Toxic metals in toenails as biomarkers of exposure: A review

Associations between plasma and urinary heavy metal concentrations and the risk of prostate cancer

Prostate cancer is a leading cause of morbidity and mortality worldwide, with incidence rates projected to double between 2020 and 2040. This growing health challenge highlights the need for improved diagnostic strategies and risk assessment tools to better understand disease etiology and progression. Among environmental factors, heavy metals have been implicated in inflammation and carcinogenesis, yet their specific role in prostate disease remains insufficiently explored. This novel study analyses the relationship between heavy metal concentrations in plasma and urine of patients with benign prostatic hyperplasia, precancerous lesions and prostate cancer. In addition to evaluating key clinical parameters, including age, total PSA levels, hemoglobin concentrations and monocyte/lymphocyte ratio, it aims to determine whether specific heavy metals contribute to the progression of prostate disease and whether they can serve as potential biomarkers for early diagnosis. Our findings reveal significant differences in vanadium and antimony concentrations in plasma, suggesting a potential role in prostate disease pathophysiology. Notably, lower plasma antimony concentrations are associated with an increased risk of PC, while plasma vanadium concentrations are significantly higher in the PL group. Regression analysis further supports the association between heavy metal concentrations and the risk of PL and PC, highlighting the potential of vanadium and copper as biomarkers or therapeutic targets for prostate health. The study also explores the impact of lead exposure on prostate cancer risk, revealing a significant association between urine lead concentration and PC. These findings underscore the complex interaction between heavy metal concentrations and prostate disease risk, emphasizing the need for further research to elucidate underlying mechanisms and explore therapeutic interventions.

Calibration of Toenail Metal Concentrations for Sample Mass Heterogeneity and Between-Batch Variability: The COMET Approach

BACKGROUND

Toenails are promising biomarkers of long-term metal exposure in epidemiological studies, but their accuracy may be compromised by systematic and random errors associated with heterogeneous toenail sample masses, as well as by substantial variability across laboratory batches.

OBJECTIVES

We propose a novel modeling approach to calibrate toenail metal concentrations for the heterogeneity in sample masses and the variability between batches.

METHODS

We developed a heteroscedastic spline mixed model relating sample mass and laboratory batch with measured concentrations, allowing for an average bias in measurements over all batches as a smooth function of sample mass, random variation in mass-related biases across batches, and mass-related heterogeneity in within-batch error variance. The model allowed partitioning the total variance of measured concentrations into the extraneous variances (due to different sample masses and laboratory batches) and the intrinsic variance (resulting from distinct metal exposures). We derived calibrated metal concentrations from the model by removing both sources of extraneous variation and estimating the predicted concentrations had all toenail samples been analyzed in a single batch and of the same mass. We provide the R script COMET (COrrected METals) to fit the proposed model, extract variance components, and calibrate metal concentrations.

RESULTS

In a multicase-control study in Spain (MCC-Spain) with toenail determinations for 16 metals in 4,473 incident cases of five common cancers and 3,450 population controls, sample mass and batch accounted for 26%-60% of the total variance of measured concentrations for most metals. In comparison with calibrated concentrations, odds ratios for measured concentrations were biased by > 10 % toward or away from the null in one-quarter of the estimated metal-cancer associations.

DISCUSSION

The proposed model allows correcting toenail metal concentrations for sample mass heterogeneity and between-batch variability and could be applied to other biological specimens of heterogeneous size, distinct laboratory techniques, and different study designs. https://doi.org/10.1289/EHP14784.

Lead and cadmium exposure was associated with faster epigenetic aging in a representative sample of adults aged 50 and older in the United States

BACKGROUND

Lead and cadmium are among the most prevalent environmental toxicants and are highly detrimental to human health. While prior studies link heavy metal exposure to reduced telomere length and increased DNA methylation age, their relationship with epigenetic age acceleration (EAA) remains understudied. This study investigates whether exposure to lead and cadmium accelerates biological aging.

METHODS

This cross-sectional study analyzed data from 2201 participants aged 50 or older from the 1999-2002 NHANES. Blood lead and cadmium levels were measured using simultaneous multi-element atomic absorption spectrometry. Eight DNA-methylation-based epigenetic clocks were included in the analysis: Hannum Age, Horvath pan-tissue Age, PhenoAge, GrimAge, GrimAge version 2, Skin Blood Age, epiTOC, and DNAmTL. EAA for each individual was calculated as the residuals from the regression of estimated epigenetic age on chronological age.

RESULTS

Of the 2201 American older adults, the mean (SE, standard error) chronological age was 65.75 (0.21), which was closest to the mean GrimAge (65.99; SE = 0.19). After adjusting for demographics, lifestyle factors, comorbidities, and cell type composition, multivariate linear regression analyses revealed associations of blood lead and cadmium levels with significantly higher Hannum Age, Grim Age, Grim Age2, Skin Blood Age (associated with lead only), as well as Phenotypic Age and DNAmTL (associated with cadmium only). Quartile-based analyses of blood lead and cadmium levels according to quartiles revealed consistent and strong associations between greater exposure to lead or cadmium (e.g., the fourth quartile of the metals) and EAA. Among lifestyle factors, smoking had a pronounced impact on accelerated aging, especially in the Grim Age and Grim Age2.

CONCLUSIONS

We found that exposure to lead and cadmium was associated with accelerated epigenetic age. These findings suggest the potential role of lead and cadmium in EAA and propose the integration of environmental factors to refine epigenetic age prediction.

Assessment of Essential and Toxic Element Levels in the Toenails of Children with Autism Spectrum Disorder

Autism spectrum disorder (ASD) has become a global public health concern, impacting the quality of life. The question of gene-environment interaction in the emergence of ASD remains a subject of ongoing debate, and exploring its pathophysiology is thoroughly related to metals as a risk factor. Therefore, this study aims to assess the levels of toxic (Al, Cd, Hg, and Pb) and essential (Cr, Mn, Fe, Ni, Cu, Zn, and Se) elements in toenail samples collected in children with ASD and neurotypical children, by ICP-MS. Parallelly, we will discuss the use of toenails as an exposure indicator. The study involved 208 children aged 3 to 14 from Marrakech, Morocco. One hundred two were diagnosed with ASD and 106 were neurotypical children. Significant statistical differences in the concentration of Cr, Mn, and Fe were documented between the two groups. Higher levels of Pb in toenails compared to reference values have been reported. No association was established between concentrations of elements and age. Spearman correlation coefficients revealed a significantly different pattern of mutual dependence for toxic and essential elements between the two groups. The strongest positive correlations were found in the neurotypical group (Fe-Mn (ρ = 0.750), and Se-Zn (ρ = 0.800)). These results provide additional, although inconclusive, evidence on the probable role of element disturbance in the pathogenesis of ASD. Further studies should be performed to explore other nutritional, cultural, sociodemographic, environmental, and methodological factors that may impact the levels of these elements in the nails and their possible correlation with the incidence of ASD.

Independent and Combined Associations between Metals Exposure and Inflammatory Markers among the General U.S. Adults

Exposure to metals can trigger a series of diseases by dysregulating the human immune system, but there is still a lack of systematic studies assessing the independent and combined effects of exposure to metals on immune function in the general population, particularly concerning inflammation markers. This cross-sectional study was designed to mainly examine the associations between urinary metal mixtures and inflammatory markers, including white blood cell (WBC), platelet count (PLT), mean platelet volume (MPV), MPV/PLT ratio (MPR), platelet-to-lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR). A total of 3451 participants aged ≥20 years were selected from the 2013-2016 National Health and Nutrition Examination Survey. Generalized linear models were used to investigate the relationships of exposure to single metals on inflammatory markers. Associations between coexposure to multiple metals and inflammatory markers were determined using weighted quantile sum regression and quantile g-computation. Barium, cadmium, lead, thallium, and cobalt showed significant associations with MPV, PLR, and NLR. Metal mixtures showed a negative association with MPV, while they had positive associations with PLR and NLR. Overall, our study highlights the significant effects of multiple metals exposure on inflammation markers, including MPV, PLR, and NLR, among U.S. adults. Thereinto, uranium, cadmium, and cobalt were identified as major contributors. Further prospective studies representative of other countries are warranted to either validate or refute our findings.

Review of non-invasive biomarkers as a tool for exposure characterization in human health risk assessments

Blood and urine are historically the most frequent matrices used for measuring chemical levels in human biomonitoring studies. As biomonitoring programs are refreshed, consideration of specific priority substances and specific population targets provide opportunities for inclusion of alternative non- or minimally invasive matrices. This review describes methods used in health risk assessment to characterize exposure and risk based upon biomarkers from noninvasive matrices other than urine or blood, including human milk, hair, fingernails, toenails, exhaled breath, deciduous teeth, sweat, semen, meconium, and feces. Illustrative examples of these methods relevant to chemical management are provided. This review suggests that, although these alternative noninvasive biomarkers are not frequently used in human health risk assessment at present, these biomarkers may prove useful in (1) characterizing exposure and health risk in vulnerable populations, (2) cumulative risk assessments, and (3) community-based risk assessments, depending upon the substance of concern. To incorporate alternative noninvasive biomarkers into human health risk assessments with confidence, more research is needed to improve our knowledge of the relationships between external dose, internal dose, and biologic consequent effects in matrices other than blood and urine.

