RESEARCH

Screening & Diagnosis

A BRIEF REVIEW OF THE LEAD ISOTOPE FINGERPRINTING METHOD

Dr. Brian L. Gulson

Introduction

Identifying the correct sources and pathways of lead in the environment and humans is fundamental to the implementation of the most cost-effective remedial actions. In the past, the main approach to identifying sources and pathways has been the statistical analysis of large databases of environmental samples and human subjects using lead concentrations. In concert with its main application in the earth sciences (isotope geochemistry), the technique of lead isotope fingerprinting has been commonly applied in environmental situations to problems focussed on establishing sources of lead in for example air, water, ice, soils, dust and paint (see references in section "Environmental Investigations"). Application of lead isotope fingerprinting has recently been applied in animal studies (references in "Animal Investigations") whereas the application to human studies is limited ("Human Investigations").

The form of this review will be to present an introduction to the lead isotope method and then briefly summarise some of the projects that we have undertaken mainly over the past 8 years at CSIRO/Macquarie University. The reference list for investigations using lead isotopes as a tracer, although comprehensive, is not exhaustive and excludes most papers in which the isotopic ratios have been measured by Inductively Coupled Plasma Mass Spectrometry, the reasons for which are given in the following section.

Lead Isotope Method

The lead isotope method makes use of the variations in isotopic abundance arising from radioactive decay over geological time of 238U, 235U and 232Th to 206Pb, 207Pb and 208Pb. 204Pb has no parent and has remained essentially constant in abundance since the time of formation of the Earth. Isotopic abundance is expressed as ratios such as 206Pb/204Pb, 207Pb/206Pb and 208Pb/206Pb or as the 204-based ratios 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb. The isotopic ratios are presented in this report as 206Pb/204Pb. For geologically old (~1700 million years) lead deposits such as Broken Hill and Mount Isa in Australia, the 206Pb/204Pb ratio is 16.00 and 16.10 respectively, whereas for geologically young (~400 million years) deposits on the same continent (such as Woodlawn or Elura), the 206Pb/204Pb ratio is ~18.1. These differences are very large as it is possible with our techniques to distinguish between the Broken Hill and Mount Isa deposits. The lead isotopic composition observed in the different sources depends on the geological source of the lead and its fate thereafter. For example, the 206Pb/204Pb ratio used in gasoline in Sydney over the last 10 years ranged from 16.4 - 17.0. Hence, the tetraethyl lead is a mixture of geologically old lead such as from the Broken Hill and/or Mount Isa mines in Australia with a small component of geologically younger lead.

Analytical Methods

All sample preparation is performed in purpose-built low contamination laboratories (‘clean rooms’) incorporating features such as filtered air intake and laminar flow hoods. Almost any sample can be analysed. Biological samples include: blood, urine, teeth, food, breast milk. Environmental samples include: air, soil, dust, water, paint, gasoline.

Samples are leached or dissolved using ultra pure reagents, with or without microwave digestion. Lead is separated from interfering elements, such as Fe and Zn, by anion-exchange chromatography in a hydrobromic acid medium. Fractions of the purified lead samples are loaded onto a rhenium filament using the silica gel technique and analysed for high precision lead isotopic composition on a thermal ionisation mass spectrometer (or TIMS) run in fully automatic mode. Isotopic ratios are measured as 208Pb/206Pb,207Pb/206Pb and 206Pb/204Pb. Data are normalised to the accepted values of the international standard NBS SRM 981, by applying a correction factor of +0.08% a.m.u. to allow comparisons between laboratories.

Four individual isotopes are measured - 208Pb, 207Pb, 206Pb and 204Pb. Each isotope is measured as it passes through a magnetic field in the mass spectrometer, and the isotopes detected are conventionally reported as the ratios mentioned above. These three ratios provide three independent measurements from which to evaluate each sample, accompanying the measurement of lead concentration in ppm. Because of the diagnostic potential of the isotopic ratios and interdependence between them as 206Pb is common to all three variables, only one or two ratios are commonly reported. Furthermore, the 206Pb/204Pb ratio is often not reported because of difficulties in measuring the low abundance 204Pb isotope. In many cases, it is also possible to recognise contaminated samples using an isotope-based method, as such samples exhibit a distinct signature.

