Late motor deficits of Chilean manganese miners: a blinded control study

The effects of manganese overexposure on brain health

Manganese (Mn) is the twelfth most abundant element on the earth and an essential metal to human health. Mn is present at low concentrations in a variety of dietary sources, which provides adequate Mn content to sustain support various physiological processes in the human body. However, with the rise of Mn utility in a variety of industries, there is an increased risk of overexposure to this transition metal, which can have neurotoxic consequences. This risk includes occupational exposure of Mn to workers as well as overall increased Mn pollution affecting the general public. Here, we review exposure due to air pollution and inhalation in industrial settings; we also delve into the toxic effects of manganese on the brain such as oxidative stress, inflammatory response and transporter dysregulation. Additionally, we summarize current understandings underlying the mechanisms of Mn toxicity.

Oxidative induction of pro-inflammatory cytokine formation by human monocyte-derived macrophages following exposure to manganese in vitro

Manganese (as Mn(2+)), a superoxide dismutase mimetic, catalyzes the formation of the relatively stable membrane-permeable reactive oxygen species (ROS) hydrogen peroxide (H2O2), a mediator of intracellular redox signaling in immune and inflammatory cells. The goal of this study was to investigate the potential for Mn(2+), via its pro-oxidative properties, to activate production of pro-inflammatory cytokines/chemokines IL-1β, IL-6, IL-8, IFNγ, TNFα, and G-CSF by human monocyte-derived macrophages in vitro. For these studies, the cells were isolated from peripheral blood mononuclear leukocytes and matured to generate a population of large CD14/CD16 co-expressing cells. The monocyte-derived macrophages were then exposed to bacterial lipopolysaccharide (LPS, 1 μg/ml) or MnCl2 (25-100 μM)-alone or in combination-for 24 h at 37 °C, after which cell-free supernatants were analyzed using a multiplex cytokine assay procedure. Exposure of the cells to LPS caused modest statistically insignificant increases in cytokine production; MnCl2 caused dose-related increases in production of all six cytokines (achieving statistical significance of p < 0.0171- < 0.0005 for IL-1β, IL-6, IL-8, IFNγ, and TNFα). In the case of LPS and MnCl2 combinations, the observed increases in production of IL-1β, IL-6, IL-8, IFNγ, and G-CSF were greater than those seen with cells exposed to the individual agents. The Mn(2+)-mediated induction of cytokine production was associated with increased production of H2O2 and completely attenuated by inclusion of the H2O2-scavenger dithiothreitol, and partially by inhibitors of NF-κB and p38MAP kinase. The findings from the studies here help to further characterize the pro-inflammatory mechanisms that may underpin clinical disorders associated with excess exposure to Mn(2+), particularly those disorders seen in the central nervous and respiratory systems.

The effect of occupational exposure to manganese dust and fume on neuropsychological functioning in Australian smelter workers

Chronic low-level occupational exposure to manganese (Mn) is reportedly associated with the development of Parkinsonian-like symptoms. In a study of 143 manganese smelter workers, inhalable Mn exposure was associated with lower performances on the Digit Symbol Coding and Stroop tests; respirable Mn exposure was associated with improved Digit Symbol Coding test performance and reduced performance on the Trail Making (Part A), Matrix Reasoning, and Stroop tests. While these relationships reached statistical significance, the magnitude of these effects was significantly smaller than the standard error of measurement of the neuropsychological tests, indicating that these differences are not of clinical significance.

Quantitative analysis of tremors in welders

Background:

Workers chronically exposed to manganese in welding fumes may develop an extra-pyramidal syndrome with postural and action tremors.

Objectives:

To determine the utility of tremor analysis in distinguishing tremors among workers exposed to welding fumes, patients with Idiopathic Parkinson’s Disease (IPD) and Essential Tremor (ET).

Methods:

Retrospective study of recorded tremor in subjects from academic Movement Disorders Clinics and Welders. Quantitative tremor analysis was performed and associated with clinical status.

Results:

Postural tremor intensity was increased in Welders and ET and was associated with visibly greater amplitude of tremor with arms extended. Mean center frequencies (Cf) of welders and patients with ET were significantly higher than the mean Cf of PD subjects. Although both the welders and the ET group exhibited a higher Cf with arms extended, welders could be distinguished from the ET subjects by a significantly lower Cf of the rest tremor than that measured in ET subjects.

Conclusions:

In the context of an appropriate exposure history and neurological examination, tremor analysis may be useful in the diagnosis of manganese-related extra-pyramidal manifestations.

Chemobrain: a translational challenge for neurotoxicology

Neurotoxicity is a frequent accompaniment of cancer chemotherapy, and held by many oncologists to be the major dose-limiting side effect. It appears in many forms, but attracted attention during the past decade primarily because of complaints by patients of impaired cognitive function they have labeled as "chemobrain". Neuropsychological testing confirmed the validity of these complaints and has generated a substantial literature examining different aspects of cognitive impairment in various clinical populations undergoing a variety of treatments. Cognitive impairment is far from the only manifestation of neurotoxicity induced by chemotherapy, however. It alters sensory function and motor function as well. A critical need for patients is a suite of methods that will enable clinicians to trace the onset and progression of neurotoxicity so as to guide and balance decisions about the course of chemotherapy. This commentary describes some of the potential methods and encourages neurotoxicologists to enlist their unique skills in the service of these needs.

