In Vivo Quantification of Heavy Metals in Bone and Toenail Using X-Ray Fluorescence (XRF)

Xinxin Zhang, Purdue University

Abstract

Background and Objective: 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 in vivo to evaluate such associations further. Bone and toenail are appropriate biomarkers to reflect longterm 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 in vivo quantification of Pb and Sr in bone, and Mn and Hg in toenail. Materials and Methods: The portable XRF device was calibrated by using the Pb- and Srdoped 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 in vivo 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. 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. Results: The uncertainty of in vivo 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 in vivo measurement ranged from 1.8 to 6.3 g/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.

Degree

Ph.D.

Advisors

Nie, Purdue University.

Subject Area

Aging|Food Science|Gerontology|Materials science|Medicine|Neurosciences|Public health|Toxicology

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