Toenail arsenic concentrations, GSTT1 gene polymorphisms, and arsenic exposure from drinking water

Arsenic and fluoride co-exposure through drinking water and their impacts on intelligence and oxidative stress among rural school-aged children of Lahore and Kasur districts, Pakistan

Arsenic (As), and fluoride (F^-) are potent contaminants with established carcinogenic and non-carcinogenic impacts on the exposed populations globally. Despite elevated groundwater As and F^- levels being reported from various regions of Pakistan no biomonitoring study has been reported yet to address the co-exposure impact of As and F^- among school children. We aimed to investigate the effects of these two contaminants on dental fluorosis and intelligence quotient (IQ) along with the induction of oxidative stress in rural children under co-exposed conditions. A total of 148 children (5 to 16 years old) from the exposed and control group were recruited in the current study from endemic rural areas of Lahore and Kasur districts, Pakistan having elevated As and F^- levels in drinking water than permissible limits. We monitored malondialdehyde and its probable association with antioxidants activity (SOD, CAT, and GR) as a biomarker of oxidative stress. GSTM1/T1 polymorphisms were measured to find the impact of As on health parameters. Mean urinary concentrations of As (2.70 vs. 0.016 µg/L, P < 0.000) and F^- (3.27 vs. 0.24 mg/L, P < 0.000) as well as the frequency of dental fluorosis were found elevated among the exposed group. The cases of children with lower IQ were observed high in the exposed group. Additionally, lower concentrations of antioxidants (SOD, CAT, and GR) were found suggesting high susceptibility to F^- toxicity. The findings suggest that F^- accounted for high variations in health parameters of children under the co-exposure conditions with As.

GSTM1 and GSTT1 Null Genotype Polymorphisms and Susceptibility to Arsenic Poisoning: a Meta-analysis

The value of the glutathione S-transferase (GST) null genotype in patients with arsenic poisoning has been recognized, but the conclusions of previous studies remain inconsistent. The objective of this study was to evaluate the relationship between GST mu 1 (GSTM1) and GST theta 1 (GSTT1) null genotype polymorphisms and susceptibility to arsenic poisoning. PubMed, Medline, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), WanFang, and WeiPu databases were systematically searched for publications up to March 31, 2020. The quality of the studies was assessed using the Newcastle-Ottawa Quality Assessment Scale. The pooled odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated to estimate the relationship between GSTM1 and GSTT1 null genotype polymorphisms and arsenic poisoning. The meta-analysis was conducted using STATA 14.0 software. Nine articles with 3324 subjects were included in the meta-analysis. A significantly negative correlation was observed between the GSTM1 null genotype and susceptibility to arsenic poisoning (OR = 0.731; 95% CI: 0.536-0.999; P = 0.049; I² = 70.5%). There was no significant correlation between the GSTT1 null genotype (OR = 1.009; 95% CI: 0.856-1.189; P = 0.915, I² = 36.8%) and GSTM1-GSTT1 double null genotype (OR = 1.105; 95% CI: 0.670-1.822; P = 0.695; I² = 64.7%) and the risk of arsenic poisoning. Egger's and Begg's tests indicated no publishing bias. Compared with controls, individuals with the GSTM1 null genotype were less susceptible to arsenic poisoning. The GSTT1 single null genotype and GSTM1-GSTT1 dual-null genotype were not associated with the risk of arsenic poisoning. The GSTM1 single null genotype may have potential as a genotoxic biomarker to identify individuals who are not prone to arsenic poisoning, and as a reference for guiding the prevention of arsenic poisoning.

WITHDRAWN: Co-exposure effects of arsenic and fluoride on intelligence and oxidative stress in school-aged children: A cohort study

This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause.

Toenails as a biomarker of exposure to arsenic: A review

This systematic review summarizes the current evidence related to the reliability of toenail total arsenic concentrations (thereafter "arsenic") as a biomarker of long-term exposure. Specifically, we reviewed literature on consistency of repeated measures over time, association with other biomarkers and metal concentrations, factors influencing concentrations, and associations with health effects. We identified 129 papers containing quantitative original data on arsenic in toenail samples covering populations from 29 different countries. We observed geographic differences in toenail arsenic concentrations, with highest median or mean concentrations in Asian countries. Arsenic-contaminated drinking water, occupational exposure or living in specific industrial areas were associated with an increased toenail arsenic content. The effects of other potential determinants and sources of arsenic exposure including diet, gender and age on the concentrations in toenails need further investigations. Toenail arsenic was correlated with the concentrations in hair and fingernails, and with urine arsenic mainly among highly exposed populations with a toenail mean or median ≥1 μg/g. Overall, there is a growing body of evidence suggesting that arsenic content from a single toenail sample may reflect long-term internal dose-exposure. Toenail arsenic can serve as a reliable measure of toxic inorganic arsenic exposure in chronic disease research, particularly promising for cancer and cardiovascular conditions.

Cord blood DNA methylation of DNMT3A mediates the association between in utero arsenic exposure and birth outcomes: Results from a prospective birth cohort in Bangladesh

BACKGROUND

Fetal epigenetic programming plays a critical role in development. DNA methyltransferase 3 alpha (DNMT3A), which is involved in de novo DNA methylation (DNAm), is a prime candidate gene as a mediator between prenatal exposures and birth outcomes. We evaluated the relationships between in utero arsenic (As) exposure, birth outcomes, and DNMT3A DNAm.

METHODS

In a prospective Bangladeshi birth cohort, cord blood DNAm of three DNMT3A CpGs was measured using bisulfite pyrosequencing. Maternal toenail As concentrations at birth were measured to estimate in utero exposure. Among vaginal births (N = 413), structural equation models (SEMs) were used to evaluate relationships between DNMT3A methylation, log₂ (toenail As), birth weight, and gestational age.