Internal Cumulated Dose of Toxic Metal(loid)s in a Population Residing near Naturally Occurring Radioactive Material Waste Stacks and an Industrial Heavily Polluted Area with High Mortality Rates in Spain

Huelva is a city in SW Spain with 150,000 inhabitants, located in the proximity of two heavy chemical industry complexes, the highest naturally occurring radioactive material (NORM) waste (phosphogypsum) stacks of Europe and a highly polluted estuary, with elevated cardiovascular disease and cancer mortality rates. This study analyses the association between cumulated exposure levels to 16 metal(loid)s (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, Tl, U, V, and Zn) measured in the toenail of a sample (n = 55 participants) of the general control population of Huelva City who were involved in the MCC-Spain study and the spatial proximity patterns to the local polluting sources. Residents of the city of Huelva have higher levels of Fe, Ni, Cr, Se, As, and Co in their toenails compared to the levels found in populations with similar characteristics living in non-polluted areas. Moreover, the highest concentrations of As, Pb, Cd, Mo, and Se were found in toenails of participants living near the NORM waste stack, while the highest Cu, Zn, and Al contents corresponded to people residing near the industrial area. The spatial distribution of most of the metal(loid)s studied appears to be mainly controlled by anthropogenic factors.

Determination of glycation biomarkers in human fingernails by isotope-dilution liquid chromatography tandem mass spectrometry (LC-MS/MS)

Glycation is a non-enzymatic, post-translational modification of proteins which is elevated in several pathologies, notably diabetes. An early-stage glycation product, glycated hemoglobin (HbA1c), is used in the clinical management of diabetes, and advanced glycation end-products (AGEs) are implicated in the etiology of diabetic complications. Fingernail clippings contain a time-integrated repository of several metabolic processes during the preceding 3-5 months, are easily sampled, and various elements and molecules have been shown to remain stable within them for long periods without refrigeration. Building upon a few underexploited studies, we investigated fingernails as a non-invasive matrix to assess glycation using liquid chromatography-mass spectrometry to quantify ungual biomarkers of early- and advanced glycation (respectively furosine, as a fructose-lysine derivative, and two AGEs (Nε-carboxymethyllysine (CML) and Nε-carboxyethyllysine (CEL)). The method was appropriately validated and provided accurate and precise measurements of two amino acids and the glycation biomarkers. Sample storage at ± 25 °C for 12 months had no effect upon these analytes, and the method was applied to fingernails from 87 people with diabetes. There was a moderate, linear correlation between ungual furosine concentrations and HbA1c at the time of nail sampling (rs = 0.339, p = 0.0011). Among subjects for whom previous measurements were available, there was no correlation between ungual glycation and HbA1c measured > 3 months before nail sampling, indicating that ungual furosine reflects early-stage glycation over a similar period to HbA1c. This study provides further evidence, using modern analytical techniques, that fingernails offer the possibility to quantitatively and non-invasively assess glycation.

Exposure to metal mixtures and telomere length in Bangladeshi children

Telomere length is associated with chronic diseases and, in younger populations, may represent a biomarker of disease susceptibility. As growing evidence suggests that environmental factors, including metals, may impact telomere length. We investigated the association between 17 metals measured in toenail samples and leukocyte relative telomere length (RTL), among 472 5- to 7-year-old children enrolled in the Bangladesh Environmental Research in Children's Health (BiRCH) cohortIn single-exposure linear regression models, a doubling of arsenic (As) and mercury (Hg) (μg/g) were associated with a -0.21 (95% CI, -0.032 to -0.010; P = .0005) and -0.017 (95% CI, -0.029 to -0.004; P = .006) difference in RTL, respectively. In Bayesian Kernel Machine Regression (BKMR) mixture models, the overall metal mixture was inversely associated with RTL (P-for-trend < 0.001). Negative associations with RTL were observed with both log2-As and log2-Hg, while an inverted U-shaped association was observed for log2-zinc (Zn) with RTL. We found little evidence of interaction among metals. Sex-stratification identified stronger associations of the overall mixture and log2-As with RTL among females compared to males. Our study suggests that As and Hg may independently influence RTL in mid-childhood. Further studies are needed to investigate potential long-term impacts of metal-associated telomere shortening in childhood on health outcomes in adult life.

Uranium in Drinking Water and Bladder Cancer: A Case-control Study in Michigan

ABSTRACT

Uranium is naturally occurring in groundwater used for drinking; however, health risks from naturally occurring concentrations are uncertain. Uranium can cause both radiological and chemical toxicity following ingestion. Bladder and kidneys receive a dose when uranium is excreted into the urine. Investigate the association between uranium in drinking water and bladder cancer risk in a case-control study. A population-based bladder cancer case-control study was conducted in 11 counties of southeastern Michigan. A total of 411 cases and 566 controls provided drinking water and toenail samples and answered questions about lifestyle and residential history. Uranium was measured in drinking water and toenails, and its association with bladder cancer was assessed via unconditional logistic regression models. Median uranium concentration in water was 0.12 μg L -1 , with a maximum of 4.99 μg L -1 , and median uranium concentration in toenails was 0.0031 μg g -1 . In adjusted regression models, there was a suggestion of a protective effect among those exposed to the upper quartile of uranium in drinking water (HR = 0.64, 95% CI: 0.43, 0.96) and toenails (HR 0.66; 95% CI 0.45, 0.96) compared to those in the lowest quartile. Our objective is to investigate additional adjustment of drinking water source at home residence at time of recruitment to address potential selection bias and confounding attenuated results toward the null for drinking water uranium (HR = 0.68, 95% CI: 0.44, 1.05) and toenail uranium (HR = 0.80, 95% CI: 0.53, 1.20). This case-control study showed no increased risk of bladder cancer associated with uranium found in drinking water or toenails.

Residential proximity to toxic metal-emitting industrial sites and toenail metal concentrations in a United States-wide prospective cohort

BACKGROUND

Industrial facilities across the United States (US) release millions of pounds of toxic chemicals, including metals. Exposure to toxic metals has been associated with adverse health outcomes, but there is limited evidence on the association between living near metal-releasing facilities and the body burden of emitted compounds.

OBJECTIVE

To investigate the association between residential proximity to toxic metal-emitting industrial facilities and toenail metal concentrations and to evaluate whether associations differed by race.

METHODS

In a sample of 1556 non-Hispanic Black (32.5%) and non-Hispanic White (67.5%) women from the Sister Study, we used the US Environmental Protection Agency Toxics Release Inventory to identify metal-emitting facilities within 3, 5, and 10 km of participants' baseline residences. We measured toenail concentrations (μg/g) of arsenic, cadmium, cobalt, chromium, and lead. Using multivariable linear regression, we examined associations between residential proximity to and emissions from metal-emitting facilities and toenail metal concentrations, stratifying by race. We explored modification of race-stratified associations by neighborhood deprivation, using the Area Deprivation Index (ADI).

RESULTS

Black participants were more likely to reside within 3 km of chromium-releasing facilities and 5 and 10 km of all observed metal-emitting sites. Living near metal-releasing facilities was not associated with higher toenail metal concentrations overall. Among Black women, higher chromium emissions exposure was associated with higher toenail chromium levels (βTertile3vs.non-exposed = 2.36 μg/g, 95% CI = 0.63, 4.10). An association with lead was observed among Black women residing in the most deprived areas (≥75th ADI percentile: β = 3.08 μg/g, 95% CI = 1.46, 4.71). No associations were observed for White participants.

CONCLUSIONS

Despite low exposure prevalence, our findings suggest that living near chromium- and lead-releasing facilities, especially at shorter distances, may be associated with higher corresponding toenail metal levels among Black women, particularly those residing in the most disadvantaged areas.

Fish intake and mercury exposure in young children

Fish consumption is one of the main sources of mercury (Hg) exposure, but few studies have examined Hg exposure from fish consumption among children. This study aimed to assess the frequency of fish intake and associations with Hg and other element concentrations among 700 three-year-old children from the New Hampshire Birth Cohort Study. Usual fish intake was derived from a validated food frequency questionnaire (Block Questionnaire for ages 2-7) and toenail element concentrations were determined using ICP-MS. Multiple linear regression analysis was used to assess the association between fish intake and toenail element concentrations. A mixture analysis, using Weighted quantile sum (WQS) regression, was used to estimate the relative contribution of fish consumption to element exposures. Twenty-three percent of children were reported to consume at least one fish meal/week on average during the previous 6 months. In adjusted linear regression models, children with any type of fish consumption versus no consumption had 108% (95% confidence interval (CI: 68%, 153%)) higher toenail Hg concentrations. To a lesser extent, children consuming "other fish (not fried) including tuna" and "fried fish or fish sticks" had 120% (95% CI: 82%, 164%), and 23% (95% CI: 2%, 51%) higher toenail concentrations, respectively, than those consuming no fish. Using WQS regression, Hg was the element most strongly related to fish consumption. Fish intake among young children was related to Hg exposure even at low levels of consumption. Future studies will need to determine the health consequences of this exposure.