The TIMS method allows isotopic ratios to be measured with a high degree of precision. Our current research has shown that the isotopic techniques employed can easily detect very small differences in isotopic ratios that are essential for valid data interpretation. This cannot be achieved using the current generation of Inductively Coupled Plasma Mass Spectrometers (ICP-MS) in which precision is an order of magnitude, or more, worse than TIMS, and accuracy may be questionable. The TIMS method is also superior to using lead concentrations alone, as these require large databases and sophisticated statistics to provide results that may be equivocal due to poor correlation between variables. The other advantage that lead isotopes has over lead concentrations is the fact that the isotopic abundance (and thus isotopic ratios) are not changed by physiological processes because of their high atomic weights. Justification of the number of samples:

The lead isotope method is sometimes criticised because of the relatively small numbers of samples used in such investigations. This criticism may be due to a lack of understanding of isotope studies, to which the concept of analysis numbers does not translate to one result for each sample. This misunderstanding is common as the use of the lead isotope technique in health and environmental research has only really come to the forefront over the past decade and it is a highly specialised field. (There are only four laboratories in the world in which high precision lead isotopic measurements of biological materials are regularly performed).

In validation and later testing for a major study (Biokinetics of Lead in Human Pregnancy), we demonstrated that it is possible to measure samples of blood and urine collected from the same person over several months, and water from same tap with the following precision (2 standard deviations):

Sample

208Pb/206Pb

207Pb/206Pb

206Pb/204Pb

Pb (ppb)

n

Blood

2.1759 ± 0.0028

0.9225 ± 0.0011

16.756 ± 0.044

7.7 ± 0.2

15

Urine

2.1748 ± 0.0024

0.9233 ± 0.0005

16.752 ± 0.026

2.2 ± 0.1

12

Water

2.2099 ± 0.0014

0.9489 ± 0.0005

16.223 ± 0.025

3.1 ± 0.1

11

For the 207Pb/206Pb ratio this means that numbers in the fourth decimal place can be significant.

Thus the high precision measurements of isotopic ratios allow for a high discriminatory power with minimal statistical manipulation, and it is possible to provide definitive answers from a small number of samples. This compensates for the drawbacks of the method (lead isotopic measurements are costly as they are extremely labour-intensive, require expensive equipment and ultra-clean laboratories). Low sample numbers are also advantageous if blood samples are taken from children (or adults), as sampling methods involve a degree of personal invasion on them.

Examples of the Use of Lead Isotope Fingerprinting

Endogenous versus Exogenous sources of lead (Biokinetics of Lead in Human Pregnancy)

This major international longitudinal study supported by the U.S. National Institute of Environmental Health Sciences using the lead isotope method has determined that lead is mobilised from the maternal skeleton during pregnancy and lactation, with a higher amount mobilised during lactation (Papers 69, 74, 77, 80, 81, 84, 86 in reference list).

Smelter communities (Port Pirie, Port Kembla, Hobart, Boolaroo)

Environmental samples (soil, house dust, house air, ambient air) and blood and urine from adult females and some children were analysed as part of the study of Biokinetics of Lead in Human Pregnancy (Paper 74). Sources and pathways were established of lead contained in ceiling dust and historical sources of lead contamination in sediments from Lake Illawarra especially arising from the Port Kembla smelter (Paper 31).

Mining Communities (Broken Hill, Mount Isa, Woodlawn)

The Broken Hill investigation established that paint and petrol were significant contributors to blood lead in some children. In addition, it demonstrated the importance of monitoring family members as a pathway for "take-home" lead. This was also the testing ground for development of the tooth method and the petri dish method. (Papers 25, 27, 63, 64, 65, 66, 71, 72, 73, 75, 76, 85). The Woodlawn study showed that the blood in workers contained lead dominantly from mining activities and "take home" mine dust which contaminated their residences (Paper 76).

Urban Areas (Sydney, Brisbane, Adelaide)

In Sydney, studies demonstrated that paint from renovating houses could contaminate neighbourhoods and was also a test of the petri dish method (Papers 26, 27).

