Lead uptake and distribution in horns from goats

Elke Arenholz, CHESS

"Spatial analysis of horns for lead accumulation may be useful as a qualitative marker of time-resolved exposures that may reflect specific periods of acute lead absorption."

Growth pattern of caprine horn. Left: Diagram of a horn for a 5-year old goat indicating the layer of horn grown at each year of age. Right: Example of a horn cross section, indicating the layer of horn grown at each year of age.

Growth pattern of caprine horn. Left: Diagram of a horn for a 5-year old goat indicating the layer of horn grown at each year of age. Right: Example of a horn cross section, indicating the layer of horn grown at each year of age.

What did the Scientists Discover?
Horns collected from goats periodically dosed with lead acetate for research purposes were analyzed using synchrotron radiation-induced micro X-ray fluorescence spectrometry (SR-μXRF) at CHESS. Elemental distribution maps were obtained for lead and other elements. Accumulations of lead were clearly visible in each of the horn samples analyzed indicating that following ingestion, absorbed lead is eventually deposited into caprine horns, resulting in discrete accumulations or “rings.”

Why is this important?
Lead is a ubiquitous environmental contaminant with a wide range of adverse health effects in humans and animals. Because of the persistence of lead in the environment and its long residence time in the body, the lead burden in the human body and in ecosystems may reflect past as well as recent exposures. Spatial analysis of horns for lead accumulation may be useful as a qualitative marker of time-resolved exposures that may reflect specific periods of acute lead absorption.

Horn growth timelines superimposed on Pb μXRF maps. Annual horn growth layers are labeled within symmetrical regions ROI-A and ROI-B, beginning with the oldest growth on the outside.
Horn growth timelines superimposed on Pb μXRF maps. Annual horn growth layers are labeled within symmetrical regions ROI-A and ROI-B, beginning with the oldest growth on the outside.

What are the broader impacts of this work?
Elemental mapping by SR-μXRF also clearly show Ca-rich layers that vary with annual periodicity, consistent with previous reports of horn mineralization. Localized enrichment of Cu, Zn, Br and S appear to coincide with the keratinized regions related to the annual growth ring pattern in horns. Spatial analysis of horns for contaminants may be useful as a qualitative marker of exposures even long after they occurred.

X-ray spectrum with the confirming presence of Pb. Other elements are indicated as well. Spectra were summed over a 0.2 x 0.1 mm rectangle indicated by the red box at upper edge the of the μXRF map inset.
 X-ray spectrum with the confirming presence of Pb. Other elements are indicated as well.  Spectra were summed over a ~0.2 x 0.1 mm rectangle indicated by the red box at upper edge the of the μXRF map inset.

Why did this research need CHESS?
All SR-μXRF analyses were carried out at CHESS’ F3 beamline. A pair of multilayers with bandpass around 0.6% was used, providing higher monochromatic X-ray flux than the standard double-crystal Si(111) monochromator. A CHESS single-bounce mono-capillary was used to generate a 20-μm full width at half maximum (FWHM) focused X-ray beam on the sample. An excitation energy of 16.2 keV was used, and X-ray fluorescence spectra were recorded using a 4-element Vortex silicon-drift detector.

Collaborators:

  • Mina W. Tehrani, New York State Department of Health and University at Albany.
  • Rong. Huang, Cornell High Energy Synchrotron Source (CHEES).
  • Diana Guimarães, New York State Department of Health and University at Albany.
  • Louisa Smieska, Cornell High Energy Synchrotron Source (CHEES).
  • Arthur Woll, Cornell High Energy Synchrotron Source (CHEES)
  • Patrick J.Parsons, New York State Department of Health and University at Albany.

Publication Citation:
Tehrani, M.W., Huang, R., Guimarães, D., Smieska, L., Woll, A., Parsons, P.J., “A study of lead uptake and distribution in horns from lead-dosed goats using synchrotron radiation-induced micro X-ray fluorescence elemental imaging.” Journal of Trace Elements in Medicine and Biology, vol. 55, pp. 143-153, Sept. 2019. https://doi.org/10.1016/j.jtemb.2019.05.013

The research was conducted at CHESS which was supported by the NSF under award DMR-1332208..