Childhood exposure to manganese and postural instability in children living near a ferromanganese refinery in Southeastern Ohio

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.

Loss of SLC30A10 manganese transporter alters expression of neurotransmission genes and activates hypoxia-inducible factor signaling in mice

The essential metal manganese (Mn) induces neuromotor disease at elevated levels. The manganese efflux transporter SLC30A10 regulates brain Mn levels. Homozygous loss-of-function mutations in SLC30A10 induce hereditary Mn neurotoxicity in humans. Our prior characterization of Slc30a10 knockout mice recapitulated the high brain Mn levels and neuromotor deficits reported in humans. But, mechanisms of Mn-induced motor deficits due to SLC30A10 mutations or elevated Mn exposure are unclear. To gain insights into this issue, we characterized changes in gene expression in the basal ganglia, the main brain region targeted by Mn, of Slc30a10 knockout mice using unbiased transcriptomics. Compared with littermates, >1000 genes were upregulated or downregulated in the basal ganglia sub-regions (i.e. caudate putamen, globus pallidus, and substantia nigra) of the knockouts. Pathway analyses revealed notable changes in genes regulating synaptic transmission and neurotransmitter function in the knockouts that may contribute to the motor phenotype. Expression changes in the knockouts were essentially normalized by a reduced Mn chow, establishing that changes were Mn dependent. Upstream regulator analyses identified hypoxia-inducible factor (HIF) signaling, which we recently characterized to be a primary cellular response to elevated Mn, as a critical mediator of the transcriptomic changes in the basal ganglia of the knockout mice. HIF activation was also evident in the liver of the knockout mice. These results: (i) enhance understanding of the pathobiology of Mn-induced motor disease; (ii) identify specific target genes/pathways for future mechanistic analyses; and (iii) independently corroborate the importance of the HIF pathway in Mn homeostasis and toxicity.

Consequences of Disturbing Manganese Homeostasis

Manganese (Mn) is an essential trace element with unique functions in the body; it acts as a cofactor for many enzymes involved in energy metabolism, the endogenous antioxidant enzyme systems, neurotransmitter production, and the regulation of reproductive hormones. However, overexposure to Mn is toxic, particularly to the central nervous system (CNS) due to it causing the progressive destruction of nerve cells. Exposure to manganese is widespread and occurs by inhalation, ingestion, or dermal contact. Associations have been observed between Mn accumulation and neurodegenerative diseases such as manganism, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. People with genetic diseases associated with a mutation in the gene associated with impaired Mn excretion, kidney disease, iron deficiency, or a vegetarian diet are at particular risk of excessive exposure to Mn. This review has collected data on the current knowledge of the source of Mn exposure, the experimental data supporting the dispersive accumulation of Mn in the brain, the controversies surrounding the reference values of biomarkers related to Mn status in different matrices, and the competitiveness of Mn with other metals, such as iron (Fe), magnesium (Mg), zinc (Zn), copper (Cu), lead (Pb), calcium (Ca). The disturbed homeostasis of Mn in the body has been connected with susceptibility to neurodegenerative diseases, fertility, and infectious diseases. The current evidence on the involvement of Mn in metabolic diseases, such as type 2 diabetes mellitus/insulin resistance, osteoporosis, obesity, atherosclerosis, and non-alcoholic fatty liver disease, was collected and discussed.

Hepatic and intestinal manganese excretion are both required to regulate brain manganese during elevated manganese exposure

Manganese (Mn) is essential but neurotoxic at elevated levels. Under physiological conditions, Mn is primarily excreted by the liver, with the intestines playing a secondary role. Recent analyses of tissue-specific Slc30a10 or Slc39a14 knockout mice (SLC30A10 and SLC39A14 are Mn transporters) revealed that, under physiological conditions: 1) excretion of Mn by the liver and intestines is a major pathway that regulates brain Mn; and surprisingly, 2) the intestines compensate for loss of hepatic Mn excretion in controlling brain Mn. The unexpected importance of the intestines in controlling physiological brain Mn led us to determine the role of hepatic and intestinal Mn excretion in regulating brain Mn during elevated Mn exposure. We used liver- or intestine-specific Slc30a10 knockout mice as models to inhibit hepatic or intestinal Mn excretion. Compared with littermates, both knockout strains exhibited similar increases in brain Mn after elevated Mn exposure in early or later life. Thus, unlike physiological conditions, both hepatic and intestinal Mn excretion are required to control brain Mn during elevated Mn exposure. However, brain Mn levels of littermates and both knockout strains exposed to elevated Mn only in early life were normalized in later life. Thus, hepatic and intestinal Mn excretion play compensatory roles in clearing brain Mn accumulated by early life Mn exposure. Finally, neuromotor assays provided evidence consistent with a role for hepatic and intestinal Mn excretion in functionally modulating Mn neurotoxicity during Mn exposure. Put together, these findings substantially enhance understanding of the regulation of brain Mn by excretion.NEW & NOTEWORTHY This article shows that, in contrast with expectations from prior studies and physiological conditions, excretion of manganese by the intestines and liver is equally important in controlling brain manganese during human-relevant manganese exposure. The results provide foundational insights about the interorgan mechanisms that control brain manganese homeostasis at the organism level and have important implications for the development of therapeutics to treat manganese-induced neurological disease.

SLC30A10 manganese transporter in the brain protects against deficits in motor function and dopaminergic neurotransmission under physiological conditions

Loss-of-function mutations in SLC30A10 induce hereditary manganese (Mn)-induced neuromotor disease in humans. We previously identified SLC30A10 to be a critical Mn efflux transporter that controls physiological brain Mn levels by mediating hepatic and intestinal Mn excretion in adolescence/adulthood. Our studies also revealed that in adulthood, SLC30A10 in the brain regulates brain Mn levels when Mn excretion capacity is overwhelmed (e.g. after Mn exposure). But, the functional role of brain SLC30A10 under physiological conditions is unknown. We hypothesized that, under physiological conditions, brain SLC30A10 may modulate brain Mn levels and Mn neurotoxicity in early postnatal life because body Mn excretion capacity is reduced in this developmental stage. We discovered that Mn levels of pan-neuronal/glial Slc30a10 knockout mice were elevated in specific brain regions (thalamus) during specific stages of early postnatal development (postnatal day 21), but not in adulthood. Furthermore, adolescent or adult pan-neuronal/glial Slc30a10 knockouts exhibited neuromotor deficits. The neuromotor dysfunction of adult pan-neuronal/glial Slc30a10 knockouts was associated with a profound reduction in evoked striatal dopamine release without dopaminergic neurodegeneration or changes in striatal tissue dopamine levels. Put together, our results identify a critical physiological function of brain SLC30A10-SLC30A10 in the brain regulates Mn levels in specific brain regions and periods of early postnatal life, which protects against lasting deficits in neuromotor function and dopaminergic neurotransmission. These findings further suggest that a deficit in dopamine release may be a likely cause of early-life Mn-induced motor disease.

Evaluation of the oxidative toxicity induced by lead, manganese, and cadmium using genetically modified nrf2a-mutant zebrafish

Heavy metal pollution has become a serious environmental concern and a threat to public health. Three of the most common heavy metals are cadmium (Cd), lead (Pb), and manganese (Mn). Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important transcription factor activated in the response to oxidative stress. In this study, mutant zebrafish with an nrf2a deletion of 7 bp were constructed by the CRISPR/Cas9 system to investigate the oxidative toxicity of these three heavy metals. The results of general toxicity tests showed that Pb exposure did not cause significant damage to mutant zebrafish compared with wild-type (WT) zebrafish. However, high Mn exposure increased mortality and malformation rates in mutant zebrafish. Of concern, Cd exposure caused significant toxic damage, including increased mortality and malformation rates, apoptosis of brain neurons, and severe locomotor behavior aberration in mutant zebrafish. The results of qRT-PCR indicated that Cd exposure could induce the activation of genes related to oxidative stress resistance in WT zebrafish, while the expression of these genes was inhibited in mutant zebrafish. This study showed that of the three heavy metals, Cd had the strongest oxidative toxicity, Mn had medium toxicity, and Pb had the weakest toxicity.

