The decrease in population bone lead levels in Canada between 1993 and 2010 as assessed by in vivo XRF

Portable x-ray fluorescence for bone lead measurement: Current approaches and future directions

PURPOSE OF REVIEW

Legacy lead exposures persist as a widespread problem. Blood lead is traditionally used for lead exposure surveillance; however, bone lead proves to be a cheaper, more accessible, and more revealing tool for surveillance that can be measured using portable x-ray fluorescence techniques. We outline how this approach excels for bone lead measurements.

RECENT FINDINGS

Portable XRF offers quick, non-invasive in vivo quantification of bone lead. Compared to traditional KXRF systems, pXRF is limited to cortical bone but allows for quicker and similar results. Current methodologies of lead exposure need re-evaluation as lead-related disease burden and trends are dependent on both cumulative and acute impacts. We examined the evolution of XRF techniques for measuring bone lead, comparing current methods with previous ones. We assessed their accuracy, identified limitations, and discussed potential advances in future techniques. Legacy lead exposures call for a revitalization of lead surveillance methods, and pXRF measurement of bone lead offers such a solution.

Lead exposure across the life course and age at death

BACKGROUND

Lead (Pb) exposure has been associated with an increased risk of all-cause mortality, even at low levels. Little is known about how the timing of Pb exposure throughout life may influence these relationships. Quantifying the amount of Pb present in various tissues of the body provides measurements of exposure from different periods of life. These include bone, tooth enamel, which is the hard outer layer of the crown, and tooth cementum, which is the calcified connective tissue covering the tooth root. The purpose of the study was to examine Pb exposure at multiple periods throughout life, including childhood (enamel), adulthood (cementum), and later life (bone), and to estimate their associations with age at death.

METHODS

208 skeleton donors (born 1910-1960) from an ongoing case-control study were included in this study. Pb was measured in tibia (shin), bone using X-Ray Florescence and in teeth using Laser-Ablation Inductively Coupled Plasma Mass Spectroscopy. After excluding unusually high measurements (>2sd), this resulted in a final sample of 111 with all exposure measures. Correlations across measures were determined using partial Spearman correlations. Associations between Pb exposure and age at death were estimated using Multivariable Linear Regression.

RESULTS

Pb measures across exposure periods were all significantly correlated, with the highest correlation between cementum and tibia measures (r = 0.61). Donors were largely female (63.0 %), White (97.3 %), and attended some college (49.5 %). Single exposure models found that higher tooth cementum Pb (-1.27; 95 % CI: -2.48, -0.06) and tibia bone Pb (-0.91; 95 % CI: -1.67, -0.15) were significantly associated with an earlier age at death. When considered simultaneously, only cementum Pb remained significant (-1.51; 95 % CI: -2.92, -0.11). Secondary analyses suggest that the outer cementum Pb may be especially associated with an earlier age at death.

CONCLUSION

Results suggest that higher Pb exposure is associated with an earlier age at death, with adulthood as the life period of most relevance. Additional studies using Pb exposure measures from different life stages should be conducted.

The feasibility of K XRF bone lead measurements in mice assessed using 3D-printed phantoms

This article describes the development of a system forin vivomeasurements of lead body burden in mice using109Cd K x-ray fluorescence (XRF). This K XRF system could facilitate early-stage studies on interventions that ameliorate or reverse organ tissue damage from lead poisoning by reducing animal numbers through a cross-sectional study approach. A novel mouse phantom was developed based on a mouse atlas and 3D-printed using PLA plastic with plaster of Paris 'bone' inserts. PLA plastic was found to be a good surrogate for soft tissue in XRF measurements and the phantoms were found to be good models of mice. As expected, lead detection limits varied with mouse size, mouse orientation, and mouse position with respect to the source and detector. The work suggests that detection limits of 10 to 20μg Pb per g bone mineral may be possible for a 2 to 3 hour XRF measurement in a single animal, an adequate limit for some pre-clinical studies. The109Cd K XRF mouse measurement system was also modeled using the Monte Carlo code MCNP. The combination of experiment and modeling found that contrary to expectation, accurate measurements of lead levels in mice required calibration using mouse-specific calibration standards due to the coherent scatter peak normalization failing when small animals are measured. MCNP modeling determined that this was because the coherent scatter signal from soft tissue, which until now has been assumed negligible, becomes significant when compared to the coherent scatter signal in bone in small animals. This may have implications for some human measurements. This work suggests that109Cd K x-ray fluorescence measurements of lead body burden are precise enough to make the system feasible for small animals if appropriately calibrated. Further work to validate the technology's measurement accuracy and performancein vivowill be required.

