XRF-measured bone lead (Pb) as a biomarker for Pb exposure and toxicity among children diagnosed with Pb poisoning

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.

Bone lead measurements of live condors in field to assess cumulative lead exposure

Lead poisoning remains the leading cause of diagnosed death for critically endangered California condors, which are annually monitored for lead exposure via blood tests. Blood tests are generally reflective of acute lead exposure. Since condors are victims to both chronic and acute lead exposure, measuring bone, which in humans is reflective of years to decades worth of exposure, is a valuable biomarker. In this study, we measured bone Pb of the tibiotarsus of 64 condors in vivo using a portable x-ray fluorescence device. The average uncertainty for measurements, typically reflective of how effective the device performed, was found to be 3.8 ± 2.2 µg/g bone mineral. The average bone lead level was found to be 26.7 ± 24.5 µg/g bone mineral. Bone lead correlated significantly with a sum of all blood lead measures over the lifetime of each condor. In the future, bone lead can potentially be used to inform treatment planning and address the chronic health implications of lead in the species.

A detailed methodology for a three-dimensional, self-structuring bone model that supports the differentiation of osteoblasts towards osteocytes and the production of a complex collagen-rich mineralised matrix

Background

There are insufficient in vitro bone models that accommodate long-term culture of osteoblasts and support their differentiation to osteocytes. The increased demand for effective therapies for bone diseases, and the ethical requirement to replace animals in research, warrants the development of such models.Here we present an in-depth protocol to prepare, create and maintain three-dimensional, in vitro, self-structuring bone models that support osteocytogenesis and long-term osteoblast survival (>1 year).

Methods

Osteoblastic cells are seeded on a fibrin hydrogel, cast between two beta-tricalcium phosphate anchors. Analytical methods optimised for these self-structuring bone model (SSBM) constructs, including RT-qPCR, immunofluorescence staining and XRF, are described in detail.

Results

Over time, the cells restructure and replace the initial matrix with a collagen-rich, mineralising one; and demonstrate differentiation towards osteocytes within 12 weeks of culture.

Conclusions

Whilst optimised using a secondary human cell line (hFOB 1.19), this protocol readily accommodates osteoblasts from other species (rat and mouse) and origins (primary and secondary). This simple, straightforward method creates reproducible in vitro bone models that are responsive to exogenous stimuli, offering a versatile platform for conducting preclinical translatable research studies.

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.

Metabolomics insights into the effects of pre-pregnancy lead exposure on bone metabolism in pregnant rats

Today's women of childbearing age with a history of high lead (Pb) exposure in childhood have large Pb body burdens, which increases Pb release during pregnancy by promoting bone Pb mobilisation. The purpose of this study was to investigate the metabolic mechanisms underlying bone Pb mobilisation and explore the bone metabolism-related pathways during pregnancy. Drinking water containing 0.05% sodium acetate or Pb acetate was provided to weaned female rats for 4 weeks followed by a 4-week washout period, and then rats were co-caged with healthy males of the same age until pregnancy. Blood and bone tissues of the female rats were collected at gestational day (GD) 3 (early pregnancy), GD 10 (middle pregnancy), and GD 17 (late pregnancy), respectively. Pb and calcium concentrations, biomarkers for bone turnover, bone microstructure, serum metabolomics, and metabolic indicators were intensively analyzed. The results demonstrated that pre-pregnancy Pb exposure elevated blood lead levels (BLLs) at GD17, accompanied by a negative correlation between BLLs and trabecular bone Pb levels. Meanwhile, Pb-exposed rats had low bone mass and aberrant bone architecture with a larger number of mature osteoclasts (OCs) compared to the control group. Moreover, the metabolomics uncovered that Pb exposure caused mitochondrial dysfunction, such as enhanced oxidative stress and inflammatory response, and suppressed energy metabolism. Additionally, the levels of ROS, MDA, IL-1β, and IL-18 involved in redox and inflammatory pathways of bone tissues were significantly increased in the Pb-exposed group, while antioxidant SOD and energy metabolism-related indicators including ATP levels, Na+-K+-ATPase, and Ca2+-Mg2+-ATPase activities were significantly decreased. In conclusion, pre-pregnancy Pb exposure promotes bone Pb mobilisation and affects bone microstructure in the third trimester of pregnancy, which may be attributed to OC activation and mitochondrial dysfunction.

A State-of-the-Science Review on Metal Biomarkers

PURPOSE OF REVIEW

Biomarkers are commonly used in epidemiological studies to assess metals and metalloid exposure and estimate internal dose, as they integrate multiple sources and routes of exposure. Researchers are increasingly using multi-metal panels and innovative statistical methods to understand how exposure to real-world metal mixtures affects human health. Metals have both common and unique sources and routes of exposure, as well as biotransformation and elimination pathways. The development of multi-element analytical technology allows researchers to examine a broad spectrum of metals in their studies; however, their interpretation is complex as they can reflect different windows of exposure and several biomarkers have critical limitations. This review elaborates on more than 500 scientific publications to discuss major sources of exposure, biotransformation and elimination, and biomarkers of exposure and internal dose for 12 metals/metalloids, including 8 non-essential elements (arsenic, barium, cadmium, lead, mercury, nickel, tin, uranium) and 4 essential elements (manganese, molybdenum, selenium, and zinc) commonly used in multi-element analyses.

RECENT FINDINGS

We conclude that not all metal biomarkers are adequate measures of exposure and that understanding the metabolic biotransformation and elimination of metals is key to metal biomarker interpretation. For example, whole blood is a good biomarker of exposure to arsenic, cadmium, lead, mercury, and tin, but it is not a good indicator for barium, nickel, and uranium. For some essential metals, the interpretation of whole blood biomarkers is unclear. Urine is the most commonly used biomarker of exposure across metals but it should not be used to assess lead exposure. Essential metals such as zinc and manganese are tightly regulated by homeostatic processes; thus, elevated levels in urine may reflect body loss and metabolic processes rather than excess exposure. Total urinary arsenic may reflect exposure to both organic and inorganic arsenic, thus, arsenic speciation and adjustment for arsebonetaine are needed in populations with dietary seafood consumption. Hair and nails primarily reflect exposure to organic mercury, except in populations exposed to high levels of inorganic mercury such as in occupational and environmental settings. When selecting biomarkers, it is also critical to consider the exposure window of interest. Most populations are chronically exposed to metals in the low-to-moderate range, yet many biomarkers reflect recent exposures. Toenails are emerging biomarkers in this regard. They are reliable biomarkers of long-term exposure for arsenic, mercury, manganese, and selenium. However, more research is needed to understand the role of nails as a biomarker of exposure to other metals. Similarly, teeth are increasingly used to assess lifelong exposures to several essential and non-essential metals such as lead, including during the prenatal window. As metals epidemiology moves towards embracing a multi-metal/mixtures approach and expanding metal panels to include less commonly studied metals, it is important for researchers to have a strong knowledge base about the metal biomarkers included in their research. This review aims to aid metals researchers in their analysis planning, facilitate sound analytical decision-making, as well as appropriate understanding and interpretation of results.