Comparative susceptibility of children and adults to neurological effects of inhaled manganese: A review of the published literature

BACKGROUND

Manganese (Mn) is neurotoxic in adults and children. Current assessments are based on the more extensive adult epidemiological data, but the potential for greater childhood susceptibility remains a concern. To better understand potential lifestage-based variations, we compared susceptibilities to neurotoxicity in children and adults using Mn biomarker data.

METHODS

We developed a literature search strategy based on a Population, Exposures, Comparators, and Outcomes statement focusing on inhalation exposures and neurological outcomes in humans. Screening was performed using DistillerSR. Hair biomarker studies were selected for evaluation because studies with air measurements were unavailable or considered inadequate for children. Studies were paired based on concordant Mn source, biomarker, and outcome. Comparisons were made based on reported dose-response slopes (children vs. adults). Study evaluation was conducted to understand the confidence in our comparisons.

RESULTS

We identified five studies evaluating seven pairings of hair Mn and neurological outcomes (cognition and motor effects) in children and adults matched on sources of environmental Mn inhalation exposure. Two Brazilian studies of children and one of adults reported intelligent quotient (IQ) effects; effects in both comparisons were stronger in children (1.21 to 2.03-fold difference). In paired analyses of children and adults from the United States, children exhibited both stronger and weaker effects compared to adults (0.37 to 1.75-fold differences) on postural sway metrics.

CONCLUSION

There is limited information on the comparative susceptibility of children and adults to inhaled Mn. We report that children may be 0.37 to 2.03 times as susceptible as adults to neurotoxic effects of Mn, thereby providing a quantitative estimate for some aspects of lifestage variation. Due to the limited number of paired studies available in the literature, this quantitative estimate should be interpreted with caution. Our analyses do not account for other sources of inter-individual variation. Additional studies of Mn-exposed children with direct air concentration measurements would improve the evidence base.

Animal Models of Childhood Exposure to Lead or Manganese: Evidence for Impaired Attention, Impulse Control, and Affect Regulation and Assessment of Potential Therapies

Behavioral disorders involving attention and impulse control dysfunction, such as ADHD, are among the most prevalent disorders in children and adolescents, with significant impact on their lives. The etiology of these disorders is not well understood, but is recognized to be multifactorial, with studies reporting associations with polygenic and environmental risk factors, including toxicant exposure. Environmental epidemiological studies, while good at establishing associations with a variety of environmental and genetic risk factors, cannot establish causality. Animal models of behavioral disorders, when properly designed, can play an essential role in establishing causal relationships between environmental risk factors and a disorder, as well as provide model systems for elucidating underlying neural mechanisms and testing therapies. Here, we review how animal model studies of developmental lead or manganese exposure have been pivotal in (1) establishing a causal relationship between developmental exposure and lasting dysfunction in the domains of attention, impulse control, and affect regulation, and (2) testing the efficacy of specific therapeutic approaches for alleviating the lasting deficits. The lead and manganese case studies illustrate how animal models can advance knowledge in ways that are not possible in human studies. For example, in contrast to the Treatment of Lead Poisoned Children (TLC) human clinical trial evaluating succimer chelation efficacy to improve cognitive functioning in lead-exposed children, our developmental lead exposure animal model showed that succimer chelation can produce lasting cognitive benefits if chelation sufficiently reduces brain lead levels. In addition, this study revealed that succimer treatment in the absence of lead exposure produces lasting cognitive dysfunction, highlighting potential risks of chelation in off-label uses, such as the treatment of autistic children without a history of lead exposure. Our animal model of developmental manganese exposure has demonstrated that manganese can cause lasting attentional and sensorimotor deficits, akin to an ADHD-inattentive behavioral phenotype, thereby providing insights into the role of environmental exposures as contributors to ADHD. These studies have also shown that oral methylphenidate (Ritalin) can fully alleviate the deficits produced by early developmental Mn exposure. Future work should continue to focus on the development and use of animal models that appropriately recapitulate the complex behavioral phenotypes of behavioral disorders, in order to determine the mechanistic basis for the behavioral deficits caused by developmental exposure to environmental toxicants, and the efficacy of existing and emerging therapies.

Biomarkers of environmental manganese exposure

We conducted a critical review on biomarkers of environmental manganese (Mn) exposure to answer the following questions: 1) are there reliable biomarkers of internal Mn exposure (Mn in biological matrices) associated with external metrics of Mn exposure (Mn in environmental media)? and 2) are there accurate reference values (RVs) for Mn in biological matrices? Three bibliographic databases were searched for relevant references and identified references were screened by two independent reviewers. Of the 6342 unique references identified, 86 articles were retained for data abstraction. Our analysis of currently available evidence suggests that Mn levels in blood and urine are not useful biomarkers of Mn exposure in non-occupational settings. The strength of the association between Mn in environmental media and saliva was variable. Findings regarding the utility of hair Mn as a biomarker of environmental Mn exposure are inconsistent. Measurements of Mn in teeth are technically challenging and findings on Mn in tooth components are scarce. In non-occupationally exposed individuals, bone Mn measurements using in vivo neutron activation analysis (IVNAA) are associated with large uncertainties. Findings suggest that Mn in nails may reflect Mn in environmental media and discriminate between groups of individuals exposed to different environmental Mn levels, although more research is needed. Currently, there is no strong evidence for any biological matrix as a valid biomarker of Mn exposure in non-occupational settings. Because of methodological limitations in studies aimed at derivation of RVs for Mn in biological materials, accurate RVs are scarce.

Manganese body burden in children is associated with reduced visual motor and attention skills

Manganese (Mn) is an essential element, however, children with moderate to high Mn exposure can exhibit neurobehavioral impairments. One way Mn appears to affect brain function is through altering dopaminergic systems involved with motor and cognitive control including frontal - striatal brain systems. Based on the risk for motor and attention problems, we evaluated neurobehavioral function in 255 children at risk for Mn exposure due to living in proximity to coal ash storage sites. Proton Induced X-ray Emissions (PIXE) analysis was conducted on finger and toenails samples. Multiple neuropsychological tests were completed with the children. Fifty-five children had Mn concentrations above the limit of detection (LOD) (median concentration = 3.95 ppm). Children with detectable Mn concentrations had reduced visual motor skills (β = -5.62, CI: -9.11, -2.12, p = 0.008) and more problems with sustained attention, based on incorrect responses on a computerized attention test, (β = 0.40, CI: 0.21, 0.59, p < 0.001) compared with children who had Mn concentrations below the LOD. Findings suggest that Mn exposure impacts attention and motor control possibly due to neurotoxicity involving basal ganglia and forebrain regions. Visual-motor and attention tests may provide a sensitive measure of Mn neurotoxicity, useful for evaluating the effects of exposure in children and leading to better treatment options.

