A neurobehavioral study of current and former welders exposed to manganese

Effects of mixed metal exposure on MRI metrics in basal ganglia

Welding fumes contain various metals. Past studies, however, mainly focused on Manganese (Mn)-related neurotoxicity. This study investigated welding-related mixed metal exposure effects on MRI metrics in the basal ganglia (BG) and their dose-response relationship. Subjects with (N = 23) and without (N = 24) a welding exposure history were examined. Metal exposure was estimated with an exposure history questionnaire and whole blood metal levels. T1 (weighted-intensity and relaxation time; estimates of brain Mn accumulation), diffusion tensor imaging (axial [AD], mean [MD], radial diffusivity, and fractional anisotropy [FA]; estimates of microstructural differences) metrics in BG (caudate nucleus, putamen, and globus pallidus [GP]), and voxel-based morphometry (for volume) were examined and related with metal exposure measures. Compared with controls, welders showed higher GP R1 (1/T1; P = 0.034) but no differences in blood metal and T1-weighted (T1W) values in any ROIs (P's > 0.120). They also had higher AD and MD values in the GP (P's < 0.033) but lower FA values in the putamen (P = 0.039) with no morphologic differences. In welders, higher blood Mn and Vanadium (V) levels predicted higher BG R1 and T1W values (P's < 0.015). There also were significant overall metal mixture effects on GP T1W and R1 values. Moreover, GP AD and MD values showed nonlinear associations with BG T1W values: They increased with increasing T1W values only above certain threshold of T1 values. The current findings suggest that Mn and V individually but also metal mixtures jointly predict GP T1 signals that may in turn contribute to altered DTI metrics in the BG after certain exposure threshold levels.

Manganese exposure and cognitive performance: A meta-analytical approach

Occupational manganese exposure is associated with serious health concerns, ultimately leading to an illness called manganism. Competing meta-analytic results were published over a decade ago, ranging from undetectable to serious effects on cognitive performance among working adults. Novel studies and findings about the relationship between occupational manganese and cognitive functions have been proposed since. First of all, a systematic literature search was carried out until October 2022 via multiple electronic databases investigating the relationship between occupational manganese exposure and cognitive functions. Differences between the exposure and control groups in cognitive testing were synthesized by effect size Hedge's g. A random effects model was deployed with a restricted likelihood estimator using Hedges' invariance weighting. Publication bias, p-hacking and exposure-effect relationships were investigated. We included 18 studies with 75 effect sizes comparing n = 888 controls and 1092 exposed participants. After exclusion of outliers, we found significantly lower performances in processing speed, attention, working memory, reaction time, cognitive control and visual attention in workers exposed to manganese. Regression analysis revealed an indication of exposure-effect relationships between manganese exposure and cognitive functioning in exposed workers. We provide results of impaired cognitive functions for working adults exposed to manganese in processing speed, attention, working memory, reaction time and visual attention. Indications of quadratic exposure-effect relationships are discussed. We provide several recommendations for further studies to investigate possible exposure effects in the context of occupational health and safety.

Synergic control in asymptomatic welders during multi-finger force exertion and load releasing while standing

Motor synergies, i.e., neural mechanisms that organize multiple motor elements to ensure stability of actions, are affected by several neurological condition. Asymptomatic welders showed impaired synergy controlling the stability of multi-finger action compared to non-welders and this impairment was associated with microstructural damage in the globus pallidus. We further explored the effect of welding-related metal exposure on multi-finger synergy and extended our investigation to posture-stabilizing synergy during a standing task. Occupational, MRI, and performance-stabilizing synergies during multi-finger accurate force production and load releasing while standing were obtained from 29 welders and 19 age- and sex-matched controls. R2* and R1 relaxation rate values were used to estimate brain iron and manganese content, respectively, and diffusion tensor imaging was used to reflect brain microstructural integrity. Associations of brain MRI (caudate, putamen, globus pallidus, and red nucleus), and motor synergy were explored by group status. The results revealed that welders had higher R2* values in the caudate (p = 0.03), putamen (p = 0.01), and red nucleus (p = 0.08, trend) than controls. No group effect was revealed on multi-finger synergy index during steady-state phase of action (ΔVZss). Compared to controls, welders exhibited lower ΔVZss (-0.106 ± 0.084 vs. 0.160 ± 0.092, p = 0.04) and variance that did not affect the performance variable (VUCM, 0.022 ± 0.003 vs. 0.038 ± 0.007, p = 0.03) in the load releasing, postural task. The postural synergy index, ΔVZss, was associated negatively with higher R2* in the red nucleus in welders (r = -0.44, p = 0.03), but not in controls. These results suggest that the synergy index in the load releasing during a standing task may reflect welding-related neurotoxicity in workers with chronic metals exposure. This finding may have important clinical and occupational health implications.

Current issues of protection of reproductive health in population residing in cold climate regions (literature review)

Relevance. 40% of the total number of employees are constantly or periodically engaged in work in open areas and in unheated industrial premises. Given that more than 70% of the country’s territory is in cold climate areas, the tasks of preserving their health are a priority. The original articles on the assessment of adverse effects of natural and climatic factors in cold climate regions on the reproductive health of the population, presented in databases and information systems: RSCI, CyberLeninka, Scopus, Web of Science and meeting the criteria for compliance with the stated purpose and quality of research, were analyzed. A significant part of reproductive losses has been proven to be related to the exposure to a number of occupational risk factors; however, workers’ engagement in outdoor operations with a higher risk of cold stress in combination with other factors remains one of the least studied problems of preventive medicine. Considering more than 70% of the country’s territory to be represented by cold climate regions, where up to 40% of the total workforce are permanently or periodically engaged in outdoor works and in unheated industrial premises, the protection of their health is a national priority. A total of two hundred three full-text publications were identified by targeted search, of which 132 fully met these inclusion criteria. Conclusion. As a result of a systematic review of published works available in national and international bibliographic indexing systems, including the results of our own research, engagement in work operations in cold climate regions has been proved to be associated with the risk of functional overstrain of most human life-supporting systems leading to health impairments. To date, there have been identified a significant number of occupational risk factors including chemical, physical, biological, psycho-emotional and ergonomic ones that might induce adverse effects on the reproductive health of women and men such as acute and chronic damage to reproductive functions, fetal development impairment and increased early perinatal mortality. At the same time, the role of cooling weather and climatic factors in the occurrence of such disorders, primarily among workers who systematically perform work operations outside heated industrial premises in cold climate regions there is least studied.

Biomarkers for occupational manganese exposure

Long-term inhalation exposure to manganese (Mn) metal or its inorganic compounds can result in manganism or subclinical neurofunctional deficits. Studies have described affected workers in Mn dioxide mining, Mn-containing ore crushing and milling facilities, manufacturing of dry-cell batteries, Mn steel and alloy production plants, and in welders. The objective of this study was to critically review existing evidence on the reliability of potential biomarkers of Mn exposure, specifically the relationship between inhalation exposure to Mn particulates in different occupational settings and Mn concentrations in blood and other biological fluids and tissues, with a particular focus on whole blood as a potentially useful medium for measuring internal tissue dose. We also examined available evidence on the relationship between Mn levels in blood and adverse clinical and subclinical neurotoxic outcomes. Three bibliographic databases were searched for relevant studies and identified references were screened by two independent reviewers. Of the 6338 unique references identified, 76 articles were retained for data abstraction. Findings indicate that the relationships between Mn in blood and both external Mn exposure indices and neurofunctional impairments are limited and inconsistent. Different sources of exposure to Mn compounds, heterogeneity in the methodological approaches, and inadequate reporting of essential information limited direct comparison of the reported findings. Among the Mn-exposure biomarkers considered in this review - including biomarkers in blood, plasma, serum, erythrocytes, urine, bone, toenails, fingernails, hair, saliva - biomarkers in whole blood may provide to be most useful in Mn biomonitoring and risk assessment.