The majority of the subjects (n>80) in the Biokinetics of Lead in Human Pregnancy study are in Sydney. Petri dish dust, tap water, 6-day duplicate diet, and blood and urine are monitored in these subjects and their children and new-born infants.

Air and petrol are monitored on a monthly basis with high volume air filters supplied by the NSW EPA and Queensland Department of Conservation and the Environment. (Papers 22, 29, 74). Ceiling dust and soils from houses around a former lead paint factory have been analysed for a company to establish their potential liability.

"Take Home" Lead

On the clothes of workers, it was convincingly demonstrated using the lead isotope method in Broken Hill (Paper 75 ), Woodlawn mine (Paper 76), and potentially from engine reconditioning shops (Paper 32).

Lead Paint Removal from Bridges

The lead isotope method has been used to monitor removal of lead paint from bridges in several Australian states. Environmental samples were used for the monitoring and in one case, blood samples of the workers were also collected as a control measure in case of lead poisoning.

Advantages of Lead Isotopes

  • Often diagnostic for sources and pathways
  • Allows distinction of skeletal Vs environmental exposures compared with indirect measures (e.g. statistics, bone XRF)
  • Small numbers of samples can provide a definitive answer
  • Low sample numbers are also advantageous if blood samples are taken from children (or adults), as sampling methods involve some degree of personal invasion on them.

Disadvantages of Lead Isotopes

  • Expensive (equipment, ultra clean labs, trained technical staff) - new model mass spectrometers may lower costs
  • Equivocal at very low blood lead concentrations (<5 m g/dl)
  • No use if ambient isotopic signatures are similar (e.g. air+paint+water+blood) as in U.S.

