2001. Environ. Tox. Chem. 25, 1698-1709.

  5. Chemical Analysis • Metal contents of total digested sediment every 2 to 4 cm. • Focused on exchangeable, organic, and iron oxide fractions • (did not do other fractions). • Age dating using Cs137 and Pb210 (USGS). • Isotopic analysis of Zn and Cu isotopes using MC-ICP-MS. Nu Plasma MC-ICP-MS USGS, Denver, CO

  6. Metal Concentrations vs. Depth

  7. Correlation of Ages to Mass Accumulation Rates (MAR) Sediment core 0 cm 25 cm 50 cm

  8. Zn Isotopic Data Zn Isotopes 66Zn = 1000 JMC 3-0749L

  9. Cu Isotopic Data Cu Isotopes 65Cu=  1000 SRM 976

  10. Discussion Smelter closure • Total variation of Zn isotopes 0.5 ‰ and Cu isotopes ~0.4 ‰ • Isotopic signatures of Zn and Cu show three distinct signatures, probably attributable to 1) background, 2) smelting, 3) urban runoff • “Light” Zn isotopes found in stream sediments of Hall Creek (0.01 ± 0.03 2σ) • Possible sources? Zn isotopes in for six different tires ranges from -0.1 to 0.14 ‰ Stream sediments Smelter start Tires

  11. Conclusions • Lake Ballinger has been heavily impacted by metal contaminants, with the heaviest input around 1960. • Zn and Cu isotopes can help to distinguish metal sources. • Appears that there are 3 main historic contributions to metals, 1) a pre 1900 zone - characterized by pre-urbanization background; 2) 1950 to 1985 - characterized by a large smelter input and rapid urbanization; 3) 1990 to present - post smelter, with Zn input from urban runoff - possibly tires.

  12. Acknowledgments • Thanks to my co-authors David M. Borrok, Peter Van Metre, and MaryLynn Musgrove. • Thanks to Ian Ridley, Rich Wanty, and Mike Pribil from the USGS for analytical assistance and support. Contact Information athapalia@miners.utep.edu http:// www.geo.utep.edu/pub/thapalia

  13. Movie clip from Silverton

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