Risk evaluation of occupational exposure of southern Brazilian flower farmers to pesticides potentially leading to cholinesterase inhibition and metals exposure

This work presents a frequency matched observational study comparing flower farmers exposed to pesticides and unexposed individuals as controls. All subjects were interviewed before plasma and urine collection. Manganese and Zinc were measured in theses samples by using dynamic reaction cell inductively coupled mass spectrometry. Cholinesterase activity was analyzed through spectrophotometry by using a modified version of the Ellman method. Seventy-eight percent of subjects reported occupational contact with pesticides, from which 37% reported exposure for over 9 years. Flower farms farmers had increased odds of having headache and irritability, respectively, by factors of 6.2 and 2.4 than the control subjects. While the odds of exposed subjects to have insomnia was smaller than control subjects by a factor of 0.34. Exposure to pesticides had a significant effect regarding the plasmatic plasma and urinary manganese levels and whole blood cholinesterase activity (p < 0.05). High levels of plasma and urinary manganese, as well as cholinesterase inhibition in whole blood, were evident in the flower farmers who participated in the study.

Higher R2* in the Red Nucleus Is Associated With Lead Exposure in an Asymptomatic Welder Cohort

Lead is a nonessential metal and may be a coexposure in welding fumes. Preclinical data indicate lead may affect iron regulation. The current study investigated blood lead concentrations and their association with brain iron accumulation in workers with chronic welding fume exposure, with a focus on iron-rich subcortical regions of the cerebellum and basal ganglia. Occupational exposure, whole blood metal, and brain MRI data were obtained from 29 controls and 42 welders. R2* (1/T2*) and R1 (T1 relaxation rate) values were used to estimate brain iron and manganese content, respectively. Blood metals and brain R2* (in the red nucleus [RN], dentate nucleus, caudate, putamen, globus pallidus, and substantia nigra) were compared between groups. Associations between brain R2* values and exposure metrics were tested within each group, and analyses were adjusted for potential confounders. Welders had significantly higher levels of whole blood lead, manganese, iron, and copper. Welders also had higher R2* RN (p = .002), but not R1. A 2nd-order polynomial modeled the association between R2* RN and a long-term welding exposure metric. In welders, but not controls, R2* RN was associated positively with whole blood lead (r = 0.54, p = .003), and negatively with whole blood manganese (r = -0.43, p = .02). Higher blood Pb and lower blood Mn independently accounted for variance in high RN R2*. Together, these data suggest that higher RN R2* values may mark lead exposure in welders. Because lead is a known neurotoxicant, additional studies are warranted to confirm this finding, and ascertain its scientific and public/occupational health implications.

Elevated Whole Blood Manganese is Associated with Impaired Cognition in Older Adults, NHANES 2013 - 2014 cycle

Manganese (Mn) is found in many commonly consumed foods and therefore its deficiency is rare. However, excessive exposure to Mn from contaminated drinking water as well as occupational exposure can result in toxic accumulation in the brain, which has been associated with impaired neurological function. The objective of this study was to examine the NHANES 2013 - 2014 cycle focusing on the relationship between whole blood Mn concentrations and cognitive tests including working memory, word recall and sustained attention in elderly adults (aged 60 years and older). The different cognitive function test scores were used in principal component analysis to develop a composite score. The relationship between blood Mn concentration and cognitive function (principal component score and Digit Symbol Substitution Test (DSST)) were investigated using regression analysis. Median (95% CI) concentrations of blood Mn, serum copper, and serum iron were 8.76 (8.5, 9.1) µg/L, 114.9µg/dL (110.3, 118.1), and 80 (78, 83) µg/dL, respectively. We found that among individuals in the highest quartile of blood Mn concentration (>11.18µg/L), there was an inverse association between blood Mn and cognitive function as assessed using DSST (β (95% CI) = -0.76 (-1.19- -0.33); p=0.003), while the inverse relationship with the composite score trended towards significance (β (95% CI) = -0.04 (-0.08- 0.00); p=0.053). These findings suggest that having elevated blood Mn may be associated with cognitive decline in aging and warrants further studies on how the different sources of Mn may contribute to this outcome.

Occupational Exposure to Manganese Among Welders: Association Between Airborne Manganese Concentration and Blood Manganese Levels

Background: Manganese (Mn) is an essential element for the human body, but it can cause adverse effects on the Central Nervous System at high doses. Exposure to manganese fumes during welding can harm welders' health. Objectives: The current study aimed to measure manganese produced by shielded metal arc welding (SMAW) in the breathing zone air and blood of welders and investigate the relationship between manganese concentrations in air and blood. Methods: In this descriptive-analytical cross-sectional study, 35 welders were enrolled as the exposed group and 40 office workers as the control group. Manganese concentration in air was measured according to NIOSH method 7301. Air and blood sample analyses were carried out by ICP-OES. Statistical analysis was performed with MINITAB 17. Data were analyzed using Pearson correlation coefficient, one-sample t-test, paired t-test, and logistic regression. The significance level was set at P < 0.05. Result: The mean concentration of welding respirable particles and manganese fumes were 9.56 ± 1.67 and 0.45 ± 0.08 mg/m3, three and 22 times the exposure limit recommended by ACGIH, respectively. Average manganese was significantly higher in the welders’ blood (0.16 ± 0.02 µg/mL) than in the controls’ blood (0.04 ± 0.002 µg/mL). There were strong and significant correlations between the welding respirable particles and manganese concentration in welders’ breathing zone and blood manganese levels. Also, with each year of work experience, the manganese concentration in the welders’ blood increased by 1.5%. Conclusions: Welders are at risk of contamination with manganese. Manganese exposure reduction through more efficient ventilation systems, reducing welder’s exposure time, staff training, and appropriate respiratory protection equipment should be applied to reduce manganese exposure among welders and prevent health complications.

Mixed metals exposure and cognitive function in Bangladeshi adolescents

BACKGROUND

Over 57 million people in Bangladesh have been chronically exposed to arsenic-contaminated drinking water. They also face environmental exposure to elevated levels of cadmium (Cd), manganese (Mn), and lead (Pb), all of which have been previously observed in environmental and biological samples for this population. These metals have been linked to adverse neurocognitive outcomes in adults and children, though their effects on adolescents are not yet fully characterized. Additionally, previous studies have linked selenium (Se) to protective effects against the toxicity of these other metals.

OBJECTIVES

To examine the associations between mixed metals exposure and cognitive function in Bangladeshi adolescents.

METHODS

The Metals, Arsenic, & Nutrition in Adolescents study (MANAs) is a cross-sectional study of 572 Bangladeshi adolescents aged 14-16 years, whose parents were enrolled in the Health Effects of Arsenic Longitudinal Study (HEALS). Biosamples were collected from these adolescents for measurement of whole blood metalloid/metal levels of As, Cd, Mn, Pb, and Se. Participants also completed an abbreviated version of The Cambridge Neuropsychological Test Automated Battery (CANTAB), a cognitive function test designed to measure performance across several aspects of executive function. Linear regression was used to examine associations for each metal while controlling for the other metals. Bayesian Kernel Machine Regression (BKMR) assessed the overall mixture effect in addition to confirming the effects of individual metal components observed via linear regression.

RESULTS

Linear regression revealed negative associations for Spatial Working Memory and both As and Mn (As B=-2.40, Mn B=-5.31, p < 0.05). We also observed negative associations between Cd and Spatial Recognition Memory (B=-2.77, p < 0.05), and Pb and Delayed Match to Sample, a measure of visual recognition and memory (B=-3.67, p < 0.05). Finally, we saw a positive association for Se and Spatial Span Length (B=0.92, p < 0.05). BKMR results were largely consistent with the regression analysis, showing meaningful associations for individual metals and CANTAB subtests, but no overall mixture effect. Via BKMR, we observed negative associations between Pb and Delayed Match to Sample, and Cd and Spatial Recognition Memory; this analysis also showed positive associations for Se and the Planning, Reaction Time, and Spatial Span subtests. BKMR posterior inclusion probability consistently reported that Se, the only component of the mixture to show a positive association with cognition, was the most important member of the mixture.

CONCLUSIONS

Overall, we found Se to be positively associated with cognition, while Mn and As were linked to poorer working memory, and Cd and Pb were associated with poorer visual recognition and memory. Our observations are consistent with previous reports on the effects of these metal exposures in adults and children. Our findings also suggest agreement between linear regression and BKMR methods for analyzing metal mixture exposures. Additional studies are needed to evaluate the impact of mixed metals exposure on adverse health and poorer cognition later in life for those exposed during adolescence. Findings also suggest that metal exposure mitigation efforts aimed at adolescents might influence lifelong cognitive outcomes in regions where environmental exposure to metals is endemic.