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.

Expanding the use of portable XRF to monitor lead exposure in an Australian duck species two decades after a ban on lead shot

There is growing worldwide recognition of the threat posed by toxic lead for wildlife and humans. Lead toxicity from ammunition has been shown to be a threat to waterbirds across the globe. Lead shot was banned for all waterfowl hunting in Victoria, Australia, in 2002. However, no assessments of lead exposure in Australian waterfowl have been published since the 1990s. Our aim was to estimate contemporary lead exposure via measuring bone lead concentrations in a harvested dabbling duck, the Pacific black duck (Anas superciliosa). We collected wings from 77 Pacific black ducks, spanning 2018 (n = 30) and 2021 (n = 47), from nine sites with long-term histories of regular waterfowl hunting. We sought to validate portable X-ray fluorescence (XRF) for this purpose by taking a piece of humerus bone from each bird, and measuring lead concentration (mg/kg), first via non-destructive XRF and then via destructive inductively coupled plasma mass spectrometry (ICP-MS) and validated the relationship via regression analysis. Portable XRF bone lead measurement demonstrated a strong correlation with ICP-MS results using root-transformed regression (R² = 0.85). Greater than 92 % of ducks had only background lead exposure (<10 mg/kg). When compared to historical studies in the same species at similar field sites from the 1990s, lead exposure levels were considerably lower, with mean lead concentrations ∼2-fold lower (3.7 c.f. 7.7 mg/kg), and the frequency of birds with severe lead exposure (>20 mg/kg) ∼3-fold lower (2.6 c.f. 7.5 %). Our results confirm that portable XRF is a useful option for measurement of bone lead in Australasian waterbird species. Our findings also demonstrate that a ban on the use of lead shot around 20 years ago has been associated with a substantial reduction in lead exposure in at least one species of waterfowl.

Bioaccumulation and human health implications of trace metals in oysters from coastal areas of China

This study recompiled a national dataset to characterize the pollution level and health risk of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in oysters along the coastal areas of China. Results showed that the median concentrations of Cd, Cu, Pb and Zn in nationwide oysters were 5.5, 335, 1.3 and 1280 mg/kg dry weight, respectively. Generally, oysters from the north coasts presented lower metal pollution and higher quality than those from the south. The regional characteristics of trace metals in oysters might be contributed by the interspecific differences. Nationally, the noncarcinogenic risk posed by these four metals in oysters was relatively low, with the risk only occurring in a few hotspots such as the Pearl River Estuary and the Jiulong River Estuary. However, more attention should be paid to the carcinogenic risk of Cd, and priority should be given to formulating control measures to mitigate Cd pollution.

Combined effects of multiple metals on hearing loss: A Bayesian kernel machine regression approach

BACKGROUND

Exposure to heavy elements is considered one of the risks of hearing loss. The combined effect of multiple metals on different hearing losses has not been extensively studied.

METHODS

This study deals with the association between different metals (Ba, Cd, Co, Cs, Mo, Pb, Mn, Sn, Sb, Tl, W) and hearing loss in the 2013-2018 National Health and Nutrition Examination Survey (NHANES). Associations were estimated by a generalized linear regression model (GLM) adjusting for age, gender, race/ethnicity, educational level, marital status, drinking status, hypertension, diabetes, smoking status, noise exposure, body mass index, and income-poverty ratio. The joint effects of mixed exposure were assessed by weighted quantile sum (WQS) model and Bayesian kernel machine regression (BKMR). The effect of multiple metals on speech-frequency hearing loss (SFHL) and high-frequency hearing loss (HFHL) was further calculated. The odds ratio (OR) indicates the risk of every metal exposure.

RESULTS

A total of 2205 adult participants were enrolled from NHANES. Cd, Pb, Sb and Sn had significant effects on total hearing loss. The WQS model found that mixed exposure to heavy elements was significantly positively associated with total hearing loss (OR: 1.136; 95% CI: 1.031, 1.253) after adjusting for various covariates. The ORs of mixed exposure in the SFHL and HFHL groups were 1.066 (95% CI: 0.994, 1.143) and 1.102 (95% CI: 1.013, 1.199), respectively. BKMR found a significant positive association between multiple metals and hearing loss. The results showed that there may be potential interactions between Cd, Pb and other metals.

CONCLUSIONS

Multiple metals have joint effects on hearing loss in the United States. The findings provide practitioners with important scientific evidence for possible interventions.

Lead and other toxic metals in plastic play foods: Results from testing citizen science, lead detection tools in childcare settings

A method development pilot study examining citizen science tools for assessing lead in childcare settings identified plastic food toys as an unexpected potential source of lead and arsenic. Collaborating researchers at three universities sought to develop a low cost, replicable approach for use in childcare centers to identify lead. Through graduate Environmental Health courses at Northeastern and Boston Universities, 197 Plastic Food Toys (PFTs) used in a childcare center were tested for lead using a portable X-Ray fluorescence (XRF) instrument and a colorimetric wipe method for detecting surface lead. The XRF identified concerning levels of lead and co-occurring arsenic in PFTs. The XRF analysis found 8.63% (17/197) of PFTs from the childcare center contained more than 100.00 ppm of lead, the U.S. Consumer Protection Safety Commission's (CPSC) upper regulatory threshold for lead in childrens' products. However, wipes did not detect removable surface lead. Lead concentrations ranged from 6.14 ppm to 11,999.00 ppm with a median of 40.00 ppm. Additionally, 7.10% of all PFTs tested had detectable levels of arsenic which ranged from 9.30 ppm to 1134.42 ppm and had a median value of 113.20 ppm. Arsenic concentrations in 6.60% of PFTs' exceeded the US voluntary standard for arsenic in children's products of 25.00 ppm (adopted from the EU standard). These findings prompted further sampling of similar newly-purchased PFTs. None of the newly-purchased PFTs tested positive for lead or arsenic (0/87). Several other elements were also identified, particularly in the used PFTs. Because these food-like toys are frequently put in children's mouths, we recommend further investigation of PFTs in circulation via citizen science combining the wipe and XRF method as they provide immediate data to participants. Additionally, CPSC should consider a systematic recall of some used PFTs to prevent exposure disparities by socio-economic status and increased surveillance for other toxic metals in new PFTs.