References

Environmental Investigations

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  15. Flegal, A.R., Maring, H., Niemeyer, S. 1993. Anthropogenic lead in Antarctic sea water. Nature, 365, 242-244.
  16. Flegal, A.R., Patterson, C.C. 1983. Vertical concentration profiles of lead in the Central Pacific at 15oN and 20oS. Earth Planet Sci Lett., 64, 19-32.
  17. Flegal, A.R., Rosman, K.J.R., Stephenson, M.D. 1987. Isotope systematic of contaminant leads in Monterey Bay. Environ Science Technol., 21, 1075-1079.
  18. Flegal, A.R., Duda, A.R., Niemeyer, S. 1989. High gradients of lead isotopic composition in north-east Pacific up-welling filaments. Nature 339, 458-460.
  19. Gobeil, C., Johnson, W.K., Macdonald, R.W., Wong, C.S. 1995. Sources and burden of lead in St. Lawrence estuary sediments: isotopic evidence. Environ Science Technol., 28, 193-201.
  20. Graney, J.R., Halliday, A.N., Keeler, G.J., Nriagu, J.O., Robbins, J.A., Norton, S.A. 1995. Isotopic record of lead pollution in lake sediments from the north eastern United States. Geochim Cosmochim Acta, 59, 1715-1728.
  21. Gulson, B.L., Tiller, K.G., Mizon, K.J., Merry, R.H. 1981. Use of lead isotopes to identify the source of lead contamination near Adelaide, South Australia. Environ Science Technol., 15, 691-696.
  22. Gulson, B.L. , Mizon, K.J., Korsch, M.J. 1983. Fingerprinting the source of lead in Sydney air using lead isotopes. In " The Urban Atmosphere-Sydney, a case study" . Eds. J.N. Carrass & G.M. Johnson (CSIRO Melbourne), 233-244.
  23. Gulson, B.L., Mizon, K.J., Korsch, M.J., Noller, B.N. 1989. Lead isotopes as seepage indicators around a uranium tailings dam. Environ Science Technol., 23, 290-294.
  24. Gulson, B.L., Lee, T.W., Mizon, K.J., Eschnauer, H. 1992. The application of lead isotope ratios to determine the contribution of the tin-lead capsule to the lead content of wine. Amer J Enology and Viticulture, 43, 180-190.
  25. Gulson, B.L., Law, A.J., Korsch, M.J., Mizon, K.J. 1994. Effect of plumbing systems on lead content of drinking water and contribution to lead body burden. Science Total Environ., 144, 279-284.
  26. Gulson, B.L., Davis, J.J., Bawden-Smith, J. 1995. Paint as a source of recontamination of houses in urban environments and its role in maintaining elevated blood leads in children. Science Total Environ., 164, 221-235.
  27. Gulson, B.L., Davis, J.J., Mizon, K.J., Korsch, M.J., Bawden-Smith, J. 1995. Sources of soil and dust and the use of dust fallout as a sampling medium. Science Total Environ., 166, 245-262.
  28. Gulson, B.L., Sheehan, A., Giblin, A.M., Chiaradia, M., Conradt, B. 1997. The efficiency of removal of lead and other elements from domestic drinking waters using a bench-top water filter system. Science Total Environ., 196, 205-216.
  29. Chiaradia, M., Gulson, B.L., James M., Jameson, C.W., Johnson, D. 1997. Identification of secondary lead sources in the air of an urban environment. Atmospheric Environment, 31, 3511-3521.
  30. Gulson, B.L., James, M., Giblin, A.M, Sheehan, A., Mitchell, P. 1997. Maintenance of elevated lead levels in drinking water from occasional use and potential impact on blood leads in children. Science Total Environ., 205, 271-275.
  31. Chiaradia, M., Chenhall, B., Depers, A.M., Gulson, B.L., Jones, B.G. 1997. Identification of historical lead sources in roof dusts and recent lake sediments from an industrialized area: indications from lead isotopes. Science Total Environ., 205, 107-128.
  32. James, M., Gulson, B.L. Engine reconditioning workshops: lead contamination and the potential risk for workers - a pilot study. Occupational Environmental Medicine, in press.
  33. Hirao, Y., Mabuchi, H., Fukuda, E., Tanaka, H., Imamura, T., Todoroki, H., Kimura, K., Matsumoto, E. 1986. Lead isotope ratios in Tokyo Bay sediments and their implications in the lead consumption of Japanese industries. Geochem J., 20, 1-15.
  34. Hopper, J.F., Ross, H.B., Sturges, W.T., Barrie, L.A. 1991. Regional source discrimination of atmospheric aerosols in Europe using the isotopic composition of lead. Tellus, 43B, 45-60.
  35. Lang, S.J., Rosman, K.J.R. 1990. Determination of lead in fresh and canned pineapple by isotope dilution mass spectrometry and isotope systematics. Anal Chim Acta, 235, 367-373.
  36. MacKenzie, A.B., Farmer, J.G., Sugden, C.L. 1997. Isotopic evidence of the relative retention and mobility of lead and radiocaesium in Scottish ombrotrophic peats. Science Total Environ., 203, 115-127.
  37. Maring, H., Settle, D.M., Buat-Menard, P., Dulac, F., Patterson, C.C. 1987. Stable lead isotope tracers of air mass trajectories in the Mediterranean region. Nature, 300, 154-156.
  38. Monna, F., Lancelot, J., Croudace, I.W., Cundy, A.B., Lewis, J.T. 1997. Pb isotopic composition of airborne particulate material from France and the southern United Kingdom: implications for lead pollution sources in urban areas. Environ Sci Technol., 31, 2277-2286.
  39. Patterson, C. C., Settle, D. M. 1987. Review of data on eolian fluxes of industrial and natural lead to the lands and seas in remote regions on a global scale. Mar. Chem., 22, 137-162.
  40. Petit, D., Mennessier, J.P., Lamberts, L. 1984. Stable lead isotopes in pond sediments as tracer of past and present atmospheric lead pollution in Belgium. Atmos Environ., 18, 1189-1193.
  41. Puchelt, H., Kramar, U., Cumming, G.L., Krstic, D., Noltner, Th., Schottle, M., Schweide, V. 1993. Anthropogenic lead contamination of soils - lead mobility and isotopic recognition. Applied Geochem Suppl Issue No.2, 71-74.
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  43. Rosman, K.J.R., Chisolm, W., Boutron, C.F., Candelone, J.-P., Gorlach, U. 1993. Isotopic evidence for the source of lead in Greenland snows since the late 1960s. Nature, 362, 333-334.
  44. Rosman, K.J.R., Chisolm, W., Boutron, C.F., Candelone, J.-P., Hong, S. 1994a. Isotopic evidence to account for changes in the concentration of Pb in Greenland between 1960 and 1988. Geochim Cosmochim Acta, 58, 3265-3269.
  45. Rosman, K.J.R., Chisolm, W., Boutron, C.F., Candelone, J.-P., Patterson, C.C. 1994b. Anthropogenic lead isotopes in Antarctica. Geophys Res Letters, 21, 2269-2672.
  46. Rosman, K. J. R., Chisholm, W., Jimi, S., Candelone, J-P., Boutron, C. F., Teissedre, P-L., Adams, F.C. 1998. Lead concentrations and isotopic signatures in vintages of French wine between 1950 and 1991. Environ. Res., 78, 161-167.
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  48. Steinman, M., Stille, P. 1997. Rare earth element behaviour and Pb, Sr, Nd isotope systematics in a heavy metal contaminated soil. Applied Geochem., 12, 607-623.
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Animal Investigations