Dual-Enhancement Electrochemiluminescence Device for Ultratrace Uranium Visualized Monitoring in Fish, Hair, and Nail Samples

Uranium is a nuclear fuel but also a hazardous contaminant due to its radioactivity and chemical toxicity. To prevent and mitigate its potential threat, the accurate monitoring of ultratrace uranium (orders of magnitude of pg g-1) in practical environmental samples has become an important scientific problem. To meet this challenge, we developed an efficient electrochemiluminescence (ECL) UO22+ detection device by a novel dual-enhancement mechanism. In detail, poly[(9,9-dioctylfuor-enyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1,3}-thiadiazole)] polymer dots (Pdots) are modified by the UO22+ DNA aptamer, and rhodamine B (RhB) is combined with dsDNA to quench the ECL signal via a resonance energy transfer (RET) process. UO22+ can cut off the DNA aptamer to release RhB, which generates an ECL enhancement process, and then, UO22+ continuously combines with the DNA chain, inducing another ECL enhancement by the RET process from UO22+ to Pdots. This device achieves an ultralow detection limit (12 pg L-1) and a wide linear range (113 pg L-1-11.3 mg L-1), which can successfully give accurate determination results to the ultratrace uranium in biosamples (<1 pg g-1) to monitor the uranium simulation of fish. This work presents an efficient strategy for ultratrace uranium determination in the environment, highlighting its significance in public health and environmental fields.

Associations of toxic metals and their mixture with hyperuricemia in Chinese rural older adults

Previous studies have related single toxic metals (TMs) to hyperuricemia (HUA) among the general population, however, the association of the TM mixture with HUA, especially in older adults, remains poorly understood. We aimed to examine the relationships between individual TMs and their mixture and HUA in Chinese rural older adults. This study consisted of 2075 rural older adults aged 60 years or over. Blood concentrations of aluminum (Al), arsenic (As), barium (Ba), cadmium (Cd), cesium (Cs), gallium (Ga), mercury (Hg), lead (Pb), thallium (Tl), and uranium (U) were detected using inductively coupled plasma mass spectrometry. The associations of single TMs with HUA were assessed using logistic regression and restricted cubic spline (RCS) models, and the association of TM mixture with HUA was explored using the elastic net with environmental risk score (ENET-ERS), quantile g-computation (QGC), and Bayesian kernel machine regression (BKMR) models, respectively. Adjusted logistic regression model showed that Cs (OR = 1.65, 95% CI 1.37-1.99) and Pb (OR = 1.46, 95% CI 1.28-1.67) were positively related to HUA, and RCS model exhibited a positive linear association of Cs and Pb with HUA. ENET-ERS and QGC models quantified a positive correlation between the TM mixture and the odds of HUA, with estimated ORs of 1.15 (95% CI 1.11-1.19) and 1.84 (95% CI 1.37-2.47), respectively, and Cs and Pb had the most weight. BKMR model demonstrated a significant linear association between the TM mixture and increased odds of HUA, with the posterior inclusion probabilities (PIPs) of both Cs and Pb being 1.00. Moreover, we observed a positive interaction between Cs and Pb on HUA. The TM mixture is associated with increased odds of HUA in rural older adults, which may mainly be driven by Cs and Pb. Subsequent studies are warranted to confirm these findings and clarify the mechanisms linking multiple TMs with HUA.

Child and Adolescent Manganese Biomarkers and Adolescent Postural Balance in Marietta CARES Cohort Participants

BACKGROUND

Manganese (Mn) plays a significant role in both human health and global industries. Epidemiological studies of exposed populations demonstrate a dose-dependent association between Mn and neuromotor effects ranging from subclinical effects to a clinically defined syndrome. However, little is known about the relationship between early life Mn biomarkers and adolescent postural balance.

OBJECTIVES

This study investigated the associations between childhood and adolescent Mn biomarkers and adolescent postural balance in participants from the longitudinal Marietta Communities Actively Researching Exposures Study (CARES) cohort.

METHODS

Participants were recruited into CARES when they were 7-9 y old, and reenrolled at 13-18 years of age. At both time points, participants provided samples of blood, hair, and toenails that were analyzed for blood Mn and lead (Pb), serum cotinine, hair Mn, and toenail Mn. In adolescence, participants completed a postural balance assessment. Greater sway indicates postural instability (harmful effect), whereas lesser sway indicates postural stability (beneficial effect). Multivariable linear regression models were conducted to investigate the associations between childhood and adolescent Mn biomarkers and adolescent postural balance adjusted for age, sex, height-weight ratio, parent/caregiver intelligence quotient, socioeconomic status, blood Pb, and serum cotinine.

RESULTS

CARES participants who completed the adolescent postural balance assessment (n = 123 ) were 98% White and 54% female and had a mean age of 16 y (range: 13-18 y). In both childhood and adolescence, higher Mn biomarker concentrations were significantly associated with greater adolescent sway measures. Supplemental analyses revealed sex-specific associations; higher childhood Mn biomarker concentrations were significantly associated with greater sway in females compared with males.

DISCUSSION

This study found childhood and adolescent Mn biomarkers were associated with subclinical neuromotor effects in adolescence. This study demonstrates postural balance as a sensitive measure to assess the association between Mn biomarkers and neuromotor function. https://doi.org/10.1289/EHP13381.

Public health assessment of Kenyan ASGM communities using multi-element biomonitoring, dietary and environmental evaluation

The Kakamega gold belt's natural geological enrichment and artisanal and small-scale gold mining (ASGM) have resulted in food and environmental pollution, human exposure, and subsequent risks to health. This study aimed to characterise exposure pathways and risks among ASGM communities. Human hair, nails, urine, water, and staple food crops were collected and analysed from 144 ASGM miners and 25 people from the ASGM associated communities. Exposure to PHEs was predominantly via drinking water from mine shafts, springs and shallow-wells (for As>Pb>Cr>Al), with up to 366 µg L-1 arsenic measured in shaft waters consumed by miners. Additional exposure was via consumption of locally grown crops (for As>Ni>Pb>Cr>Cd>Hg>Al) besides inhalation of Hg vapour and dust, and direct dermal contact with Hg. Urinary elemental concentrations for both ASGM workers and wider ASGM communities were in nearly all cases above bioequivalents and reference upper thresholds for As, Cr, Hg, Ni, Pb and Sb, with median concentrations of 12.3, 0.4, 1.6, 5.1, 0.7 and 0.15 µg L-1, respectively. Urinary As concentrations showed a strong positive correlation (0.958) with As in drinking water. This study highlighted the importance of a multidisciplinary approach in integrating environmental, dietary, and public health investigations to better characterise the hazards and risks associated with ASGM and better understand the trade-offs associated with ASGM activities relating to public health and environmental sustainability. Further research is crucial, and study results have been shared with Public Health and Environmental authorities to inform mitigation efforts.

What does scientometry tell us about mercury toxicology and its biological impairments?

Mercury is a toxic pollutant that poses risks to both human and environmental health, making it a pressing public health concern. This study aimed to summarize the knowledge on mercury toxicology and the biological impairments caused by exposure to mercury in experimental studies and/or diagnosis in humans. The research was conducted on the main collection of Web of Science, employing as a methodological tool a bibliometric analysis. The selected articles were analyzed, and extracted data such as publication year, journal, author, title, number of citations, corresponding author's country, keywords, and the knowledge mapping was performed about the type of study, chemical form of mercury, exposure period, origin of exposure, tissue/fluid of exposure measurement, mercury concentration, evaluation period (age), mercury effect, model experiments, dose, exposure pathway, and time of exposure. The selected articles were published between 1965 and 2021, with Clarkson TW being the most cited author who has also published the most articles. A total of 38% of the publications were from the USA. These studies assessed the prenatal and postnatal effects of mercury, emphasizing the impact of methylmercury on neurodevelopment, including motor and cognitive evaluations, the association between mercury and autism, and an evaluation of its protective effects against mercury toxicity. In observational studies, the blood, umbilical cord, and hair were the most frequently used for measuring mercury levels. Our data analysis reveals that mercury neurotoxicology has been extensively explored, but the association among the outcomes evaluated in experimental studies has yet to be strengthened. Providing metric evidence on what is unexplored allows for new studies that may help governmental and non-governmental organizations develop guidelines and policies.

Human biomonitoring of trace metals from different altitudinal settings of Pakistan

Human biomonitoring of toxic trace elements is of critical importance for public health protection. The current study aims to assess the levels of selected trace metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) into paired human nail and hair samples (n = 180 each) from different altitudinal setting along the Indus River, and which were measured by using inductively coupled plasma mass spectrometry (ICP-MS). The human samples (hair and nail) were collected from four different ecological zones of Pakistan which include frozen mountain zone (FMZ), wet mountain zone (WMZ), riverine delta zone (RDZ), and low-lying southern areas (LLZ). Our results showed the following occurrence trends into studied hair samples: higher values (ppm) of Zn (281), Co (0.136), and Mn (5.65) at FMZ; Cr (1.37), Mn (7.83), and Ni (1.22) at WMZ; Co (0.15), Mn (11.89), and Ni (0.99) at RDZ; and Mn (8.99) and Ni (0.90) at LLZ. While in the case of nails, the levels (ppm) of Mn (9.91) at FMZ and Mn (9.38, 24.1, and 12.5), Cr (1.84, 3.87, and 2.33), and Ni (10.69, 8.89, and 12.6) at WMZ, RDZ and LLZ, respectively, showed higher concentration. In general, among the studied trace elements, Mn and Ni in hair/nail samples were consistently higher and exceeded the WHO threshold/published reference values in most of the studied samples (> 50-60%) throughout the Indus basin. Similarly, hair/nail Pb values were also higher in few cases (2-10%) at all studied zones and exceeded the WHO threshold/published reference values. Our area-wise comparisons of studied metals exhibited altitudinal trends for Cd, Cr, Zn, and Mn (p < 0.05), and surprisingly, the values were increasing from south to north (at higher altitudes) and indicative of geogenic sources of the studied toxic elements, except Mn, which was higher at lower floodplain areas. Estimated daily intake (EDI) values showed that food and drinking water had the highest contribution towards Zn, Cu, Mn, and Ni and accumulation at all studied zones. Whereas, dust also acts as the main exposure route for Mn, Co, Cr, and Cd followed by the food, and water.