Bone lead variability in bone repository skeletal samples measured with portable x-ray fluorescence

Bone lead serves as a better, more accessible biomarker to many communities experiencing chronic exposure to lead. A new method using low energy x-ray fluorescence in a handheld device (portable XRF) allows us to measure this chronic biomarker in only a few minutes. However, many unknowns remain about this biomarker measured using a new low energy x-ray technique. The low energy of the new method was theorized to measure a slightly different portion of the bone than previous techniques, which could influence measurements at different bone sites and types. We tested how bone measurements varied across five bone sites: mid-tibial shaft, proximal tibia, distal tibia (ankle), ilium, and cranium. We found bone lead measurements are not significantly different between skeletal elements when measured using a portable XRF. On average, bone lead in the repository samples was measured to be 21.6 ± 21.3 μg/g with an XRF detection limit of 2.1 ± 0.5 μg/g. Cumulative lead exposure can be effectively measured using the portable XRF on a variety of bone types, but the tibia should be preferentially measured to compare between studies and individuals.

Lead exposure and serum metabolite profiles in pregnant women in Mexico City

BACKGROUND

Lead (Pb) exposure is a global health hazard causing a wide range of adverse health outcomes. Yet, the mechanisms of Pb toxicology remain incompletely understood, especially during pregnancy. To uncover biological pathways impacted by Pb exposure, this study investigated serum metabolomic profiles during the third trimester of pregnancy that are associated with blood Pb and bone Pb.

METHODS

We used data and specimens from 99 women enrolled in the Programming Research in Obesity, Growth, Environment, and Social Stressors birth cohort in Mexico City. Maternal Pb exposure was measured in whole blood samples from the third trimester of pregnancy and in the tibia and patella bones at 1 month postpartum. Third-trimester serum samples underwent metabolomic analysis; metabolites were identified based on matching to an in-house analytical standard library. A metabolome-wide association study was performed using multiple linear regression models. Class- and pathway-based enrichment analyses were also conducted.

RESULTS

The median (interquartile range) blood Pb concentration was 2.9 (2.6) µg/dL. Median bone Pb, measured in the tibia and patella, were 2.5 (7.3) µg/g and 3.6 (9.5) µg/g, respectively. Of 215 total metabolites identified in serum, 31 were associated with blood Pb (p < 0.05). Class enrichment analysis identified significant overrepresentation of metabolites classified as fatty acids and conjugates, amino acids and peptides, and purines. Tibia and patella Pb were associated with 14 and 8 metabolites, respectively (p < 0.05). Comparing results from bone and blood Pb, glycochenodeoxycholic acid, glycocholic acid, and 1-arachidonoylglycerol were positively associated with blood Pb and tibia Pb, and 7-methylguanine was negatively associated with blood Pb and patella Pb. One metabolite, 5-aminopentanoic acid, was negatively associated with all three Pb measures.

CONCLUSIONS

This study identified serum metabolites in pregnant women associated with Pb measured in blood and bone. These findings provide insights on the metabolic profile around Pb exposure in pregnancy and information to guide mechanistic studies of toxicological effects for mothers and children.

A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration using the strontium Kβ/Kαratio

Objective. Lead (Pb) is a well-known toxic element.In vivobone Pb concentration measurement is a long-term exposure metric complementary to blood Pb concentration measurement which is a metric of recent exposure.In vivohuman tibia bone Pb measurements using Pb K-shell or L-shell x-ray fluorescence (KXRF or LXRF) emissions were developed in the 1980s. KXRF bone Pb measurements using Cd-109 gamma rays and coherent-to-fluorescence ratio to account for differences between phantom andin vivomeasurements, was employed in human studies. Bone Pb LXRF method employed x-ray tubes. However, calibration procedures using ultrasound measurements of the soft tissue thickness (STT) proved inaccurate.Approach. In this study, bone and soft tissue (ST) phantoms simulatedin vivobone Pb measurements. Seven plaster-of-Paris cylindrical bone phantoms containing 1.01 mg g-1of strontium (Sr) were doped with Pb in 0, 8, 16, 29, 44, 59, and 74 μg g-1concentrations. Polyoxymethylene (POM), resin, and wax were each used to fabricate four ST phantoms in the approximate 1-4 mm thickness range. Pb LXRF measurements were performed using a previously developed optimal grazing incidence position method.Main results. Linear attenuation coefficients measurements of ST materials indicated that POM and resin mimicked well attenuation of Pb x-rays in skin and adipose tissue, respectively. POM and resin data indicated a bone Pb detection limit of 20 μg g-1for a 2 mm STT. Derived relationships between the Pb concentration, Pb LXRF and Sr Kβ/Kαratio data did not require STT knowledge. Applied to POM and resin data, the new calibration method yielded unbiased results.Significance.In vivobone Pb measurements in children were suggested following considerations of radiation dose, STT, detectability and distribution of Pb and Sr in bone. This research meets with the concerns regarding the negative effects of low levels of Pb exposure on neurodevelopment of children.

Lead exposure and association with angiogenic factors and hypertensive disorders of pregnancy

OBJECTIVES

Lead exposure has been associated with hypertensive disorders of pregnancy. Angiogenic factors, including soluble fms-like tyrosine kinase 1 (sFlt1) and placental growth factor (PlGF), are aberrant in preeclampsia, but have not been correlated with lead levels. We evaluated the association of lead exposure with angiogenic factors.