The association of bone and blood manganese with motor function in Chinese workers

Manganese (Mn) is an essential element. However, Mn overexposure is associated with motor dysfunction. This cross-sectional study assessed the association between bone Mn (BnMn) and whole blood Mn (BMn) with motor function in 59 Chinese workers. BnMn and BMn were measured using a transportable in vivo neutron activation analysis system and inductively coupled plasma mass spectrometry, respectively. Motor function (manual coordination, postural sway, postural hand tremor, and fine motor function) was assessed using the Coordination Ability Test System (CATSYS) and the Purdue Pegboard. Relationships between Mn biomarkers and motor test scores were analyzed with linear regression models adjusted for age, education, current employment, and current alcohol consumption. BMn was significantly inversely associated with hand tremor intensity (dominant hand (β=-0.04, 95 % confidence interval (CI):-0.07, -0.01; non-dominant hand β=-0.05, 95 % CI:-0.08, -0.01) hand tremor center frequency (non-dominant hand β=-1.61, 95 % CI:-3.03, -0.19) and positively associated with the Purdue Pegboard Assembly Score (β = 4.58, 95 % CI:1.08, 8.07). BnMn was significantly inversely associated with finger-tapping performance (non-dominant hand β=-0.02, 95 % CI:-0.04,-0.004), mean sway (eyes closed and foam β=-0.68, 95 % CI:-1.31,-0.04), and positively associated with hand tremor center frequency (dominant hand, β = 0.40, 95 % CI:0.002, 0.80). These results suggest BMn is related to better postural hand tremor and fine motor control and BnMn is related to worse motor coordination and postural hand tremor but better (i.e., less) postural sway. The unexpected positive results might be explained by choice of biomarker or confounding by work-related motor activities. Larger, longitudinal studies in this area are recommended.

Biomonitoring of toxic metals, organochlorine pesticides, and polybrominated biphenyl 153 in Michigan urban anglers

The 32-mile Detroit River and surrounding tributaries have been designated as a Great Lakes Area of Concern due to pollution from decades of municipal and industrial discharges, sewer overflows and urban development. The Agency for Toxic Substances and Disease Registry and the Michigan Department of Health and Human Services conducted a biomonitoring study to assess exposures to persistent toxic substances in Detroit urban shoreline anglers who may be at high exposure risk due to consumption of locally caught fish. Using a modified venue-based sampling approach, 287 adult shoreline anglers along the Detroit River were recruited and participated in the program. Study participants provided blood and urine specimens and completed a questionnaire interview. In this report, we examine percentile estimates for blood lead, blood manganese, urine arsenic, urine mercury, urine cadmium, organochlorine pesticides in serum (mirex, hexachlorobenzene, chlordane), and serum polybrominated biphenyl 153 (PBB 153) concentrations among study participants. Multiple linear regression was used to identify predictors of contaminant concentrations. The Detroit urban anglers' blood lead concentrations were 2 times higher than the general adult U.S. population (median (95% CI): 2.9 μg/dL (1.8-2.3) vs. 0.94 μg/dL (0.90-0.98)). PBB 153 levels were 1.8 times higher than the general adult U.S. population at the 95th percentile (95th percentile, 95% CI: 62.7 ng/g of lipid, 53.2-75.2 vs. 34.6 ng/g of lipid, 12.8-66.8). Percentile estimates of the other study pollutants were similar to background levels found in the general U.S. population. Eating more locally caught fish was not associated with increased body burdens for any of the contaminants examined in this report. Higher blood lead was associated with increased age, male sex, current smoking, residing in a home built before 1960, an annual income less than $25,000, and a work history of lead paint removal. Evidence of PBB exposure in our study cohort likely reflects the continued effect of a widespread contamination of livestock feed in 1973 among Michigan's lower peninsula population. These study results help determine if the pollutants examined warrant further consideration in subsequent population-based biomonitoring of frequent consumers of fish from the Detroit River and surrounding waterways. The biomonitoring data from this study also served to inform public health officials regarding the potential need for environmental public health actions to reduce harmful exposures.

Particle characterisation and bioaccessibility of manganese in particulate matter in silico- and ferromanganese smelters

The aim of this study was to characterise particulate matter (PM) collected in the furnace area during SiMn and high carbon (HC)-FeMn production in terms of single particle analysis and to determine the bioaccessibility of Mn in the PM in a simulated lung fluid. Airborne PM was collected with Sioutas cascade impactors and respirable cyclones in the breathing zone of tappers and crane operators. Stationary samples were collected from the furnace area with a nanoMOUDI cascade impactor and an ESPnano electrostatic particle collector. Individual particles were characterised by scanning and transmission electron microscopy. Bioaccessibility of Mn was studied in terms of the dissolution of Mn in Gamble solution (24 hours leaching at 37 °C) relative to total Mn. Slag particles, alloy fragments, Mn and Fe oxides as well as carbonaceous particles were observed in the size fraction > 1 μm aerodynamic diameter (d_ae). Thermally generated condensation particles dominated the d_ae size range of 0.18-1 μm collected from the tapping fumes, while carbonaceous particles dominated the fraction below 0.18 μm. Condensation generated particles from the furnace area of HC-FeMn production were coated with an amorphous Si-O rich surface layer which seemed to hold primary particles together as aggregates. In the same size range, the particles from the furnace area of SiMn production were dominated by spherical condensation particles rich in Si, Mn and O, but without a Si-O rich surface layer. Instead, the Mn oxides were enclosed in an amorphous Si-O rich matrix. The bioaccessibility of Mn was low to moderate (<30%), but higher for SiMn furnace workers (highest median = 23%) than HC-FeMn furnace workers (highest median = 12%). This difference in bioaccessibility was significant for PM with d_ae up to 2.5 μm, and most pronounced in the d_ae size range between 0.25 and 1.0 μm. Also, a significantly higher bioaccessibility of Mn was found for PM larger than d_ae of 0.5 μm collected among crane operators compared to tappers in the HC-FeMn smelter.

Role of Oxidative Stress in the Pathogenesis of Amyotrophic Lateral Sclerosis: Antioxidant Metalloenzymes and Therapeutic Strategies

Amyotrophic lateral sclerosis (ALS) affects motor neurons in the cerebral cortex, brainstem and spinal cord and leads to death due to respiratory failure within three to five years. Although the clinical symptoms of this disease were first described in 1869 and it is the most common motor neuron disease and the most common neurodegenerative disease in middle-aged individuals, the exact etiopathogenesis of ALS remains unclear and it remains incurable. However, free oxygen radicals (i.e., molecules containing one or more free electrons) are known to contribute to the pathogenesis of this disease as they very readily bind intracellular structures, leading to functional impairment. Antioxidant enzymes, which are often metalloenzymes, inactivate free oxygen radicals by converting them into a less harmful substance. One of the most important antioxidant enzymes is Cu²⁺Zn²⁺ superoxide dismutase (SOD1), which is mutated in 20% of cases of the familial form of ALS (fALS) and up to 7% of sporadic ALS (sALS) cases. In addition, the proper functioning of catalase and glutathione peroxidase (GPx) is essential for antioxidant protection. In this review article, we focus on the mechanisms through which these enzymes are involved in the antioxidant response to oxidative stress and thus the pathogenesis of ALS and their potential as therapeutic targets.

Association of exposure to manganese and fine motor skills in welders - Results from the WELDOX II study

The aim of this study was to evaluate the effect of exposure to manganese (Mn) on fine motor functions. A total of 48 welders and 30 unexposed workers as controls completed questionnaires, underwent blood examinations, and a motor test battery. The shift exposure of welders to respirable Mn was measured with personal samplers. For all subjects accumulations of Mn in the brain were assessed with T1-weighted magnetic resonance imaging. Welders showed normal motor functions on the Movement Disorder Society-Sponsored Revision of the Unified Parkinson Disease Rating Scale part III. Furthermore welders performed excellent on a steadiness test, showing better results than controls. However, welders were slightly slower than controls in motor tests. There was no association between fine motor test results and the relaxation rates R1 in globus pallidus and substantia nigra as MRI-based biomarkers to quantify Mn deposition in the brain.

