Determination of arsenic and mercury level in scalp hair from a selected population in Penang, Malaysia using XRF technique

Microchemistry of Single Hair Strands Below and Above the Scalp: Impacts of External Contamination on Cuticle and Cortex Layers

External contamination of hair is the most significant challenge to it becoming an accepted matrix for monitoring endogenous metal exposure and nutritional deficiency. Here we use laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to quantify elemental concentrations in hair strands below and above the scalp in the cuticle and cortex layers to determine the extent of external contamination in a reference population. Evidence of hair strand contamination occurred for barium, calcium, iron, magnesium, and strontium in both the outer cuticle and the inner cortex layers, with increasing concentrations from root to tip. Aluminum, boron, copper, lead, and manganese showed significant contamination in the cuticle layer only, suggesting some protection of the inner cortex. Phosphorus and potassium decreased outside the scalp suggesting loss by washing, while chromium, mercury, selenium, sodium, titanium, and zinc showed no evidence of loss or external contamination above the scalp. The results clearly show that for most elements, hair chemistry above the scalp is unreliable for use in interpretation of endogenous exposures or deficiencies, and that the below-scalp portion provides a more accurate monitoring tool. This is the first paper to provide a reference range of elemental hair chemistry that is not impacted by the external environment.

Chromogenic probe adhered porous polymer monolith as real-time solid-state sensor for the detection of ultra-trace toxic mercury ions

The escalating predicament of water pollution has spurred the development of new chromogenic materials for the efficient detection/screening of toxic mercuric (Hg2+) ions. In this study, we report a simple and efficient detection stratagem by infusing a chromogenic ion-receptor (BTDA), i.e., 4-(benzothiazol-2-yl)-N, N-dimethylaniline onto a structurally intertwined meso-/macro-pore polymer template for the target-specific sensing of ultra-trace Hg2+. The structural/surface features of the monolithic polymer template, prepared from glycidyl methacrylate (GMA) monomer crosslinked with ethylene glycol dimethacrylate (EGDMA), facilitate voluminous infusion and uniform decoration of ion-receptor molecules across the continuous porous poly(GMA-co-EGDMA) framework, resulting in a solid-state colorimetric sensory system. The bimodal polymer network's intriguing surface and structural morphology of the chromogenic sensor material are interpreted using scanning/transmission electron microscopy, X-ray diffraction, photoelectron spectroscopy, energy dispersive X-ray spectrometry, optical spectroscopy, surface area, porosity and thermal analysis. The proposed Hg2+ sensor offers a linear response range of 1-150 μg/L, with a detection and quantification limit of 0.29 and 0.97 μg/L, respectively. The poly(GMA-co-EGDMA)-BTDA sensor exhibits a quick ion-sensing response (40 s) with distinct color transitions from pastel yellow to olive as a function of increasing Hg2+ concentration. The matrix tolerance studies for the proposed sensory system reveal high selectivity for Hg2+, with a recovery of ≥99.2% in on-site environmental samples. The sensor material exhibits excellent data reproducibility and reliability up to seven cycles of reusability.

Assessing the role of the gut microbiome in methylmercury demethylation and elimination in humans and gnotobiotic mice

