Investigating Heavy Metal Contamination of the Puget Sound Environment with New Isotopic Tracers
Rachel Weber, Senior, Earth and Space Sciences, Mary Gates Scholar Mentor: Bruce Nelson, Earth and Space Sciences
Tacoma Smelter Background Analytical Methods
The Tacoma Smelter operated for approximately 100 ¾ Ion Exchange Chromatography years at the southern end of Puget Sound and is a known source of heavy metal contamination to the The core sediments were initially leached to separate local environment. the contaminants (leaches) from the natural sediments (residues), so that we can analyze both. Previous studies confirm significant local Lead, copper, and zinc were separated from the contamination based on a dramatic increase of metal leaches and the residues by ion exchange concentrations in sediments deposited in the Puget chromatography. Sound following commissioning of the smelter, shown to the right in Figure 1. Lead was separated first by loading both the leaches and the dissolved residues onto a 100 μL teflon column, These metals, such as lead, copper, and zinc, are toxic containing a strongly basic anion exchange resin, and to the environment and pose a potential regional eluting the lead with hydrochloric acid. health hazard. Copper and zinc were separated next by loading the Quartermaster Harbor The extent of regional contamination, mechanisms of samples onto 1.6 mL of a strongly basic anion dispersal, and chemical form of metal contamination in Tacoma Smelter Stack exchange resin in a 4 cm long glass column. Copper the environment are not well known. and zinc were eluted separately in hydrochloric acid.
¾ MC-ICP-MS
Washington State Department of Ecology, 2004 Lead isotopes were analyzed by multi-collector inductively-coupled-plasma mass-spectrometry. Figure 1. Lead concentrations in the southern Puget Sound region indicate significant contamination surrounding the Tacoma Smelter. However, isotope ratios are more robust than metal concentrations for tracing contaminants Image 1. Tacoma Smelter Stack, 1986. because, once in the environment, isotope ratios are not altered by chemical reaction and transport.
Goals 206Pb/204Pb vs. Depth in Quartermaster Harbor Sediment Core The main goal of our study is to analyze lead, copper, and zinc isotope ratios in contaminated sediments in 0 order to calibrate isotopic tracers of heavy metals 10 Tacoma emitted by the Tacoma Smelter. Smelter 20 Pb 30 Preliminary data from lead isotope analyses of a Leaches Residues sediment core from Quartermaster Harbor identify a 40 clear isotopic fingerprint diagnostic of smelter-derived 50 lead, as shown to the right in Figure 2. 60 70 We will do a more thorough analysis of lead isotope 80 Figure 3. NuPlasma MC-ICP-MS Schematic Diagram. ratios in the sediment core from Quartermaster Harbor, 17.8 18 18.2 18.4 18.6 18.8 19 19.2 as well as, for the first time, test the use of copper and 206Pb/204P zinc isotope ratios as a fingerprint of smelter derivation Tara Smiley, UW Isotope Geochemistry Laboratory, 2008 for these metals. Pb is a radiogenic system, while Cu Results and Zn are stable isotope systems. Figure 2. Our preliminary lead isotope analysis shows a dramatic shift in the 206Pb/204Pb ratio at a depth of approximately 30 cm. MC-ICP-MS technology allows, for the first time, precise These isotopic tracers can then be used to determine There are equally dramatic shifts in the 207Pb/204Pb and 208Pb/204Pb analyses of variations in isotope ratios of Cu and Zn. the extent, pattern, and mechanism of heavy metal ratios, identifying a clear isotopic fingerprint of Tacoma Smelter Pb. We have obtained pure separates of the Zn and Cu contamination in the Puget Sound region. The analytical error is smaller than the data points in this figure. from the samples previously analyzed for Pb isotopes. The final step will be Cu and Zn isotopic analyses.