Manganese mitigates against hepatorenal oxidative stress, inflammation and caspase-3 activation in rats exposed to hexachlorobenzene

The present study investigated the individual and collective effect of organochlorinated fungicide hexachlorobenzene (HCB) and manganese (Mn), a metal, on the hepatorenal function in adult rats. Rats were divided into four groups of rats comprising of control, HCB alone (15 mg/kg), Mn alone (10 mg/kg) and co-exposure group that were orally treated for 25 consecutive days. After sacrifice, hepatorenal damage and antioxidant status markers, myeloperoxidase (MPO) activity, levels of nitric oxide, total antioxidant capacity (TAC), total oxidative stress (TOS) and lipid peroxidation (LPO) were analyzed spectrophotometrically. Levels of tumor necrosis factor alpha (TNF-α), interleukin-1 β (IL-1β) and caspase-3 activity were assessed using ELISA. Results revealed that the HCB administration significantly (p < 0.05) increased the biomarkers of hepatorenal toxicity, decreased the antioxidant status and TAC, raised the levels of TOS and LPO as well as increased the levels of TNF-α, IL-1β and caspase-3 activity. Rats co-exposed to HCB and Mn showed decreased biomarkers of hepatorenal damage, increased antioxidant status and TAC with simultaneous reduction in the levels of TOS and LPO significantly (p < 0.05). Furthermore, the increased levels of TNF-α, IL-1β and caspase-3 activity were significantly (p < 0.05) reduced in the liver and kidney of rats' co-expose to HCB and Mn. Histological examination showed that damages induced by HCB were assuaged in rats co-treated with HCB and Mn. In conclusion, the results demonstrated that co-treatment of HCB and Mn in rats' alleviated HCB-induced oxidative stress, inflammation and caspase-3 activation in the liver and kidney of the rats.

NF-κB Signaling in Astrocytes Modulates Brain Inflammation and Neuronal Injury Following Sequential Exposure to Manganese and MPTP During Development and Aging

Chronic exposure to manganese (Mn) is associated with neuroinflammation and extrapyramidal motor deficits resembling features of Parkinson's disease. Activation of astrocytes and microglia is implicated in neuronal injury from Mn but it is not known whether early life exposure to Mn may predispose glia to more severe inflammatory responses during aging. We therefore examined astrocyte nuclear factor kappa B (NF-κB) signaling in mediating innate immune inflammatory responses during multiple neurotoxic exposures spanning juvenile development into adulthood. MnCl2 was given in drinking water for 30-day postweaning to both wildtype mice and astrocyte-specific knockout (KO) mice lacking I kappa B kinase 2, the central upstream activator of NF-κB. Following juvenile exposure to Mn, mice were subsequently administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at 4 months of age. Animals were evaluated for behavioral alterations and brain tissue was analyzed for catecholamine neurotransmitters. Stereological analysis of neuronal and glial cell counts from multiple brain regions indicated that juvenile exposure to Mn amplified glial activation and neuronal loss from MPTP exposure in the caudate-putamen and globus pallidus, as well as increased the severity of neurobehavioral deficits in open field activity assays. These alterations were prevented in astrocyte-specific I kappa B kinase 2 KO mice. Juvenile exposure to Mn increased the number of neurotoxic A1 astrocytes expressing C3 as well as the number of activated microglia in adult mice following MPTP challenge, both of which were inhibited in KO mice. These results demonstrate that exposure to Mn during juvenile development heightens the innate immune inflammatory response in glia during a subsequent neurotoxic challenge through NF-κB signaling in astrocytes.

Hair levels of heavy metals and essential elements in Chinese children with autism spectrum disorder

BACKGROUND

Disproportional heavy metals and essential elements were reported in children with autism spectrum disorder (ASD) that is obscure in etiology. Inevitably, the association is biased by diet and environmental factors.

METHODS

Fifty pairs, one with ASD and the other living together from the same special school with cerebral palsy (CP), were recruited in Hangzhou (China), aged from 2 to 11 years old (74.0 % male). All samples were divided into two subgroups: preschool-aged (2-5 years old) and school-aged (6-10 years old). Heavy metals (As, Hg, Pb) and essential elements (Al, Ca, Cu, Mg, Mn, Zn) in hair were quantified by inductively coupled plasma mass spectrometry analysis and flame atomic absorption spectroscopy.

RESULTS

The children with ASD generally had lower hair levels of Mn (ASD 0.124 μg/g, CP 0.332 μg/g, P = 0.001) compared to the children with CP. After stratification for age, there were no significant differences detected in preschool-aged group. In school-aged group, the results exhibited the children with ASD had higher hair Pb (1.485 μg/g, 0.690 μg/g, P = 0.007) and Cu/Zn ratio (0.092, 0.060, P = 0.003), while hair Hg (0.254 μg/g, 0.353 μg/g, P = 0.016)、Mn (0.089 μg/g, 0.385 μg/g, P = 0.002)、Mg (17.81 μg/g, 24.53 μg/g, P = 0.014) and Zn (100.15 μg/g, 135.83 μg/g, P = 0.007) showed an opposite pattern.

CONCLUSIONS

These results suggest an imbalance of Mn in Chinese children with ASD.

A Review on the Environmental Exposure to Airborne Manganese, Biomonitoring, and Neurological/Neuropsychological Outcomes

The occupational exposure to airborne manganese (Mn) has been linked for decades with neurological effects. With respect to its environmental exposure, the first reviews on this matter stated that the risk posed to human health by this kind of exposure was still unknown. Later, many studies have been developed to analyze the association between environmental Mn exposure and health effects, most of them including the measure of Mn in selected human biomarkers. This review aims at collecting and organizing the literature dealing with the environmental airborne Mn exposure (other routes of exposure were intentionally removed from this review), the biomonitoring of this metal in different body matrices (e.g., blood, urine, nails, hair), and the association between exposure and several adverse health effects, such as, e.g., neurocognitive, neurodevelopmental, or neurobehavioral outcomes. From the different exposure routes, inhalation was the only one considered in this review, to take into account the areas influenced by industrial activities closely related to the Mn industry (ferromanganese and silicomanganese plants, Mn ore mines, and their processing plants) and by traffic in countries where a fuel additive, methylcyclopentadienyl manganese tricarbonyl (MMT), has been used for years. In these areas, high air Mn levels have been reported in comparison with the annual Reference Concentration (RfC) given by the US EPA for Mn, 50 ng/m³. This review was performed using Scopus and MEDLINE databases with a keyword search strategy that took into account that each valid reference should include at least participants that were exposed to environmental airborne Mn and that were subjected to analysis of Mn in biomarkers or subjected to neurological/neuropsychological tests or both. Overall, 47 references matching these criteria were included in the discussion. Most of them report the measure of Mn in selected biomarkers (N = 43) and the assessment of different neurological outcomes (N = 31). A negative association is usually obtained between Mn levels in hair and some neurological outcomes, such as cognitive, motor, olfactory, and emotional functions, but not always significant. However, other biomarkers, such as blood and urine, do not seem to reflect the chronic environmental exposure to low/moderate levels of airborne Mn. Further studies combining the determination of the Mn exposure through environmental airborne sources and biomarkers of exposure and the evaluation of at least cognitive and motor functions are needed to better understand the effects of chronic non-occupational exposure to airborne Mn.

Biomarkers of environmental manganese exposure and associations with childhood neurodevelopment: a systematic review and meta-analysis

BACKGROUND

Although prior studies showed a correlation between environmental manganese (Mn) exposure and neurodevelopmental disorders in children, the results have been inconclusive. There has yet been no consistent biomarker of environmental Mn exposure. Here, we summarized studies that investigated associations between manganese in biomarkers and childhood neurodevelopment and suggest a reliable biomarker.