The risk of methylmercury (MeHg) toxicity following ingestion of contaminated foodstuffs (e.g., fish) is directly related to the kinetics of MeHg elimination among individuals. Yet, the factors driving the wide range of inter-individual variability in MeHg elimination within a population are poorly understood. Here, we investigated the relationship between MeHg elimination, gut microbiome demethylation activity, and gut microbiome composition using a coordinated human clinical trial and gnotobiotic mouse modeling approach together with metagenomic sequence analysis. We first observed MeHg elimination half-lives (t1/2) ranging from 28 to 90 days across 27 volunteers. Subsequently, we found that ingestion of a prebiotic induced changes in the gut microbiome and mixed effects (increased, decrease, and no effect) on elimination in these same individuals. Nonetheless, elimination rates were found to correlate with MeHg demethylation activity in cultured stool samples. In mice, attempts to remove the microbiome via generation of germ-free (GF) animals or through antibiotic (Abx) treatment both diminished MeHg demethylation to a similar extent. While both conditions substantially slowed elimination, Abx treatment resulted in significantly slower elimination than the GF condition, indicating an additional role for host-derived factors in supporting elimination. Human fecal microbiomes transplanted to GF mice restored elimination rates to that seen in control mice. Metagenomic sequence analysis of human fecal DNA did not identify genes encoding proteins typically involved in demethylation (e.g., merB, organomercury lyase). However, the abundance of several anaerobic taxa, notably Alistipes onderdonkii, were positively correlated with MeHg elimination. Surprisingly, mono-colonization of GF free mice with A. onderdonkii did not restore MeHg elimination to control levels. Collectively, our findings indicate the human gut microbiome uses a non-conventional pathway of demethylation to increase MeHg elimination that relies on yet to be resolved functions encoded by the gut microbes and the hostClinical Trial NCT04060212, prospectively registered 10/1/2019.

Quantitative analysis of human hairs and nails

Hair and nails are human biomarkers capable of providing a continuous assessment of the concentrations of elements inside the human body to indicate the nutritional status, metabolic changes, and the pathogenesis of various human diseases. Laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence (XRF) spectrometry are robust and multi-element analytical techniques able to analyze biological samples of various kinds for disease diagnosis. The primary objective of this review article is to focus on the major developments and advances in LIBS and XRF for the elemental analysis of hair and nails over the last 10-year period. The developments in the qualitative and quantitative analyses of human hair and nail samples are discussed in detail, with special emphasis on the key aspects of elemental imaging and distribution of essential and non-essential elements within the hair and nail tissue samples. Microchemical imaging applications by LIBS and XRF (including micro-XRF and scanning electron microscopy, SEM) are also presented for healthy as well as diseased tissue hair and nail samples in the context of disease diagnosis. In addition, main challenges, prospects, and complementarities of LIBS and XRF toward analyzing human hair and nails for disease diagnosis are also thoroughly discussed here.

Editor's Highlight: Variation in Methylmercury Metabolism and Elimination Status in Humans Following Fish Consumption

Evaluating the potential for methylmercury (MeHg) toxicity relies on accurately predicting the mercury (Hg) body burden that results from eating fish. Hg body burden is directly determined by the slow elimination kinetics of MeHg in the human body (kel = 0.014 days-1 or t1/2 =50 days). Existing studies on MeHg half-life in humans demonstrate a wide range values (t1/2 = 30 to >150 days) and has lead to uncertainty in the derivation of a regulatory standard for acceptable daily oral intake. The causes of variation in MeHg toxicokinetics in humans remain little explored. Here we characterize variation in human MeHg metabolism and elimination rate (kel) in 37 adult volunteers who consumed 3 fish meals. We determined MeHg elimination rates via longitudinal Hg analysis in single hairs using laser ablation inductively coupled plasma mass spectrometry. We also measured MeHg metabolism (biotransformation) via speciation of fecal Hg. We find an average kel = 0.0157 days-1 (t1/2 = 44 days) amongst a more than 2-fold variation in kel across the cohort (0.0248-0.0112 days-1; t1/2 = 28-62 days). Although MeHg biotransformation varied widely between individuals, it showed a positive association with elimination rates across the cohort. A more than 2-fold change in kel over a period of 2 years was seen in some individuals. In 2 individuals, who received antibiotic for unrelated health issues, elimination rate was seen to slow significantly. Associations of kel with age, body mass index, gender, and fish eating habits were not observed. We establish that a measure of methylmercury metabolism and eliminaiton status (MerMES) can reduce uncertainty in determining an individual's MeHg toxicokinetics subsequent to eating fish.

