Friday, September 17, 2010

The lead isotope systematics of pregnancy and lactation

ResearchBlogging.orgIsotope geochemistry is useful for so many things that its application to fetal and maternal health can be overlooked. However, this does not diminish the value of isotopic studies to this field. Consider, for example, the groundbreaking ‘Russian Bride’* experiments of Gulson et al.

Determining calcium loss and lead exposure in pregnant women is not easy. Most of the bodies calcium is stored in bones, and because lead substitutes for calcium in most minerals (biogenic or otherwise), bone hydroxyapatite can also be a potential source for lead, if bone resorption occurs. But detecting this is not always easy.

Bone density measurements can be done by X-rays, but in pregnant women this risks giving the unborn child super powers. Bone biopsies are painful and intrusive. So isotope geochemistry is a much less harmful way of measuring whether or not bone resorption is occurring, and whether or not it is contributing lead to the bloodstream.

In the study reported in these papers, European immigrant women who became pregnant a few years after migrating to Australia were studied. This is important- soft tissues exchange lead rapidly with the environment, whole bone matter can take decade to equilibrate. Most environmental lead in Australia comes from the Proterozoic Mt. Isa and Broken Hill mines. These lie on (and help define) the earth isotopic evolution curve, so have a 208Pb/206Pb ratio of about 2.23. Most Eastern European women who grew up in the Eastern Bloc were primarily exposed to Paleozoic lead with an isotopic 208Pb/206Pb ratio of about 2.10. So their soft tissues and bones should have different isotopic signatures.

Figure 1. An Australian immigrant will have different Pb isotopic signatures in bones and soft tissues.

If such a person starts to resorb bone calcium, this should also liberate Pb substituting for calcium, and the blood Pb isotopic ratio should move towards the skeletal value. This is exactly what Gulson et al. saw during pregnancy and lactation in women who did not take calcium supplements.

B.L. Gulson, C.W. Jameson, K.R. Mahaffey, K.J. Mizon, M.J. Korsch, G. Vimpani; Pregnancy increases mobilization of lead from maternal skeleton; The Journal of Laboratory and Clinical Medicine, Volume 130, Issue 1, Pages 51-62 (July 1997)

GULSON B. L. ; MAHAFFEY K. R. ; JAMESON C. W. ; MIZON K. J. ; KORSCH M. J. ; CAMERON M. A. ; EISMAN J. A. ; Mobilization of lead from the skeleton during the postnatal period is larger than during pregnancy; The Journal of laboratory and clinical medicine 1998, vol. 131, no4, pp. 324-329

GULSON, B., MIZON, K., KORSCH, M., PALMER, J., & DONNELLY, J. (2003). Mobilization of lead from human bone tissue during pregnancy and lactation—a summary of long-term research The Science of The Total Environment, 303 (1-2), 79-104 DOI: 10.1016/S0048-9697(02)00355-8
* For what it's worth, every Russian bride I knew during the time period of this study had an advanced degree in physics, and was working in Australian academia or industry to win their family's bread.

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