RESULTS

In an adjusted SEM including birth weight and gestational age, maternal toenail As levels were associated with DNMT3A DNAm (B = 0.40; 95% CI: 0.15, 0.66) and gestational age (B = -0.19 weeks; 95% CI: 0.36, -0.03). DNMT3A DNAm was associated with gestational age (B = -0.10 weeks; 95% CI: 0.16, -0.04) and birth weight (B = -11.0 g; 95% CI: 21.5, 0.4). There was an indirect effect of As on gestational age mediated through DNMT3A DNAm (B = -0.04; 95% CI: 0.08, -0.01), and there were indirect effects of maternal toenail As levels on birth weight through pathways including gestational age (B = -14.4 g; 95% CI: 29.2, -1.9), DNMT3A DNAm and gestational age (B = -3.1 g; 95% CI: 6.6, -0.8), and maternal weight gain and gestational age (B = -5.1 g; 95% CI: 9.6, -1.5). The total effect of a doubling in maternal toenail As concentration is a decrease in gestational age of 2.1 days (95% CI: 0.9, 3.3) and a decrease in birth weight of 29 g (95% CI: 14, 46).

CONCLUSIONS

DNMT3A plays a critical role in fetal epigenetic programming. In utero arsenic exposure was associated with greater methylation of CpGs in DNMT3A which partially mediated associations between prenatal As exposure and birth outcomes. Additional studies are needed to verify this finding.

Gene-environment interaction and maternal arsenic methylation efficiency during pregnancy

BACKGROUND

Single nucleotide polymorphisms (SNPs) may influence arsenic methylation efficiency, affecting arsenic metabolism. Whether gene-environment interactions affect arsenic metabolism during pregnancy remains unclear, which may have implications for pregnancy outcomes.

OBJECTIVE

We aimed to investigate main effects as well as potential SNP-arsenic interactions on arsenic methylation efficiency in pregnant women.

METHOD

We recruited 1613 pregnant women in Bangladesh, and collected two urine samples from each participant, one at 4-16 weeks, and the second at 21-37 weeks of pregnancy. We determined the proportions of each arsenic metabolite [inorganic As (iAs)%, monomethylarsonic acid (MMA)%, and dimethylarsinic acid (DMA)%] from the total urinary arsenic level of each sample. A panel of 63 candidate SNPs was selected for genotyping based on their reported associations with arsenic metabolism (including in As3MT, N6AMT1, and GSTO2 genes). We used linear regression models to assess the association between each SNP and DMA% with an additive allelic assumption, as well as SNP-arsenic interaction on DMA%. These analyses were performed separately for two urine collection time-points to capture differences in susceptibility to arsenic toxicity.

RESULT

Intron variants for As3MT were associated with DMA%. rs9527 (β = -2.98%, PFDR = 0.008) and rs1046778 (β = 1.64%, PFDR = 0.008) were associated with this measure in the early gestational period; rs3740393 (β = 2.54%, PFDR = 0.002) and rs1046778 (β = 1.97%, PFDR = 0.003) in the mid-to-late gestational period. Further, As3MT, GSTO2, and N6AMT1 polymorphisms showed different effect sizes on DMA% conditional on arsenic exposure levels. However, SNP-arsenic interactions were not statistically significant after adjusting for false discovery rate (FDR). rs1048546 in N6AMT1 had the highest significance level in the SNP-arsenic interaction test during mid-to-late gestation (β = -1.8% vs. 1.4%, PGxE_FDR = 0.075). Finally, As3MT and As3MT/CNNM2 haplotypes were associated with DMA% at both time points.

CONCLUSION

We found that not all genetic associations reported in arsenic methylation efficiency replicate in pregnant women. Arsenic exposure level has a limited effect in modifying the association between genetic variation and arsenic methylation efficiency.

DNA methylation in cord blood as mediator of the association between prenatal arsenic exposure and gestational age

Prenatal arsenic exposure is associated with adverse birth outcomes and disease risk later in life, which could be mediated through epigenetic dysregulation. We evaluated the association between arsenic and gestational age (GA) that was mediated through DNA methylation (DNAm) using data from a Bangladeshi birth cohort. Arsenic exposure was measured in maternal drinking water at ≤16 weeks GA and maternal toenails collected ≤1 month postpartum. Cord blood DNAm was measured using Infinium HumanMethylation450 arrays (n = 44, discovery phase). Top loci identified in the discovery phase were then pyrosequenced in a second group (n = 569, validation phase). Structural equation models (SEM) evaluated the direct and indirect effects of arsenic and DNAm on GA. In the discovery phase, arsenic was associated with differential DNAm of 139 loci that were associated with GA (P < 1.10X10-6; |β regression|>0.10). Each doubling in water arsenic concentration decreased GA by 2 days, which was fully mediated through the main principal component of the top-ten CpGs (P < 0.001). In the validation phase, there were direct and indirect effects of miR214-3 and MCC DNAm on GA. In an adjusted SEM model, mediation of the association between arsenic and GA by miR124-3 was borderline significant (P = 0.061). This study therefore identified DNAm at specific loci in cord blood that mediated the effect of arsenic exposure on GA. Specifically, prenatal arsenic exposure was associated with lower methylation of miR124-3 that mediated the exposure-response of arsenic on GA. Future research should evaluate if these epigenetic changes are persistent and associated with disease risk.

Arsenic exposure and intestinal microbiota in children from Sirajdikhan, Bangladesh

BACKGROUND

Arsenic has antimicrobial properties at high doses yet few studies have examined its effect on gut microbiota. This warrants investigation since arsenic exposure increases the risk of many diseases in which gut microbiota have been shown to play a role. We examined the association between arsenic exposure from drinking water and the composition of intestinal microbiota in children exposed to low and high arsenic levels during prenatal development and early life.

RESULTS

16S rRNA gene sequencing revealed that children with high arsenic exposure had a higher abundance of Proteobacteria in their stool compared to matched controls with low arsenic exposure. Furthermore, whole metagenome shotgun sequencing identified 332 bacterial SEED functions that were enriched in the high exposure group. A separate model showed that these genes, which included genes involved in virulence and multidrug resistance, were positively correlated with arsenic concentration within the group of children in the high arsenic group. We performed reference free genome assembly, and identified strains of E.coli as contributors to the arsenic enriched SEED functions. Further genome annotation of the E.coli genome revealed two strains containing two different arsenic resistance operons that are not present in the gut microbiome of a recently described European human cohort (Metagenomics of the Human Intestinal Tract, MetaHIT). We then performed quantification by qPCR of two arsenic resistant genes (ArsB, ArsC). We observed that the expression of these two operons was higher among the children with high arsenic exposure compared to matched controls.

CONCLUSIONS

This preliminary study indicates that arsenic exposure early in life was associated with altered gut microbiota in Bangladeshi children. The enrichment of E.coli arsenic resistance genes in the high exposure group provides an insight into the possible mechanisms of how this toxic compound could affect gut microbiota.