Benchtop x-ray fluorescence to quantify elemental content in nails non-destructively

Metals continue to impose health issues among world populations. A non-invasive alternative biomarker for assessment of metals and other elements has been explored in other studies using toenail samples. Some benefits of using toenails as biomarkers over blood samples include cost efficiency, ease of collection, and a longer biological half-life within samples. The objective of this study was to employ desktop XRF for the purpose of measuring metal concentrations in human nail samples, thus conducting a non-destructive assessment. These benefits paired with comparable accuracy in exposure detection could prove toenail samples to be a preferred biomarker for many studies. Current elemental quantification techniques in toenail samples could be improved. The standard practice for measuring metal exposure in toenails, inductively coupled plasma mass spectrometry (ICP-MS), has a counterpart in x-ray fluorescence. While maintaining similar quantification capabilities, x-ray fluorescence could provide decreased cost, preservation of samples, and ease of operation. Portable XRF machines have been tested for measuring toenail samples, but they have drastically increased detection limits in comparison to ICP-MS. New benchtop XRF systems should give comparable detection limits to ICP-MS. This study compares the benchtop XRF measurements of lead (Pb), copper (Cu), iron (Fe), and Selenium (Se) levels to that of ICP-MS measurements of toenail samples and calculates estimated detection limits for 23 other elements. We found strong correlations for the toenail lead (R2 = 0.92), copper (R2 = 0.95), selenium (R2 = 0.60), and iron (R2 = 0.77) comparison between desktop XRF and ICP-MS measurements. Median minimum detection limits over the 23 elements were found to be 0.2 μg/g using a 7.5-min measurement. Benchtop XRF provides a lower detection limit than previously studied portable XRF machines, which gives it the capability of accurately detecting almost any desired element in nail samples. Benchtop XRF provides a non-destructive alternative to ICP-MS in surveillance of nail samples.

Trace Element Distribution and Arsenic Speciation in Toenails as Affected by External Contamination and Evaluation of a Cleaning Protocol

Trace element concentrations in toenail clippings have increasingly been used to measure trace element exposure in epidemeological research. Conventional methods such as inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography ICP-MS (HPLC-ICP-MS) are commonly used to measure trace elements and their speciation in toenails. However, the impact of the removal of external contamination on trace element quantification has not been thoroughly studied. In this work, the microdistribution of trace elements (As, Ca, Co, Cu, Fe, K, Mn, Ni, Rb, S, Sr, Ti, and Zn) in dirty and washed toenails and the speciation of As in situ in toenails were investigated using synchrotron X-ray fluorescence microscopy (XFM) and laterally resolved X-ray absorption near edge spectroscopy (XANES). XFM showed different distribution patterns for each trace element, consistent with their binding properties and nail structure. External (terrestrial) contamination was identified and distinguished from the endogenous accumulation of trace elements in toenails─contaminated areas were characterized by the co-occurrence of Co, Fe, and Mn with elements such as Ti and Rb (i.e., indicators of terrestrial contamination). The XANES spectra showed the presence of one As species in washed toenails, corresponding to As bound to sulfhydryl groups. In dirty specimens, a mixed speciation was found in localized areas, containing AsIII-S species and AsV species. ArsenicV is thought to be associated with surface contamination and exogenous As. These findings provide new insights into the speciation of arsenic in toenails, the microdistribution of trace elements, and the effectiveness of a cleaning protocol in removing external contamination.

Blood and hoof biodistibution of some trace element (Lithium, Copper, Zinc, Strontium and, Lead) in horse from two different areas of Sicily

BACKGROUND AND PURPOSE

Biological monitoring of trace element horses is a well-known tool for investigating potential bioaccumulation in urbanized and industrialized geographical areas. Some biomaterials such as hoof are considered as an important indicator of environmental pollution. Hooves can store trace elements for a long time compared to blood and this represents a scientific key to long-term monitoring of exposure to environmental pollutants. In the present study, samples of equine hoof and blood were taken from an experimental group of horses living in an industrialized area of Sicily (Italy) and from a control group of horses housed in a non-industrialized area of Sicily to evaluate the bioaccumulation of different trace elements in different substrates.

METHODS

Hoof and blood mineral concentration of Li- Lithium, Cu- Copper, Zn- Zinc, Sr- Strontium and, Pb- Lead was processed by means of Thermo Scientific iCAP-Q ICP-MS spectrometer. Student T-test was applied to evaluate the differences between groups and substrates. Correlation analysis between substrates and hematological parameters was performed.

RESULTS

Statistical analysis showed a significant statistical difference for Li (p < 0.0001) and Pb (p < 0.0001) between blood and hoof in both groups. A statistically significant difference was observed for Li (p < 0.0001), Cu(p < 0.01), Zn (p < 0.0001) and Pb (p < 0.0001) between substrates in the experimental group. The statistical analysis showed a significant difference of blood Zn (p < 0.01) and hoof Pb (p < 0.01) concentration between groups. Our results revealed a statistically higher concentration of minerals in the blood substrate than in the hoof in both groups. Li (p < 0.0001) and Zn (p < 0.001) were positively correlated between control and experimental group in blood substrate. No correlations were found (P > .05) in hoof between groups for other elements. A positive correlation with WBC was observed in Cu concentration for hoof substrate (p < 0.02) in control group and for Zn in experimental group (p < 0.02). A positive correlation with HGB and HCT was observed for Cu hoof concentration (p < 0.02) in experimental group and PLT resulted positively correlated (p < 0.02) with Pb blood substrate in control group.

CONCLUSIONS

Horses were not overexposed to these elements in the analyzed groups. The study highlights the role of a new bioaccumulation substrate such as the horse hoof identified as an analytical matrix for the monitoring of heavy metal concentrations in domestic animals.

Association between Mediterranean diet and metal mixtures concentrations in pregnant people from the New Hampshire Birth Cohort Study

Diet is a primary source of nutrients but also toxic metal exposure. In pregnancy, balancing essential metal exposure while reducing non-essential ones is vital for fetal and maternal health. However, the effect of metal mixtures from diets like the Mediterranean, known for health benefits, remains unclear. This study aimed to explore the association between Mediterranean diet adherence and metals exposure, both individually and as mixtures. The study involved 907 pregnant participants from the New Hampshire Birth Cohort Study. We calculated the relative Mediterranean diet score (rMED) through a validated food frequency questionnaire, which includes 8 traditional Mediterranean dietary components. Also, at ~24-28 weeks of gestation, we used ICP-MS to measure speciation of Al, Cd, Co, Cu, Fe, Hg, Mo, Ni, Sb, Se, Sn, Zn, and As in urine, as well as Pb, Hg, As, Ni, and Se in toenails. We used multiple linear regression and Weighted Quantile Sum regression to analyze the association between rMED and metal mixtures. The models were adjusted for age, pre-pregnancy BMI, smoking during pregnancy, and educational level. High adherence to the Mediterranean diet was associated with increased urinary Al (® = 0.26 (95 % confidence interval (CI) = 0.05; 0.46)), Cd (β = 0.12 (95%CI = 0.00; 0.24)), Mo (β = 0.10 (95%CI = 0.00; 0.20)), and AsB (β = 0.88 (95%CI = 0.49; 1.27)) as well as toenail Hg (β = 0.44 (95%CI = 0.22; 0.65)), Ni (β = 0.37 (95%CI = 0.06; 0.67)), and Pb (β = 0.22 (95%CI = 0.03; 0.40)) compared to those with low adherence. The intake of fruits and nuts, fish and seafood, legumes, cereals, meat, and olive oil were found to be related to the metal biomarkers within the rMED. In conclusion, the Mediterranean diet enhances essential metal intake but may also increase exposure to harmful ones.

Associations of Perinatal Metal and Metalloid Exposures with Early Child Behavioral Development Over Time in the New Hampshire Birth Cohort Study

Research on the neurodevelopmental effects of metal(loid)s has focused mainly on outcomes assessed at one time point, even though brain development progresses over time. We investigated biomarkers of perinatal exposure to metals and changes in child behavior over time. We followed 268 participants from the prospective New Hampshire Birth Cohort Study between birth and age 5 years. We measured arsenic (As), copper (Cu), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in toenails from 6-week-old infants. The Behavioral Symptoms Index (BSI), externalizing, and internalizing symptoms were assessed using the Behavior Assessment System for Children, 2nd edition (BASC-2) at ages 3 and 5 years. Multivariable linear regression was used to estimate associations of metals with behavior change, calculated as the difference in symptom raw scores between 3 and 5 years, in addition to the associations for symptom scores at 3 and 5 years separately. Sex-specific associations were also explored using stratified models and a sex-metal interaction term. Adjusted associations of metals and change in behavior varied by exposure and outcome. Each 1 μg/g increase in ln toenail Cu was associated with improved behavior between 3 and 5 years [BSI: β = - 3.88 (95%CI: - 7.12, - 0.64); Externalizing problems: β = - 2.20 (95%CI: - 4.07, - 0.33)]. Increasing Zn was associated with increased externalizing behavior over time (β = 3.42 (95%CI: 0.60, 6.25). Sex-stratified analyses suggested more pronounced associations among boys compared to girls. Perinatal exposure to metals may alter behavioral development between ages 3 and 5 years. Findings support the need for more research on associations between metals and neurodevelopment over longer time periods.