Environmental effects on trace elements in the fingernails of centenarians and their offspring

Bio-monitoring is commonly used to investigate trace elements, and the human nail provides an ideal medium for such testing. Toxic and essential trace metals (Cd, Pb, Fe, and Se) in the fingernails of participants from the Hainan Province were investigated. Samples included 136 centenarians and 197 offspring (101 older adult children and 96 middle-aged grandchildren) who were also sampled for comparison. As a hotspot for longevity, participants in the Hainan Province were found to have high essential nutrients of Fe and Se, and lacked the toxic element Pb. A similar trend was found for trace elements in soil and rice in the Hainan Province. The trace elements preserved in nails revealed dietary and environmental influences that varied among different generations. For the grandchildren's generation, the environment played an important role in elements in their nails, and a significant correlation and linear relationships were found, especially for Fe and Se. As the participants increased in age (from the grandchildren to the centenarians), the correlation between various elements decreased. For centenarians, the influence of beneficial or harmful properties of the elements became more important than their environment. The results also pointed to the important role of trace elements in human health, especially Fe and Se as essential elements. This study can provide information on the factors that influence the existence of trace elements in the human body and demonstrate the advantage of using the human fingernail in bio-monitoring.

Validation of in vivo toenail measurements of manganese and mercury using a portable X-ray fluorescence device

BACKGROUND AND OBJECTIVE

Toenail metal concentrations can be used as an effective biomarker for exposure to environmental toxicants. Typically toenail clippings are measured ex vivo using inductively coupled plasma mass spectrometry (ICP-MS). X-ray fluorescence (XRF) toenail metal measurements done on intact toenails in vivo could be used as an alternative to alleviate some of the disadvantages of ICP-MS. In this study, we assessed the ability to use XRF to measure toenail metal concentrations in real-time without having to clip the toenails (i.e., in vivo) in two occupational settings for exposure assessment of manganese and mercury.

MATERIALS AND METHODS

The portable XRF method used a 3-min in vivo measurement of toenails prior to clipping and was assessed against ICP-MS measurement of toenail clippings taken immediately after the XRF measurement and work history for a group of welders (n = 16) assessed for manganese exposure and nail salon workers (n = 10) assessed for mercury exposure.

RESULTS AND CONCLUSIONS

We identified that in vivo XRF metal measurements were able to discern exposure to manganese in welders and mercury in nail salon workers. We identified significant positive correlations between ICP-MS of clippings and in vivo XRF measures of both toenail manganese (R = 0.59, p = 0.02) and mercury (R = 0.74, p < 0.001), as well as between in vivo XRF toenail manganese and work history among the welders (R = 0.55, p = 0.03). We identified in vivo XRF detection limits to be 0.5 µg/g for mercury and 2.6 µg/g for manganese. Further work should elucidate differences in the timing of exposure using the in vivo XRF method over toenail clippings and modification of measurement time and x-ray setting to further decrease the detection limit. In vivo portable, XRF measurements can be used to effectively measure toenail Mn and Hg in occupational participants in real-time during study visits and at a fraction of the cost.

Susceptibility to Environmental Heavy Metal Toxicity among Americans with Kidney Disease

Background

The consequences of low levels of environmental heavy metal exposure, as found widely in the United States, in those with impaired renal function remain underexplored.

Methods

We examined the cross-sectional association of indices of renal function with lead and cadmium levels in blood and urine among National Health and Nutrition Examination Survey (NHANES) participants. We used the 1999-2002 cycle, which included measures of cystatin C, in order to quantify renal function most precisely and defined chronic kidney disease (CKD) as an estimated glomerular filtration rate (eGFR) <60 ml/min per 1.73 m².

Results

In weighted and adjusted analyses of 5638 participants, lead levels were 0.23 (95% CI, 0.03 to 0.42) μg/dl higher among participants with CKD, and 0.05 (95% CI, 0.01 to 0.09) μg/dL higher per 10 ml/min per 1.73 m² lower eGFR. Cadmium levels were 0.02 (95% CI, 0.01 to 0.03) μg/L higher per 10 ml/min per 1.73 m² lower eGFR. Black race significantly modified the association of lower eGFR with higher circulating lead levels (P interaction <0.001). A 10 ml/min per 1.73 m² lower eGFR was associated with a 0.13 (95% CI, 0.06 to 0.21) μg/dl higher lead level among Black participants compared with 0.03 (95% CI, -0.04 to 0.11) μg/dl higher level among White participants. Among the 1852 participants with urinary metal measurements, despite higher circulating levels, those with CKD had significantly lower urinary lead levels (-0.16 [95% CI, -0.30 to -0.01] ng/ml) and urinary lead/creatinine ratios (-0.003 [95% CI, -0.004 to -0.001]).

Conclusions

CKD is associated with higher blood lead levels, particularly among Blacks, and simultaneously, lower urinary lead levels, consistent with the hypothesis that CKD confers a state of heighted susceptibility to heavy metal environmental exposure by reducing its elimination. Given that low levels of exposure remain highly prevalent in the United States, further efforts to protect patients with CKD from heavy metal toxicity may be warranted.

Bone manganese is a sensitive biomarker of ongoing elevated manganese exposure, but does not accumulate across the lifespan

Studies have established associations between environmental and occupational manganese (Mn) exposure and executive and motor function deficits in children, adolescents, and adults. These health risks from elevated Mn exposure underscore the need for effective exposure biomarkers to improve exposure classification and help detect/diagnose Mn-related impairments. Here, neonate rats were orally exposed to 0, 25, or 50 mg Mn/kg/day during early life (PND 1-21) or lifelong through ∼ PND 500 to determine the relationship between oral Mn exposure and blood, brain, and bone Mn levels over the lifespan, whether Mn accumulates in bone, and whether elevated bone Mn altered the local atomic and mineral structure of bone, or its biomechanical properties. Additionally, we assessed levels of bone Mn compared to bone lead (Pb) in aged humans (age 41-91) living in regions impacted by historic industrial ferromanganese activity. The animal studies show that blood, brain, and bone Mn levels naturally decrease across the lifespan without elevated Mn exposure. With elevated exposure, bone Mn levels were strongly associated with blood Mn levels, bone Mn was more sensitive to elevated exposures than blood or brain Mn, and Mn did not accumulate with lifelong elevated exposure. Elevated early life Mn exposure caused some changes in bone mineral properties, including altered local atomic structure of hydroxyapatite, along with some biomechanical changes in bone stiffness in weanlings or young adult animals. In aged humans, blood Mn ranged from 5.4 to 23.5 ng/mL; bone Mn was universally low, and decreased with age, but did not vary based on sex or female parity history. Unlike Pb, bone Mn showed no evidence of accumulation over the lifespan, and may not be a biomarker of cumulative long-term exposure. Thus, bone may be a useful biomarker of recent ongoing Mn exposure in humans, and may be a relatively minor target of elevated exposure.