Manganese Exposure Aggravates β-Amyloid Pathology by Microglial Activation

Human epidemiological evidence and animal experimental data suggest that chronic manganese (Mn) exposure increases the risk of Alzheimer’s disease (AD) and amyloid plaques, a hallmark of AD brain pathology, but the underlying mechanisms were not fully understood. Using the transgenic APP/PS1/Tau triple transgenic AD (3×Tg-AD) mouse model and mouse-derived microglia and neuroblastoma cell lines, we found that chronic 5-month Mn treatment increased beta amyloid peptide (Aβ) expression and Aβ plaques in the cerebral cortex and hippocampus in these 3×Tg-AD mice. Furthermore, we found that the β- and γ-secretase cleavage activities were markedly increased, while α-secretase cleavage activity was reduced in the brain of Mn-treated AD mice; these effects increase Aβ production and thus are amyloidogenic. Equally important, Mn treatment alone did not alter β-secretase 1 (BACE1) gene expression or Aβ production in amyloidogenic mutant amyloid precursor protein (APP) gene hAPPsw-transfected N2a cells (APPsw-N2a), but in APPsw-N2a cells either co-cultured with microglia or cultured with microglia-conditioned media, Mn exposure increased BACE1 expression and amyloidogenesis. We further determined that Mn exposure promoted the activation of microglia both in 3×Tg-AD mouse brains and in cultured microglia cells, and increased the secretion of the inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Taken together, these results suggest that Mn may increase the release of IL-1β and TNF-α from microglia that in turn stimulates the expression of BACE1 gene and protein and consequently Aβ production; this novel molecular mechanism not only advances our understanding about the amyloidogenic effect of chronic Mn exposure reported for special human populations but also indicates Mn dyshomeostasis as a potential contributor to AD pathogenesis.

The effects of occupational exposure to manganese fume on neurobehavioral and neurocognitive functions: An analytical cross-sectional study among welders

This study aimed to measure concentrations of manganese fume in breathing zone (BZ) and blood among welders to assess neurocognitive and neurobehavioral functions among them. In this study 38 welders and 27 administrative employees participated. Q16 questionnaire was used to evaluate neurobehavioral symptoms. The computerized Stroop test and Continuous Performance Test (CPT) were used to assess neurocognitive functions. Sampling and analysis of manganese fumes in the BZ and blood samples were performed according to NIOSH-7300 and NIOSH-8005 methods, respectively. Average concentration of manganese in the welders' BZ and blood was 0.81 ± 0.21 mg/m³ and 18.33 ± 5.84 µg/l. Frequency of neurobehavioral symptoms was significantly higher in welders compared with control group. Spearman correlation test showed a moderate correlation between Mn concentrations in the BZ and blood Mn levels (r_s = 0.352). There were statistical moderate and strong correlations between the frequency of neurobehavioral symptoms and manganese concentrations in the BZ (r=0.504) and blood Mn levels (r=0.643).The Pearson correlation coefficient (r=0.433-0.690) obtained on the psychological tests showed a moderate to strong correlation between manganese concentrations in the welders' BZ and blood and some indices of the Stroop test and CPT. The results of this study can confirm the effect of manganese inhalation on creating neurobehavioral and neurocognitive impairments in welders.

Cognitive profile of patients with manganese-methcathinone encephalopathy

Manganese-methcathinone encephalopathy (MME) is a rare parkinsonian syndrome described in drug addicts who have self-injected a home-made mixture containing methcathinone and manganese. We assessed 14 patients with MME and compared their results with 14 matched control subjects. The patients had a parkinsonian syndrome with symmetrical bradykinesia, dystonias, and postural, gait and speech impairment, with moderate restrictions in activities of daily living. Their cognitive status was assessed with the Russian version of the Wechsler Adult Intelligence Scale (WAIS) and with tests of attention (Trail Making Test, Bourdon-Wiersma Dot Cancellation Test), memory (Auditory Verbal Learning Test, Rey-Osterrieth Complex Figure), motor skills (Grooved Pegboard), visuospatial skills (Money Road Map Test, Benton Judgment of Line Orientation), and executive abilities (Verbal Fluency, 5-Point Test, Wisconsin Card Sorting Test). Only a few significant differences emerged. After controlling for multiple comparisons, the results in the WAIS Object Assembly subtest, the Grooved Pegboard test (dominant and nondominant hand) and the Verbal Fluency test remained significant.

Manganese Exposure and Cognition Across the Lifespan: Contemporary Review and Argument for Biphasic Dose-Response Health Effects

Manganese (Mn) is both an essential micronutrient and potential neurotoxicant. This dual role underlies a growing body of literature demonstrating that Mn exhibits a biphasic dose-response relationship with neurocognitive outcomes. We reviewed recent epidemiologic studies from 2007 to 2016 that investigated the relationship between Mn exposure and cognitive outcomes across the lifespan: early life, school-aged children, and adulthood. In total, 27 research articles were included in this review: 12 pediatric and 15 adult studies (10 occupational and five environmental exposures). The majority of these studies provided evidence of the negative effects of Mn exposure on cognition. The pediatric literature provides evidence that both high and low levels of Mn are negatively associated with intellectual development. Future Mn research should include examination of non-linear relationships and multiple neurotoxicants across the lifespan and particularly during critical developmental windows.

Thalamic GABA levels and occupational manganese neurotoxicity: Association with exposure levels and brain MRI

Excessive occupational exposure to Manganese (Mn) has been associated with clinical symptoms resembling idiopathic Parkinson's disease (IPD), impairing cognitive and motor functions. Several studies point towards an involvement of the brain neurotransmitter system in Mn intoxication, which is hypothesized to be disturbed prior to onset of symptoms. Edited Magnetic Resonance Spectroscopy (MRS) offers the unique possibility to measure γ-amminobutyric acid (GABA) and other neurometabolites in vivo non-invasively in workers exposed to Mn. In addition, the property of Mn as Magnetic Resonance Imaging (MRI) contrast agent may be used to study Mn deposition in the human brain. In this study, using MRI, MRS, personal air sampling at the working place, work history questionnaires, and neurological assessment (UPDRS-III), the effects of chronic Mn exposure on the thalamic GABAergic system was studied in a group of welders (N=39) with exposure to Mn fumes in a typical occupational setting. Two subgroups of welders with different exposure levels (Low: N=26; mean air Mn=0.13±0.1mg/m3; High: N=13; mean air Mn=0.23±0.18mg/m3), as well as unexposed control workers (N=22, mean air Mn=0.002±0.001mg/m3) were recruited. The group of welders with higher exposure showed a significant increase of thalamic GABA levels by 45% (p<0.01, F(1,33)=9.55), as well as significantly worse performance in general motor function (p<0.01, F(1,33)=11.35). However, welders with lower exposure did not differ from the controls in GABA levels or motor performance. Further, in welders the thalamic GABA levels were best predicted by past-12-months exposure levels and were influenced by the Mn deposition in the substantia nigra and globus pallidus. Importantly, both thalamic GABA levels and motor function displayed a non-linear pattern of response to Mn exposure, suggesting a threshold effect.

Olfactory toxicity in rats following manganese chloride nasal instillation: A pilot study

Following inhalation, manganese travels along the olfactory nerve from the olfactory epithelium (OE) to the olfactory bulb (OB). Occupational exposure to inhaled manganese is associated with changes in olfactory function. This pilot study evaluated two related hypotheses: (a) intranasal manganese administration increases OE and OB manganese concentrations; and (b) intranasal manganese exposure impairs performance of previously trained rats on a go-no-go olfactory discrimination (OD) task. Male Fischer 344 rats were trained to either lever press ("go") in response to a positive conditioned stimulus (CS+: vanillin) or to do nothing ("no go") when a negative conditioned stimulus (CS-: amyl acetate) was present. Following odor training, rats were randomly assigned to either a manganese (200mM MnCl₂) or 0.9% saline treatment group (n=4-5 rats/group). Administration of either saline or manganese was performed on isoflurane-anesthetized rats as 40μL bilateral intranasal instillations. Rats were retested 48h later using the vanillin/amyl acetate OD task, then euthanized, followed by collection of the OE and OB. Manganese concentrations in tissue samples were analyzed by ICP-MS. An additional cohort of rats (n=3-4/group) was instilled similarly with saline or manganese and nasal and OB pathology assessed 48h later. Manganese-exposed rats had increased manganese levels in both the OE and OB and decreased performance in the OD task when compared with control animals. Histopathological evaluation of the caudal nasal cavity showed moderate, acute to subacute suppurative inflammation of the olfactory epithelium and submucosa of the ethmoid turbinates and mild suppurative exudate in the nasal sinuses in animals given manganese. No histologic changes were evident in the OB. The nasal instillation and OD procedures developed in this study are useful methods to assess manganese - induced olfactory deficits.