Validation of a Dish-Based Semiquantitative Food Questionnaire in Rural Bangladesh

A locally validated tool was needed to evaluate long-term dietary intake in rural Bangladesh. We assessed the validity of a 42-item dish-based semi-quantitative food frequency questionnaire (FFQ) using two 3-day food diaries (FDs). We selected a random subset of 47 families (190 participants) from a longitudinal arsenic biomonitoring study in Bangladesh to administer the FFQ. Two 3-day FDs were completed by the female head of the households and we used an adult male equivalent method to estimate the FD for the other participants. Food and nutrient intakes measured by FFQ and FD were compared using Pearson's and Spearman's correlation, paired t-test, percent difference, cross-classification, weighted Kappa, and Bland-Altman analysis. Results showed good validity for total energy intake (paired t-test, p < 0.05; percent difference <10%), with no presence of proportional bias (Bland-Altman correlation, p > 0.05). After energy-adjustment and de-attenuation for within-person variation, macronutrient intakes had excellent correlations ranging from 0.55 to 0.70. Validity for micronutrients was mixed. High intraclass correlation coefficients (ICCs) were found for most nutrients between the two seasons, except vitamin A. This dish-based FFQ provided adequate validity to assess and rank long-term dietary intake in rural Bangladesh for most food groups and nutrients, and should be useful for studying dietary-disease relationships.

Hypomethylation of inflammatory genes (COX2, EGR1, and SOCS3) and increased urinary 8-nitroguanine in arsenic-exposed newborns and children

Early-life exposure to arsenic increases risk of developing a variety of non-malignant and malignant diseases. Arsenic-induced carcinogenesis may be mediated through epigenetic mechanisms and pathways leading to inflammation. Our previous study reported that prenatal arsenic exposure leads to increased mRNA expression of several genes related to inflammation, including COX2, EGR1, and SOCS3. This study aimed to investigate the effects of arsenic exposure on promoter DNA methylation and mRNA expression of these inflammatory genes (COX2, EGR1, and SOCS3), as well as the generation of 8-nitroguanine, which is a mutagenic DNA lesion involved in inflammation-related carcinogenesis. Prenatally arsenic-exposed newborns had promoter hypomethylation of COX2, EGR1, and SOCS3 in cord blood lymphocytes (p<0.01). A follow-up study in these prenatally arsenic-exposed children showed a significant hypomethylation of these genes in salivary DNA (p<0.01). In vitro experiments confirmed that arsenite treatment at short-term high doses (10-100μM) and long-term low doses (0.5-1μM) in human lymphoblasts (RPMI 1788) caused promoter hypomethylation of these genes, which was in concordance with an increase in their mRNA expression. Additionally, the level of urinary 8-nitroguanine was significantly higher (p<0.01) in exposed newborns and children, by 1.4- and 1.8-fold, respectively. Arsenic accumulation in toenails was negatively correlated with hypomethylation of these genes and positively correlated with levels of 8-nitroguanine. These results indicated that early-life exposure to arsenic causes hypomethylation of COX2, EGR1, and SOCS3, increases mRNA expression of these genes, and increases 8-nitroguanine formation. These effects may be linked to mechanisms of arsenic-induced inflammation and cancer development later in life.

In utero arsenic exposure and epigenome-wide associations in placenta, umbilical artery, and human umbilical vein endothelial cells

Exposure to arsenic early in life has been associated with increased risk of several chronic diseases and is believed to alter epigenetic programming in utero. In the present study, we evaluate the epigenome-wide association of arsenic exposure in utero and DNA methylation in placenta (n = 37), umbilical artery (n = 45) and human umbilical vein endothelial cells (HUVEC) (n = 52) in a birth cohort using the Infinium HumanMethylation450 BeadChip array. Unadjusted and cell mixture adjusted associations for each tissue were examined along with enrichment analyses relative to CpG island location and omnibus permutation tests of association among biological pathways. One CpG in artery (cg26587014) and 4 CpGs in placenta (cg12825509; cg20554753; cg23439277; cg21055948) reached a Bonferroni adjusted level of significance. Several CpGs were differentially methylated in artery and placenta when controlling the false discovery rate (q-value<0.05), but none in HUVEC. Enrichment of hypomethylated CpG islands was observed for artery while hypermethylation of open sea regions were present in placenta relative to prenatal arsenic exposure. The melanogenesis pathway was differentially methylated in artery (Max F P < 0.001), placenta (Max F P < 0.001), and HUVEC (Max F P = 0.02). Similarly, the insulin-signaling pathway was differentially methylated in artery (Max F P = 0.02), placenta (Max F P = 0.02), and HUVEC (Max F P = 0.02). Our results show that prenatal arsenic exposure can alter DNA methylation in artery and placenta but not in HUVEC. Further studies are needed to determine if these alterations in DNA methylation mediate the effect of prenatal arsenic exposure and health outcomes later in life.

Biological and behavioral factors modify urinary arsenic metabolic profiles in a U.S. population

BACKGROUND

Because some adverse health effects associated with chronic arsenic exposure may be mediated by methylated arsenicals, interindividual variation in capacity to convert inorganic arsenic into mono- and di-methylated metabolites may be an important determinant of risk associated with exposure to this metalloid. Hence, identifying biological and behavioral factors that modify an individual's capacity to methylate inorganic arsenic could provide insights into critical dose-response relations underlying adverse health effects.

METHODS

A total of 904 older adults (≥45 years old) in Churchill County, Nevada, who chronically used home tap water supplies containing up to 1850 μg of arsenic per liter provided urine and toenail samples for determination of total and speciated arsenic levels. Effects of biological factors (gender, age, body mass index) and behavioral factors (smoking, recent fish or shellfish consumption) on patterns of arsenicals in urine were evaluated with bivariate analyses and multivariate regression models.

RESULTS

Relative contributions of inorganic, mono-, and di-methylated arsenic to total speciated arsenic in urine were unchanged over the range of concentrations of arsenic in home tap water supplies used by study participants. Gender predicted both absolute and relative amounts of arsenicals in urine. Age predicted levels of inorganic arsenic in urine and body mass index predicted relative levels of mono- and di-methylated arsenic in urine. Smoking predicted both absolute and relative levels of arsenicals in urine. Multivariate regression models were developed for both absolute and relative levels of arsenicals in urine. Concentration of arsenic in home tap water and estimated water consumption were strongly predictive of levels of arsenicals in urine as were smoking, body mass index, and gender. Relative contributions of arsenicals to urinary arsenic were not consistently predicted by concentrations of arsenic in drinking water supplies but were more consistently predicted by gender, body mass index, age, and smoking.