METHODS

We searched PubMed and Web of Science for potentially relevant articles published until December 31th 2019 in English. We also conducted a meta-analysis to quantify the effects of manganese exposure on Intelligence Quotient (IQ) and the correlations of manganese in different indicators.

RESULTS

Of 1754 citations identified, 55 studies with 13,388 subjects were included. Evidence from cohort studies found that higher manganese exposure had a negative effect on neurodevelopment, mostly influencing cognitive and motor skills in children under 6 years of age, as indicated by various metrics. Results from cross-sectional studies revealed that elevated Mn in hair (H-Mn) and drinking water (W-Mn), but not blood (B-Mn) or teeth (T-Mn), were associated with poorer cognitive and behavioral performance in children aged 6-18 years old. Of these cross-sectional studies, most papers reported that the mean of H-Mn was more than 0.55 μg/g. The meta-analysis concerning H-Mn suggested that a 10-fold increase in hair manganese was associated with a decrease of 2.51 points (95% confidence interval (CI), - 4.58, - 0.45) in Full Scale IQ, while the meta-analysis of B-Mn and W-Mn generated no such significant effects. The pooled correlation analysis revealed that H-Mn showed a more consistent correlation with W-Mn than B-Mn. Results regarding sex differences of manganese associations were inconsistent, although the preliminary meta-analysis found that higher W-Mn was associated with better Performance IQ only in boys, at a relatively low water manganese concentrations (most below 50 μg/L).

CONCLUSIONS

Higher manganese exposure is adversely associated with childhood neurodevelopment. Hair is the most reliable indicator of manganese exposure for children at 6-18 years of age. Analysis of the publications demonstrated sex differences in neurodevelopment upon manganese exposure, although a clear pattern has not yet been elucidated for this facet of our study.

Brain manganese and the balance between essential roles and neurotoxicity

Manganese (Mn) is an essential micronutrient required for the normal development of many organs, including the brain. Although its roles as a cofactor in several enzymes and in maintaining optimal physiology are well-known, the overall biological functions of Mn are rather poorly understood. Alterations in body Mn status are associated with altered neuronal physiology and cognition in humans, and either overexposure or (more rarely) insufficiency can cause neurological dysfunction. The resultant balancing act can be viewed as a hormetic U-shaped relationship for biological Mn status and optimal brain health, with changes in the brain leading to physiological effects throughout the body and vice versa. This review discusses Mn homeostasis, biomarkers, molecular mechanisms of cellular transport, and neuropathological changes associated with disruptions of Mn homeostasis, especially in its excess, and identifies gaps in our understanding of the molecular and biochemical mechanisms underlying Mn homeostasis and neurotoxicity.

Birth outcomes associated with maternal exposure to metals from informal electronic waste recycling in Guiyu, China

BACKGROUND

Informal electronic waste (e-waste) recycling is a rapidly growing industry. Informal e-waste recycling creates a mixture of chemicals that can be harmful to humans, especially vulnerable populations like pregnant women and young children.

OBJECTIVES

We aimed to analyze the associations between birth outcomes and living in a community with a history of informal e-waste recycling.

METHODS

The e-waste Recycling Exposure and Community Health (e-REACH) Study enrolled pregnant women in Guiyu, an informal e-waste recycling site (n = 314), and an unexposed control site (Haojiang) (n = 320) at delivery. We analyzed maternal whole blood samples for lead (Pb), cadmium (Cd), chromium (Cr), and manganese (Mn). We captured data in newborns on birth weight, birth length, head circumference, body mass index (BMI), and Ponderal Index (PI). We compared the birth outcomes between sites after adjustment for covariates, and examined the associations with individual and the mixture of metals.

RESULTS

The neonates from Guiyu had smaller head circumference (adj β -1.96 cm, 95% CI -2.39, -1.52), BMI (adj β -0.77 kg/m2, 95% CI -1.03, -0.51), and PI (adj β -2.01 kg/m3, 95% CI -2.54, -1.47). Birth weights were lower in Guiyu compared to Haojiang, but the difference was not significant (β -51, 95% CI -132, 29). Cumulative exposure to metals was related to lower head circumference, BMI, and PI, but not related to birth weight.

DISCUSSION

We observed slight and statistically significant differences in the head size, BMI, and PI of neonates, but not birth weight, from Guiyu when compared to neonates from Haojiang. Cumulative metal exposure may partially account for the findings.

Verbal Memory and Learning in Schoolchildren Exposed to Manganese in Mexico

Manganese (Mn) is an essential nutrient for cellular function, but in high concentrations, it is neurotoxic. Environmental exposure to Mn has been associated with cognitive effects in children. This study aimed to assess the effect of environmental exposure to Mn on verbal memory and learning in schoolchildren residents from two municipalities in the state of Hidalgo, Mexico. Cross-sectional studies were conducted in 2006 and 2013 with a total of 265 schoolchildren of 7 to 11 years old. Children's Auditory Verbal Learning Test-2 (CAVLT-2) was used to assess verbal memory and learning. Mn exposure tertiles were defined according to hair manganese (MnH) levels determined by atomic absorption spectrophotometry. Linear regression models were used to estimate the association between MnH levels and CAVLT-2 scores. The models were adjusted by potential confounders. The lowest and highest exposure tertiles were defined below and above MnH levels of ≤ 0.72 and ≥ 3.96 μg/g, respectively. Mn exposure was significantly associated with an average of 5- to 9-point decrease in learning curves and summary CAVLT-2 scores in the highest tertile. This study adds to the evidence of decreased verbal memory and learning in schoolchildren environmentally exposed to manganese.

Metal concentrations in pregnant women and neonates from informal electronic waste recycling

Electronic waste (e-waste) is the fastest growing solid waste stream worldwide and mostly ends up in developing countries where residents use primitive methods for recycling. The most infamous e-waste recycling town, Guiyu in Southeast China, has been recycling since the mid-1990s. E-waste contains several harmful chemicals, including lead (Pb), cadmium (Cd), chromium (Cr), and manganese (Mn). In 2011-12, the e-waste Recycling Exposures and Community Health (e-REACH) Study enrolled 634 pregnant women living in Guiyu and Haojiang, a control site, both in Shantou, China. The women completed a questionnaire and gave maternal blood, cord blood, and maternal urine, which were analyzed for Pb, Cd, Cr, and Mn. Maternal blood Pb, Cd, and Cr concentrations were significantly higher in Guiyu compared to Haojiang. In Guiyu, the geometric mean of Pb concentration in maternal blood was 6.66 µg/dL (range: 1.87-27.09 µg/dL) and was 1.74-fold greater than in Haojiang (95% CI: 1.60, 1.89). In cord blood, Pb concentration was 1.53-fold higher in Guiyu (95% CI: 1.38, 1.68). In maternal urine, Cd (ratio: 2.15, 95% CI: 1.72, 2.69) and Mn (ratio: 2.60, 95% CI: 2.04, 3.31) concentrations were significantly higher in Guiyu in comparison to Haojiang. In conclusion, pregnant women in Guiyu were at risk for increased exposure to heavy metals.

A systematic literature review of epidemiologic studies of developmental manganese exposure and neurodevelopmental outcomes

BACKGROUND

Neurotoxic effects of high-level occupational exposure to manganese (Mn) are well established; however, whether lower-level environmental exposure to Mn in early life causes neurodevelopmental toxicity in children is unclear.

METHODS

A systematic literature review was conducted to identify and evaluate epidemiologic studies of specific Mn biomarkers assessed during gestation, childhood, or adolescence in association with neurodevelopmental outcomes, focusing on quantitative exposure-response estimates with specific endpoints that were assessed in multiple independent study populations. Study quality was evaluated using the revised RTI item bank and the Cochrane Risk of Bias tool, and the overall weight of epidemiologic evidence for causality was evaluated according to the Bradford Hill considerations.