Association between Bone Lead Concentration and Aggression in Youth from a Sub-Cohort of the Birth to Twenty Cohort

BACKGROUND

An association between blood-lead levels and aggression has been demonstrated in children and adolescent youth in South Africa. However, there are limited studies that have assessed aggression as an outcome for cumulative lead exposure using bone lead concentration. This study aims to assess the association between bone lead concentration and aggressive behaviour among a sample of youth in South Africa.

METHODS

Bone lead in 100 participants (53 males and 47 females) recruited and followed in the Birth to Twenty (BT20) Cohort were measured using 109 Cd-based, K-shell X-ray fluorescence (KXRF). The Buss-Perry Aggression questionnaire was used to measure aggressive behaviour. Linear regression models were fitted to determine the association between aggression score for physical, verbal, anger and hostility and bone lead, adjusting for known confounders.

RESULTS

A one-microgram-per-gram increase in bone lead was found to increase the score for all four scales of aggression, but significantly only for anger (β = 0.2 [95% CI 0.04-0.370]). Psychosocial factors such as a history of family violence and exposure to neighbourhood crime were significant predictors for aggression.

CONCLUSIONS

The study provides a preliminary overview of the relationship between cumulative lead exposure and behavioural problems such as aggression. A larger sample, across exposed communities, may prove more definitive in further investigating the association between these two important public health factors and to maximize generalizability.

Assessment of In Vitro and In Vivo Bioremediation Potentials of Orally Supplemented Free and Microencapsulated Lactobacillus acidophilus KLDS Strains to Mitigate the Chronic Lead Toxicity

Lead (Pb) is a pestilent and relatively nonbiodegradable heavy metal, which causes severe health effects by inducing inflammation and oxidative stress in animal and human tissues. This is because of its significant tolerance and capability to bind Pb (430 mg/L) and thermodynamic fitness to sequester Pb in the Freundlich model (R² = 0.98421) in vitro. Lactobacillus acidophilus KLDS1.1003 was selected for further in vivo study both in free and maize resistant starch (MRS)–based microencapsulated forms to assess its bioremediation aptitude against chronic Pb lethality using adult female BALB/c mice as a model animal. Orally administered free and microencapsulated KLDS 1.1003 provided significant protection by reducing Pb levels in the blood (127.92 ± 5.220 and 101.47 ± 4.142 µg/L), kidneys (19.86 ± 0.810 and 18.02 ± 0.735 µg/g), and liver (7.27 ± 0.296 and 6.42 ± 0.262 µg/g). MRS-microencapsulated KLDS 1.0344 improved the antioxidant index and inhibited changes in blood and serum enzyme concentrations and relieved the Pb-induced renal and hepatic pathological damages. SEM and EDS microscopy showed that the Pb covered the surfaces of cells and was chiefly bound due to the involvement of the carbon and oxygen elements. Similarly, FTIR showed that the amino, amide, phosphoryl, carboxyl, and hydroxyl functional groups of bacteria and MRS were mainly involved in Pb biosorption. Based on these findings, free and microencapsulated L. acidophilus KLDS 1.0344 could be considered a potential dietetic stratagem in alleviating chronic Pb toxicity.

Portable X-ray Fluorescence as a Rapid Determination Tool to Detect Parts per Million Levels of Ni, Zn, As, Se, and Pb in Human Toenails: A South India Case Study

Chronic exposure to inorganic pollutants adversely affects human health. Inductively coupled plasma mass spectrometry (ICP-MS) is the most common method used for trace metal(loid) analysis of human biomarkers. However, it leads to sample destruction, generation of secondary waste, and significant recurring costs. Portable X-ray fluorescence (XRF) instruments can rapidly and nondestructively determine low concentrations of metal(loid)s. In this work, we evaluated the applicability of portable XRF as a rapid method for analyzing trace metal(loid)s in toenail samples from three populations (n = 97) near the city of Chennai, India. A Passing-Bablok regression analysis of results from both methods revealed that there was no proportional bias among the two methods for nickel (measurement range ∼25 to 420 mg/kg), zinc (10 to 890 mg/kg), and lead (0.29 to 4.47 mg/kg). There was a small absolute bias between the two methods. There was a strong proportional bias (slope = 0.253, 95% CI: 0.027, 0.614) between the two methods for arsenic (below detection to 3.8 mg/kg) and for selenium when the concentrations were lower than 2 mg/kg. Limits of agreement between the two methods using Bland-Altman analysis were derived for nickel, zinc, and lead. Overall, a suitably calibrated and evaluated portable XRF shows promise in making high-throughput assessments at population scales.

Portable X-ray fluorescence for bone lead measurements of Australian eagles

Lead (Pb) toxicity from ammunition has been shown to be a threat to scavenging birds across the globe. Toxic levels of lead have recently been found in Australia's largest bird of prey, the wedge-tailed eagle (Aquila audax), through inductively coupled plasma mass spectrometry (ICP-MS) analysis of liver and bone samples. However, ICP-MS is consumptive (causing damage to archived specimens), time-consuming, and expensive. For these reasons, portable X-ray fluorescence (XRF) devices have been optimized to measure bone lead in North American avian species, humans, and other environmental samples. In this study, we assessed portable XRF for bone lead measurement in Australian raptors in two parts. First, we validated the method using tissues from wedge-tailed eagles from Tasmania (A. a. fleayi), analysing bone samples taken from sites on the femur immediately adjacent to sites for which we had ICP-MS data (n = 89). Second, we measured lead via portable XRF in the skulls of wedge-tailed eagles from south-eastern mainland Australia (A. a. audax) collected during a criminal prosecution (n = 92). Portable XRF bone lead measurement demonstrated an excellent correlation with ICP-MS results using root-transformed regression (R² = 0.88). Calculated equivalent ICP-MS values revealed that greater than 50% of the eagles from mainland Australia had elevated lead levels (>10 mg/kg) and 13% had severe lead exposure (>20 mg/kg). Our results support previous studies of North American avian species and suggest that portable XRF could be a useful and inexpensive option for measurement of bone lead in Australian scavenger species.