CONCLUSIONS

These findings suggest that analyses of dose-response relations in arsenic-exposed populations should account for biological and behavioral factors that modify levels of inorganic and methylated arsenicals in urine. Evidence of significant effects of these factors on arsenic metabolism may also support mode of action studies in appropriate experimental models.

Prolonged exposure to arsenic in UK private water supplies: toenail, hair and drinking water concentrations

Chronic exposure to arsenic (As) in drinking water is an established cause of cancer and other adverse health effects. Arsenic concentrations >10 μg L(-1) were previously measured in 5% of private water supplies (PWS) in Cornwall, UK. The present study investigated prolongued exposure to As by measuring biomarkers in hair and toenail samples from 212 volunteers and repeated measurements of As in drinking water from 127 households served by PWS. Strong positive Pearson correlations (rp = 0.95) indicated stability of water As concentrations over the time period investigated (up to 31 months). Drinking water As concentrations were positively correlated with toenail (rp = 0.53) and hair (rp = 0.38) As concentrations - indicative of prolonged exposure. Analysis of washing procedure solutions provided strong evidence of the effective removal of exogenous As from toenail samples. Significantly higher As concentrations were measured in hair samples from males and smokers and As concentrations in toenails were negatively associated with age. A positive association between seafood consumption and toenail As and a negative association between home-grown vegetable consumption and hair As was observed for volunteers exposed to <1 As μg L(-1) in drinking water. These findings have important implications regarding the interpretation of toenail and hair biomarkers. Substantial variation in biomarker As concentrations remained unaccounted for, with soil and dust exposure as possible explanations.

A cross sectional study of anemia and iron deficiency as risk factors for arsenic-induced skin lesions in Bangladeshi women

BACKGROUND

In the Ganges Delta, chronic arsenic poisoning is a health concern affecting millions of people who rely on groundwater as their potable water source. The prevalence of anemia is also high in this region, particularly among women. Moreover, arsenic is known to affect heme synthesis and erythrocytes and the risk of arsenic-induced skin lesions appears to differ by sex.

METHODS

We conducted a case-control study in 147 arsenic-exposed Bangladeshi women to assess the association between anemia and arsenic-induced skin lesions.

RESULTS

We observed that the odds of arsenic-related skin lesions were approximately three times higher among women who were anemic (hemoglobin < 120 g/L) compared to women with normal hemoglobin levels [Odds Ratio (OR) = 3.32, 95% Confidence Intervals (CI): 1.29, 8.52] after adjusting for arsenic levels in drinking water and other covariates. Furthermore, 75% of the women with anemia had adequate iron stores (serum ferritin ≥ 12 μg/L), suggesting that the majority of anemia detected in this population was unrelated to iron depletion.

CONCLUSIONS

Considering the magnitude of arsenic exposure and prevalence of anemia in Bangladeshi women, additional research is warranted that identifies the causes of anemia so that effective interventions can be implemented while arsenic remediation efforts continue.

Infant toenails as a biomarker of in utero arsenic exposure

A growing body of evidence suggests that in utero and early-life exposure to arsenic may have detrimental effects on children, even at the low to moderate levels common in the United States and elsewhere. In a sample of 170 mother-infant pairs from New Hampshire, we determined infant exposure to in utero arsenic by evaluating infant toenails as a biomarker using inductively coupled plasma mass spectrometry. Infant toenail arsenic concentration correlated with maternal postpartum toenail concentrations (Spearman's correlation coefficient 0.34). In adjusted linear models, a doubling of maternal toenail arsenic concentration was associated with a 53.8% increase in infant toenail arsenic concentration as compared with 20.4% for a doubling of maternal urine arsenic concentration. In a structural equation model, a doubling of the latent variable integrating maternal toenail and urine arsenic concentrations was associated with a 67.5% increase in infant toenail arsenic concentration. A similar correlation between infant and maternal postpartum toenail concentrations was observed in a validation cohort of 130 mother-infant pairs from Rhode Island. In utero exposure to arsenic occurs through maternal water and dietary sources, and infant toenails appear to be a reliable biomarker for estimating arsenic exposure during the critical window of gestation.

Biomarkers of arsenic exposure and effects in a Canadian rural population exposed through groundwater consumption

Drinking water intake of arsenic (As) from private wells may represent a significant exposure pathway and induce oxidative DNA damage. We measured total As concentrations in hair and nails, and concentrations of the different species of As and its metabolites as well as 8-OHdG in urine of 110 non-smoking adults living in a rural region of the Province of Quebec, Canada. Significant differences in exposure biomarker levels were observed between individuals consuming drinking water with As levels of≤1.0,>1.0 -≤10 and>10 μg/l. Multivariate linear regression analysis also showed a significant relationship between estimated daily drinking water intakes of As and biomarker levels. Conversely, 8-OHdG levels were not significantly related to daily drinking water intakes of As or to hair, nail or urinary exposure biomarker levels, according to multivariate linear regression analysis. Even at the relatively low levels of As found in well water of our participants, water consumption significantly increases their body load of As, as confirmed by multiple matrix measurements, which reflected exposure over different time frames. However, this increased internal As dose was not associated with higher oxidative damage to DNA as reflected by urinary 8-OHdG levels.

Effect of prenatal arsenic exposure on DNA methylation and leukocyte subpopulations in cord blood

Prenatal arsenic exposure is associated with increased risk of disease in adulthood. This has led to considerable interest in arsenic's ability to disrupt fetal programming. Many studies report that arsenic exposure alters DNA methylation in whole blood but these studies did not adjust for cell mixture. In this study, we examined the relationship between arsenic in maternal drinking water collected ≤ 16 weeks gestational age and DNA methylation in cord blood (n = 44) adjusting for leukocyte-tagged differentially methylated regions. DNA methylation was quantified using the Infinium HumanMethylation 450 BeadChip array. Recursively partitioned mixture modeling examined the relationship between arsenic and methylation at 473,844 CpG sites. Median arsenic concentration in water was 12 µg/L (range<1- 510 µg/L). Log 10 arsenic was associated with altered DNA methylation across the epigenome (P = 0.002); however, adjusting for leukocyte distributions attenuated this association (P = 0.013). We also observed that arsenic had a strong effect on the distribution of leukocytes in cord blood. In adjusted models, every log 10 increase in maternal drinking water arsenic exposure was estimated to increase CD8+ T cells by 7.4% (P = 0.0004) and decrease in CD4+ T cells by 9.2% (P = 0.0002). These results show that prenatal exposure to arsenic had an exposure-dependent effect on specific T cell subpopulations in cord blood and altered DNA methylation in cord blood. Future research is needed to determine if these small changes in DNA methylation alter gene expression or are associated with adverse health effects.