Association of exposure to manganese and iron with relaxation rates R1 and R2*- magnetic resonance imaging results from the WELDOX II study

OBJECTIVE

Magnetic resonance imaging is a non-invasive method that allows the indirect quantification of manganese (Mn) and iron (Fe) accumulation in the brain due to their paramagnetic features. The WELDOX II study aimed to explore the influence of airborne and systemic exposure to Mn and Fe on the brain deposition using the relaxation rates R1 and R2* as biomarkers of metal accumulation in regions of interest in 161 men, including active and former welders.

MATERIAL AND METHODS

We obtained data on the relaxation rates R1 and R2* in regions that included structures within the globus pallidus (GP), substantia nigra (SN), and white matter of the frontal lobe (FL) of both hemispheres, as well as Mn in whole blood (MnB), and serum ferritin (SF). The study subjects, all male, included 48 active and 20 former welders, 41 patients with Parkinson's disease (PD), 13 patients with hemochromatosis (HC), and 39 controls. Respirable Mn and Fe were measured during a working shift for welders. Mixed regression models were applied to estimate the effects of MnB and SF on R1 and R2*. Furthermore, we estimated the influence of airborne Mn and Fe on the relaxation rates in active welders.

RESULTS

MnB and SF were significant predictors of R1 but not of R2* in the GP, and were marginally associated with R1 in the SN (SF) and FL (MnB). Being a welder or suffering from PD or HC elicited no additional group effect on R1 or R2* beyond the effects of MnB and SF. In active welders, shift concentrations of respirable Mn>100μg/m³ were associated with stronger R1 signals in the GP. In addition to the effects of MnB and SF, the welding technique had no further influence on R1.

CONCLUSIONS

MnB and SF were significant predictors of R1 but not of R2*, indicative of metal accumulation, especially in the GP. Also, high airborne Mn concentration was associated with higher R1 signals in this brain region. The negative results obtained for being a welder or for the techniques with higher exposure to ultrafine particles when the blood-borne concentration was included into the models indicate that airborne exposure to Mn may act mainly through MnB.

Nonmotor Symptoms in Vascular and Other Secondary Parkinsonism

Vascular parkinsonism (VP) is a relatively frequent variant of secondary parkinsonism caused by ischemic or hemorrhagic lesions of basal ganglia, midbrain, or their links with frontal cortex. According to different investigations, various forms of cerebrovascular disease cause 1%-15% of parkinsonism cases. Nonmotor symptoms are frequently found in VP and may negatively influence on quality of life. However, nonmotor symptoms such as hallucinations, orthostatic hypotension, REM-sleep behavior disorder, and anosmia are rarely revealed in VP, which may be noted to another diagnosis or mixed pathology. Clinical value of nonmotor symptoms in normal pressure hydrocephalus, toxic, and drug-induced parkinsonism is also discussed.

Welding-related brain and functional changes in welders with chronic and low-level exposure

Although an essential nutrient, manganese (Mn) can be toxic at high doses. There is, however, uncertainty regarding the effects of chronic low-level Mn-exposure. This review provides an overview of Mn-related brain and functional changes based on studies of a cohort of asymptomatic welders who had lower Mn-exposure than in most previous work. In welders with low-level Mn-exposure, we found: 1) Mn may accumulate in the brain in a non-linear fashion: MRI R1 (1/T1) signals significantly increased only after a critical level of exposure was reached (e.g., ≥300 welding hours in the past 90days prior to MRI). Moreover, R1 may be a more sensitive marker to capture short-term dynamic changes in Mn accumulation than the pallidal index [T1-weighted intensity ratio of the globus pallidus vs. frontal white matter], a traditional marker for Mn accumulation; 2) Chronic Mn-exposure may lead to microstructural changes as indicated by lower diffusion tensor fractional anisotropy values in the basal ganglia (BG), especially when welding years exceeded more than 30 years; 3) Mn-related subtle motor dysfunctions can be captured sensitively by synergy metrics (indices for movement stability), whereas traditional fine motor tasks failed to detect any significant differences; and 4) Iron (Fe) also may play a role in welding-related neurotoxicity, especially at low-level Mn-exposure, evidenced by higher R2* values (an estimate for brain Fe accumulation) in the BG. Moreover, higher R2* values were associated with lower phonemic fluency performance. These findings may guide future studies and the development of occupation- and public health-related polices involving Mn-exposure.

Short-term manganese inhalation decreases brain dopamine transporter levels without disrupting motor skills in rats

Manganese (Mn) is used in industrial metal alloys and can be released into the atmosphere during methylcyclopentadienyl manganese tricarbonyl combustion. Increased Mn deposition in the brain after long-term exposure to the metal by inhalation is associated with altered dopamine metabolism and neurobehavioral problems, including impaired motor skills. However, neurotoxic effects of short-term exposure to inhaled Mn are not completely characterized. The purpose of this study is to define the neurobehavioral and neurochemical effects of short-term inhalation exposure to Mn at a high concentration using rats. Male Sprague-Dawley rats were exposed to MnCl2 aerosol in a nose-only inhalation chamber for 3 weeks (1.2 µm, 39 mg/m(3)). Motor coordination was tested on the day after the last exposure using a rotarod device at a fixed speed of 10 rpm for 2 min. Also, dopamine transporter and dopamine receptor protein expression levels in the striatum region of the brain were determined by Western blot analysis. At a rotarod speed of 10 rpm, there were no significant differences in the time on the bar before the first fall or the number of falls during the two-minute test observed in the exposed rats, as compared with controls. The Mn-exposed group had significantly higher Mn levels in the lung, blood, olfactory bulb, prefrontal cortex, striatum, and cerebellum compared with the control group. A Mn concentration gradient was observed from the olfactory bulb to the striatum, supporting the idea that Mn is transported via the olfactory pathway. Our results demonstrated that inhalation exposure to 39 mg/m(3) Mn for 3 weeks induced mild lung injury and modulation of dopamine transporter expression in the brain, without altering motor activity.

Cognitive control dysfunction in workers exposed to manganese-containing welding fume

BACKGROUND

Chronic exposure to manganese (Mn) is a health concern in occupations such as welding because of well-established motor effects due to basal ganglia dysfunction. We hypothesized that cognitive control (the ability to monitor, manipulate, and regulate ongoing cognitive demands) would also be affected by chronic Mn exposure.

METHODS

We examined the relationship between Mn exposure and cognitive control performance in 95 workers with varying intensity and duration (median 15.5 years) of exposure to welding fume. We performed linear regression to assess the association between exposure to Mn-containing welding fume and cognitive control tasks.

RESULTS

Overall performance was inversely related to intensity of welding exposure (P = 0.009) and was driven by the Two-Back and Letter Number Sequencing tests that assess working memory (both P = 0.02).

CONCLUSIONS

Occupational exposure to Mn-containing welding fume may be associated with poorer working memory performance, and workers may benefit from practices that reduce exposure intensity. Am. J. Ind. Med. 60:181-188, 2017. © 2016 Wiley Periodicals, Inc.