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.

Blood lead levels and lung cancer mortality: An updated analysis of NHANES II and III

Previous analyses within the National Health and Nutrition Examination Survey (NHANES) II and III cycles suggested an association between blood lead levels (BLLs) and lung cancer mortality, although the evidence was limited by small case numbers. To clarify this relationship, we conducted updated analyses of 4,182 and 15,629 participants in NHANES II and III, respectively, (extending follow-up 20 and 8 years) aged ≥20 with BLL measurements and mortality follow-up through 2014. We fit multivariable Cox models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) relating BLLs and lung cancer with adjustment for smoking and other factors. We did not observe an overall association between BLLs and lung cancer after adjustment for smoking (both surveys) and serum cotinine and environmental tobacco smoke exposure (NHANES III), although suggestive associations were observed among women (NHANES II: HR 2.7, 95% CI 0.7, 10.0 for ≥20.0 µg/dl vs. <10.0 µg/dl, P_trend = 0.07; NHANES III: HR 11.2, 95% CI 2.1, 59.4 for ≥10.0 µg/dl vs. <2.5 µg/dl, P_trend = 0.04). After stratifying on smoking status, an association with elevated BLLs was observed in NHANES II only among former smokers (HR 3.2, 95% CI 1.3, 8.0 for ≥15 vs. <15 µg/dl) and in NHANES III only among current smokers (HR 1.7, 95% CI 1.1, 2.8 for ≥5 vs. <5 µg/dl). In summary, we found elevated BLLs to be associated with lung cancer mortality among women in both NHANES II and III. Given the absence of an association among non-smokers, we cannot rule out residual confounding as an explanation for our findings.

Evaluation of a portable XRF device for in vivo quantification of lead in bone among a US population

BACKGROUND

Lead (Pb) concentration in bone is a reliable biomarker for cumulative Pb exposure and studying associated health outcomes. However, the standard K-shell fluorescence (KXRF) bone Pb measurement technology has limitations in large-scale population studies.

OBJECTIVE

We compared measurements from a portable XRF device and a KXRF device.

METHODS

We measured bone Pb concentrations in vivo using portable XRF and KXRF, each measured at the mid-tibia bone in 71 people, 38-95 years of age (mean ± SD = 63 ± 11 years) living in or near three Indiana communities, US; 10 participants were occupationally exposed. We estimated the correlation between bone Pb concentrations measured by both devices. 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. Finally, we quantified the associations of estimated bone Pb concentration with age and age with soft tissue thickness.

RESULTS

The mean bone Pb concentration measured via portable XRF was 12.3 ± 16.7 mg Pb/kg dry bone. The uncertainty of a 3-minute (N = 60) in vivo portable XRF measurement ranged from 1.8 to 6.3 mg/kg, in the context of soft tissue thickness ranging from 2 to 6 mm. This uncertainty was reduced by a factor of 1.4 with 5-minute measurements (N = 11). Bone Pb measurements via portable XRF and KXRF were significantly correlated: r = 0.48 for all participants, and r = 0.73 among participants with soft tissue thickness < 6 mm (72% of the sample). Bone Pb concentrations were higher among participants who were older or were occupationally exposed to Pb. Soft tissue thickness decreased with age.

CONCLUSION

With its ease of use, portability, and comparable sensitivity with conventional KXRF systems, the portable XRF could be a valuable tool for non-invasive quantification of bone Pb in vivo, especially for people with thinner soft tissue.

Cadmium and Lead Exposure, Nephrotoxicity, and Mortality

The present review aims to provide an update on health risks associated with the low-to-moderate levels of environmental cadmium (Cd) and lead (Pb) to which most populations are exposed. Epidemiological studies examining the adverse effects of coexposure to Cd and Pb have shown that Pb may enhance the nephrotoxicity of Cd and vice versa. Herein, the existing tolerable intake levels of Cd and Pb are discussed together with the conventional urinary Cd threshold limit of 5.24 μg/g creatinine. Dietary sources of Cd and Pb and the intake levels reported for average consumers in the U.S., Spain, Korea, Germany and China are summarized. The utility of urine, whole blood, plasma/serum, and erythrocytes to quantify exposure levels of Cd and Pb are discussed. Epidemiological studies that linked one of these measurements to risks of chronic kidney disease (CKD) and mortality from common ailments are reviewed. A Cd intake level of 23.2 μg/day, which is less than half the safe intake stated by the guidelines, may increase the risk of CKD by 73%, and urinary Cd levels one-tenth of the threshold limit, defined by excessive ß₂-microglobulin excretion, were associated with increased risk of CKD, mortality from heart disease, cancer of any site and Alzheimer's disease. These findings indicate that the current tolerable intake of Cd and the conventional urinary Cd threshold limit do not provide adequate health protection. Any excessive Cd excretion is probably indicative of tubular injury. In light of the evolving realization of the interaction between Cd and Pb, actions to minimize environmental exposure to these toxic metals are imperative.

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.

Early lead exposure and childhood adiposity in Mexico city

BACKGROUND

Prenatal and early childhood lead exposures have been associated with reduced weight in infants and young children, while studies that have examined such associations in children during peripubescence are rare.

OBJECTIVES

We investigated the associations of prenatal and early-life exposure to lead with indices of adiposity in peripubertal children living in Mexico City.

METHODS

Maternal bone lead (as a proxy for cumulative fetal exposure) was assessed at 1 month postpartum. Blood samples were obtained from children annually from 1 to 4 years. Multivariable linear regression models were used to examine the association between each lead biomarker and BMI z-score, waist circumference, sum of skinfolds and body fat percentage in 248 children aged 8-16 years.

RESULTS

After adjusting for covariates, maternal patella lead was associated with lower child BMI z-score (β = -0.02, 95% CI: 0.03, -0.01, p = 0.004), waist circumference (β = -0.12 cm, 95% CI: 0.22, -0.03, p = 0.01), sum of skinfolds (β = -0.29 mm, 95% CI: 0.50, -0.08, p = 0.007) and body fat percentage (β = -0.09%, 95% CI: 0.17, -0.01, p = 0.03). No significant associations were detected from the postnatal exposure period.