Dietary arsenic consumption and urine arsenic in an endemic population: response to improvement of drinking water quality in a 2-year consecutive study

We assessed the association between arsenic intake through water and diet, and arsenic levels in first morning-void urine under variable conditions of water contamination. This was done in a 2-year consecutive study in an endemic population. Exposure of arsenic through water and diet was assessed for participants using arsenic-contaminated water (≥50 μg L(-1)) in a first year (group I) and for participants using water lower in arsenic (<50 μg L(-1)) in the next year (group II). Participants with and without arsenical skin lesions were considered in the statistical analysis. Median dose of arsenic intake through drinking water in groups I and II males was 7.44 and 0.85 μg kg body wt.(-1) day(-1) (p <0.0001). In females, it was 5.3 and 0.63 μg kg body wt.(-1) day(-1) (p <0.0001) for groups I and II, respectively. Arsenic dose through diet was 3.3 and 2.6 μg kg body wt.(-1) day(-1) (p = 0.088) in males and 2.6 and 1.9 μg kg body wt.(-1) day(-1) (p = 0.0081) in females. Median arsenic levels in urine of groups I and II males were 124 and 61 μg L(-1) (p = 0.052) and in females 130 and 52 μg L(-1) (p = 0.0001), respectively. When arsenic levels in the water were reduced to below 50 μg L(-1) (Indian permissible limit), total arsenic intake and arsenic intake through the water significantly decreased, but arsenic uptake through the diet was found to be not significantly affected. Moreover, it was found that drinking water mainly contributed to variations in urine arsenic concentrations. However, differences between male and female participants also indicate that not only arsenic uptake, but also many physiological factors affect arsenic behavior in the body and its excretion. As total median arsenic exposure still often exceeded 3.0 μg kg body wt.(-1) day(-1) (the permissible lower limit established by the Joint Expert Committee on Food Additives) after installation of the drinking water filters, it can be concluded that supplying the filtered water only may not be sufficient to minimize arsenic availability for an already endemic population.

Toenail metal concentration as a biomarker of occupational welding fume exposure

In populations exposed to heavy metals, there are few biomarkers that capture intermediate exposure windows. We sought to determine the correlation between toenail metal concentrations and prior 12-month work activity in welders with variable, metal-rich, welding fume exposures. Forty-eight participants, recruited through a local union, provided 69 sets of toenail clippings. Union-supplied and worker-verified personal work histories were used to quantify hours welded and respirator use. Toenail samples were digested and analyzed for lead (Pb), manganese (Mn), cadmium (Cd), nickel (Ni), and arsenic (As) using ICP-MS. Spearman correlation coefficients were used to examine the correlation between toenail metal concentrations. Using mixed models to account for multiple participation times, we divided hours welded into three-month intervals and examined how weld hours correlated with log-transformed toenail Pb, Mn, Cd, Ni, and As concentrations. Highest concentrations were found for Ni, followed by Mn, Pb and As, and Cd. All the metals were significantly correlated with one another (rho range = 0.28-0.51), with the exception of Ni and As (rho = 0.20, p = 0.17). Using mixed models adjusted for age, respirator use, smoking status, and BMI, we found that Mn was associated with weld hours 7-9 months prior to clipping (p = 0.003), Pb was associated with weld hours 10-12 months prior to clipping (p = 0.03) and over the entire year (p = 0.04). Cd was associated with weld hours 10-12 months prior to clipping (p = 0.05), and also with the previous year's total hours welded (p = 0.02). The association between Ni and weld hours 7-9 months prior to clipping approached significance (p = 0.06). Toenail metal concentrations were not associated with the long-term exposure metric, years as a welder. Results suggest Mn, Pb, and Cd may have particular windows of relevant exposure that reflect work activity. In a population with variable exposure, toenails may serve as useful biomarkers for occupational metal fume exposures to Mn, Pb, and Cd during distinct periods over the year prior to sample collection.

The Influence of Arsenic, Lead, and Mercury on the Development of Cardiovascular Diseases

As a group, cardiovascular disease (CVD) is the leading cause of death worldwide. It killed twice as many people as infectious and parasitic disease and three times as many people as all forms of cancer. There are other crucial risk factors next to the major risk factors identified by the Framingham Heart Study. In the last few years, detailed studies showed the correlation between environmental pollution and the development of CVD. The question, which environmental toxin is particularly harmful, is answered by CERCLA Priority List of Hazardous Substances with the following toxins: arsenic, lead, and mercury. The effect of these potential toxic metals on the development of cardiovascular diseases includes pathomechanisms as the accumulation of free radicals, damage of endothelial nitric oxide synthase, lipid peroxidation, and endocrine influences. This leads to the damage of vascular endothelium, atherosclerosis, high blood pressure, and an increased mortality from cardiovascular diseases. The cardiovascular effects of arsenic, lead, and mercury exposure and its impact on cardiovascular mortality need to be included in the diagnosis and the treatment of CVD.

What is the best biomarker to assess arsenic exposure via drinking water?