RESULTS

Twenty-two epidemiologic studies were identified that estimated associations between early-life Mn biomarkers and neurodevelopmental outcomes. Seven of these studies provided adjusted estimates for the association with child intelligence assessed using versions of the Wechsler Intelligence Scales for Children; no other specific neurodevelopmental endpoints were assessed in more than three independent study populations each. Among the studies of child intelligence, five studies in four independent populations measured blood Mn, three studies measured hair Mn, and one measured dentin Mn. Overall, cross-sectional associations between Mn biomarkers and measures of child intelligence were mostly statistically nonsignificant but in a negative direction; however, the lone prospective cohort study found mostly null results, with some positive (favorable) associations between dentin Mn and child intelligence. Studies were methodologically limited by their cross-sectional design and potential for confounding and selection bias, as well as unaddressed questions on exposure assessment validity and biological plausibility.

CONCLUSIONS

The statistical associations reported in the few studies of specific Mn biomarkers and specific neurodevelopmental endpoints do not establish causal effects based on the Bradford Hill considerations. Additional prospective cohort studies of Mn biomarkers and validated neurodevelopmental outcomes, and a better understanding of the etiologic relevance of Mn biomarkers, are needed to shed light on whether environmental exposure to Mn causes adverse neurodevelopmental effects in children.

Manganese suppresses oxidative stress, inflammation and caspase-3 activation in rats exposed to chlorpyrifos

The present study investigated the individual and combined impact of organophosphorus pesticide chlorpyrifos (CPF) and manganese (Mn), a naturally occurring trace metal, on hepatorenal function in adult rats. The four experimental groups namely control, CPF alone (5 mg/kg), Mn alone (10 mg/kg) and the co-exposure group consisted of eight rats which were orally gavage for 14 consecutive days. Following sacrifice, the biomarkers of hepatorenal damage, antioxidant enzyme activities, myeloperoxidase (MPO) activity as well as levels of nitric oxide, reactive oxygen and nitrogen (RONS) species and lipid peroxidation (LPO) were analysed spectrophotometrically. Further, the concentration of tumour necrosis factor alpha (TNF-α), interleukin-1 β (IL-1β) and caspase-3 activity were assessed using ELISA. Results showed that the CPF-induced increase in biomarkers of hepatorenal toxicity were significantly (p < 0.05) alleviated in rats co-expose to CPF and Mn. Moreover, the decrease in antioxidant status as well as the elevation in RONS and LPO were significantly assuaged in rats co-treated with CPF and Mn. In addition, CPF mediated increase in TNF-α, IL-1β and caspase-3 activity were significantly diminished in the liver and kidney of rats co-exposed to CPF and Mn. Light microscopic examination evidenced that the severity of histopathological lesions induced by CPF were alleviated in rats co-exposed to CPF and Mn. In conclusion, the results highlight that co-exposure to CPF and Mn in rats assuaged CPF-induced oxidative stress, inflammation and caspase-3 activation in the liver and kidney of the rats.

Determinants of Hair Manganese, Lead, Cadmium and Arsenic Levels in Environmentally Exposed Children

Biomarkers of environmental metal exposure in children are important for elucidating exposure and health risk. While exposure biomarkers for As, Cd, and Pb are relatively well defined, there are not yet well-validated biomarkers of Mn exposure. Here, we measured hair Mn, Pb, Cd, and As levels in children from the Mid-Ohio Valley to determine within and between-subject predictors of hair metal levels. Occipital scalp hair was collected in 2009-2010 from 222 children aged 6-12 years (169 female, 53 male) participating in a study of chemical exposure and neurodevelopment in an industrial region of the Mid-Ohio Valley. Hair samples from females were divided into three two centimeter segments, while males provided a single segment. Hair was cleaned and processed in a trace metal clean laboratory, and analyzed for As, Cd, Mn, and Pb by magnetic sector inductively coupled plasma mass spectrometry. Hair Mn and Pb levels were comparable (median 0.11 and 0.15 µg/g, respectively) and were ~10-fold higher than hair Cd and As levels (0.007 and 0.018 µg/g, respectively). Hair metal levels were higher in males compared to females, and varied by ~100-1000-fold between all subjects, and substantially less (<40-70%) between segments within female subjects. Hair Mn, Pb, and Cd, but not As levels systematically increased by ~40-70% from the proximal to distal hair segments of females. There was a significant effect of season of hair sample collection on hair Mn, Pb, and Cd, but not As levels. Finally, hair metal levels reported here are ~2 to >10-fold lower than levels reported in other studies in children, most likely because of more rigorous hair cleaning methodology used in the present study, leading to lower levels of unresolved exogenous metal contamination of hair.

Environmentally relevant manganese overexposure alters neural cell morphology and differentiation in vitro

Manganese (Mn) is a trace metal and micronutrient that is necessary for neurological function. Because of its ability to cross the blood brain barrier, excessive amounts of Mn are neurotoxic and can lead to a neurological disorder, manganism. Environmental overexposure to Mn correlates with impaired cognitive development in children. Though symptoms of manganism and overexposure are well defined, the changes in cellular mechanisms underlying these symptoms are not fully understood. We used cultured adult neural stem cells (NSCs) from young adult rats as an accessible model to investigate the effect of Mn on cellular mechanisms underlying neural differentiation. Concentrations of Mn below current EPA limits caused a dose- and time-dependent collapse of neurites and restructuring of cellular morphology. This effect was confirmed in B35 neuroblastoma cells. These findings indicate that Mn alters cytoskeleton dynamics during differentiation. In addition, Mn overexposure caused downregulation of DCX, a neuronal migration marker, and GFAP, a neural stem cell and astrocyte marker, in NSCs. We conclude that environmentally relevant concentrations of Mn impair cytoskeletal structure and morphology, and may impair differentiation in NSCs. These effects of Mn overexposure on brain cell function could underlie manganism and neurocognitive and developmental defects associated with environmental Mn overexposure.

Acute diesel exhaust exposure and postural stability: a controlled crossover experiment

Recent epidemiological evidence connects ambient air pollutants to adverse neurobehavioural effects in adults. In animal models, subchronic controlled exposures to diesel exhaust (DE) have also showed evidence of neuroinflammation. Evidence suggests that DE not only affects outcomes commonly associated with cognitive dysfunction, but also balance impairment. We conducted a controlled human exposure experiment with 28 healthy subjects (average age = 28 years (SD = 7.1; range = 21-49); and 40% female) who were exposed to two conditions, filtered air (FA) and DE (300 μg PM2.5/m3) for 120 min, in a double-blinded crossover study with randomized exposures separated by four weeks. Postural stability was assessed by the Balance Error Scoring System (BESS), a brief, easily-administered test of static balance. The BESS consists of a sequence of three stances performed on two surfaces. With hands on hips and eyes closed, each stance is held for 20 s. "Error" points are awarded for deviations from those stances. Pre- and immediately post-exposure BESS "error" point totals were calculated and the difference between the two timepoints were compared for each of the two exposure conditions. A mixed effect model assessed the significance of the association. While our data demonstrates a trend of reduced postural stability in response to exposure to DE, exposure was not significantly associated with BESS value. This is the first study to investigate changes in postural stability as a result of exposure to DE in human subjects.

Sex differences in sensitivity to prenatal and early childhood manganese exposure on neuromotor function in adolescents

INTRODUCTION

While studies have suggested that exposure to manganese (Mn) may be associated with neurodevelopment in school-age children, there is limited information on prenatal and postnatal Mn exposures and tremor or motor function in children.

