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The use of Pb isotope ratios determined by magnetic sector ICP-MS for tracing Pb pollution in marine sediments near Casey Station, East Antarctica


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Townsend, AT and Snape, I 2002 , 'The use of Pb isotope ratios determined by magnetic sector ICP-MS for tracing Pb pollution in marine sediments near Casey Station, East Antarctica' , Journal of Analytical Atomic Spectrometry, vol. 17 , pp. 922-928 , doi: 10.1039/b203449m.

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Magnetic sector inductively coupled plasma mass spectrometry (ICP-SMS) was used to measure lead
concentrations and isotope ratios in marine sediments and other samples collected from near the Australian
Antarctic Station Casey. Precisions obtained from the repetitive analysis of a standard Broken Hill Pb sample
at a concentration of approximately 40 ng g-1 in solution were less than plus or minus 0.2% for ratios involving 204Pb, and less than plus or minus 0.1% for those
referenced to 206Pb or 207Pb (n ~ 12 replicates over 2 days, values as 1s). Ratios were accurate to within
less than plus or minus 0.1% for the analysis of this standard sample. Comparative measurements between ICP-SMS and TIMS
had typical differences in values of less than 0.4% for contaminated samples, irrespective of ratio. For marine sediment
samples with Pb concentrations in the sample digest of greater than 10 ng g-1, instrumental capability was characterised
by isotopic precisions ranging from 0.1-0.5% (1s) for ratios involving 204Pb, and less than 0.25% (1s) for ratios with
206Pb or 207Pb as the basis (typically found from triplicate analyses). For sediments of low Pb concentration
(less than 10 ng g-1 in the sample digest), isotope ratios to 204Pb were found to be limited by instrument counting
statistics when using standard ICP-SMS. To help overcome this problem, Pb isotope ratios for these samples
were measured with a capacitive decoupling Pt guard electrode employed, offering considerable signal
enhancement (5-10x). These natural background sediments were found to display typical Pb isotope ratios of
40.5, 15.5, 18.6 and 1.19 for 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb and 206Pb/207Pb. For comparison, the most
contaminated samples had Pb isotope ratios of approximately 36.2, 15.4, 16.4 and 1.06 for 208Pb/204Pb,
207Pb/204Pb, 206Pb/204Pb and 206Pb/207Pb, respectively. Evidence of simple two component mixing between
anthropogenic and natural geogenic Pb was found near Casey Station. Runoff from the Thala Valley tip site,
adjacent to the bay, was identified as a clear source of Pb pollution, with impacted sediments displaying an
isotopic signature approaching that of abandoned lead batteries collected from the tip. These batteries
possessed Pb isotope ratios identical to Australian Broken Hill lead. In this study, the use of Pb isotope data
has proved to be a sensitive method of assessing contamination levels in the Antarctic marine environment
adjacent to a waste disposal site. Lead isotope ratios have proved superior to simple elemental concentration
determinations when distinguishing between impacted and non-impacted samples. ICP-SMS has been shown to
offer relatively fast, accurate and cost effective Pb isotope ratios, with precisions suitable for many
environmental applications.

Item Type: Article
Authors/Creators:Townsend, AT and Snape, I
Journal or Publication Title: Journal of Analytical Atomic Spectrometry
DOI / ID Number: 10.1039/b203449m
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