Arsenic (As) is a ubiquitous element. The current WHO guideline for As in drinking water is 10 μg/L. Furthermore, about 130 million people have only access to drinking water containing more than 10 g As/L. Although numerous studies have shown the related adverse effects of As, sensitive appropriate biomarkers are still required for studies of environmental epidemiology. A review of the literature has shown that various biomarkers are used for such research. Their limits and advantages are highlighted in this paper: (i) the detection of As or its derivatives in the blood is an indication of the dose ingested but it is not evidence of chronic intoxication. (ii) The detection of As in urine is an indispensible procedure because it is a good marker for internal dose. It has been demonstrated to correlate well for a number of chronic effects related to As levels in drinking water. However confounding factors must be taken into account to avoid misinterpretation and this may require As speciation. (iii) As in the hair and nails reflects the level of long term exposure but it is difficult to relate the level with the dose ingested. (iv) Some studies showed a correlation between urinary As and urinary and blood porphyrins. However, it is difficult to use only porphyrins as a biomarker in a population survey carried out without doing further studies. (v) Genotoxic effects are based on the characterization of these potential effects. Most studies have detected increases in DNA damage, sister chromatid exchange, micronuclei or chromosomal aberrations in populations exposed to As in drinking water. Micronuclei assay is the technique of choice to follow these populations, because it is sensitive and easy to use. To conclude, whatever epidemiological studies are, the urinary and toenail biomarkers are useful to provide indications of internal dose. Moreover, micronuclei assay can be complementary use as biomarker of early effects.

A case-control study of polymorphisms in xenobiotic and arsenic metabolism genes and arsenic-related bladder cancer in New Hampshire

Arsenic is associated with bladder cancer risk even at low exposure levels. Genetic variation in enzymes involved in xenobiotic and arsenic metabolism may modulate individual susceptibility to arsenic-related bladder cancer. Through a population-based case-control study in NH (832 cases and 1191 controls), we investigated gene-environment interactions between arsenic metabolic gene polymorphisms and arsenic exposure in relation to bladder cancer risk. Toenail arsenic concentrations were used to classify subjects into low and high exposure groups. Single nucleotide polymorphisms (SNPs) in GSTP1, GSTO2, GSTZ1, AQP3, AS3MT and the deletion status of GSTM1 and GSTT1 were determined. We found evidence of genotype-arsenic interactions in the high exposure group; GSTP1 Ile105Val homozygous individuals had an odds ratio (OR) of 5.4 [95% confidence interval (CI): 1.5-20.2; P for interaction=0.03] and AQP3 Phe130Phe carriers had an OR=2.2 (95% CI: 0.8-6.1; P for interaction=0.10). Bladder cancer risk overall was associated with GSTO2 Asn142Asp (homozygous; OR=1.4; 95% CI: 1.0-1.9; P for trend=0.06) and GSTZ1 Glu32Lys (homozygous; OR=1.3; 95% CI: 0.9-1.8; P for trend=0.06). Our findings suggest that susceptibility to bladder cancer may relate to variation in genes involved in arsenic metabolism and oxidative stress response and potential gene-environment interactions requiring confirmation in other populations.

Exposure, metabolism, and health effects of arsenic in residents from arsenic-contaminated groundwater areas of Vietnam and Cambodia: a review

In this review, we summarize the current knowledge on exposure, metabolism, and health effects of arsenic (As) in residents from As-contaminated groundwater areas of Vietnam and Cambodia based on our findings from 2000 and other studies. The health effects of As in humans include severe gastrointestinal disorders, hepatic and renal failure, cardiovascular disturbances, skin pigmentation, hyperkeratosis, and cancers in the lung, bladder, liver, kidney, and skin. Arsenic contamination in groundwater is widely present at Vietnam and Cambodia and the highest As levels are frequently found in groundwater from Cambodia. Sand filter system can reduce As concentration in raw groundwater. The results of hair and urine analyses indicate that residents from these As-contaminated areas are exposed to As. In general, sex, age, body mass index, and As exposure level are significantly associated with As metabolism. Genetic polymorphisms in arsenic (+III) methyltransferase and glutathione-S-transferase isoforms may be influenced As metabolism and accumulation in a Vietnamese population. It is suggested oxidative DNA damage is caused by exposure to As in groundwater from residents in Cambodia. An epidemiologic study on an association of As exposure with human health effects is required in these areas.

Genetic variations associated with interindividual sensitivity in the response to arsenic exposure

People are exposed to arsenic compounds environmentally, occupationally or therapeutically. In some areas, where arsenic is present in high proportions in the drinking water, this exposure represents an important health concern. Chronic exposure to arsenic leads to hyperkeratosis and loss of skin pigmentation, as well as to significant increases of different types of cancer in skin, lung, bladder and liver; in addition, other pathologies, such as vascular diseases, hepatotoxicity and diabetes, have also been related to arsenic exposure. Since high interindividual variability is observed among people exposed to equivalent doses, genetic susceptibility factors have been postulated to be involved. When inorganic arsenic enters into the body it undergoes metabolic conversion, in a process where methylation plays a crucial role. Trivalent forms, both inorganic and organic, are the most toxic and genotoxic and, for this reason, metabolic variations owing to variant alleles in genes involved in such a process have been the aim of several studies. Genes involved in other mechanisms, such as antioxidant defense and DNA-repair lesions, among others, have also been the subject of association studies. A survey of those studies related to individual susceptibility is summarized here. Results with genes involved in folate one-carbon metabolism and in arsenic transport across the cell membrane provide promising data for future studies.

Activation of inflammation/NF-kappaB signaling in infants born to arsenic-exposed mothers

The long-term health outcome of prenatal exposure to arsenic has been associated with increased mortality in human populations. In this study, the extent to which maternal arsenic exposure impacts gene expression in the newborn was addressed. We monitored gene expression profiles in a population of newborns whose mothers experienced varying levels of arsenic exposure during pregnancy. Through the application of machine learning-based two-class prediction algorithms, we identified expression signatures from babies born to arsenic-unexposed and -exposed mothers that were highly predictive of prenatal arsenic exposure in a subsequent test population. Furthermore, 11 transcripts were identified that captured the maximal predictive capacity to classify prenatal arsenic exposure. Network analysis of the arsenic-modulated transcripts identified the activation of extensive molecular networks that are indicative of stress, inflammation, metal exposure, and apoptosis in the newborn. Exposure to arsenic is an important health hazard both in the United States and around the world, and is associated with increased risk for several types of cancer and other chronic diseases. These studies clearly demonstrate the robust impact of a mother's arsenic consumption on fetal gene expression as evidenced by transcript levels in newborn cord blood.

GSTM1 and APE1 genotypes affect arsenic-induced oxidative stress: a repeated measures study

BACKGROUND

Chronic arsenic exposure is associated with an increased risk of skin, bladder and lung cancers. Generation of oxidative stress may contribute to arsenic carcinogenesis.