    1. Casteel, S.W., Cowart, R.P., Weis, C.P., Henningsen, G.M., Hoffman, E., Brattin, W.J., Guzman, R.E., Starost, M.F., Payne, J.T., Stockham, S.L., Becker, S.V., Drexler, J.W., Turk, J.R. 1997. Bioavailability of lead to juvenile swine dosed with soil from the Smuggler Mountain npl site of Aspen, Colorado. Fund Appl Toxicol., 36, 177-87.
    2. Flegal, A.R., Smith, D.R. 1992. Lead levels in pre-industrial humans. New England J Med., 326, 1293-1294.
    3. Franklin, C.A., Inskip, M.J., Baccanale, C.L., O’Flaherty, E.J., Manton, W.I., Schanzer, D.L., Edwards, C.M.H., Blenkinsop, J.B. 1995. Transplacental transfer of lead in nonhuman primates (Macaca fascicularis): use of serially administered stable isotope tracers of lead to elicit contribution of maternal bone lead to blood lead and the fetus. Toxicol., 15, 194 [abstract].
    4. Franklin, C.A., Inskip, M.J., Baccanale, C.L., Edwards, C.M.H., Manton, W.I., Edwards, E., O’Flaherty, E.J. 1997. Use of sequentially administered stable lead isotopes to investigate changes in blood lead during pregnancy in a non-human primate (Macaca fascicularis). Fund Appl Toxicol., 39, 109-119.
    5. Inskip, M.J., Franklin, C.A, Baccanale, C.L., Manton, W.I., O’Flaherty, E.J., Edwards, C.M.H., Blenkinsop, J.B., Edwards, E.B. 1996. Measurement of the flux of lead from bone to blood in a non-human primate (Macaca fascicularis) by sequential administration of stable lead isotopes. Fund Applied Toxicol., 33, 235-235.
    6. O’Flaherty, E.J., Inskip, M.J., Franklin, C.A., Durbin, P.W., Manton, W.I., Baccanale, C.L. 1998. Evaluation and modification of a physiologically based model of lead kinetics using data from a sequential isotope study in cynomolgus monkeys. Toxicol Appl Pharmacol., 149, 1-16.
    7. Smith, D.R., Flegal, A.R. 1992. Stable isotopic tracers of lead mobilised by DMSA chelation in low lead-exposed rats. Toxic Applied Pharmacol., 116, 85-91.
    8. Smith, D.R., Niemeyer, S., Estes, J.A., Flegal, A.R. 1990. Stable lead isotopes evidence anthropogenic contamination in Alakan sea otters. Environ Sci Technol., 24, 1517-1521.
    9. Smith, D., Bayer, L., Strupp, B. J. 1998. Efficacy of succimer chelation for reducing brain Pb levels in a rodent model. Environ Res., 78, 168-176.
    10. Sugden, C.L, Farmer, J.G., MacKenzie, A.B. 1993. Isotopic ratios of lead in contemporary environmental material from Scotland. Environ Geochem Health, 15, 59-65.