Mercury Hair Concentration among Primary School Children in Malaysia

The main concern regarding mercury exposure is the adverse health effect on the developing nervous system. The objective of this cross-sectional study was to determine hair mercury levels and their association with socio-demographic characteristics, complaints about mercury poisoning symptoms and the fish consumption pattern among children in Malaysia. A cross-sectional study was conducted among 215 school children aged 11 years old. Hair was collected from the children and the total mercury was analyzed using oxygen combustion–gold amalgamation atomic absorption spectrophotometry. Anthropometric data, a fish consumption questionnaire and mercury poisoning symptoms were collected during a personal interview. The mean hair mercury level among primary school children was 0.63 ± 0.59 µg/g with the geometric mean of 0.47 µg/g. A total of 14% of respondents had hair mercury levels above 1 µg/g. A multiple binary logistic regression analysis outlined that fish consumption of at least one meal per week increased the likelihood of having a high mercury level (odds ratio (OR) 3.7, 95% confidence interval (CI) 1.3–10.4). This study confirms the existence of a mercury burden among Malaysian children and the level is high compared to other regional studies. This study provides important baseline data regarding the mercury level among children in Malaysia.

Human health implications, risk assessment and remediation of As-contaminated water: A critical review

Arsenic (As) is a naturally occurring metalloid and Class-A human carcinogen. Exposure to As via direct intake of As-contaminated water or ingestion of As-contaminated edible crops is considered a life threatening problem around the globe. Arsenic-laced drinking water has affected the lives of over 200 million people in 105 countries worldwide. Limited data are available on various health risk assessment models/frameworks used to predict carcinogenic and non-carcinogenic health effects caused by As-contaminated water. Therefore, this discussion highlights the need for future research focusing on human health risk assessment of individual As species (both organic and inorganic) present in As-contaminated water. Various conventional and latest technologies for remediation of As-contaminated water are also reviewed along with a discussion of the fate of As-loaded waste and sludge.

Environmental exposures of trace elements assessed using keratinized matrices from patients with chronic kidney diseases of uncertain etiology (CKDu) in Sri Lanka

An alarming increase in chronic kidney disease with unknown etiology (CKDu) has recently been reported in several provinces in Sri Lanka and chronic exposures to toxic trace elements were blamed for the etiology of this disease. Keratinized matrices such as hair and nails were investigated to determine the possible link between CKDu and toxic element exposures. Elements Li, B, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Ba, Hg and Pb of hair and nails of patients and age that matched healthy controls were determined with Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The results showed that trace element contents in the hair of patients varies in the order of Zn>Fe>Al>Mn>Cu>Ba>Sr>Ni>Pb>Cr>B>Hg>Se>Mo>Co>As>Li>Cd while Fe>Al>Zn>Ni>Cu>Mn>Cr>Ba>Sr>B>Pb>Se>Mo>Co>Hg>Li>As>Cd in nail samples. The hair As levels of 0.007-0.165μgg^-1 were found in CKDu subjects. However, no significant difference was observed between cases and controls. The total Se content in hair of CKDu subjects ranged from 0.043 to 0.513μgg^-1 while it was varied from 0.031 to 1.15μgg^-1 in controls. Selenium in nail samples varied from 0.037μgg^-1 to 4.10μgg^-1 in CKDu subjects and from 0.042μgg^-1 to 2.19μgg^-1 in controls. This study implies that substantial proportions of Sri Lankan population are Se deficient irrespective of gender, age and occupational exposure. Although some cutaneous manifestations were observed in patient subjects, chemical analyses of hair and nails indicated that patients were not exposed to toxic levels of arsenic or the other studied toxic elements. Therefore the early suggested causative factors such as exposure to environmental As and Cd, can be ruled out.