METHODS

To investigate the association between arsenic exposure and oxidative stress, urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) was evaluated in a cohort of 97 women recruited from an arsenic-endemic region of Bangladesh in 2003. Arsenic exposure was measured in urine, toenails, and drinking water. Drinking water and urine samples were collected on three consecutive days. Susceptibility to oxidative stress was evaluated by genotyping relevant polymorphisms in glutathione-s transferase mu (GSTM1), human 8-oxoguanine glycosylase (hOGG1) and apurinic/apyrimidinic endonuclease (APE1) genes using the Taqman method. Data were analyzed using random effects Tobit regression to account for repeated measures and 8-OHdG values below the detection limit.

RESULTS

A consistent negative effect for APE1 was observed across water, toenail and urinary arsenic models. APE1 148 glu/glu + asp/glu genotype was associated with a decrease in logged 8-OHdG of 0.40 (95%CI -0.73, -0.07) compared to APE1 148 asp/asp. An association between total urinary arsenic and 8-OHdG was observed among women with the GSTM1 null genotype but not in women with GSTM1 positive. Among women with GSTM1 null, a comparison of the second, third, and fourth quartiles of total urinary arsenic to the first quartile resulted in a 0.84 increase (95% CI 0.27, 1.42), a 0.98 increase (95% CI 033, 1.66) and a 0.85 increase (95% CI 0.27, 1.44) in logged 8-OHdG, respectively. No effects between 8-OHdG and toenail arsenic or drinking water arsenic were observed.

CONCLUSION

These results suggest the APE1 variant genotype decreases repair of 8-OHdG and that arsenic exposure is associated with oxidative stress in women who lack a functional GSTM1 detoxification enzyme.

Association between total ingested arsenic and toenail arsenic concentrations

The association between arsenic exposure from drinking water and toenail arsenic concentrations appears to be non-linear at low exposure levels. To investigate whether this observation is a result exposure misclassification, a dietary exposure assessment was conducted in a cohort of 47 women concurrently enrolled in a prospective longitudinal biomonitoring study in Pabna, Bangladesh. Arsenic intake was evaluated using a duplicate diet study design which collected food and water samples for a total of 6 days. Total inorganic arsenic was measured in 24-hour composite food samples (N=282) using inductively coupled plasma-mass spectrometry coupled with a dynamic reaction cell (ICP-DRC-MS). Average annual tubewell arsenic concentrations and toenail arsenic concentrations were computed for each participant using biomonitoring data from the prospective study. Separate multivariate regression models evaluated the association between drinking water, total dietary intake, and total dietary dose with toenail arsenic, a biomarker of internal dose. In these models, dietary intakes were adjusted using the residual method to provide estimate that was independent of water arsenic concentrations. Median daily arsenic intake from food and drinking water was 48.3 microg/day and 4.2 microg/day. Taking into consideration participant's body weight, the median daily arsenic dose was 1.0 microg/kg-day from food and 0.1 microg/kg-day from drinking water although drinking water exposure was highly skewed and was the dominant exposure route for the upper 25th percentile of the distribution. The regression model that used total daily arsenic intake from food (beta=0.46; 95%CI: 0.18-0.73) and drinking water (95%CI: 0.26-0.38) explained the most variability in toenail arsenic concentrations (R(2)(a)=0.71). The effect estimates for food and drinking water are similar suggesting that both sources have a similar contribution to internal dose.

Dietary arsenic exposure in bangladesh

BACKGROUND

Millions of people in Bangladesh are at risk of chronic arsenic toxicity from drinking contaminated groundwater, but little is known about diet as an additional source of As exposure.

METHODS

We employed a duplicate diet survey to quantify daily As intake in 47 women residing in Pabna, Bangladesh. All samples were analyzed for total As, and a subset of 35 samples were measured for inorganic arsenic (iAs) using inductively coupled plasma mass spectrometry equipped with a dynamic reaction cell.

RESULTS

Median daily total As intake was 48 microg As/day [interquartile range (IQR), 33-67) from food and 4 microg As/day (IQR, 2-152) from drinking water. On average, iAs comprised 82% of the total As detected in dietary samples. After adjusting for the estimated inorganic fraction, 34% [95% confidence interval (CI), 21-49%] of all participants exceeded the World Health Organization's provisional tolerable daily intake (PTDI) of 2.1 microg As/kg-day. Two of the 33 women who used a well with < 50 microg As/L exceeded this recommendation.

CONCLUSIONS

When drinking water concentrations exceeded the Bangladesh drinking water standard of 50 microg As/L, ingested water was the dominant source of exposure. However, as drinking water As concentrations decrease, the relative contribution of dietary As sources becomes more important to ingested dose. The combined intake from both diet and drinking water can cause some individuals to exceed the PTDI in spite of using a tube well that contains < 50 microg As/L.

Mass spectrometric quantitation of nicotine, cotinine, and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in human toenails

Numerous studies have quantified total cotinine (the sum of cotinine and cotinine-N-glucuronide) and total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol [NNAL; the sum of NNAL and its O- and N-glucuronides (NNAL-Glucs)] in the urine and blood of smokers, smokeless tobacco users, and nonsmokers exposed to environmental tobacco smoke. Analysis of hair and nails has several advantages over blood and urine testing, such as accumulation of xenobiotics during long-term exposure, ease of collection, and indefinite stability of samples. We developed sensitive methods for quantitation of nicotine, cotinine, and NNAL in human toenails. Nicotine and cotinine were analyzed by gas chromatography-mass spectrometry-selected ion monitoring. NNAL was assayed using liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring. The detection limits of the methods were 0.01 ng/mg toenail for nicotine, 0.012 ng/mg toenail for cotinine, and 0.02 pg/mg toenail for NNAL. In 35 smokers, the mean nicotine level was 5.9 +/- 5.6 ng/mg toenail, mean cotinine was 1.6 +/- 1.3 ng/mg toenail, and mean NNAL was 0.41 +/- 0.67 pg/mg toenail. Samples collected from six nonsmokers were negative for NNAL. In smokers, NNAL correlated with cotinine (r = 0.77; P < 0.0001). The results of this study for the first time show the presence of cotinine and NNAL in human toenails. These sensitive and quantitative methods should be useful in epidemiologic studies of the role of chronic tobacco smoke exposure, including environmental tobacco smoke exposure, in human cancer.