Micro-distribution of arsenic in toenail clippings using laser ablation inductively coupled plasma mass spectrometry: implications for biomonitoring

Toenails are a common monitoring tool for arsenic exposure, but the risk of external contamination of toenails has cast doubt on its usefulness. The main objective of this study is to investigate the micro-distribution of arsenic through the dorsoventral plane of nail clippings to understand endogenous vs exogenous sources. We used laser-ablation inductively coupled plasma mass spectrometry to measure arsenic through a dorsoventral cross-section of the nail plate collected from reference (N = 17) and exposed individuals (N = 35). Our main results showed (1) bulk toenail concentrations measured using ICP-MS in this study ranged from 0.54 to 4.35 µg/g; (2) there was a double-hump pattern in arsenic concentrations, i.e., dorsal and ventral layers had higher arsenic than the inner layer; (3) the double-hump was more pronounced in the exposed group (ventral: 6.25 μg/g; inner: 0.75 μg/g; dorsal: 0.95 μg/g) than the reference group (ventral: 0.58 μg/g; inner: 0.15 μg/g; dorsal: 0.29 μg/g) on average; (4) the distribution was, in part, associated with different binding affinity of nail layers (i.e., ventral > dorsal > inner); (5) most individuals in the higher exposure group showed > 25% contamination in ventral and dorsal nail layers; and (6) there were no statistically significant correlations between LA-ICP-MS arsenic with either bulk toenail arsenic or urine arsenic from the same individuals. Our results on micro-distribution and binding affinity provide insight into the impact of external contamination on arsenic concentrations and show how LA-ICP-MS can access the protected inner nail layer to provide a more accurate result.

Metal levels in waste pickers in Brasilia, Brazil: hair and nail as exposure matrices

The aim of this cross-sectional study was to compare workplace conditions and metal exposures in 431 waste pickers who worked nearby at the Estrutural Dump in Brasilia utilizing hair (n = 310) and nail (n = 355) as matrices of exposure. Waste pickers were grouped according to their workplace (open waste dump: G1 and sorting plants: G2). Hair and nail samples were collected and analyzed using ICP-MS. The work duration in the facilities was significantly different between the groups with averages of 16.46 (8.48) yrs and 9.26 (6.28) yrs for hair donors in G1 and G2, and 15.92 (7.72) yrs and 8.55 (5.77) yrs for toenail donors in G1 and G2, respectively. The arithmetic means (μg/g) of cadmium, copper, lead, and manganese in hair were significantly higher in G2 (0.076 ± 0.133; 19.61 ± 18.16; 2.27 ± .56 and 3.87 ± 5.59, respectively) compared to G1 (0.069 ± 0.235; 15.72 ± 15.18; 1.72 ± 4.04 and 3.65 ± 5.5, respectively). Concentrations of arsenic, barium, cadmium, copper, cobalt, lead, manganese, and molybdenum in nail were significantly higher in G2 (0.57 ± 0.39; 22.74 ± 42.06; 0.1 ± 0.08; 22.7 ± 51.60; 0.48 ± 0.45; 4.69 ± 9.43; 19.07 ± 20.75; 1.80 ± 1.76, respectively) compared to G1 (0.40 ± 0.28; 15.32 ± 22.31; 0.08 ± 0.11; 11.91 ± 16.25; 0.37 ± 0.37; 3.94 ± 15.04; 13.01 ± 19.08; 1.16 ± 1.80, respective. Our findings suggest that the studied population was exposed to toxic metals and indicates the need for chemical exposure prevention policies to monitor chemical risk exposures in waste pickers.

Biomonitoring of exposure to multiple metal components in urine, hair and nails of apprentice welders performing shielded metal arc welding (SMAW)

Welding fumes are associated with various diseases. Increased air levels of metals were reported during welding. However, few multielement biomonitoring studies were conducted to assess the actual dose of metal components absorbed in apprentice welders in a learning environment. This research aimed to establish the nature and level of exposure to welding fumes and their metallic components in apprentice welders performing 'Shielded Metal Arc Welding' (SMAW), based on multi-element and multi-matrix analyses. A total of 86 apprentice welders were recruited in three different schools in Montreal, Québec, Canada. Twenty-one elements were measured in urine, hair, fingernail, and toenail samples collected at the beginning of the program and at the end of SMAW practical training. Concentrations of welding fumes and 12 metals were also determined in personal respirable air samples collected over a typical workday in a subgroup of 19 apprentices. Levels of manganese (Mn), iron (Fe) and nickel (Ni) in urine and Mn in hair were higher in samples taken at the end of the SMAW module compared to the beginning of training, while there was no significant difference for the other elements or for nail concentrations. Geometric mean concentrations [5th-95th percentiles] reached 0.31 [0.032-2.84], 9.4 [3.1-51] and 0.87 [0.35-3.1] μg/g creat. in post-shift urine, respectively, for Mn, Fe and Ni, and 0.37 [0.46-6.4] μg Mn/g hair at the end of SWAW. Median concentrations [5th-95th percentiles] were 29 [4.6-1200], 120 [27-3100] and 0.31 [ Collapse

Key Words

• Biomonitoring
• Metalloids
• Metals
• Occupational exposure
• Shielded metal arc welding
• Welding fume exposure

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MESH Headings

• Humans
• Nails/chemistry
• Air Pollutants, Occupational/analysis
• Biological Monitoring
• Welding
• Metal Workers
• Metals/analysis
• Occupational Exposure/analysis
• Manganese/analysis
• Nickel
• Gases

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Affiliation(s)

Jairo Buitrago Cortes Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U436, P.O. Box 6128, Main Station, Montreal, Quebec, H3C 3J7, Canada
Philippe Sarazin Chemical and Biological Hazards Prevention, Institut de recherche Robert-Sauvé en santé et en sécurité du travail, 505 Boulevard de Maisonneuve O, Montréal, Québec, H3A 3C2, Canada
Denis Dieme Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U436, P.O. Box 6128, Main Station, Montreal, Quebec, H3C 3J7, Canada
Jonathan Côté Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U436, P.O. Box 6128, Main Station, Montreal, Quebec, H3C 3J7, Canada
Capucine Ouellet Chemical and Biological Hazards Prevention, Institut de recherche Robert-Sauvé en santé et en sécurité du travail, 505 Boulevard de Maisonneuve O, Montréal, Québec, H3A 3C2, Canada
Naïma El Majidi Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U436, P.O. Box 6128, Main Station, Montreal, Quebec, H3C 3J7, Canada
Michèle Bouchard Department of Environmental and Occupational Health, Chair in Toxicological Risk Assessment and Management, and Public Health Research Center (CReSP), University of Montreal, Roger-Gaudry Building, U436, P.O. Box 6128, Main Station, Montreal, Quebec, H3C 3J7, Canada.

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Characterization of the internal working-life exposome using minimally and non-invasive sampling methods - a narrative review

During recent years, we are moving away from the 'one exposure, one disease'-approach in occupational settings and towards a more comprehensive approach, taking into account the totality of exposures during a life course by using an exposome approach. Taking an exposome approach however is accompanied by many challenges, one of which, for example, relates to the collection of biological samples. Methods used for sample collection in occupational exposome studies should ideally be minimally invasive, while at the same time sensitive, and enable meaningful repeated sampling in a large population and over a longer time period. This might be hampered in specific situations e.g., people working in remote areas, during pandemics or with flexible work hours. In these situations, using self-sampling techniques might offer a solution. Therefore, our aim was to identify existing self-sampling techniques and to evaluate the applicability of these techniques in an occupational exposome context by conducting a literature review. We here present an overview of current self-sampling methodologies used to characterize the internal exposome. In addition, the use of different biological matrices was evaluated and subdivided based on their level of invasiveness and applicability in an occupational exposome context. In conclusion, this review and the overview of self-sampling techniques presented herein can serve as a guide in the design of future (occupational) exposome studies while circumventing sample collection challenges associated with exposome studies.

Human biomonitoring of environmental contaminants in Gulf Countries - current status and future directions

BACKGROUND

This systematic review aimed to evaluate the status of Human Biomonitoring (HBM) in the Gulf Cooperation Council (GCC) region and provide recommendations for future research, considering the increased environmental contaminants that pose a threat to human health in this rapidly industrializing area.

METHODS

A thorough search was performed in PubMed and Web of Science databases up to February 2023 to identify biomonitoring studies on human exposure and levels in the GCC region. Two independent reviewers assessed study eligibility, conducted data extraction and risk of bias assessment. The NIH Quality Assessment Tools and PRISMA guidelines were utilized for quality evaluation and reporting of results.