METHODS

We measured Mn levels in dentine of shed teeth, representing prenatal, early postnatal, and cumulative childhood exposure windows, from 195 children (predominantly right-handed, 92%) in Italy. Pursuit Aiming, Luria Nebraska Motor Battery, as well as Tremor and Sway system from Computerized Adaptive Testing System (CATSYS) were administered at 11-14 years old. We examined the relationships of tooth Mn (ln-transformed) with motor function using multivariable linear regressions and generalized additive models, adjusting for age, sex, and socioeconomic status index. Effect modification by sex was also examined.

RESULTS

We found that higher prenatal Mn was associated with better body stability in boys in a number of sway tests (including mean sway, transversal sway, sagittal sway, sway area, and sway intensity), while Mn was associated with poorer performance in girls on all of these metrics (all p for Mn × sex interaction < 0.05). Higher prenatal Mn was also modestly associated with better hand/finger and eye-hand coordination in boys compared to girls in sex-stratified analyses, although interaction models did not reach statistical significance. For tremor, on the other hand, higher early postnatal Mn was associated with increased right-hand center frequency in girls (p for interaction < 0.01), but increased Mn level at the later postnatal period was associated with increased center frequency in boys (p for interaction = 0.01).

CONCLUSIONS

This study, which used a direct measure of prenatal and childhood Mn exposure, suggested sex-specific critical windows of early life Mn exposure in relation to neuromotor function in adolescents. The sex-specific associations might be strongest with measures of whole body stability, for which the critical exposure window was during the prenatal period.

Impact of air manganese on child neurodevelopment in East Liverpool, Ohio

BACKGROUND

East Liverpool, Ohio, the site of a hazardous waste incinerator and a manganese (Mn) processor, has had air Mn concentrations exceeding United States Environmental Protection Agency reference levels for over a decade. Save Our County, Inc., a community organization, was formed to address community environmental health concerns related to local industry. Researchers from the University of Cincinnati partnered with Save Our County to determine if air Mn had an impact on the neurocognitive function of children in the community.

METHODS

Children 7-9 years of age from East Liverpool and its surrounding communities, were enrolled (N=106) in the Communities Actively Researching Exposure Study from between March 2013-June 2014. Blood and hair were analyzed for Mn and lead, and serum was analyzed for cotinine. We used linear regression to assess associations between biological measures and IQ subscale scores.

RESULTS

Geometric mean blood lead (n=67), blood Mn (n=66), hair Mn (n=98), and serum cotinine (n=69) concentrations were 1.13±1.96μg/dL, 10.06±1.30μg/L, and 360.22±2.17ng/g, 0.76±6.12μg/L respectively. After adjusting for potential confounders, hair Mn was negatively associated with Full Scale IQ.

CONCLUSIONS

Hair Mn was negatively associated with child IQ scores. Community partners were instrumental in the conception and implementation of this study.

Association between ambient particulate matter and disorders of vestibular function

BACKGROUND

Exposure to environmental chemicals has been suggested to alter the physiologic state of the inner and middle ear. However, it is unknown if particulate matter exposure is associated with acute vestibular dysfunction.

OBJECTIVES

To estimate the effects of particulate matter exposure on the number of hospital visits related to three major diseases of vestibular dysfunction, Meniere's disease (MD), benign paroxysmal positional vertigo (BPPV), and vestibular neuronitis (VN).

METHODS

Our study subject is from Korean National Health Insurance Service-National Sample Cohort, which is dynamic cohort consist of 1 million participants representing the Korean population. Among total cohort participants, we used the hospital visit data of 210,000 individuals who resided in Seoul from 2007 to 2010. Time series analysis using the Poisson generalized additive model and case-crossover analysis using conditional logistic regression were used to investigate the association between daily particulate matter levels (PM_2.5, particulate matter <2.5μg/m³; PM₁₀, particulate matter <10μg/m³; PM_10-2.5, PM₁₀- PM_2.5) and number of MD, BPPV, and VN hospital visits.

RESULTS

Time series analysis showed that an interquartile range (IQR) increase in PM₁₀ and PM_10-2.5 on lag day 1 was associated with an increased risk of MD hospital visits [relative risk (RR), 95% confidence interval (CI), PM₁₀: 1.09 (1.02-1.15); PM_10-2.5: 1.06 (1.02-1.10)]. In addition, elderly individuals (≥60 years old) showed an increased risk of MD hospital visits after particulate matter exposure when compared to younger individuals. An IQR increase in particulate matter on lag day 1 was associated with a marginally significant increase in VN hospital visits [RR (95%CI), PM_2.5: 1.11 (0.98-1.25); PM₁₀: 1.07 (0.99-1.15); PM_10-2.5: 1.04 (0.99-1.09)]. However, no association between particulate matter exposure and BPPV hospital visits was noted. Case-crossover analyses showed similar results to the time-series analysis across all three diseases.

CONCLUSION

MD hospital visits were associated with ambient particulate matter exposure. Elderly individuals, in particular, were more susceptible to particulate matter exposure than younger individuals.

Sodium para-aminosalicylate protected cultured basal ganglia astrocytes from manganese-induced DNA damages and alteration of amino acid neurotransmitter levels

Sodium para-aminosalicylate (PAS-Na) was first applied successfully in clinical treatment of two manganism patients with good prognosis. However, the mechanism of how PAS-Na protects against Mn-induced neurotoxicity is still elusive. The current study was conducted to explore the effects of PAS-Na on Mn-induced basal ganglia astrocyte injury, and the involvement of amino acid neurotransmitter in vitro. Basal ganglia astrocytes were exposed to 500 μM manganese chloride (MnCl2) for 24 hr, following by 50, 150, or 450 μM PAS-Na treatment for another 24 hr. MnCl2 significantly decreased viability of astrocytes and induced DNA damages via increasing the percentage of tail DNA and Olive tail moment of DNA. Moreover, Mn interrupted amino acid neurotransmitters by decreasing Gln levels and increasing Glu, Gly levels. In contrast, PAS-Na treatment reversed the aforementioned Mn-induced toxic effects on basal ganglia astrocytes. Taken together, our results demonstrated that excessive Mn exposure may induce toxic effects on basal ganglia astrocytes, while PAS-Na could protect basal ganglia astrocytes from Mn-induced neurotoxicity.

Pathways of inhalation exposure to manganese in children living near a ferromanganese refinery: A structural equation modeling approach

Manganese (Mn) is both essential element and neurotoxicant. Exposure to Mn can occur from various sources and routes. Structural equation modeling was used to examine routes of exposure to Mn among children residing near a ferromanganese refinery in Marietta, Ohio. An inhalation pathway model to ambient air Mn was hypothesized. Data for model evaluation were obtained from participants in the Communities Actively Researching Exposure Study (CARES). These data were collected in 2009 and included levels of Mn in residential soil and dust, levels of Mn in children's hair, information on the amount of time the child spent outside, heat and air conditioning in the home and level of parent education. Hair Mn concentration was the primary endogenous variable used to assess the theoretical inhalation exposure pathways. The model indicated that household dust Mn was a significant contributor to child hair Mn (0.37). Annual ambient air Mn concentration (0.26), time children spent outside (0.24) and soil Mn (0.24) significantly contributed to the amount of Mn in household dust. These results provide a potential framework for understanding the inhalation exposure pathway for children exposed to ambient air Mn who live in proximity to an industrial emission source.