Human Investigations
    1. Angle, C.R., Manton, W.I., Stanek, K.L. 1995. Stable isotope identification of lead sources in pre-school children - the Omaha study. Clin. Toxicol., 33, 657-662.
    2. Faccheti, S. 1989. Lead in petrol. The isotopic lead experiment. Acc. hem. Res., 22, 370-374.
    3. Gulson, B.L., Howarth, D., Mizon, K.J., Korsch, M.J., Davis, J.J. 1994. The source of lead in humans from Broken Hill mining community. Environ Geochem Health, 16, 19-25.
    4. Gulson, B.L., Wilson, D. 1994 History of lead exposure in children revealed from isotopic analyses of teeth. Arch Environ Health, 49, 279-283.
    5. Gulson, B.L., Mizon, K.J., Law, A.J., Korsch, M.J., Davis, J.J. 1994. Source and Pathways of Lead in Humans from Broken Hill Mining Community - an Alternative Use of Exploration Methods. Econ Geol., 89, 889-908.
    6. Gulson, B.L., Howarth, D., Davis, J.J., Mizon, K.J., Korsch, M.J., Law, A.J. 1994. Lead bioavailability in the Environment of Children: Blood Lead Levels in Children can be Elevated in a mining Community. Arch Environ Health, 49, 326-331.
    7. Stauber, J.L., Florence, T.M., Gulson, B.L., Dale, L.S. 1994. Percutaneous absorption of inorganic lead compounds. Science Total Environ., 145, 55-70.
    8. Gulson, B.L., Calder, I.C., 1995. Lead mobilisation during pregnancy. Med J Aust., 163, 47.
    9. Gulson, B.L., Mahaffey, K.R., Mizon, K.J., Korsch, M.J., Cameron, M., Vimpani G.1995. Contribution of tissue lead to blood lead in adult female subjects based on stable lead isotope methods. J Lab Clinical Med., 125, 703-712. (Editorial Comment p. 677).
    10. Gulson, B.L. 1996a. Nails - Concern over their use in lead exposure assessment. Science Total Environ., 177, 323-327.
    11. Gulson, B.L. 1996b Tooth analyses of sources and intensity of lead exposure in children. Environ Health Perspec., 104, 306-312.
    12. Gulson, B.L., Mizon, K.J., Korsch, M.J., Howarth D. 1996b. Non-ore body sources are significant contributors to blood lead of some children with low to moderate lead exposure in a major lead mining community. Science Total Environ., 181, 223-230.
    13. Gulson, B.L., Mizon, K.J., Korsch, M.J., Howarth, D. 1996a. Impact on blood lead in children and adults following relocation from their source of exposure and contribution of skeletal tissue to blood lead. Bull Environ Contam Toxicol., 56, 543-550.
    14. Gulson, B.L., Pisaniello, D., McMichael, A.J., Mahaffey, K.R., Luke, C., Mizon, K.J., Korsch, M.J., Ashbolt, R., Vimpani, G., Pederson, D.C. 1996d. Stable lead isotope profiles in smelter and general urban communities. Comparison of biological and environmental measures. Environ Geochem Health., 18, 147-163.
    15. Gulson, B.L., Mizon, K.J., Korsch, M.J., Howarth D. 1996c. Importance of monitoring family members in establishing sources and pathways of lead in blood. Science Total Environ., 188, 173-182.
    16. Chiaradia, M., Gulson B.L., MacDonald, K. 1997. Contamination of houses by occupationally exposed workers from a lead-zinc-copper mine and impact on blood leads in the families. Occupational and Environmental Medicine, 54, 117-124.
    17. Gulson, B.L., Jameson, C.W., Mahaffey, K.R., Mizon, K.J., Korsch, M.J., Vimpani G. 1997. Pregnancy increases mobilisation of lead from maternal skeleton. J. Lab Clin Med., 130, 51-62.
    18. Gulson, B.L., Gillings, B.R., Jameson, C.W. 1997. Stable lead isotopes in teeth as indicators of past domicile - a potential new tool in forensic science. J Forensic Sciences, 42, 787-791.
    19. Gulson, B.L., Gillings, B.R. 1997. Lead exchange in teeth and bone - pilot study using stable lead isotopes. Environ Health Perspec., 105, 820-824.