RESULTS

A total of 38 eligible articles were included in this systematic review out of 662 articles screened. The majority of the publications were from Saudi Arabia (n = 24) and Kuwait (n = 10), while limited representation was found from Qatar (n = 3) and the UAE (n = 1). No articles were identified from Oman and Bahrain. The studies focused on metals, organohalogen compounds, pesticides, polycyclic aromatic hydrocarbons, and phthalates. The findings revealed elevated levels of metals and established correlations between metal exposure and adverse health effects, including infant neurodevelopmental issues, vitamin D deficiency, and oxidative stress. The presence of organohalogen compounds and pesticides was prevalent in the GCC region, with significant associations between exposure to these compounds and negative health outcomes. Notably, high levels of perchlorate were observed in the Kuwaiti population, and a study from Saudi Arabia found an association between per- and polyfluorinated substances and increased odds of osteoporosis.

CONCLUSIONS

This review emphasizes the need to address environmental health challenges in the GCC region through improved HBM research methods and strategies. Implementing biomonitoring programs, conducting cohort studies, investing in tools and expertise, promoting collaboration, and engaging the community are crucial for reliable HBM data in the GCC.

Associations between parental and postnatal metal mixture exposure and developmental delays in a Taiwanese longitudinal birth cohort of preschool children

Studies have evaluated the impact of environmental exposure to neurotoxic metals on developmental delays (DDs). However, comprehensive understanding regarding the associations between parental and postnatal exposure to metal mixtures and the occurrence of DDs in offspring is limited. In this study, we assessed the relationships between parental and postnatal exposure to three metals (arsenic [As], cadmium [Cd], and lead [Pb], levels of which were measured in toenails) and suspected DDs (SDDs) in preschool children within a Taiwanese longitudinal birth cohort. In total between 2017 and 2021, 154 pairs of parents and their children under the age of 6 years were recruited, and 462 toenail samples and 154 completed questionnaires were collected. Metal concentrations in toenails were quantified using inductively coupled plasma-mass spectrometry after acid digestion of the toenails. We applied multivariable logistic regression and Bayesian kernel machine regression to evaluate the overall effect and to identify key components of the metal mixture that were associated with the SDD risk. Higher concentrations of As, Cd, and Pb were found in the toenails of the parents of children with SDDs compared with the toenails of the parents of children without SDDs. Our examination of the combined effects of exposure to the metal mixture revealed that As concentration in the father's toenail and Cd concentration in the mother's toenail were positively correlated with the risk of SDDs in their offspring. Notably, the effect of exposure to the metal mixture on the risk of SDDs was stronger in boys than in girls. Our findings suggest that parents taking measures to minimize their exposure to metals might enhance their children's developmental outcomes.

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.

Effects of preterm birth and postnatal exposure to metal mixtures on neurodevelopment in children at 24 months of age

The effects of early-life metal exposure on neurodevelopment in very low birth weight preterm (VLBMP) children (with a birth weight of <1500 g and a gestational age of <37 weeks) have not been clearly established. We aimed to investigate associations of childhood exposure to multiple metals and preterm low birth weight with neurodevelopment among children at 24 months of corrected age. VLBWP children (n = 65) and normal birth weight term (NBWT) children (n = 87) were enrolled from Mackay Memorial Hospital in Taiwan between December 2011 and April 2015. Lead (Pb), cadmium (Cd), arsenic (As), methylmercury (MeHg), and selenium (Se) concentrations in the hair and fingernails were analyzed as biomarkers for metal exposure. The Bayley Scale of Infant and Toddler Development, Third Edition, was used to determine neurodevelopment levels. VLBWP children had significantly lower scores in all development domains compared to NBWT children. We also investigated preliminary exposure levels of VLBWP children to metals as reference values for future epidemiological and clinical survey. Fingernails are a useful biomarker for metal exposure to evaluate the effects on neurological development. A multivariable regression analysis revealed that fingernail Cd concentrations were significantly negatively associated with cognition (β = -0.63, 95% confidence interval (CI): -1.17 to -0.08) and receptive language function (β = -0.43, 95% CI: -0.82 to -0.04) among VLBWP children. VLBWP children with a 10-μg/g increase in the As concentration in their nails had a 8.67-point lower composite score in cognitive ability and a 1.82-point lower score in gross-motor functions. Effects of preterm birth and postnatal exposure to Cd and As were associated with poorer cognitive, receptive language, and gross-motor abilities. VLBWP children are at risk for neurodevelopmental impairments when exposed to metals. Further large-scale studies are needed assess to the risk of neurodevelopmental impairments when vulnerable children are exposed to metal mixtures.

Metals and per- and polyfluoroalkyl substances mixtures and birth outcomes in the New Hampshire Birth Cohort Study: Beyond single-class mixture approaches

We aimed to investigate the joint, class-specific, and individual impacts of (i) PFAS, (ii) toxic metals and metalloids (referred to collectively as "metals"), and (iii) essential elements on birth outcomes in a prospective pregnancy cohort using both established and recent mixture modeling approaches. Participants included 537 mother-child pairs from the New Hampshire Birth Cohort Study. Concentrations of 6 metals and 5 PFAS were measured in maternal toenail clippings and plasma, respectively. Birth weight, birth length, and head circumference at birth were abstracted from medical records. Joint, index-wise, and individual associations of the metals and PFAS concentrations with birth outcomes were evaluated using Bayesian Kernel Machine Regression (BKMR) and Bayesian Multiple Index Models (BMIM). After controlling for potential confounders, the metals-PFAS mixture was associated with a larger head circumference at birth, which was driven by manganese. When using BKMR, the difference in the head circumference z-score when changing manganese from its 25th to 75th percentiles while holding all other mixture components at their medians was 0.22 standard deviations (95% posterior credible interval [CI]: -0.02, 0.46). When using BMIM, the posterior mean of index weight estimates assigned to manganese for head circumference z-score was 0.72 (95% CI: 0, 0.99). Prenatal exposure to the metals-PFAS mixture was not associated with birth weight or birth length by either BKMR or BMIM. Using both traditional and new mixture modeling approaches, prenatal exposure to manganese was associated with a larger head circumference at birth after accounting for exposure to PFAS and multiple toxic and essential metals.

Heavy metals in paired samples of hair and nails in China: occurrence, sources and health risk assessment

The occurrence of heavy metals including chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb) was investigated in paired samples of hair and nails collected from 121 volunteers in 16 cities, China. Results showed that the mean concentrations of Zn, Cu, As, Pb, Cr, Ni and Cd were 205, 18.0, 7.79, 6.18, 3.54, 2.02, 0.533 μg g^-1 in hair and 103, 8.09, 0.760, 7.27, 6.07, 8.81, 0.485 μg g^-1 in nails, respectively. The concentrations of Zn, Ni, Cr, Cd and Pb were positively correlated in paired samples of hair and nails, whereas a negative correlation was found for Cu and As between hair and nails. Higher concentrations of heavy metals were found in northern China than southern China. The multivariate analysis of variance revealed that dwelling environment was the dominant factor influencing the levels of Cd in hair (p < 0.05), while age was the dominant factor influencing the levels of Cr in nails (p < 0.05). Moreover, industrial pollution and smoking were also the important factors leading to the accumulation of heavy metals in human body. Principal component analysis (PCA) showed that industrial pollution and decoration material immersion were the main factors for the high concentrations of Cr and Ni in hair, accounting for 62.9% of the total variation; As in hair was dominantly related to groundwater pollution. The concentrations of heavy metals were within the recommended ranges in nails from this study. However, the mean levels of Cr, Ni and As in hair exceeded their recommended reference values, indicating potential health risks from heavy metals for residents in China.

Feasibility of remote self-collection of dried blood spots, hair, and nails among people with HIV with hazardous alcohol use

BACKGROUND

The use of biomarkers in behavioral HIV research can help to address limitations of self-reported data. The COVID-19 pandemic forced many researchers to transition from standard in-person data collection to remote data collection. We present data on the feasibility of remote self-collection of dried blood spots (DBS), hair, and nails for the objective assessment of alcohol use, antiretroviral therapy adherence, and stress in a sample of people with HIV (PWH) who are hazardous drinkers.

METHODS

Standardized operating procedures for remote self-collection of DBS, hair, and nails were developed for an ongoing pilot study of a transdiagnostic alcohol intervention for PWH. Prior to each study appointment, participants were mailed a kit containing materials for self-collection, instructions, a video link demonstrating the collection process, and a prepaid envelope for returning samples.

RESULTS

A total of 133 remote study visits were completed. For DBS and nail collection at baseline, 87.5% and 83.3% of samples, respectively, were received by the research laboratory, of which 100% of samples were processed. Although hair samples were intended to be analyzed, most of the samples (77.7%) were insufficient or the scalp end of the hair was not marked. We, therefore, decided that hair collection was not feasible in the framework of this study.

CONCLUSION

An increase in remote self-collection of biospecimens may significantly advance the field of HIV-related research, permitting the collection of specimens without resource-intensive laboratory personnel and facilities. Further research is needed on the factors that impeded participants' ability to complete remote biospecimen collection.