CONCLUSIONS

We observed a significant and inverse association of prenatal lead exposure with body composition in Mexican children, suggesting the potential role of early lead exposure in the fetal programming of child growth. Further research on the biological mechanisms underlying these associations is needed.

Decreased erythrocyte CD44 and CD58 expression link e-waste Pb toxicity to changes in erythrocyte immunity in preschool children

Lead (Pb) toxicity damages blood cells and disturbs the immune micro-environment. When Pb enters the circulatory system, >95% of Pb accumulates in erythrocytes. We therefore conducted this study to explore the long-term effect of Pb exposure on expression of erythrocyte adhesion molecules (CD44 and CD58) and related downstream cytokine concentrations. We enrolled a total of 267 preschool children, 2-7 years of age, from Guiyu (e-waste-exposed group, n = 132) and Haojiang (reference group, n = 135) in November and December 2015. We measured child blood Pb, biomarkers including erythrocyte CD44 and CD58, erythrocyte count, leukocyte count and inflammatory cytokines (IL-1β, IL-12p70 and IFN-γ), and calculated erythrocyte Pb levels. Regression model demonstrated that higher erythrocyte Pb was associated with lower CD44 and CD58. Compared to low erythrocyte Pb levels (quartile 1), high erythrocyte Pb levels (quartile 4) were related to lower levels of erythrocyte CD44 and CD58. Elevated blood Pb correlated with higher IL-12p70 and IFN-γ, and lower IL-2. The mediation effect of erythrocyte CD44 on the relationship of erythrocyte Pb with IL-1β and IL-12p70 was significant, and the effect of erythrocyte Pb on IFN-γ was mediated by erythrocyte CD58. The data provides novel translational insight into the relationship between elevated Pb exposure and the change of erythrocyte immunity and downstream cytokine secretion in preschool children.

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.

A Dosimetry Study of Portable X-ray Fluorescence in Vivo Metal Measurements

Portable x-ray fluorescence devices have grown in popularity for possible metal exposure assessment using in vivo measurements of bone and toenail. These measurements are accompanied by a small radiation dose, which is typically assessed by radiation safety committees to be minimal. However, an understanding of precise dose under different instrument conditions is still needed. This study set out to do a thorough investigation of the exact dose measurements using optically stimulated dosimeters, thermoluminescent dosimeters, and simulation with a Monte Carlo N-Particle transport code to assess the skin and total-body effective dose typical of portable x-ray fluorescence devices. We showed normal linear relationships between measurement time, x-ray tube current, and radiation dose with the device, and we showed a second order polynomial relationship with increasing voltage and radiation dose. Dose was quantified using thermoluminescent dosimeters, optically stimulated dosimeters, and simulations, which gave similar dose estimations. Skin dose for a standard 50-kV, 40-μA measurement for bone and toenail in vivo was 48.5 and 28.7 mSv, respectively, according to simulation results. Total-body effective dose was shown as 3.4 and 2.0 μSv for in vivo bone and toenail measurements, respectively, for adults using the portable x-ray fluorescence device.

Early lead exposure and pubertal development in a Mexico City population

BACKGROUND

Previous studies have examined the association between blood lead levels and pubertal timing in adolescent girls; however, the evidence is lacking on the role of lead exposure during sensitive developmental periods on sexual maturation.

OBJECTIVES

To examine the association of prenatal and early childhood lead exposure with pubertal stages among 264 boys and 283 girls aged 9.8-18.0 years in Mexico City.

METHODS

We measured maternal bone lead (a proxy for cumulative fetal exposure to lead from maternal bone stores mobilized during pregnancy) at 1 month postpartum. Blood lead was measured annually from 1 to 4 years. Pubertal stage was assessed by a pediatrician. We examined the association between lead and pubertal stages of breast, pubic hair and genitalia using ordinal regression. Age at menarche was evaluated using Cox proportional-hazard models.

RESULTS

Multivariate models showed that maternal patella lead and early childhood blood lead were inversely associated with breast growth (patella OR = 0.72, 95% CI: 0.51-1.00; blood OR = 0.70, 95% CI: 0.53-0.93) in girls. Girls with maternal patella lead in the 3rd tertile and child blood lead in the 2nd tertile had a later age at menarche compared with girls in the 1st tertile (patella HR = 0.60, 95% CI: 0.41-0.88; blood HR = 0.65, 95% CI 0.46-0.91). Additionally, early childhood blood lead was negatively associated with pubic hair growth (OR = 0.68, 95% CI: 0.51-0.90) in girls. No associations were found in boys.

CONCLUSIONS

These data suggest that higher prenatal and early childhood exposure to lead may be associated with delayed pubertal development in girls but not boys. Our findings are consistent with previous analyses and reinforce the reproductive effects of lead for girls.

Blood lead, bone lead and child attention-deficit-hyperactivity-disorder-like behavior

BACKGROUND AND OBJECTIVE

Mounting evidence showed that lead exposure increased the risk of child attention-deficit-hyperactivity disorder (ADHD). Epidemiologic studies have typically used the blood-lead as a biomarker of lead exposure; blood-lead levels mostly reflect recent lead exposure. However, few studies have examined the relationship between bone-lead, a biomarker of cumulative exposure, and ADHD. Therefore, we aimed to compare the associations of bone-lead vs blood-lead levels with child ADHD symptoms and comorbidities.

METHODS

A total of 164 children aged 3-15 years were enrolled during 2014-2015. The Vanderbilt-ADHD-Diagnostic-Parent-Rating Scale (VADPRS) was used to evaluate the children's ADHD symptoms and comorbidities. Children's blood and bone lead concentrations were assessed, the latter using a non-invasive K-X-ray-fluorescence technique. According to blood-lead levels, children were classified into high (blood-lead ≥ 10.0 μg/dL) and low (blood-lead < 10.0 μg/dL) blood-lead groups. According to bone-lead levels, children were classified into high (bone-lead ≥ 2.66 μg/g) and low (bone-lead < 2.66 μg/g) bone-lead groups. We associated blood/bone lead with VADPRS data using multi-variable binary logistic regression models.

RESULTS

Children in the high blood-lead group had higher hyperactivity/impulsivity (P = 0.02) scores than the corresponding low blood-lead group. Children in the high bone-lead group had higher hyperactivity/impulsivity (P = 0.02) and oppositional-defiant-disorder (ODD) (P = 0.03) scores than the corresponding low bone-lead group. After adjusting for relevant confounders, children in the high bone-lead group were more likely to have ODD-behavior than the low group (OR = 6.7, 95%CI: 1.2-36.5). However, no adjusted association was observed between blood-lead and any ADHD-domain score.