    20. Gulson, B.L., Mahaffey, K.R., Jameson, C.W.,Vidal, M., Law A.J., Mizon, K.J., Korsch, M.J. 1997. Dietary intake for mother-child pairs and implications for pharmacokinetic models. Environ Health Perspec., 105, 1334-1342.
    21. Gulson, B.L., Jameson, C.W., Mahaffey, K.R., Mizon, K.J., Korsch, M.J., Cameron, M.A., Vimpani, G., Eisman, J.A. 1998. Mobilisation of lead from the skeleton during the post-natal period is larger than during pregnancy. J Lab Clin Med., 131, 324-329.
    22. Gulson, B.L., Cameron, M.A., Smith, A.J., Mizon, K.J., Korsch, K.J., Vimpani, G., McMichael, A.J., Pisaniello, D., Jameson, C.W., Mahaffey, K.R. 1998. Blood lead-urine relationships in adults and children. Environ Res., 78, 152-160.
    23. Gulson, B.L., Stockley, C.S., Lee T.H., Gray, B., Mizon, K.J., Patison, N. 1998. Contribution of lead in wine to the total dietary intake of lead in humans with and without a meal: a pilot study. J Wine Research 9, 5-14.
    24. Gulson, B.L., Jameson, C.W., Mahaffey, K.R., Mizon, K.J., Patison, N., Law, A.J., Korsch, M.J. 1998. Relationships of Lead in Breast Milk to Lead in Blood, Urine and Diet of the Infant and Mother. Environ Health Perspec., 106, 667-674.
    25. Gulson, B.L., Ah Yui, L., Howarth, D. 1998. Delayed visual maturation and lead pollution. Science Total Environ., 224, 215-219.
    26. Gulson, B.L., Gray, B., Mahaffey, K.R., Jameson, C.W., Mizon, K.J., Patison, N., Korsch, M.J. 1999. Comparison of the rates of exchange of lead in the blood of newly born infants and their mothers with lead from their current environment. J Lab Clin Medicine, 133, 1711-178.
    27. Heusler-Bitschy, S., Knutti, R., Schlatter, Ch. 1988. Inter-individual variability of the kinetics of lead in man. Trace Elem Anal Chem Med Biol., 5, 627-634.
    28. Keinonen, M. 1989. The isotopic composition of lead in man and the environment in Finland: isotope ratios of lead as indicators of pollutant source. Report series in radiochemistry, University of Helsinki, Finland.
    29. Manea-Krichten, M., Patterson, C., Miller, G., Settle, D., Erel, Y. 1991. Comparative increases of lead and barium with age in human tooth enamel, rib and ulna. Science Total Environ., 107, 179-203.
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    33. Smith, D., Markowitz, M.E., Crick, J., Rosen, J.F., Flegal, A.R. 1994. The effects of Succimer on the absorption of lead in adults determined by using the stable isotope 204Pb. Environ Research 67, 39-53.
    34. Smith, D.R., Flegal, A.R. 1996. Use of endogenous stable lead isotopes to determine release of lead from the skeleton. Environ Health Perspect., 104, 60-66.
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Not in List Yet (for "Environmental Investigations")
    1. Veron, A. J., Church, T. M., Flegal, A. R. 1998. Lead isotopes in the western North Atlantic: Transient tracers of pollutant inputs. Environ. Res., 78, 104-111.
    2. Veron, A. J., Church, T. M., Flegal, A. R., Patterson, C. C., Erel, Y. 1993. Response of lead cycling in the Sargasso Sea to changes in tropospheric input. J. Geophys. Res., 98, 18269-18276.
    3. Veron, A. J., Church, T. M., Patterson, C. C., Erel, Y., Merrill, J. T. 1992. Continental origin and industrial sources of trace metals in the north-west Atlantic troposphere. J. Atmos. Chem., 14, 339-351.
    4. Veron, A. J., Church, T. M., Patterson, C. C., Flegal, A. R. 1994. Use of stable lead isotopes to characterise the sources of anthropogenic lead in North Atlantic surface waters. Geochim. Cosmochim. Acta, 58, 3199-3206.

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