Survey to identify the metal accumulation pathway in humans using hair and nail as biomarkers from fisherfolk population

Human hair and nail samples from Cuddalore fisherfolk populations were used as biomarkers for assessing metal concentrations in humans. Hair samples from 80 participants (47 men and 33 women) and nail samples from 40 participants (21 men and 19 women) were collected, and the concentrations of Cd, Cu, Pb, and Zn were assessed using an atomic absorption spectrophotometer (AAS). Metal data from AAS were compared with the survey questionnaire's personal and dietary parameters. Results indicate that both personal and dietary parameters may influence metal exposure; however, majority of the sources may have originated from metal-contaminated seafood. Higher metal accumulation in communities, especially those which consume seafood on a daily basis, may increase the possibility for them to get affected by metal-related diseases. Based on environmental parameters, people who live ≤500 m from industrial zones accumulate more metals. Further extensive studies with more individuals and more questionnaire parameters are needed to identify the metal accumulation pathway in humans.

The Influence of Environmental Exposure to Heavy Metals on the Occurrence of Selected Elements in the Maxillary Bone

The elemental composition of the body's calcified tissues may reflect the environmental exposure of the population to heavy metals. The aim of the study was to assess whether the elemental composition of the maxillary bone from individuals belonging to a given population reflects the environmental exposure of this population to lead and cadmium. The research material consisted of cortical bone from the anterolateral walls of the maxilla collected from 126 patients during Caldwell-Luc maxillary sinus surgery on residents of two cities differing in terms of the lead and cadmium pollution of the natural environment. The content levels of lead, cadmium, iron, manganese, chromium, copper, and iron were determined by using atomic absorption spectrophotometry. The content levels of lead and cadmium in the samples of the maxillary bones of residents of Bielsko-Biala were 3.26 ± 2.42 µg/g and 0.74 ± 0.38 µg/g, respectively, whereas in the samples from the residents of Katowice, they were 7.66 ± 2.79 µg/g and 1.12 ± 0.08 µg/g, respectively. It was found that the lead and cadmium levels in the maxillary bone corresponded to the environmental exposure to these heavy metals in the place of residence, which was proven here via the example of the residents of two cities with different concentrations of these heavy metals in the air over long time periods. Additionally, higher content levels of essential metals such as manganese, chromium, copper, and iron are characteristic of the maxillary bone samples of residents of the area that is more polluted with heavy metals.

Reduced Level of Prolylhydroxyproline in the Nail Clippings of Oral Cancer Patients and its Role as an Activator of Phospholipase C-β2

BACKGROUND

The oral cancer microenvironment plays an important role in the development and progression of the disease which depicts the heterogeneous nature of diseases. Several cellular and non-cellular factors, including dipeptides, have been reported to drive tumor progression and metastasis. Among various secreted molecules in the tumor microenvironment, prolylhydroxyproline (Pro-Hyp) is a collagen-degraded product with specific relevance to fibrosis and oral cancer. However, the detection of Pro-Hyp in the nails of oral cancer patients is a potential biomarker, and our understanding of the biological relevance of Pro-Hyp is highly limited.

METHODS

Here, the authors have attempted to use a novel and in-house vertical tube gel electrophoresis (VTGE) protocol to evaluate the level of Pro-Hyp in the nails of oral cancer patients and healthy subjects. Furthermore, we employed molecular docking and molecular dynamics (MD) simulations to predict the biological function of Pro-Hyp. ADME profiles such as the druglikeness and leadlikeness of Pro-Hyp and a known PLC-β2 activator, m-3M3FBS, were evaluated by the SWISS-ADME server.

RESULTS

We report that among various key metabolites, Pro-Hyp, a dipeptide, is reduced in the nails of oral cancer patients. Molecular docking and MD simulations helped to suggest the potential role of Pro-Hyp as an activator of Phospholipase C-β2 (PLC-β2). Pro-Hyp displayed good binding affinity (-7.6 kcal/mol) with specific interactions by a conventional hydrogen bond with key residues, such as HIS311, HIS312, VAL641, and GLU743. MD simulations showed that the activator binding residues and stability of complexes are similar to the well-known activator m-3M3FBS of PLC-β2. ADME profiles such as the druglikeness and leadlikeness of Pro-Hyp were found to be highly comparable and even better than those of m-3M3FBS.

CONCLUSION

This study is one of the first reports on Pro-Hyp as a metabolite biomarker in the nails of oral cancer patients. Furthermore, the implications of Pro-Hyp are proposed to activate PLC-β2 as a pro-tumor signaling cascade. In the future, diagnostic and therapeutic approaches may be explored as biomarkers and mimetic of Pro-Hyp.

Metal Exposures in Residents Living Near an Urban Oil Drilling Site in Los Angeles, California

Urban environmental justice communities are potentially exposed to multiple toxic metals, through contaminated air, soil, water, and food. However, information on metals and their sources is lacking. This study uses non-negative matrix factorization (NMF) in a community-based participatory research study to identify potential sources and to understand how these metals cluster in a population near an urban oil drilling site. We recruited 203 Latinx, Black, and Asian residents who lived within 1 km of an oil drilling site in south Los Angeles and collected toenail clippings to assess exposure to arsenic (As), cadmium (Cd), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and antimony (Sb). Using NMF, we identified three clusters based on concentrations in the participants' toenails. As, Cd, Pb, and Sb grouped together, indicative of an industrial source. A second grouping was composed of Ni and Mn, which may be related to oil drilling. We also identified a third source factor predominantly driven by Hg and As, which may arise from dietary sources. Utilizing NMF, a dimension reduction method, we identified a source factor high in Ni and Mn in residents living in a neighborhood near an active oil drilling site.

Decreased hearing levels at frequencies for understanding speech in tannery workers exposed to a high level of trivalent chromium in Bangladesh

Hexavalent chromium [Cr(VI)], which has a strong corrosive effect, has been reported to cause perforation of the eardrum. Trivalent chromium [Cr(III)] also has a weak corrosive effect. However, there has been no study on the effects of exposure to Cr, either Cr(VI) or Cr(III), on hearing levels in animals or humans. In this study, the effect of Cr(III) exposure on hearing levels was determined in a human study. Then the reproducibility of the results obtained in the human study and the etiology were investigated in an animal study. The mean levels of total chromium (t-Cr) in hair and toenails from 100 Bangladeshi tannery workers were >20-fold and >360-fold higher, respectively, than those in hair and toenails from 49 Bangladeshi non-tannery workers (office workers). Multivariate analysis revealed decreases of hearing levels (DHLs) at 1 k and 4 k Hz, frequencies that are crucial for understanding language, but not at 8 k and 12 k Hz, in the tannery workers. Since >99.99% of t-Cr in the wastewater that the workers were in direct contact with in the tanneries was Cr(III), the epidemiological results suggest Cr(III)-mediated DHLs in the tannery workers. The results of animal experiments in this study further showed that treatment with eardrops but not intraperitoneal injection with the same amount of Cr(III) that tannery workers might be exposed to resulted in DHL with a damaged eardrum in mice. Previous studies suggested that Cr(III) can directly reach the eardrums of tannery workers via droplets in the air. Cr(III) could also reach the eardrum via picking an ear canal with a finger contaminated with tannery wastewater including Cr(III). Taken together, the results of both human and animal studies suggest the risk of DHLs caused by damage of the eardrum through external exposure to Cr(III) via the ear canal.

Multi-matrix biomonitoring approach to assess exposure to metals and trace elements in the Lebanese population and associations with drinking water consumption

This study is the first attempt to assess exposure to metals and trace elements in subgroups of the Lebanese population using a multi-matrix biomonitoring approach. Concentrations of 11 metals and trace elements (aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), selenium (Se), uranium (U), zinc (Zn)) were measured in urine, hair and toenails. Biological levels were compared according to age, sex, smoking status, socioeconomic status, geographical area and drinking water source. While most urinary and toenail concentrations of metals and trace elements were not different between males and females, measured concentrations of several elements in hair were higher in females compared to males. Urinary concentrations of some metals (Al, Cu, Se and Zn) were higher in children compared to teenagers and adults. Hair and toenail concentrations of several elements (As, Cd, Pb, Mn, Se in hair and toenails plus Al, Fe in toenails) were also significantly higher in children compared to teenagers and/or adults. Smoking status had no influence on metal and trace element concentrations. Levels of Cd, Pb and Mn were also higher in samples from subgroups with lower economic status (Cd and Pb in the three matrices and Mn in hair and toenails). Very few correlations were identified between sources of drinking water and urine, hair, and toenail concentrations of metals and trace elements. However, a correlation was observed between hair and toenails levels of As, Cd and Pb. Overall, results highlight that a special attention should be given to metal and trace element exposure in this population (including Pb, As, Cd, Mn, and Se). It could be relevant to scale up this kind of investigation with a large human biomonitoring initiative in the Lebanese population in order to generalize results, and assess trends over time.

