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Isotopic Evidence for Sources of Lead Contamination in SW Illinois

Isotopic Evidence for Sources of Lead Contamination in SW Illinois. Richard B. Brugam, Luci Kohn, Zhi Qing Lin, Phillip Williams Matthew Wilson Southern Illinois University Edwardsville. Stable isotopes of Lead Potential indicators of Contamination. Radioactive Decay Series.

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Isotopic Evidence for Sources of Lead Contamination in SW Illinois

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  1. Isotopic Evidence for Sources of Lead Contamination in SW Illinois Richard B. Brugam, Luci Kohn, Zhi Qing Lin, Phillip Williams Matthew Wilson Southern Illinois University Edwardsville

  2. Stable isotopes of Lead Potential indicators of Contamination Radioactive Decay Series • Four important ones • 204Pb – “cosmogenic” • 206Pb – from 238U • 207Pb – from 235U • 208Pb – from 232Th • Isotopes uniquely mark all Pb sources • Each lead mine has a particular isotopic “signature” • Ratios unchanged by most natural processes

  3. Each mine produces ore with a specific isotopic signature • Isotopic composition can be used to identify sources of Pb at a polluted site • We will use ratio 206Pb/207Pb • No δ notation • These are true ratios

  4. Potential Sources 206Pb/207Pb in Southwestern Illinois • SE Missouri Mines = 1.34 • Peoria Loess = 1.24 • Bunker Hill Mine = 1.06

  5. Mixing Model Rm= Ra* fa([Pba]/[Pbm])+Rb*fb([Pbb]/[Pbm]) Where: Rm = Isotopic Composition of the mixture Ra = Isotopic Composition of source a Rb = Isotopic Composition of source b fa = fraction of mixture from a fb = fraction of mixture from b Pba = Pb concentration of a Pbb = Pb concentration of b Pbm = Pb concentration of mixture Source: Faure, G and T.M. Messing. 2005. Isotopes: Principles and Applications, Third Edition. John Wiley and Sons, Inc.

  6. Predictions • Graph 206Pb/207Pb ratio of samples against Pb concentration from mixture results in hyperbola • Graph of 206Pb/207Pb ratio of samples against 1/[Pb] is a straight line • One end is isotopic composition of contaminant • Other end is isotopic composition of background

  7. SE Mo Pb Mine • Soils Pine Lake Subdivision site • Location of St. Louis smelting in Collinsville,IL • Closed 1930 • Sediment Horseshoe Lake, Madison County, IL • May have been slightly contaminated by French colonial Pb smelters in the mid-1700’s • Location of NL Industries smelter • Closed 1980 • Sediment Cougar Lake • SIUE Campus • Uncontaminated • Sediment Beaver Dam Lake, Macoupin County • Uncontaminated Galena – PbS ore

  8. Methods • Analyzed soil and sediment for Pb using EPA method 3050b • Leach with nitric acid and hydrogen peroxide • Leachate analyzed for Pb concentration and Pb isotopes

  9. Test at Pine Lake Smelter Site Isotopic composition of SE Missouri Pb is 1.34

  10. Source of Pb at Pine Lake smelter site is probably SE Missouri ore

  11. All sites show linear relationship between 1/[Pb] and isotopic composition • Uncontaminated end of mixing curve is Peoria Loess • Cougar Lake and Beaver Dam lake have nearly flat curves • Implies little contamination

  12. Horseshoe Lake Situation is more complex

  13. Conclusions • Mixing curves apply to SW Illinois Sites • Pine Lake Subdivision • Pb sources are Peoria Loess and SE Missouri • Cougar Lake and Beaver Dam Lake • Only source is Peoria Loess • Horseshoe Lake • Different Pb sources at different times • 1600 to 1750 – Peoria Loess • 1750 to 1938 – SE Missouri • 1938 to present – Unknown – Maybe Bunker Hill

  14. Acknowledgements • We are especially grateful to the SIUE Institute for Urban Research for providing funding • The Illinois Groundwater Consortium provided funding for work at Horseshoe Lake • Brian Vermilion and Indu Bala helped in field sampling at Horseshoe Lake • Dennis Staley helped in field sampling at Pine Lake Subdivision

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