Manganese and Developmental Neurotoxicity

Manganese (Mn) is an essential metal that plays a fundamental role for brain development and functioning. Environmental exposure to Mn may lead to accumulation in the basal ganglia and development of Parkinson-like disorders. The most recent research is focusing on early-life overexposure to Mn and the potential vulnerability of younger individuals to Mn toxicity also in regard to cognitive and executive functions through the involvement of the frontal cortex.Neurodevelopmental disturbances are increasing in the society, and understanding the potential role of environmental determinants is a key for prevention. Therefore, assessing the environmental sources of Mn exposure and the mechanisms of developmental neurotoxicity and defining appropriate biomarkers of exposure and early functional alterations represent key issues to improve and address preventive strategies. These themes will be reviewed in this chapter.

"Manganese-induced neurotoxicity: a review of its behavioral consequences and neuroprotective strategies"

Manganese (Mn) is an essential heavy metal. However, Mn’s nutritional aspects are paralleled by its role as a neurotoxicant upon excessive exposure. In this review, we covered recent advances in identifying mechanisms of Mn uptake and its molecular actions in the brain as well as promising neuroprotective strategies. The authors focused on reporting findings regarding Mn transport mechanisms, Mn effects on cholinergic system, behavioral alterations induced by Mn exposure and studies of neuroprotective strategies against Mn intoxication. We report that exposure to Mn may arise from environmental sources, occupational settings, food, total parenteral nutrition (TPN), methcathinone drug abuse or even genetic factors, such as mutation in the transporter SLC30A10. Accumulation of Mn occurs mainly in the basal ganglia and leads to a syndrome called manganism, whose symptoms of cognitive dysfunction and motor impairment resemble Parkinson’s disease (PD). Various neurotransmitter systems may be impaired due to Mn, especially dopaminergic, but also cholinergic and GABAergic. Several proteins have been identified to transport Mn, including divalent metal tranporter-1 (DMT-1), SLC30A10, transferrin and ferroportin and allow its accumulation in the central nervous system. Parallel to identification of Mn neurotoxic properties, neuroprotective strategies have been reported, and these include endogenous antioxidants (for instance, vitamin E), plant extracts (complex mixtures containing polyphenols and non-characterized components), iron chelating agents, precursors of glutathione (GSH), and synthetic compounds that can experimentally afford protection against Mn-induced neurotoxicity.

Effects of manganese exposure on visuoperception and visual memory in schoolchildren

BACKGROUND

Manganese (Mn) is an essential metal involved in multiple physiological functions. Environmental exposure to airborne Mn is associated with neurocognitive deficits in humans. Children, whose nervous system is in development, are particularly susceptible to Mn neurotoxicity.

OBJECTIVE

The objective of this study was to assess the association between Mn environmental exposure, and effects on visuoperception and visual memory in schoolchildren.

METHODS

We assessed schoolchildren between 7 and 11 years old, with similar socioeconomic status, from the mining district of Molango (n=148) and Agua Blanca (n=119, non-mining area) in Hidalgo state, Mexico. The Rey-Osterrieth Complex Figure (ROCF) test was used to assess visuoperception and short-term visual memory. Hair manganese (MnH) concentrations were determined. Linear regression models were constructed to estimate the associations between MnH and ROCF scores, adjusted for potential confounders.

RESULTS

The geometric mean MnH was nine times higher in schoolchildren from the Mn mining area (5.25μg/g) than in schoolchildren from the non-mining area (0.55μg/g). For the ROCF Copy trial, MnH was significantly associated with an increase in distortion errors (tangency, closure), angle errors, overtracing (partial overtracing). In the Immediate Recall trial, MnH was significantly associated with increased overtracing (partial overtracing) and omissions, and negatively associated with the number of perceptual drawn units, total score and percentage immediate recall.

CONCLUSIONS

MnH is associated with alterations in visuoperception and short-term visual memory in schoolchildren exposed to airborne Mn.

Comparison of stationary and personal air sampling with an air dispersion model for children's ambient exposure to manganese

Manganese (Mn) is ubiquitous in the environment and essential for normal growth and development, yet excessive exposure can lead to impairments in neurological function. This study modeled ambient Mn concentrations as an alternative to stationary and personal air sampling to assess exposure for children enrolled in the Communities Actively Researching Exposure Study in Marietta, OH. Ambient air Mn concentration values were modeled using US Environmental Protection Agency's Air Dispersion Model AERMOD based on emissions from the ferromanganese refinery located in Marietta. Modeled Mn concentrations were compared with Mn concentrations from a nearby stationary air monitor. The Index of Agreement for modeled versus monitored data was 0.34 (48 h levels) and 0.79 (monthly levels). Fractional bias was 0.026 for 48 h levels and -0.019 for monthly levels. The ratio of modeled ambient air Mn to measured ambient air Mn at the annual time scale was 0.94. Modeled values were also time matched to personal air samples for 19 children. The modeled values explained a greater degree of variability in personal exposures compared with time-weighted distance from the emission source. Based on these results modeled Mn concentrations provided a suitable approach for assessing airborne Mn exposure in this cohort.

Ergonomics and Beyond: Understanding How Chemical and Heat Exposures and Physical Exertions at Work Affect Functional Ability, Injury, and Long-Term Health

OBJECTIVE

To honor Tom Waters's work on emerging occupational health issues, we review the literature on physical along with chemical exposures and their impact on functional outcomes.

BACKGROUND

Many occupations present the opportunity for exposure to multiple hazardous exposures, including both physical and chemical factors. However, little is known about how these different factors affect functional ability and injury. The goal of this review is to examine the relationships between these exposures, impairment of the neuromuscular and musculoskeletal systems, functional outcomes, and health problems with a focus on acute injury.

METHOD

Literature was identified using online databases, including PubMed, Ovid Medline, and Google Scholar. References from included articles were searched for additional relevant articles.

RESULTS

This review documented the limited existing literature that discussed cognitive impairment and functional disorders via neurotoxicity for physical exposures (heat and repetitive loading) and chemical exposures (pesticides, volatile organic compounds [VOCs], and heavy metals).

CONCLUSION

This review supports that workers are exposed to physical and chemical exposures that are associated with negative health effects, including functional impairment and injury. Innovation in exposure assessment with respect to quantifying the joint exposure to these different exposures is especially needed for developing risk assessment models and, ultimately, preventive measures.

APPLICATION

Along with physical exposures, chemical exposures need to be considered, alone and in combination, in assessing functional ability and occupationally related injuries.

Community Engagement and Data Disclosure in Environmental Health Research

Federal funding agencies increasingly support stakeholder participation in environmental health studies, and yet there is very little published research on engagement of community members in the development of data disclosure (DD) strategies. The Ohio Environmental Protection Agency reported airborne manganese (Mn) concentrations in East Liverpool, Ohio, 30 times higher than the reference concentration, which led to an academic–community research partnership to address community concern about Mn exposure, particularly among children. Children and their families were recruited to participate in a pilot study. Samples of blood and hair were collected from the children and analyzed for metals. DD mechanisms were developed using an iterative approach between community and academic partners. Individual DD letters were mailed to each participating family, and a community meeting was held. A post-meeting survey was administered to gauge community perception of the DD strategies. The purpose of this article is to demonstrate the effectiveness of engaging community partners in the conduct of environmental health research and in the development of DD strategies for individuals and the community at large. Scientists should include community partners in the development of DD strategies to enhance translation of the research findings and support the right of study participants to know their individual results.