Understanding the excretion rates of methylmercury and inorganic mercury from human body via hair and fingernails

Effective biomarkers are necessary to better understand the human mercury (Hg) exposure levels. However, mismatched biomarker sampling method causes extra uncertainty in assessing the risk of Hg exposure. To compare the differences between hair and fingernail, and further understand the excretion rates of methylmercury (MeHg) and inorganic mercury (IHg) via hair and fingernails, the total mercury (THg), MeHg, and IHg concentrations in paired hair and fingernail samples were investigated through paired samples collected from two typical mining areas, Wanshan mercury mine area (WMMA) and Hezhang zinc smelting area (HZSA). The positive correlation in THg, MeHg, and IHg concentrations (p <0.01) between hair and fingernail samples indicated that those two biomarkers can be corrected in application of assessing human Hg exposure. Compared to fingernails, the hair was suggested to be a more sensitive biomarker as the concentration of THg, MeHg and IHg were 2 ∼ 4 times higher than those in fingernails. Furthermore, the amounts of THg, MeHg, and IHg excreted via hair were 70 ∼ 226 times higher than that excreted via fingernails, and the hair plays a more important role than fingernails in the excretion of Hg from human bodies. Present study therefore provides some new insights to better understand the fate of human assimilated Hg.

Validation of an Analytical Method for the Determination of Manganese and Lead in Human Hair and Nails Using Graphite Furnace Atomic Absorption Spectrometry

This article describes the validation of analytical methods for the determination of Manganese (Mn) and lead (Pb) by graphite furnace atomic absorption spectrometry (GFAAS) in human hair and nail samples. Method validation parameters such as linearity, repeatability, reproducibility, and precision were determined. In addition, the limit of detection (LOD), the limit of quantification (LOQ), and measurement uncertainty were calculated. The developed method was linear in the concentration ranges of 0.001–0.015 and 0.002–0.020 µg·L−1 of Mn and Pb, respectively. The determination coefficients obtained were greater than 0.995. The recoveries obtained after the addition of the standard concentration for the metals ranged from 84.80–107.98%, with a precision not exceeding 12.97% relative standard deviation. The calculated LOD and LOQ for Mn and Pb are within the ranges established by Commission Regulation (EU) No. 836/2011. The expanded uncertainty was estimated to be less than 9.93–6.59% for Mn and Pb. Matrix effects were also studied, finding a smooth effect in both matrices. The analysis of 30 samples of each type revealed the presence of Mn in 30 and Pb in 13 samples. Overall, the proposed validation method was considered optimal for the determination of Mn and Pb.

Adult Exposures to Toxic Trace Elements as Measured in Nails along the Interoceanic Highway in the Peruvian Amazon

Deforestation, artisanal and small-scale gold mining (ASGM), and the rapid development related to highway expansion cause opportunities for toxic trace element exposure in the Amazon region of Madre de Dios (MDD), Peru, one of the most biologically diverse places in the world. The objective of this study was to assess the exposure to arsenic, cadmium, lead, and mercury among adults in Madre de Dios. In total, 418 adult (18+ years) participants in the Investigacion de Migracion, Ambiente, y Salud (IMAS) (Migration, Environment, and Health Study) participated in this study. Consent, survey data, and biospecimens were collected between August and November 2014. Nail elements were measured by inductively coupled plasma sector field mass spectrometry. Differences by selected individual and household characteristics and local land uses were tested using one-way ANOVAs and linear mixed models. Adults in ASGM-affected areas had higher nail arsenic and nail cadmium than their non-ASGM counterparts. Higher household fish consumption was positively associated with nail mercury and nail lead. The results indicate that adult exposure to arsenic, cadmium, lead, and mercury is heterogeneous across Madre de Dios, and the exposures related to ASGM communities and fish consumption suggest that exposures from artisanal and small-scale mining are environmentally widespread. Further investigation is warranted to ascertain potential health impacts.

Nickel's Role in Pancreatic Ductal Adenocarcinoma: Potential Involvement of microRNAs

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancer types with a limited overall survival rate due to the asymptomatic progression of symptoms in metastatic stages of the malignancy and the lack of an early reliable diagnostic biomarker. MicroRNAs (miRs/miRNAs) are small (~18–24 nucleotides), endogenous, non-coding RNAs, which are closely linked to the development of numerous malignancies comprising PDAC. Recent studies have described the role of environmental pollutants such as nickel (Ni) in PDAC, but the mechanisms of Ni-mediated toxicity in cancer are still not completely understood. Specifically, Ni has been found to alter the expression and function of miRs in several malignancies, leading to changes in target gene expression. In this study, we found that levels of Ni were significantly higher in cancerous tissue, thus implicating Ni in pancreatic carcinogenesis. Hence, in vitro studies followed by using both normal and pancreatic tumor cell lines and increasing Ni concentration increased lethality. Comparing LC50 values, Ni-acetate groups demonstrated lower values needed than in NiCl₂ groups, suggesting greater Ni-acetate. Panc-10.05 cell line appeared the most sensitive to Ni compounds. Exposure to Ni-acetate resulted in an increased phospho-AKT, and decreased FOXO1 expression in Panc-10.05 cells, while NiCl₂ also increased PTEN expression in Panc-10.05 cells. Specifically, following NiCl₂ exposure to PDAC cells, the expression levels of miR-221 and miR-155 were significantly upregulated, while the expression levels of miR-126 were significantly decreased. Hence, our study has suggested pilot insights to indicate that the environmental pollutant Ni plays an important role in the progression of PDAC by promoting an association between miRs and Ni exposure during PDAC pathogenesis.

Associations between Biomarkers of Metal Exposure and Dry Eye Metrics in Shipyard Welders: A Cross-Sectional Study

Shipyard welders are often exposed to welding metal fumes. Ocular surfaces are continually exposed to environmental hazards. However, limited information on the associations between metal exposure and dry eye metrics in occupational settings is available. This study employed a cross-sectional design that involved the participation of 59 welders and 25 administrative staff in a shipyard in northern Taiwan from September 2020 to October 2020. The participants' individual information, laboratory data, exposure to particulate matter < 2.5 μm, urinary, and toenail metal concentrations were collected. Dry eye metrics were evaluated using standardized questionnaires and a noninvasive ocular surface analyzer. Urinary V and Cr and toenail V, Cr, Mn, Fe, Ni, Zn, As, and Cd and Pb were significantly higher in the exposed group than in the control group. After adjustment for confounding factors, dry eye metrics were associated with urinary Cd (β = 0.407; p = 0.007) and toenail Pb (β = 0.482; p = 0.002). The participants with higher urinary Cd exhibited higher odds ratios for elevated dry eye metrics. Our study revealed that exposure to welding procedures increases several metal biomarkers. In addition, urinary Cd, and toenail Pb might be related to dry eye disease in shipyard welders.

Biomarkers of disease in human nails: a comprehensive review

Diagnostic, monitoring, response, predictive, risk, and prognostic biomarkers of disease are all widely studied, for the most part in biological fluids or tissues, but there is steadily growing interest in alternative matrices such as nails. Here we comprehensively review studies dealing with molecular or elemental biomarkers of disease, as opposed to semiological, pharmacological, toxicological, or biomonitoring studies. Nails have a long history of use in medicine as indicators of pathological processes and have also been used extensively as a matrix for monitoring exposure to environmental pollution. Nail clippings are simple to collect noninvasively as well as to transport and store, and the matrix itself is relatively stable. Nails incorporate, and are influenced by, circulating molecules and elements over their several months of growth, and it is widely held that markers of biological processes will remain in the nail, even when their levels in blood have declined. Nails thus offer the possibility to not only look back into a subject's metabolic history but also to study biomarkers of processes that operate over a longer time scale such as the post-translational modification of proteins. Reports on ungual biomarkers of metabolic and endocrine diseases, cancer, and psychological and neurological disorders will be presented, and an overview of the sampling and analytical techniques provided.

Timing of Toenail Collection and Concentrations of Metals in Pancreatic Cancer. Evidence Against Disease Progression Bias

Trace elements such as cadmium, arsenic, zinc or selenium increase or decrease risk of a wide range of human diseases. Their levels in toenails may provide a measure of mid-term intake of trace elements for studies in humans. However, in biologically and clinically aggressive diseases as pancreatic cancer, the progression of the disease could modify such concentrations and produce reverse causation bias. The aim was to analyze the influence of specific time intervals between several clinical events and the collection of toenails upon concentrations of trace elements in patients with pancreatic cancer. Subjects were 118 incident cases of pancreatic adenocarcinoma prospectively recruited in eastern Spain. Toenails were collected at cancer diagnosis, and soon thereafter interviews were conducted. Information on cancer signs and symptoms was obtained from medical records and patient interviews. Levels of 12 trace elements were determined in toenail samples by inductively coupled plasma mass spectrometry. General linear models adjusting for potential confounders were applied to analyze relations between log concentrations of trace elements and the time intervals, including the interval from first symptom of cancer to toenail collection (iST). Toenail concentrations of the 12 trace elements were weakly or not influenced by the progression of the disease or the diagnostic procedures. Concentrations of aluminum were slightly higher in subjects with a longer iST (age, sex and stage adjusted geometric means: 11.44 vs. 7.75 µg/g for iST > 120 days vs. ≤ 40 days). There was a weak inverse relation of iST with concentrations of zinc and selenium (maximum differences of about 20 and 0.08 µg/g, respectively). Conclusions: concentrations of the trace elements were weakly or not influenced by the development of the disease before toenail collection. Only concentrations of aluminum increased slightly with increasing iST, whereas levels of zinc and selenium decreased weakly. Even in an aggressive disease as pancreatic cancer, toenail concentrations of trace elements may provide a valid measure of mid-term intake of trace elements, unaffected by clinical events and disease progression.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12403-021-00436-2.

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.