Susceptibility to arsenic-induced skin lesions from polymorphisms in base excision repair genes

Genetic polymorphisms in the base excision DNA repair pathway may influence individual susceptibility to arsenic and the development of arsenic-induced skin lesions. Data from a case-control study of 792 cases and 792 matched controls conducted in Bangladesh from 2001 to 2003 were analyzed using conditional logistic regression to assess the associations between four common base excision repair (BER) genetic polymorphisms X-ray repair cross-complementing group 1 (XRCC1) Arg399Gln, XRCC1 Arg194Trp, human 8-oxoguanine DNA glycosylase (hOGG1) Ser326Cys and apurinic/apyrimidinic endonuclease (APE1) Asp148Glu and arsenic-induced skin lesions including melanosis and keratosis. Adjusted for toenail arsenic, body mass index, education, smoking and betel nut use, individuals with the APE1 148Glu/Glu polymorphism had a 2-fold increased odds of skin lesions compared with individuals with the 148Asp/Asp genotype (1.93; 95% confidence interval 1.15, 3.19). Gene-environment interactions between toenail arsenic and XRCC1 Arg194Trp and APE1 Asp148Glu were observed. Within the lowest arsenic tertile, APE1 148Glu/Glu had 2.5 times the odds ratio compared with wild-type, whereas within the highest tertile of arsenic the odds ratios for skin lesions did not differ. In contrast, at low arsenic levels, the odds ratios for skin lesions did not differ much by XRCC1 Arg194Trp genotype. However, at the highest tertile of arsenic, the XRCC1 194Arg/Arg polymorphism conferred a 3-fold larger odds ratio for skin lesions compared with XRCC1 194Trp/Trp. Individuals may have different odds for developing skin lesions based in part on their genetic profile for BER and their arsenic exposure history. Future research on arsenic-induced skin lesions should consider the impact of genetic variation to individual susceptibility to arsenic toxicity.

Glutathione S-transferases M1 and T1 polymorphisms and arsenic content in hair and urine in two ethnic clans exposed to indoor combustion of high arsenic coal in Southwest Guizhou, China

A total of 2,402 cases of arsenic-related skin lesions (as of 2002) in a few villages of China's Southwest Guizhou Autonomous Prefecture represent a unique case of endemic arseniasis related with indoor combustion of high arsenic coal. A significant difference of skin lesion prevalence was observed between two clans of different ethnicities (Hmong and Han) in one of the hyperendemic villages in this prefecture. This study was focused on a possible involvement of GST T1 and M1 polymorphisms in risk modulation of skin lesions and in the body burden of As in this unique case of As exposure. GST T1 and M1 polymorphisms were genotyped by an allele-specific PCR-based procedure. Total As contents in hair and urine samples as well as environmental samples of the homes of the two ethnic clans were analyzed. No significant deviations in the population frequencies of GST T1 and M1 0/0 genotypes or their combination were recorded between diagnosed skin lesion patients and asymptomatic individuals in both clans. Significantly higher As contents in hair and urine were observed in GSTM1 0/0 carriers, not in GSTT1 0/0 carriers. After stratified by ethnicity and gender, a statistically significant association of the GSTM1 0/0 genotype and higher As content in hair was only confirmed in the subgroups of ethnic Han clan members and all male villagers, not in ethnic Hmong clan members or in females. GST T1 and M1 homozygous deletions were not associated with an increased susceptibility to skin lesions in long-term exposure to indoor combustion of high As coal. The polymorphic status at the locus of GSTM1 might modulate individual's body burden of total As in some Chinese ethnic groups.

Developmental and genetic modulation of arsenic biotransformation: a gene by environment interaction?

The complexity of arsenic toxicology has confounded the identification of specific pathways of disease causation. One focal point of arsenic research is aimed at fully characterizing arsenic biotransformation in humans, a process that appears to be quite variable, producing a mixture of several arsenic species with greatly differing toxic potencies. In an effort to characterize genetic determinants of variability in arsenic biotransformation, a genetic association study of 135 subjects in western Sonora, Mexico was performed by testing 23 polymorphic sites in three arsenic biotransformation candidate genes. One gene, arsenic 3 methyltransferase (AS3MT), was strongly associated with the ratio of urinary dimethylarsinic acid to monomethylarsonic acid (D/M) in children (7-11 years) but not in adults (18-79 years). Subsequent analyses revealed that the high D/M values associated with variant AS3MT alleles were primarily due to lower levels of monomethylarsonic acid as percent of total urinary arsenic (%MMA5). In light of several reports of arsenic-induced disease being associated with relatively high %MMA5 levels, these findings raise the possibility that variant AS3MT individuals may suffer less risk from arsenic exposure than non-variant individuals. These analyses also provide evidence that, in this population, regardless of AS3MT variant status, children tend to have lower %MMA5 values than adults, suggesting that the global developmental regulation of arsenic biotransformation may interact with genetic variants in metabolic genes to result in novel genetic effects such as those in this report.

Gender-specific protective effect of hemoglobin on arsenic-induced skin lesions

Chronic arsenic poisoning remains a public health crisis in Bangladesh. As arsenic has been shown to bind to human hemoglobin (Hb), hematologic mechanisms may play a role in the pathway through which arsenic exerts its toxicity. Two separate studies, a case-control and a cohort, were conducted to investigate the role of Hb in the development of arsenic-induced skin lesions. In the first, conditional logistic regression was used to investigate the effect of Hb on skin lesions among 900 case-control pairs from Pabna, Bangladesh, in which individuals were matched on gender, age, and location. In the second, mixed linear regression models were used to examine the association between toenail arsenic, urinary arsenic, and Hb within a cohort of 184 individuals from 50 families in the same region who did not have arsenic-induced skin lesions. Hb was significantly associated with skin lesions but this association was gender specific. In males, a 40% reduction in the odds of skin lesions occurred for every 1 g/dL increase in Hb (odds ratio, 0.60; 95% confidence interval, 0.49-0.73). No effect was observed for females (odds ratio, 1.16; 95% confidence interval, 0.92-1.46). In the cohort of 184 individuals, no associations between toenail arsenic or urinary arsenic species and Hb levels were observed. Low Hb levels may exacerbate the detrimental health effects of chronic arsenic poisoning. Whereas providing clean water remains the optimal solution to Bangladesh's problem of arsenic poisoning, improving nutrition and reducing iron-deficiency anemia may ameliorate negative health effects, such as skin lesions in individuals who have been exposed.