CONCLUSION

High levels of cumulative lead exposure in children may be an independent risk factor of ODD-behavior.

Childhood lead biokinetics and associations with age among a group of lead-poisoned children in China

Childhood lead exposure has been shown to have a significant effect on neurodevelopment. Many of the biokinetics involved with lead biomarkers in children still remain unknown. Two hundred fifty (157 in the exposed group and 93 controls) children were enrolled in our study and lead exposed children returned for multiple visits for measurement of blood and bone lead and chelation treatment. We demonstrated that the correlation between blood and bone lead increased with subsequent visits. We calculated the blood lead half-life for 50 patients, and found a significant (p-value < 0.001) positive correlation with age. For ages 1-3 years (N = 17), the blood lead half-life was found to be 6.9 ± 4.0 days and for 3+ years it was found to be (N = 33) 19.3 ± 14.1 days. In conclusion, the turnover of lead in children is faster than in adults. Our results indicate that blood lead is a more acute biomarker of exposure than previously thought, which will impact studies of children's health using blood lead as a biomarker.

Lead exposure biomarkers in the Common Loon

Lead in fishing tackle is a significant source of exposure to the environment, wildlife, and potentially humans. Common Loons (Gavia immer) are exposed to lead by eating fish which have lead tackle, or ingesting fishing weights or spent ammunition when they ingest small stones to aid in digestion. Blood lead is traditionally used as a biomarker of exposure in loons, but it only reflects recent exposures. Cumulative exposure measured via bone lead may better reflect the overall health of loons and their aquatic habitat. This study compared a portable x-ray fluorescence (XRF) device for measurement of bone lead with and without tissue overlying the bone on loon cadavers with measurements made by inductively coupled plasma mass spectrometry (ICP-MS) of different tissues from the loons. For this study we had 75 bone samples, 19 body fluid samples, and 17 liver lead samples. We found significant correlations between portable XRF bone lead measurements made with overlying tissue and ICP-MS measures of bone lead (R = 0.88), body fluid lead (R = 0.65), and liver lead (R = 0.71). Bone lead was found to be higher in loons collected from non-coastal regions. In assessing lead-related cause of death, bone lead proved more predictive than liver lead. Future studies should investigate the value of these biomarkers for both aquatic health and loon health to further validate our findings.

Validation of x-ray fluorescence measurements of metals in toenail clippings against inductively coupled plasma mass spectrometry in a Nigerian population<sup/>

OBJECTIVE

Metal exposures have been linked with many adverse health outcomes affecting nearly every system in the body. Exposure to metals has been tracked primarily using blood. Blood metal concentrations have drawbacks as biomarkers stemming from the metals' short biologic half-lives, shipping and storage requirements, and invasive collection procedures. Toenails, which capture a longer exposure period, can be collected non-invasively and stored at room temperature, and can be more feasible and cost-effective for large-scale population studies.

APPROACH

Inductively coupled plasma mass spectrometry (ICP-MS) has been used for analysis of toenail metal concentrations, but x-ray fluorescence (XRF) has many advantages in versatility and cost effectiveness over these analyses. This study compared toenail concentrations of manganese (Mn) and lead (Pb) measured with XRF against ICP-MS, in samples collected from 20 adults in Nigeria. To do this we developed a novel calibration method that corrects XRF measurements for toenail weight and thickness to reduce the variability in XRF measurements of toenail clippings.

MAIN RESULTS

We found a high correlation (R  =  0.91) between toenail manganese metal measurements made with XRF and ICP-MS and a correlation of (R  =  0.32) between toenail lead XRF and ICP-MS with over half of the lead results below the detection limit of the instrumentation.

SIGNIFICANCE

XRF can be used effectively to quantify metals at the part per million level or lower depending on the XRF equipment used in the measurements.

Hearing loss in children with e-waste lead and cadmium exposure

Environmental chemical exposure can cause neurotoxicity and has been recently linked to hearing loss in general population, but data are limited in early life exposure to lead (Pb) and cadmium (Cd) especially for children. We aimed to evaluate the association of their exposure with pediatric hearing ability. Blood Pb and urinary Cd were collected form 234 preschool children in 3-7years of age from an electronic waste (e-waste) recycling area and a reference area matched in Shantou of southern China. Pure-tone air conduction (PTA) was used to test child hearing thresholds at frequencies of 0.25, 0.5, 1, 2, 4 and 8kHz. A PTA≥25dB was defined as hearing loss. A higher median blood Pb level was found in the exposed group (4.94±0.20 vs 3.85±1.81μg/dL, p<0.001), while no significance was found for creatinine-adjusted Cd. Compared with the reference group, the exposed group had a higher prevalence of hearing loss (28.8% vs 13.6%, p<0.001). The PTA in the left, right and both ears, and hearing thresholds at average low and high frequency, and single frequency of 0.5, 1 and 2kHz were all increased in the exposed group. Positive correlations of child age and nail biting habit with Pb, and negative correlations of parent education level and child washing hands before dinner with Pb and Cd exposure were observed. Logistic regression analyses showed the adjusted OR of hearing loss for Pb exposure was 1.24 (95% CI: 1.029, 1.486). Our data suggest that early childhood exposure to Pb may be an important risk factor for hearing loss, and the developmental auditory system might be affected in e-waste polluted areas.

Feasibility of a portable X-ray fluorescence device for bone lead measurements of condor bones

Lead based ammunition is a primary source of lead exposure, especially for scavenging wildlife. Lead poisoning remains the leading cause of diagnosed death for the critically endangered California condors, which are annually monitored via blood tests for lead exposure. The results of these tests are helpful in determining recent exposure in condors and in defining the potential for exposure to other species including humans. Since condors are victim to acute and chronic lead exposure, being able to measure both would lend valuable information on the rates of exposure and accumulation through time. A commercial portable X-ray fluorescence (XRF) device has been optimized to measure bone lead in vivo in humans, but this device could also be valuable for field measurements of bone lead in avian species. In this study, we performed measurements of bone Pb in excised, bare condor bones using inductively coupled plasma mass spectrometry (ICP-MS), a cadmium 109 (Cd-109) K-shell X-ray fluorescence (KXRF) system, and a portable XRF system. Both KXRF and portable XRF bone Pb measurement techniques demonstrated good correlations with ICP-MS results (r=0.93 and r=0.92 respectively), even with increasing skin thickness (r=0.86 between ICP-MS and portable XRF at 1.54mm of soft tissue). In conclusion, our results suggest that a portable XRF could be a useful option for measurement of bone Pb in avian species in the field.

