<p><b><i>Background and
Objective:</i></b> Pb
is a well-known toxic metal that can accumulate in bones over time and still
threatening large populations nowadays, even those who are environmentally
exposed to it. Strontium (Sr) is a metal directly related to bone health and
has been used in the treatment of osteoporosis disease as a supplement. Manganese
(Mn) is an essential nutrient in the body, yet excessive Mn is toxic and
affecting many organ systems. Another toxic metal, mercury (Hg), has been
poising different populations primarily through seafood consumptions,
especially inducing neurological disorders in infants and fetuses. Even though significant associations between
the above metal exposures and health outcomes have been recognized over the decades,
the current technologies are limited in assessing cumulative long-term
exposures <i>in vivo</i> to evaluate such
associations further. Bone and toenail are appropriate biomarkers to reflect
long-term exposure due to the longer half-life of these metals in them than in the traditional biomarkers. Therefore, this work evaluated the usefulness of portable x-ray
fluorescence (XRF) technology on <i>in
vivo</i> quantification of Pb and Sr in bone, and Mn and Hg in toenail.</p>
<p><b><i>Materials and
Methods:</i></b> The
portable XRF device was calibrated by using the Pb- and Sr-doped
bone-equivalent phantoms, and Mn- and Hg-doped nail-equivalent phantoms, correspondingly
in different projects. Seventy-six adults (38-95 years of age, 63 ± 11 years)
from Indiana, USA, were recruited to participate in this study. For the <i>in vivo</i> bone measurements, each
participant was measured at the mid-tibia bone using the portable XRF and K-shell
XRF system (KXRF). We estimated the correlation between the bone Pb concentration
measured by both devices to evaluate the use of the portable XRF in the bones. Using
the portable XRF, the bone Sr exposure of the study population were
simultaneously assessed with the bone Pb exposures. Besides, we analyzed the
mid-tibia bone Sr data of a Chinese population, which were measured with the
same portable XRF device by our research group. We also examined the extent to
which the detection limit (DL) of the portable XRF was influenced by scan time
and overlying soft tissue thickness for both Pb and Sr. </p>
<p>For the
exposure assessment of Mn and Hg in toenails, we first established system
calibrations and determined the DL with phantoms. In order to validate the portable XRF in a population
study, the recruited participants were measured at the big toenail by the device,
and their toenail clippings were analyzed by the inductively coupled plasma
spectrometry (ICP-MS). Besides, we analyzed the toenail data of an
occupationally-exposed population, collected by our collaborators in Boston. A
portable XRF device with the same model as ours was used in that study. </p>
<p><b><i>Results:</i></b> The uncertainty of <i>in vivo</i>
individual bone measurement increased with higher soft tissue thickness
overlying bone, and reduced with extending measurement time. With thickness ranging
from 2 to 6 mm, the uncertainty of a 3-minute <i>in vivo</i> measurement ranged from 1.8 to 6.3 ug/g (ppm) for bone Pb and from
1.3 to 2.3 ppm for bone Sr. Bone Pb measurements via portable XRF and KXRF were
highly correlated: R=0.48 for all participants, and R=0.73 among participants
with soft tissue thickness < 6 mm (72% of the sample). A trend of different bone
Sr concentrations was observed across the races and sexes. </p>
<p>The DL
of the portable XRF with 3-minute toenail measurements was 3.59 ppm for Mn and
0.58 ppm for Hg. The portable XRF and ICP-MS measurements were highly
correlated in the occupational populations for both Mn (R = 0.59) and Hg (R =
0.75). A positive correlation
(R = 0.34) was found for toenail Mn measurements in the environmentally-exposed
population, while a non-significant correlation was observed for toenail Hg due to the extremely low-level
of Hg (Mean = 0.1 ppm) in the study population. </p>
<p><b><i>Discussion and
Conclusion:</i></b>
The portable XRF could be a valuable tool for non-invasive <i>in vivo</i> quantification of bone Pb and Sr, especially for people
with thinner soft tissue; and of toenail Mn and Hg, especially for people with
moderate- to high-level exposures. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12482198 |
| Date | 23 June 2020 |
| Creators | Xinxin Zhang (8974130) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/IN_VIVO_QUANTIFICATION_OF_HEAVY_METALS_IN_BONE_AND_TOENAIL_USING_X-RAY_FLUORESCENCE_XRF_/12482198 |
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