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

• 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

Radioactive Decay Series

• 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

Potential Sources 206Pb/207Pb in Southwestern Illinois

• SE Missouri Mines = 1.34

• Peoria Loess = 1.24

• Bunker Hill Mine = 1.06

Mixing ModelRm= Ra* fa([Pba]/[Pbm])+Rb*fb([Pbb]/[Pbm])

Where:Rm = Isotopic Composition of the mixtureRa = Isotopic Composition of source aRb = Isotopic Composition of source bfa = fraction of mixture from afb = fraction of mixture from bPba = Pb concentration of aPbb = Pb concentration of bPbm = Pb concentration of mixture

Source: Faure, G and T.M. Messing. 2005. Isotopes: Principles and Applications,

Third Edition. John Wiley and Sons, Inc.

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

• 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

SE Mo Pb Mine

Galena – PbS ore

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

Test at Pine Lake Smelter Site

Pb Concentration (mg/Kg)

0 2000 4000 6000 8000 10000 12000

20

6 Pb/

20

7P

b

1.27

1.28

1.29

1.30

1.31

1.32

1/[Pb]

0.00 0.01 0.02 0.03 0.04 0.05 0.06

20

6 Pb/

20

7P

b

1.27

1.28

1.29

1.30

1.31

1.32

Isotopic composition of SEMissouri Pb is 1.34

Source of Pb at Pine Lake smelter site is probably SE

Missouri ore

Pine Lake Subdivision

1/[Pb]

0.00 0.02 0.04 0.06 0.08 0.10

206 P

b/2

07P

b

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

Cougar Lake

1/[Pb]

0.00 0.02 0.04 0.06 0.08 0.10

206 P

b/2

07P

b

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

Beaver Dam

1/[Pb]

0.00 0.02 0.04 0.06 0.08 0.10

206 P

b/2

07P

b

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1/[Pb]

0.00 0.02 0.04 0.06 0.08 0.10

206 P

b/20

7 Pb

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34Pinewood SubdivisionCougar Lake CoreBeaver Dam LakePeoria Loess

• 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

Horseshoe Lake

Situation is more complex

Concentration

Pb Concentration (mg/Kg)

0 50 100 150 200 250 300 350

Ag

e (y

rs. C

.E.)

1600

1700

1800

1900

2000

Core H17Core H3

Isotopic Composition

206Pb/207Pb

1.211.22

1.231.24

1.251.26

1.27

Ag

e (y

rs. C

.E.)

1600

1700

1800

1900

2000

1/[Pb]

0.00 0.01 0.02 0.03 0.04 0.05 0.06

206 P

b/20

7 Pb

1.21

1.22

1.23

1.24

1.25

1.26

1.27

1938 to Present

1758 to 19381600 to 1758

Peoria Loess

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

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