Techniques to Understand Source Attribution and Exposure Risks at - - PowerPoint PPT Presentation

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Techniques to Understand Source Attribution and Exposure Risks at - - PowerPoint PPT Presentation

Mar 11, 2023 147 likes •428 views

Techniques to Understand Source Attribution and Exposure Risks at Impacted Sites Kirk G. Scheckel Office of Research and Development National Risk Management Research Laboratory Cincinnati, OH U.S. Environmental Protection Agency Source

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Techniques to Understand Source Attribution and Exposure Risks at Impacted Sites

Kirk G. Scheckel Office of Research and Development National Risk Management Research Laboratory Cincinnati, OH

U.S. Environmental Protection Agency

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Source Attribution vs. Exposure Risk

The source of Pb contamination and the risk of Pb contamination must be considered at two distinct issues Source Attribution

  • Pb Isotopes

Where did the Pb come from?

  • Examine ratios of 4 common

Pb isotopes from source material, background, and suspected impacted samples

  • Isotopic ratios do not change
  • ver time

‘Genetics’

Exposure Risk

  • Pb Speciation

Form of Pb drives risk. Solubility linked to speciation of Pb. Form of Pb is environmental driven – can change over time.

‘Fingerprints’

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Pb Isotopes vs. Speciation

Pb oxide Pb carbonate Pb sulfate

Transformation Reactions in Soil

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Speciation – Synchrotron Spectroscopy

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Principal Synchrotron Techniques Used in Environmental Science

Arsenic on

  • X-ray Fluorescence (XRF): chemical

Bangladesh Biotite

composition (quantification, mapping)

  • X-ray Absorption Fine Structure

(XAFS) Spectroscopy: chemical

495oC

Cl

Copper

2.09Å

speciation (oxidation state, coordination,

Speciation in Fluid

Cu1+

nearest neighbors)

Inclusions

  • Surface Scattering and Diffraction:

surface structure, sorption processes

Surface

  • Microtomography: 3D imaging of

internal microstructure (porosity, fluid flow,

As3+

composition)

Arsenic in Cattail Root Plaque U.S. Environmental Protection Agency Reactions 5

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X-ray Absorption Spectroscopy

X-ray Absorption Spectroscopy: Measure energy-dependence of the x-ray absorption coefficient µ(E) [either log(I0 /I) or (If / I0 )]

  • f a core-level of a selected element

XANES = X-ray Absorption Near-Edge Spectroscopy

Element Specific: Elements with Z>20 can be examined. Valence Probe: XANES gives chemical state and formal valence of selected element. Local Structure Probe: EXAFS gives atomic species, distance, and number of near-neighbor atoms around a selected element.. Low Concentration: concentrations down to 1 ppm for XANES, 10 ppm for EXAFS. Natural Samples: samples can be in solution, liquids, amorphous solids, soils, aggregates, plant roots, surfaces, etc. Small Spot Size: XANES and EXAFS measurements can be made on samples down to ~1 microns in size.

EXAFS = Extended X-ray Absorption Fine-Structure

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Source Attribution

Site documentation (e.g., manifests, written statements, interviews with employees) and analytical sampling data.

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Isotope Chemistry 101 Isotopes are variants of a particular chemical element which differ in neutron number with the same number of protons.

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Isotope Chemistry 101

Atomic number: 82

Lead (Pb)

Neutrons serve the purpose

  • f keeping atoms stable;
  • ffsetting repulsive positive

charges in the nucleus and balancing negative charges of electrons on the nucleus.

Atomic mass: 207.2

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Pb Isotopes

Isotopic measurements are concentration based; for ‘genetic’ ratios are utilized to determine compositional relationships:

208Pb/206Pb vs 207Pb/206Pb

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Pb Isotopes

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Pb Isotopes

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Pb Isotopes

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Pb Isotopes - Environmental Forensics

Attribution: Pb Isotopic Analysis via MC-ICP-MS

  • USGS (Denver, CO) Multicollector-Inductively Coupled

Plasma Mass Spectrometer Lab.

  • Abundance of Pb isotopes in a sample depends strictly on the

concentrations of primordial Pb, U and Th and the lengths of the decay processes, i.e., half-lives

  • Lead is present in the environment as four main isotopes:

208Pb (52%), 206Pb (24%), 207Pb (23%) and 204Pb (1%)

  • Lead isotopic studies therefore provide a convenient approach

for studying and tracing lead source pollution in different environmental compartments

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Pb Isotopes - Environmental Forensics

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Pb Isotopes - Environmental Forensics

The Big River Mine Tailings/St. Joe Minerals Corp. Site is located in a former mining region known as the "Old Lead Belt,” which is 70 miles south of St. Louis (St. Francois County). This site is composed of eight large areas of mine waste in this rural region, approximately 110 square miles in size. In 1977, heavy rains caused an estimated 50,000 cubic yards of tailings to slough into the Big River. Flooding events are common. A barite mine area in Washington County is a suspected second source

  • f Pb contamination in the Big River.

The Big River also flows through Jefferson County, depositing into the Meramec River and finally the Mississippi.

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Pb Isotopes - Environmental Forensics

  • St. Francois

Washington Jefferson

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Pb Isotopes - Environmental Forensics

  • St. Francois

Washington Jefferson

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Pb Isotopes - Environmental Forensics

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  • St. Francois

Washington Jefferson

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Pb Isotopes - Environmental Forensics

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  • St. Francois

Washington Jefferson

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Pb Isotopes - Environmental Forensics

206Pb/207Pb

Binary Mixing 206Pb/207Pb

1.37 1.36 1.35

Outlier (35 ppm)

1.34 Source Signature -- Sediment Source Signature -- 1.33 Soil Trend 1 -- Sediment 1.32

Potential second source

Trend 1 -- Soil

and background samples

1.31 Trend 2 -- Sediment Trend 2 -- Soil 1.30 Outlier -- Sediment 1.29

Source, soil, and sediment samples

1.28 0.005 0.01 0.015 0.02 0.025 0.03 1/[Pb]

Collected sediment and soil samples were subjected to Pb isotopic analysis and shown here via binary mixing of

206Pb/207Pb vs 1/[Pb]

  • concentration. Four

groups are identified as 1) source, soil and sediment samples, 2&3) potential second source and background samples (indistinguishable), and 4) one outlier.

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Pb Isotopes - Environmental Forensics

  • St. Francois

Washington Jefferson

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Pb Isotopes - Environmental Forensics

  • St. Francois

Washington Jefferson

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Pb Isotopes - Environmental Forensics

  • St. Francois

Washington Jefferson

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Conclusions The source of Pb contamination and the risk of Pb contamination must be considered at two distinct issues

Source Attribution

  • Pb Isotopes

Where did the Pb come from?

  • Examine ratios of 4 common

Pb isotopes from source material, background, and suspected impacted samples

  • Isotopic ratios do not change
  • ver time

‘Genetics’

Exposure Risk

  • Pb Speciation

Form of Pb drives risk. Solubility linked to speciation of Pb. Form of Pb is environmental driven – can change over time. A snapshot of current conditions.

‘Fingerprints’

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Questions?

Kirk Scheckel Director, Land Remediation & Technology Division Scheckel.Kirk@epa.gov 513-487-2865

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