Effects of pulmonary exposure to chemically-distinct welding fumes on neuroendocrine markers of toxicity

Exposure to welding fumes may result in disorders of the pulmonary, cardiovascular, and reproductive systems. Welders are also at a greater risk of developing symptoms similar to those seen in individuals with idiopathic Parkinson's disease. In welders, there are studies that suggest that alterations in circulating prolactin concentrations may be indicative of injury to the dopamine (DA) neurons in the substantia nigra. The goal of these studies was to use an established model of welding particulate exposure to mimic the effects of welding fume inhalation on reproductive functions. Since previous investigators suggested that changes in circulating prolactin may be an early marker of DA neuron injury, movement disorders, and reproductive dysfunction, prolactin, hypothalamic tyrosine hydroxylase (TH) levels (a marker of DA synthesis), and other measures of hypothalamic-pituitary-gonadal (HPG) function were measured after repetitive instillation of welding fume particulates generated by flux core arc-hard surfacing (FCA-HS), manual metal arc-hard surfacing (MMA-HS) or gas metal arc-mild steel (GMA-MS) welding, or manganese chloride (MnCl₂). Exposure to welding fume particulate resulted in the accumulation of various metals in the pituitary and testes of rats, along with changes in hypothalamic TH and serum prolactin levels. Exposure to particulates with high concentrations of soluble manganese (Mn) appeared to exert the greatest influence on TH activity levels and serum prolactin concentrations. Thus, circulating prolactin levels may serve as a biomarker for welding fume/Mn-induced neurotoxicity. Other reproductive measures were collected, and these data were consistent with epidemiological findings that prolactin and testosterone may serve as biomarkers of welding particulate induced DA neuron and reproductive dysfunction.

Oxidative Stress, DNA Methylation, and Telomere Length Changes in Peripheral Blood Mononuclear Cells after Pulmonary Exposure to Metal-Rich Welding Nanoparticles

Welding fume is a complex mixture of different potentially cytotoxic and genotoxic metals, such as chromium (Cr), manganese (Mn), nickel (Ni), and iron (Fe). Documented health effects have been observed in workers exposed to welding fume. The objective of the study was to use an animal model to identify potential biomarkers of epigenetic changes (e.g., changes in telomere length, DNA methylation) in isolated peripheral blood mononuclear cells (PBMCs) after exposure to different welding fumes. Male Sprague-Dawley rats were exposed by intratracheal instillation (ITI) of 2.0 mg/rat of gas metal arc-mild steel (GMA-MS) or manual metal arc-stainless steel (MMA-SS) welding fume. Vehicle controls received sterile saline by ITI. At 4 h, 14 h, 1 d, 3 d, 10 d, and 30 d, bronchoalveolar lavage (BAL) was performed to assess lung inflammation. Whole blood was collected, and PBMCs were isolated. Dihydroethidium (DHE) fluorescence and 4-hydroxylnonenal protein adduct (P-HNE) formation were measured in PBMCs to assess reactive oxygen species (ROS) production. DNA alterations in PBMCs were determined by evaluating changes in DNA methylation and telomere length. Metal composition of the two fumes was different: MMA-SS (41 % Fe, 29 % Cr, 17 % Mn, 3 % Ni) versus GMA-MS (85 % Fe, 14 % Mn). The more soluble and chemically complex MMA-SS sample induced a more persistent and greater inflammatory response compared to the other groups. Also, oxidative stress markers increased at 24 h in the PBMCs recovered from the MMA-SS group compared to other group. No significant differences were observed when comparing DNA methylation between the welding fume and control groups at any of the time points, whereas the MMA-SS sample significantly increased telomere length at 1 and 30 d after a single exposure compared to the other groups. These findings suggest that genotoxic metals in MMA-SS fume (e.g., Cr and Ni), that are absent in the GMA-MS fume, may enhance lung toxicity, as well as induce markers of oxidative stress and increase telomere length in PBMCs. Importantly, the measurement of telomere length in cells isolated from peripheral blood may serve as a potential biomarker of response in the assessment of toxicity associated with welding fumes.

Association of neurobehavioral performance with R2* in the caudate nucleus of asymptomatic welders

OBJECTIVES

Welding fumes contain several metals including manganese (Mn) and iron (Fe) that may affect the nervous system. Previous studies of potential welding-related neurotoxicity have focused primarily on Mn exposure. The current study examined neurobehavioral and brain imaging changes in asymptomatic welders and their associations with both Mn and Fe exposure measurements.

METHODS

Data were obtained from subjects with (n=46) and without (controls; n=31) a history of welding exposure. Occupational questionnaires estimated recent (HrsW; welding hours and E₉₀; cumulative exposure, past 90days) and lifetime (YrsW; total welding years and ELT; cumulative exposure, lifetime) exposure. Brain MRI pallidal index (PI), R1 (1/T1), and R2* (1/T2*) were measured to estimate Mn and Fe concentrations in the basal ganglia [caudate nucleus (CN), putamen, and globus pallidus], amygdala, and hippocampus. Comprehensive neuropsychological tests were conducted to examine behavioral differences between welders and controls. Correlation analyses were conducted between neuropsychological tests and those exposure measurements that showed significant group differences.

RESULTS

Compared to controls, welders had significantly higher R2* in the CN and lower performance on the Phonemic Fluency test. Correlation analyses revealed that welders' Phonemic Fluency scores were inversely associated with R2* in the CN, but not with the PI or R1 in any brain region of interest studied.

DISCUSSION

The results showed that neurobehavioral performance for the asymptomatic welders in our study was worse than individuals who had not welded, and suggest the differences may be associated with higher Fe accumulation in the CN.

Tremor and hand-arm vibration syndrome (HAVS) in road maintenance workers

Objectives

The aim of this study was to evaluate postural and rest tremor among workers using vibrating hand tools, taking into account the possible effects of toxicants such as alcohol and tobacco. A further aim was to study workers diagnosed with hand-arm vibration syndrome (HAVS) at the time of examination.

Methods

This study comprises 103 road maintenance workers, 55 exposed to vibrating hand tools (age 41.0 years; range 21–62) and 48 referents (age 38.5 years; range 19–64). They were examined with the CATSYS Tremor Pen^®. Exposure to vibrating tools and serum biomarkers of alcohol and tobacco consumption were measured.

Results

Cumulative exposure to vibrating tools was associated with increased postural (p < 0.01) and rest tremor (p < 0.05) and with a higher Center Frequency of postural tremor (p < 0.01) among smokers and users of smokeless tobacco. Rest tremor Center Frequency was higher than postural tremor frequency (p < 0.001).

Conclusions

The main findings indicate an association between cumulative exposure to hand-held vibrating tools, tremor parameters and consumption of tobacco products. The hand position is important when testing for tremor. Rest tremor had a higher Center Frequency. Postural tremor was more strongly associated with exposure than rest tremor. The finding of increased tremor among the HAVS subjects indicated that tremor might be a part of the clinical picture of a HAVS diagnosis. As with all cross-sectional studies, inferences should be made with caution when drawing conclusions about associations between exposure and possible effects. Future research using longitudinal design is required to validate the findings of the present study.

Synergy as a new and sensitive marker of basal ganglia dysfunction: A study of asymptomatic welders

BACKGROUND

Multi-digit synergies, a recently developed, theory-based method to quantify stability of motor action, are shown to reflect basal ganglia dysfunction associated with parkinsonian syndromes. In this study, we tested the hypothesis that multi-digit synergies may capture early and subclinical basal ganglia dysfunction. We chose asymptomatic welders to test the hypothesis because the basal ganglia are known to be most susceptible to neurotoxicity caused by welding-related metal accumulation (such as manganese and iron).

METHODS

Twenty right-handed welders and 13 matched controls were invited to perform single- and multi-finger pressing tasks using the fingers of the right or left hand. Unified Parkinson's Disease Rating Scale and Grooved Pegboard scores were used to gauge gross and fine motor dysfunction, respectively. High-resolution (3T) T1-weighted, T2-weighted, T1 mapping, susceptibility, and diffusion tensor MRIs were obtained to reflect manganese, iron accumulation, and microstructural changes in basal ganglia. The synergy index stabilizing total force and anticipatory synergy adjustments were computed, compared between groups, and correlated with estimates of basal ganglia manganese [the pallidal index, R1 (1/T1)], iron [R2* (1/T2*)], and microstructural changes [fractional anisotropy and mean diffusivity].

RESULTS

There were no significant differences in Unified Parkinson's Disease Rating Scale (total or motor subscale) or Grooved Pegboard test scores between welders and controls. The synergy index during steady-state accurate force production was decreased significantly in the left hand of welders compared to controls (p=0.004) but did not reach statistical significance in the right hand (p=0.16). Anticipatory synergy adjustments, however, were not significantly different between groups. Among welders, higher synergy indices in the left hand were associated significantly with higher fractional anisotropy values in the left globus pallidus (R=0.731, p<0.001) but not with the pallidal index, R1, or R2* values in the basal ganglia.