Methods for Individualized Determination of Methylmercury Elimination Rate and De-Methylation Status in Humans Following Fish Consumption

Methylmercury (MeHg) exposure via fish in the diet remains a priority public health concern. Individual variation in response to a given MeHg exposure and the biotransformation of MeHg that follows complicate our understanding of this issue. MeHg elimination from the human body occurs slowly (elimination rate (kel) approximately 0.01 day(-1) or approximately 70 days half-life [t1/2]) and is a major determinant of the Hg body burden resulting from fish consumption. The underlying mechanisms that control MeHg elimination from the human body remain poorly understood. We describe here improved methods to obtain a MeHg elimination rate via longitudinal Hg analysis in hair using laser ablation-inductively coupled plasma-mass spectrometry. We measured MeHg elimination rates in eight individuals following the consumption of 3 fish meals in two 75-day trials separated by a 4-month washout period. In addition, since MeHg biotransformation to inorganic Hg (I-Hg) is associated with Hg excretion, we speciated Hg in feces samples to estimate individual MeHg de-methylation status. We observed a wide range of MeHg elimination rates between individuals and within individuals over time (kel = 0.0163-0.0054 day(-1); estimated t1/2 = 42.5-128.3 days). The ratio of MeHg and I-Hg in feces also varied widely among individuals. While the %I-Hg in feces was likely influenced by dental amalgams, findings with subjects who lacked amalgams suggest that faster MeHg elimination is associated with a higher %I-Hg in feces indicating more complete de-methylation. We anticipate these methods will contribute to future investigations of genetic and dietary factors that influence MeHg disposition in people.

Application of brown bear (Ursus arctos) records for retrospective assessment of mercury

Because mercury (Hg) is released into the atmosphere, wildlife living in habitats located far from point sources of metal may still be at risk. Mercury accumulation, previously considered a risk for aquatic ecosystems, is also found in many wildlife terrestrial species. The aim of the present study was to examine total Hg concentrations in the brown bear (Ursus arctos) by measurement of metal in hair from museum collections in Iran. Another objective of this investigation was to characterize the risk of Hg exposure in bears in several parts of Iran. Brown bear (Ursus arctos) hair samples (n = 35) were collected from 14 provinces in Iran for analysis of Hg contamination, performed using an advanced mercury analyzer (model Leco 254 AMA, USA) according to ASTM standard D-6722. Total Hg levels in Iranian bears from all areas ranged from 115.81 to 505.82 μg/kg, with a mean of 193.39 ng/g. Mercury concentrations in brown bear hair from different provinces in Iran were as follows in descending order: Khorasan Razavi > Esfahan > Khozestan > Yazd > Lorestan > Charmahalva Bakhtiari > Bushehr > Mazandaran > Markazi > Tehran > Ardebil > Gilan > East Azerbaijan. The highest content of Hg was found in the south (206.62 ± 31.95 ng/g), whereas the lowest levels were detected in the west (167.71 ± 32.97 ng/g). Overall total Hg content in bear hair was below harmful levels for this species. A decreasing trend was noted in the period 1986-2006, which may be mainly due to reduction of global Hg emissions. Data suggest that food habits and habitat are two important factors that influence Hg accumulation in bears.

Urinary arsenic speciation profile in ethnic group of the Atacama desert (Chile) exposed to variable arsenic levels in drinking water

Ethnic groups from the Atacama Desert (known as Atacameños) have been exposed to natural arsenic pollution for over 5000 years. This work presents an integral study that characterizes arsenic species in water used for human consumption. It also describes the metabolism and arsenic elimination through urine in a chronically exposed population in northern Chile. In this region, water contained total arsenic concentrations up to 1250 μg L(-1), which was almost exclusively As(V). It is also important that this water was ingested directly from natural water sources without any treatment. The ingested arsenic was extensively methylated. In urine 93% of the arsenic was found as methylated arsenic species, such as monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)]. The original ingested inorganic species [As(V)], represent less than 1% of the total urinary arsenic. Methylation activity among individuals can be assessed by measuring primary [inorganic As/methylated As] and secondary methylation [MMA/DMA] indexes. Both methylation indexes were 0.06, indicating a high biological converting capability of As(V) into MMA and then MMA into DMA, compared with the control population and other arsenic exposed populations previously reported.