Common Polymorphisms in the Solute Carrier SLC30A10 are Associated With Blood Manganese and Neurological Function

Manganese (Mn) is an essential nutrient in humans, but excessive exposure to Mn may cause neurotoxicity. Despite homeostatic regulation, Mn concentrations in blood vary considerably among individuals. We evaluated if common single-nucleotide polymorphisms (SNPs) in SLC30A10, which likely encodes an Mn transporter, influence blood Mn concentrations and neurological function. We measured blood Mn concentrations by ICP-MS or atomic absorption spectroscopy and genotyped 2 SLC30A10 non-coding SNPs (rs2275707 and rs12064812) by TaqMan PCR in cohorts from Bangladesh (N = 406), the Argentinean Andes (N = 198), and Italy (N = 238). We also measured SLC30A10 expression in whole blood by TaqMan PCR in a sub-group (N = 101) from the Andean cohort, and neurological parameters (sway velocity and finger-tapping speed) in the Italian cohort. The rs2275707 variant allele was associated with increased Mn concentrations in the Andes (8%, P = .027) and Italy (10.6%, P = .012), but not as clear in Bangladesh (3.4%, P = .21; linear regression analysis adjusted for age, gender, and plasma ferritin). This allele was also associated with increased sway velocity (15%, P = .033; adjusted for age and sex) and reduced SLC30A10 expression (−24.6%, P = .029). In contrast, the rs12064812 variant homozygous genotype was associated with reduced Mn concentrations, particularly in the Italian cohort (−18.4%, P = .04), and increased finger-tapping speed (8.7%, P = .025). We show that common SNPs in SLC30A10 are associated with blood Mn concentrations in 3 unrelated cohorts and that their influence may be mediated by altered SLC30A10 expression. Moreover, the SNPs appeared to influence neurological functions independent of blood Mn concentrations, suggesting that SLC30A10 could regulate brain Mn levels.

Manganese Exposure and Neurocognitive Outcomes in Rural School-Age Children: The Communities Actively Researching Exposure Study (Ohio, USA)

BACKGROUND

Manganese (Mn) plays a vital role in brain growth and development, yet excessive exposure can result in neurotoxicity. Marietta, Ohio, is home to the nation's longest-operating ferromanganese refinery, and community concern about exposure led to the development of the research study.

OBJECTIVES

Our overall goal was to address the community's primary research question: "Does Mn affect cognitive development of children?" We evaluated the relationships between Mn exposure as measured by blood and hair Mn, along with other neurotoxicants including blood lead (Pb) and serum cotinine, and child cognition.

METHODS

Children 7-9 years of age were enrolled (n = 404) in the Communities Actively Researching Exposure Study (CARES) from Marietta and Cambridge, Ohio, and their surrounding communities from October 2008 through March 2013. Blood and hair were analyzed for Mn and Pb, and serum was analyzed for cotinine. We used penalized splines to assess potential nonlinear associations between biological measures and IQ subscale scores, followed by multivariable regression models with categorical variables based on quartiles of the distribution for biological measures with nonlinear associations and continuous variables for biological measures with linear associations.

RESULTS

Geometric mean blood (n = 327) and hair Mn (n = 370) concentrations were 9.67 ± 1.27 μg/L and 416.51 ± 2.44 ng/g, respectively. After adjusting for potential confounders, both low and high blood and hair Mn concentrations were associated with lower Full Scale IQ and subscale scores, with significant negative associations between the highest quartile and middle two quartiles of blood Mn (β -3.51; 95% CI: -6.64, -0.38) and hair Mn (β -3.66; 95% CI: -6.9, -0.43%) and Full Scale IQ.

CONCLUSIONS

Both low and high Mn concentrations in blood and hair were negatively associated with child IQ scores. Serum cotinine was negatively associated with child cognitive function.

Secondhand Tobacco Smoke Exposure and Neuromotor Function in Rural Children

OBJECTIVE

To investigate the relationship between secondhand tobacco smoke (SHS) exposure and neuromotor function in children.

STUDY DESIGN

We studied 404 children aged 7-9 years who were exposed to SHS and other environmental neurotoxicants. Parents reported smoking habits, and serum cotinine levels were measured in children to determine SHS exposure. The Halstead-Reitan Finger Oscillation Test, Purdue Grooved Pegboard Test-Kiddie version, and Bruininks-Oseretsky Test of Motor Proficiency 2-Short Form were used to assess neuromotor function. Multivariable regression models that accounted for potential confounders were used to evaluate the associations.

RESULTS

Approximately 50% of the children were exposed to SHS based on serum cotinine measures. Exposure to SHS was significantly associated with motor impairment in children, including diminished visuomotor coordination (P = .01), fine motor integration (P = .01), balance (P = .02), and strength (P = .04) after adjusting for exposures to lead and manganese, age, sex, body mass index, measures of parental cognitive abilities, parental education, and quality of home environment.

CONCLUSION

SHS is a neurotoxicant that may be associated with impaired childhood neuromotor function.

Oral methylphenidate alleviates the fine motor dysfunction caused by chronic postnatal manganese exposure in adult rats

Developmental manganese (Mn) exposure is associated with motor dysfunction in children and animal models, but little is known about the underlying neurochemical mechanisms or the potential for amelioration by pharmacotherapy. We investigated whether methylphenidate (MPH) alleviates fine motor dysfunction due to chronic postnatal Mn exposure, and whether Mn exposure impairs brain extracellular dopamine (DA) and norepinephrine (NE) in the prefrontal cortex (PFC) and striatum in adult animals. Rats were orally exposed to 0 or 50 mg Mn/kg/day from postnatal day 1 until the end of the study (PND 145). The staircase test was used to assess skilled forelimb function. Oral MPH (2.5 mg/kg/day) was administered daily 1 h before staircase testing for 16 days. DA and NE levels were measured by dual probe microdialysis. Results show that Mn exposure impaired reaching and grasping skills and the evoked release of DA and NE in the PFC and striatum of adult rats. Importantly, oral MPH treatment fully alleviated the fine motor deficits in the Mn-exposed animals, but did not affect forelimb skills of control rats not exposed to Mn. These results suggest that catecholaminergic hypofunctioning in the PFC and striatum may underlie the Mn-induced fine motor dysfunction, and that oral MPH pharmacotherapy is an effective treatment approach for alleviating this dysfunction in adult animals. The therapeutic potential of MPH for the treatment of motor dysfunction in Mn-exposed children and adults appears promising pending further characterization of MPH efficacy in other functional areas (eg, attention) believed to be affected by developmental Mn exposure.

Copper-based electrochemical sensor with palladium electrode for cathodic stripping voltammetry of manganese

In this work, we report on the development of a palladium-based, microfabricated point-of-care electrochemical sensor for the determination of manganese using square wave cathodic stripping voltammetry. Heavy metals require careful monitoring, yet current methods are too complex for a point-of-care system. Voltammetry offers an attractive approach to metal detection on the microscale, but traditional carbon, gold, or platinum electrodes are difficult or expensive to microfabricate, preventing widespread use. Our sensor uses palladium working and auxiliary electrodes and integrates them with a copper-based reference electrode for simple fabrication and compatibility with microfabrication and printed circuit board processing, while maintaining competitive performance in electrochemical detection. Copper electrodes were prepared on glass substrate using a combination of microfabrication procedures followed by electrodeposition of palladium. The disposable sensor system was formed by bonding a poly(dimethylsiloxane) (PDMS) well to the glass substrate. Cathodic stripping voltammetry of manganese using our new disposable palladium-based sensors exhibited 334 nM (18.3 ppb) limit of detection in borate buffer. The sensor was used to demonstrate manganese determination in natural water samples from a pond in Burnet Woods, located in Cincinnati, OH, and the Ohio River.