CONCLUSIONS

These data suggest that multi-digit synergy metrics may serve as preclinical markers for basal ganglia dysfunction in welders and other populations at risk for neurodegenerative diseases involving parkinsonian symptoms. This finding may have important clinical, scientific, and public/occupational health implications.

Longitudinal T1 relaxation rate (R1) captures changes in short-term Mn exposure in welders

OBJECTIVES

We demonstrated recently that the T1 relaxation rate (R1) captured short-term Mn exposure in welders with chronic, relatively low exposure levels in a cross-sectional study. In the current study, we used a longitudinal design to examine whether R1 values reflect the short-term dynamics of Mn exposure.

METHODS

Twenty-nine welders were evaluated at baseline and 12 months. Occupational questionnaires estimated short-term welding exposure using welding hours in the 90days prior to each study visit (HrsW₉₀). In addition, blood Mn levels, the pallidal index (PI; globus pallidus T1-weighted intensity (T1WI)/frontal white matter T1WI), and R1 values in brain regions of interest (ROIs) were determined as Mn biomarkers at each visit. Associations between changes in estimated welding exposure and changes in purported Mn biomarkers were assessed by Spearman's correlations with adjustment for age and baseline R1, HrsW₉₀, and blood Mn values.

RESULTS

Changes in welding hours (HrsW₉₀: the short-term welding exposure estimate), was associated significantly with changes in R1 values in the putamen (r=0.541, p=0.005), caudate (R=0.453, p=0.023), globus pallidus (R=0.430, p=0.032), amygdala (R=0.461, p=0.020), and hippocampus (R=0.447, p=0.025), but not with changes in blood Mn levels or the PI.

DISCUSSION

Changes in R1 values correlated with changes in the short-term welding exposure estimate, but not with more traditional measures of Mn exposure (blood Mn levels or PI). These results suggest that R1 may serve as a useful marker to capture the short-term dynamics in Mn brain accumulation related to welding exposure.

Setting evidence-based occupational exposure limits for manganese

In 2004, a review by the Institute of Environment and Health (IEH) made recommendations on occupational exposure limits (OELs) for manganese and its inorganic compounds for inhalable and respirable fractions respectively. These OELs were based on a detailed comprehensive evaluation of all the scientific data available at that time. Since then, more published studies have become available and a number of occupational standard-setting committees (EU SCOEL, US ACGIH-TLV, and German MAK) have proposed OEL's for manganese and its inorganic compounds that are somewhat lower that those proposed in the 2004 review. Based on current understanding, the key toxicological and human health issues that are likely to influence a health-based recommendation relate to: neurotoxicology; reproductive and developmental toxicology; and mutagenicity/carcinogenicity. Of these, it is generally considered that neurotoxicity presents the most sensitive endpoint. As such, many of the studies that have been reported since the IEH review have sought to use those neurofunctional tests that appear to be particularly sensitive at identifying the subtle neurological changes thought to associate with manganese toxicity. These recent studies have, however, continued to be limited to a significant extent by reliance on cross-sectional designs and also by use of unreliable exposure estimation methods. Consequently the strength of the potential association between manganese exposure and these subtle subclinical cognitive or neuromotor changes is still poorly characterised and the relevance of these minor differences in terms of either their clinical or quality of life consequences remains unknown. Based upon the overall evidence, it is concluded that the 8-h time weighted averages (TWA) for respirable (0.05mg/m³ as Mn) and inhalable (0.2mg/m³ as Mn) fractions as recommended by the SCOEL in 2011 are the most methodologically-sound, as they are based on the best available studies, most suited to the development of health-based OELs for both respirable and inhalable fractions. The dose-response characterisation informed by the examined studies used can be considered to establish a true human NOAEL for all the neurofunctional endpoints examined within the selected studies.

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.

Relations of biomarkers of manganese exposure and neuropsychological effects among welders and ferroalloy smelters

The objective of present study was to assess relationship between biomarkers of Manganese (Mn) and neuropsychological effects. The study was carried out on 27 welders and 31 ferroalloy smelters as Mn-exposed groups and 30 office workers as unexposed controls. Air Mn concentrations were determined according to NIOSH method 7300. The biological samples were prepared using microwave assisted acid digestion and all samples were analyzed by graphite furnace- atomic absorption spectroscopy (GF-AAS) in order to determine manganese. Questionnaire 16 (Q16) and Cambridge Neuropsychological Test Automated Battery (CANTAB) were used to evaluate the neuropsychological effects. The mean concentrations of air Mn for the welder and ferroalloy smelter groups were 0.023 ± 0.012 mg/m(3) and 0.008 ± 0.005 mg/m(3), respectively. Manganese concentrations in blood, urine, and toenail samples of exposed workers ranged between 1.80-32.60 (µg/l), 1.00-42.50 (µg/l), and 0.10-6.08 (µg/g), respectively. Mean Mn concentrations in all biological samples of cases were significantly higher than unexposed controls (p<0.05). A moderate relationship was observed between biomarkers of Mn exposure, air Mn, Q16 as well as some neurocognitive outcome measures. The present study shows that blood Mn, urine Mn and toenail Mn could be used to distinguish Mn-exposed workers from unexposed population at the group level.

Manganese neurotoxicity: behavioral disorders associated with dysfunctions in the basal ganglia and neurochemical transmission

Manganese (Mn) is an essential element required for many physiological functions. While it is essential at physiological levels, excessive accumulation of Mn in the brain causes severe dysfunctions in the central nervous system known as manganism. Manganism is an extrapyramidal disorder characterized by motor disturbances associated with neuropsychiatric and cognitive disabilities similar to Parkinsonism. As the primary brain regions targeted by Mn are the basal ganglia, known to be involved in the pathophysiology of extrapyramidal disorders, this review will examine the impact of Mn exposure on the basal ganglia circuitry and neurotransmitters in relation to motor and non-motor disorders. The collected data from recent available studies in humans and experimental animal models provide new information about the mechanisms by which Mn affects behavior, neurotransmitters, and basal ganglia function observed in manganism. The effects of the alterations of metals on basal ganglia and neurochemical functioning are critical to develop effective modalities not only for the treatment of vulnerable populations (e.g., Mn-exposed workers) but also for understanding the etiology of neurodegenerative diseases where brain metal imbalances are involved, such as Parkinson's disease. We examine the impact of manganese (Mn) exposure on the basal ganglia circuitry and neurotransmitters in relation with motor and non-motor disorders. The collected data from available studies show that when accumulated in the globus pallidus, Mn influences the subthalamic (STN) and substantia nigra (SN) neurons, which are at the origin of changes in the thalamus and the cortex.

Environmental exposure to manganese in air: Associations with cognitive functions

Manganese (Mn), an essential element, can be neurotoxic in high doses. This cross-sectional study explored the cognitive function of adults residing in two towns (Marietta and East Liverpool, Ohio, USA) identified as having high levels of environmental airborne Mn from industrial sources. Air-Mn site surface emissions method modeling for total suspended particulate (TSP) ranged from 0.03 to 1.61 μg/m(3) in Marietta and 0.01-6.32 μg/m(3) in East Liverpool. A comprehensive screening test battery of cognitive function, including the domains of abstract thinking, attention/concentration, executive function and memory was administered. The mean age of the participants was 56 years (±10.8 years). Participants were mostly female (59.1) and primarily white (94.6%). Significant relationships (p<0.05) were found between Mn exposure and performance on working and visuospatial memory (e.g., Rey-O Immediate β=-0.19, Rey-O Delayed β=-0.16) and verbal skills (e.g., Similarities β=-0.19). Using extensive cognitive testing and computer modeling of 10-plus years of measured air monitoring data, this study suggests that long-term environmental exposure to high levels of air-Mn, the exposure metric of this paper, may result in mild deficits of cognitive function in adult populations.