Quantification of manganese and mercury in toenail in vivo using portable X-ray fluorescence (XRF)

BACKGROUND AND OBJECTIVE

Toenail is an advantageous biomarker to assess exposure to metals such as manganese and mercury. Toenail Mn and Hg are in general analyzed by chemical methods such as inductively coupled plasma mass spectrometry and atomic absorption spectrophotometry. In this project, a practical and convenient technology-portable X-ray florescence (XRF)-is studied for the noninvasive in vivo quantification of manganese and mercury in toenail.

MATERIAL AND METHODS

The portable XRF method has advantages in that it does not require toenail clipping and it can be done in 3 min, which will greatly benefit human studies involving the assessment of manganese and mercury exposures. This study mainly focused on the methodology development and validation which includes spectral analysis, system calibration, the effect of toenail thickness, and the detection limit of the system. Manganese- and mercury-doped toenail phantoms were made. Calibration lines were established for these measurements.

RESULTS

The results show that the detection limit for manganese is 3.65 μg/g (ppm) and for mercury is 0.55 μg/g (ppm) using 1 mm thick nail phantoms with 10 mm soft tissue underneath.

DISCUSSION AND CONCLUSION

We conclude that portable XRF is a valuable and sensitive technology to quantify toenail manganese and mercury in vivo.

Measurements of Strontium Levels in Human Bone In Vivo Using Portable X-ray Fluorescence (XRF)

Measurement of bone strontium (Sr) is vital to determining the effectiveness of Sr supplementation, which is commonly used for the treatment of osteoporosis. Previous technology uses radioisotope sources and bulky equipment to measure bone Sr. This study demonstrates the effectiveness of portable X-ray fluorescence (XRF) for bone Sr measurement and validates it using data from a population of 238 children. We identified correlations between bone Sr and age in our participants.

Calibration of the 125I-induced x-ray fluorescence spectrometry-based system of in vivo bone strontium determinations using hydroxyapatite as a phantom material: a simulation study

OBJECTIVE

The calibration of in vivo x-ray fluorescence systems of bone strontium quantification, based on ¹²⁵I excitation, is dependent on a coherent normalization procedure. Application of this procedure with the use of plaster of Paris (poP) as a phantom material requires the application of a coherent conversion factor (CCF) to make the calibration functions transferable between the phantom material and human bone. In this work we evaluate, with the use of Monte Carlo simulation, the potential benefit of employing a newly developed hydroxyapatite phantom material into the calibration protocol.

APPROACH

Simulations being performed on bare bone phantoms, as the emission spectrum in this case is equivalent to an emission spectrum of an adequately corrected measurement for soft tissue attenuation of emitted strontium signal. We report that the application of hydroxyapatite phantoms does in fact remove the need for a coherent correction factor (CCF).

MAIN RESULTS

The newly developed phantoms can thus be used for the calibration of in vivo bone strontium systems removing one step of the calibration protocol. Calibration is, however, limited to cases in which the concentration is relative to the amount of calcium in the specimen, which is, the most useful quantity in a clinical sense. Determining concentrations on a per-mass-of-material basis, that is, a concentration not normalized to the calcium content of the phantom/bone, results in large biases in estimated bone strontium content.

SIGNIFICANCE

The use of an HAp phantom material was found to remove the need for a CCF. It was also found that in the case of an incomplete conversion ratio when preparing the phantom material that there would be little effect on the differential coherent cross-section and thereby the coherent normalization-based calibration protocol.

Theoretical modeling of a portable x-ray tube based KXRF system to measure lead in bone

OBJECTIVE

K-shell x-ray fluorescence (KXRF) techniques have been used to identify health effects resulting from exposure to metals for decades, but the equipment is bulky and requires significant maintenance and licensing procedures. A portable x-ray fluorescence (XRF) device was developed to overcome these disadvantages, but introduced a measurement dependency on soft tissue thickness. With recent advances to detector technology, an XRF device utilizing the advantages of both systems should be feasible.

APPROACH

In this study, we used Monte Carlo simulations to test the feasibility of an XRF device with a high-energy x-ray tube and detector operable at room temperature.

MAIN RESULTS

We first validated the use of Monte Carlo N-particle transport code (MCNP) for x-ray tube simulations, and found good agreement between experimental and simulated results. Then, we optimized x-ray tube settings and found the detection limit of the high-energy x-ray tube based XRF device for bone lead measurements to be 6.91 µg g^-1 bone mineral using a cadmium zinc telluride detector.

SIGNIFICANCE

In conclusion, this study validated the use of MCNP in simulations of x-ray tube physics and XRF applications, and demonstrated the feasibility of a high-energy x-ray tube based XRF for metal exposure assessment.

Detection of lead in bone phantoms and arsenic in soft tissue phantoms using synchrotron radiation and a portable x-ray fluorescence system

The differences and commonalities between x-ray fluorescence results obtained using synchrotron radiation and a portable x-ray fluorescence device were examined using arsenic in soft tissue phantoms and lead in bone phantoms. A monochromatic beam energy of 15.8 keV was used with the synchrotron, while the portable device employed a rhodium anode x-ray tube operated at 40 kV. Bone phantoms, dosed with varying quantities of lead, were made of Plaster of Paris and placed underneath skin phantoms of either 3.1 mm or 3.9 mm thickness. These skin phantoms were constructed from polyester resin, and dosed with varying amounts of arsenic. Using an irradiation time of 120 s, arsenic Kα and Kβ, and lead Lα and Lβ characteristic x-ray peaks were analysed. This information was used to calculate calibration line slopes and minimum detection limits for each data set. As expected, minimum detection limits were much lower at the synchrotron for detecting arsenic and lead. Both approaches produced lower detection limits for arsenic in soft tissue than for lead in bone when simultaneous detection was attempted. Although arsenic Kα and lead Lα emissions share similar energies, it was possible to detect both elements in isolation by using the arsenic Kβ and lead Lβ characteristic x-rays. Greater thickness of soft tissue phantom reduced the ability to detect the underlying lead. Experiments with synchrotron radiation could help guide future efforts toward optimizing a portable x-ray fluorescence in vivo measurement device.