STUDY DESIGN

This cross sectional study utilized a convenience sample of singleton pregnancies ≥34 weeks' gestation. Blood lead and angiogenic factors were measured before delivery; bone lead was measured postpartum. We dichotomized bone and blood lead into the top tertile versus the bottom tertiles and used log-binomial regression to assess the association between lead and a high angiogenic ratio.

MAIN OUTCOME MEASURES

The outcomes were high sFlt1 to PlGF ratio and development of a hypertensive disorder of pregnancy.

RESULTS

We enrolled 102 participants, of whom 98 had at least one lead measurement and an angiogenic factor result. Median bone lead was 3.8 ug/g (2.0 - 6.6) and median blood lead was 0.2 ug/dL (0.2 - 0.4). Incidence of hypertensive disorders of pregnancy was 31%. When comparing the highest tertile of bone lead to the bottom two tertiles, there was no association with a high sFlt1/PlGF ratio or hypertensive disorders of pregnancy. Similar results were observed for the exposure of blood lead.

CONCLUSIONS

Lead exposure was not an important contributor to an elevated angiogenic factor ratio or hypertensive disorders of pregnancy in our U.S.

POPULATION

However, lead exposure was modest in our population and we cannot exclude a relationship with hypertensive disorders of pregnancy.

Elemental analysis in living human subjects using biomedical devices

Today, patients undergoing dialysis are at low risk for aluminum-induced dementia. Workers are unlikely to experience cadmium-induced emphysema and the public's exposure to lead is an order of magnitude lower than in 1970. The research field of in vivo elemental analysis has played a role in these occupational and environmental health improvements by allowing the effects of people's chronic exposure to elements to be studied using non-invasive, painless, and relatively low-cost technology. From the early 1960s to the present day, researchers have developed radiation-based systems to measure the elemental content of organs at risk or storage organs. This reduces the need for (sometimes painful) biopsy and the risk of infection. Research and development has been undertaken on forty-nine in vivo measurement system designs. Twenty-nine different in vivo elemental analysis systems, measuring 22 different elements, have been successfully taken from design and testing through to human measurement. The majority of these systems employ either neutron activation analysis or x-ray fluorescence analysis as the basis of the measurement. In this review, we discuss eight of the successful systems, explaining the rationale behind their development, the methodology, the health data that has resulted from application of these tools, and provide our opinion on potential future technical developments of these systems. We close by discussing four technologies that may lead to new directions and advances in the whole field.

Comparison of bone lead measured via portable x-ray fluorescence across and within bones

BACKGROUND

Bone lead measured via x-ray fluorescence (XRF) has been used for decades in health studies. A portable XRF device for bone lead measurement is gaining in popularity for its ease of use and shorter measurement times. Previous XRF devices have measured different bone types in order to sample both cortical and trabecular bone, in which lead has different half residence times.

OBJECTIVE

The portable XRF uses lower energy to measure bone lead than previous devices, and, thus, only measures the surface of the bone. Because all bones have a cortical shell, we hypothesized that portable XRF bone lead measurements would be similar regardless of the bone measured.

METHODS

This study tested differences in portable XRF bone lead measurements across different cortical and trabecular bones in measurements made on 31 cadavers. We also compared tissue thicknesses overlying different bones, which can impact portable XRF measurements.

RESULTS

The correlation coefficients found between bones were higher (rho ~0.4) than previous K-shell XRF bone measurements in cortical and trabecular over the same range of values (rho~0.2). The concentrations were shown to vary non-significantly across different bones within individuals.

Lead (Pb) in Alzheimer’s Dementia: A Systematic Review of Human Case- Control Studies

Background:

Alzheimer’s Dementia (AD) has a complex pathophysiology that is incompletely understood. Chronic, low-level environmental lead (Pb) exposure is associated with cognitive impairment, hypertension and mortality, and has been proposed as a potential cause of AD.

Objective:

We aimed to review the literature to clarify the potential role of Pb in AD and to guide future research.

Methods:

Through a series of systematic reviews, we identified case-control studies comparing AD to controls on 6 measures of Pb exposure or accumulation: blood, bone, cerebrospinal fluid, hair/nail, postmortem pathology, and urine. We completed meta-analyses where possible.

Results:

The number of identified case-control studies of AD, by measurement method, was: 15 by blood, 0 by bone, 5 by Cerebrospinal Fluid (CSF), 3 by hair/nail, 3 by postmortem, and 1 by urine. Two meta-analyses were possible for 7 studies reporting whole blood Pb and for 8 studies of serum Pb. Both were negative. The largest study of CSF Pb showed lower levels in AD. Similarly, lower hair Pb levels were found in AD.

Conclusion:

The available case-control studies are insufficient to draw conclusions on the role of Pb in AD. Most methods do not address long-term or early-life exposure. The preferred measure of chronic Pb is in bone, which has not been utilized in case-control AD studies. Future research should measure bone Pb in AD, together with other biomarkers, such as amyloid and tau imaging, and markers of cerebrovascular pathology.