Pharmacokinetic evaluation of the equivalency of gavage, dietary, and drinking water exposure to manganese in F344 rats

Concerns exist as to whether individuals may be at greater risk for neurotoxicity following increased manganese (Mn) oral intake. The goals of this study were to determine the equivalence of 3 methods of oral exposure and the rate (mg Mn/kg/day) of exposure. Adult male rats were allocated to control diet (10 ppm), high manganese diet (200 ppm), manganese-supplemented drinking water, and manganese gavage treatment groups. Animals in the drinking water and gavage groups were given the 10 ppm manganese diet and supplemented with manganese chloride (MnCl(2)) in drinking water or once-daily gavage to provide a daily manganese intake equivalent to that seen in the high-manganese diet group. No statistically significant difference in body weight gain or terminal body weights was seen. Rats were anesthetized following 7 and 61 exposure days, and samples of bile and blood were collected. Rats were then euthanized and striatum, olfactory bulb, frontal cortex, cerebellum, liver, spleen, and femur samples were collected for chemical analysis. Hematocrit was unaffected by manganese exposure. Liver and bile manganese concentrations were elevated in all treatment groups on day 61 (relative to controls). Increased cerebellum manganese concentrations were seen in animals from the high-manganese diet group (day 61, relative to controls). Increased (relative to all treatment groups) femur, striatum, cerebellum, frontal cortex, and olfactory bulb manganese concentrations were also seen following gavage suggesting that dose rate is an important factor in the pharmacokinetics of oral manganese. These data will be used to refine physiologically based pharmacokinetic models, extending their utility for manganese risk assessment by including multiple dietary exposures.

Effects of chronic manganese exposure on attention and working memory in non-human primates

Manganese (Mn) is essential for a variety of physiological processes, but at elevated levels, can be neurotoxic. While cognitive dysfunction has been recently appreciated to occur as a result of chronic Mn exposures, it is still unclear as to which cognitive domains are most susceptible to disruption by Mn exposure. We previously described early appearing Mn-induced changes in performance on a paired associate learning task in monkeys chronically exposed to Mn and suggested that performance of this task might be a sensitive tool for detecting cognitive dysfunction resulting from Mn exposure. As chronic Mn exposure has been suggested to be associated with attention, working memory and executive function deficits, the present study was conducted to assess the extent to which detrimental effects of chronic Mn exposure could be detected using tasks specifically designed to preferentially assess attention, working memory, and executive function. Six cynomolgus monkeys received Mn exposure over an approximate 12 month period and three served as control animals. All animals were trained to perform a self-ordered spatial search (SOSS) task and a five choice serial reaction time (5-CSRT) task. Deficits in performance of the SOSS task began to appear by the fourth month of Mn exposure but only became consistently significantly impaired beginning at the ninth month of Mn exposure. Performance on the 5-CSRT became significantly affected by the third month of Mn exposure. These data suggest that in addition to the paired associate learning task, cognitive processing speed (as measured by the 5-CSRT) may be a sensitive measure of Mn toxicity and that brain circuits involved in performance of the SOSS task may be somewhat less sensitive to disruption by chronic Mn exposure.

Risk factors for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease. It is typically fatal within 2-5 years of symptom onset. The incidence of ALS is largely uniform across most parts of the world, but an increasing ALS incidence during the last decades has been suggested. Although recent genetic studies have substantially improved our understanding of the causes of ALS, especially familial ALS, an important role of non-genetic factors in ALS is recognized and needs further study. In this review, we briefly discuss several major genetic contributors to ALS identified to date, followed by a more focused discussion on the most commonly examined non-genetic risk factors for ALS. We first review factors related to lifestyle choices, including smoking, intake of antioxidants, physical fitness, body mass index, and physical exercise, followed by factors related to occupational and environmental exposures, including electromagnetic fields, metals, pesticides, β-methylamino-L-alanine, and viral infection. Potential links between ALS and other medical conditions, including head trauma, metabolic diseases, cancer, and inflammatory diseases, are also discussed. Finally, we outline several future directions aiming to more efficiently examine the role of non-genetic risk factors in ALS.

Extrapyramidal system neurotoxicity: animal models

The central nervous system's extrapyramidal system provides involuntary motor control to the muscles of the head, neck, and limbs. Toxicants that affect the extrapyramidal system are generally clinically characterized by impaired motor control, which is usually the result of basal ganglionic dysfunction. A variety of extrapyramidal syndromes are recognized in humans and include Parkinson's disease, secondary parkinsonism, other degenerative diseases of the basal ganglia, and clinical syndromes that result in dystonia, dyskinesia, essential tremor, and other forms of tremor and chorea. This chapter briefly reviews the anatomy of the extrapyramidal system and discusses several naturally occurring and experimental models that target the mammalian (nonhuman) extrapyramidal system. Topics discussed include extrapyramidal syndromes associated with antipsychotic drugs, carbon monoxide, reserpine, cyanide, rotenone, paraquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and manganese. In most cases, animals are used as experimental models to improve our understanding of the toxicity and pathogenesis of these agents. Another agent discussed in this chapter, yellowstar thistle poisoning in horses, however, represents an important spontaneous cause of parkinsonism that naturally occurs in animals. The central focus of the chapter is on animal models, especially the concordance between clinical signs, neurochemical changes, and neuropathology between animals and people.

Significance and Usefulness of Biomarkers of Exposure to Manganese

Manganese (Mn) accomplishes functions essential to maintaining human health, but at the same time this trace element can be toxic at low levels of exposure and accurate estimation of internal exposure is needed. A biomarker of exposure to Mn is meaningful only if there is sufficient knowledge of the toxicokinetics determining its presence in a biological medium (e.g. whole blood, plasma, urine, hair, nail). Moreover, biological monitoring of exposure to Mn is useful only when the biomarker is sufficiently specific and sensitive to distinguish exposed from non-exposed subjects, when it is dose-related to the external exposure (current, recent, or time-integrated), and when it displays reasonable dose–effect/response relationships with the occurrence of adverse effects on the central nervous system, the critical target for Mn exposure. Human investigations in which biomarkers of Mn exposure meet all these criteria are hard to locate. Overall, the available studies report poor or no associations on an individual basis between external (Mn in air or drinking water) and internal (Mn in blood, urine, hair, or nail) Mn exposure indices. This may be to some extent explained by features inherent of the Mn metabolism (homeostatic control), the Mn biomarker's half-life with respect to the exposure window, and the variable nature of external exposure scenarios. Studies particularly dealing with Mn inhalation exposure, different or poorly described methodological approaches, or air sampling strategies may render direct comparison and interpretation of results a tedious task. Nevertheless, several studies report significant dose–effect associations between biomarkers of Mn exposure and subclinical deficits of psychomotor or neuropsychological test performances. Because directly associated with the site of toxic action and providing the magnetic resonance imaging is done no later than three months after Mn exposure ceased, the Mn T1 relaxation time is potentially the better biomarker of Mn exposure in a clinical context (e.g. after long-term parenteral nutrition, chronic liver failure, methcathinone drug abuse). Magnetic resonance imaging is, however, unpractical as a tool for biological monitoring of exposure to Mn in the occupational setting (inhalation) and in the general population (air, drinking water). In conclusion, it would be inappropriate to recommend, on the basis of the currently available evidence, a reliable well-validated biomarker of exposure to Mn, or to establish a health-based threshold value for subclinical neurotoxic effects.

Reconsideration of the WHO NCTB strategy and test selection

The World Health Organization-recommended neurobehavioral core test battery (NCTB) became the international standard for identifying adverse human behavioral effects due to neurotoxic chemical exposure when it was first proposed in 1983. Since then the WHO NCTB has been repeatedly cited as the basis for test selection in human neurotoxicology research. A discussion group was held before the International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health to review the NCTB and reconsider its tests. The workshop made three consensus recommendations to the International Congress on Occupational Health (ICOH) Scientific Committee on Neurotoxicology and Psychophysiology (SCNP):. 1. A 'screening' battery of broadly sensitive tests is needed as guidance to the field of human neurotoxicology 2. The SCNP should convene a panel to reconsider the functions measured and the tests in the WHO NCTB 3. Three disciplines should be represented in the panel recommending a revised NCTB: neuropsychology; experimental psychology; neurology. This recommendation will be pursued at the next meeting of the International Congress on Occupational Health (ICOH) Scientific Committee on Neurotoxicology and Psychophysiology (SCNP).