Neuropsychological testing for the assessment of manganese neurotoxicity: a review and a proposal

BACKGROUND

Manganese exposure can cause neurobehavioral and neurological signs and symptoms. A review of the literature was carried out in order to identify the most sensitive and effective methods to assess these outcomes.

METHODS

Studies on manganese exposure performed with neuropsychological tests were reviewed using Medline. Test methods, obtained outcomes, and dose-response relationships were considered. Based on the review and additional considerations, a testing battery for adult and children was identified.

RESULTS

A total number of 31 studies were reviewed and divided in 18 occupational, 7 environmental, and 6 on children. A large variety of tests exploring motor and cognitive functions and mood were applied. Neurobehavioral effects were dose-dependent in several studies and determined by much lower exposure levels compared to 1 mg Mn/m(3) in total dust which is considered to be the minimum concentration able to induce the classical clinical features of "manganism." Although through a wide variety of tests, the observed outcomes support the knowledge that manganese exposure can cause neurobehavioral effects. Motor functions are mainly affected in adults, and cognitive functions and behavior are more affected in children.

CONCLUSIONS

Literature on manganese neurobehavioral effect is quite consistent, however, further improvement may be achieved by using better structured and more comparable evaluation methods. Based on the analysis of the existing experiences a test battery including tests of motor functions, response speed, cognitive functions, intellectual abilities, mood, and symptom questionnaires is suggested. We recommend that the tests indicated should always be included in future studies as a core battery.

Neurobehavioral functioning after cessation of manganese exposure: a follow-up after 14 years

BACKGROUND

Little is known on the long-term course of early manganese (Mn) neurotoxic effects. Mn alloy workers were examined in a follow-up study 14 years after exposure ceased at a Canadian facility.

METHODS

The same battery of neurofunctional tests used in the initial examination in 1990 was administered to 77 Mn-workers and 81 referents in 2004.

RESULTS

Manganese-workers had poorer scores compared to referents both in the initial and follow-up examinations for several motor tasks of the Luria Motor Scale. At follow-up, older Mn-workers (>45 years at cessation of exposure) had poorer scores than referents for tests of cognitive flexibility. Cumulated exposure was associated with poorer test scores for certain neuromotor and cognitive tests and on a mood scale. Differences on certain tests observed at initial examination were not present at follow-up.

CONCLUSIONS

Manganese exposure was associated with persistent deficits for certain neuromotor functions, cognitive flexibility, and adVerse mood states, while recovery occurred for other functions.

State-of-the-science review: Does manganese exposure during welding pose a neurological risk?

Recent studies report that exposure to manganese (Mn), an essential component of welding electrodes and some steels, results in neurotoxicity and/or Parkinson's disease (PD) in welders. This "state-of-the-science" review presents a critical analysis of the published studies that were conducted on a variety of Mn-exposed occupational cohorts during the last 100 yr, as well as the regulatory history of Mn and welding fumes. Welders often perform a variety of different tasks with varying degrees of duration and ventilation, and hence, to accurately assess Mn exposures that occurred in occupational settings, some specific information on the historical work patterns of welders is desirable. This review includes a discussion of the types of exposures that occur during the welding process--for which limited information relating airborne Mn levels with specific welding activities exists--and the human health studies evaluating neurological effects in welders and other Mn-exposed cohorts, including miners, millers, and battery workers. Findings and implications of studies specifically conducted to evaluate neurobehavioral effects and the prevalence of PD in welders are also discussed. Existing exposure data indicate that, in general, Mn exposures in welders are less than those associated with the reports of clinical neurotoxicity (e.g., "manganism") in miners and smelter workers. It was also found that although manganism was observed in highly exposed workers, the scant exposure-response data available for welders do not support a conclusion that welding is associated with clinical neurotoxicity. The available data might support the development of reasonable "worst-case" exposure estimates for most welding activities, and suggest that exposure simulation studies would significantly refine such estimates. Our review ends with a discussion of the data gaps and areas for future research.

A neurobehavioral study of current and former welders exposed to manganese

Neurobehavioral functions were studied in 96 welders currently exposed to the geometric mean (GM) concentration of 121 microg/m(3) (range 7-2322) manganese (Mn) in welding fume (air-Mn) based on the individual mean from two successive days of sampling. They were compared to 96 age-matched referents. The arithmetic mean (AM) concentration of Mn in whole blood (B-Mn) was 8.6 microg/L versus 6.9 microg/L in the referents. Associations between the Digit Symbol and Finger Tapping test scores and B-Mn and air-Mn, respectively, were observed. The welders exposed to the highest air-Mn concentrations (GM 423 microg/m(3) range 204-2322) had statistically significantly poorer Finger Tapping test score as compared to their age-matched referents. The welders with the highest AM concentration of B-Mn (12.6 microg/L) scored statistically significantly poorer on the Digit Symbol test when compared to the age-matched referents (AM B-Mn 7.5 microg/L). The same neurobehavioral test battery was applied to 27 patients diagnosed, and financially compensated, as having welding related manganism. They were on average 44.9 (range 34-51) years old at the time of diagnosis, which on average was 5.8 years prior to this study. They had worked as welders for 23.1 years on average (range 15-30). The most affected neurobehavioral functions were associated with impaired Finger Tapping speed and Grooved Pegboard performance. The patients had no alterations in hand tremor as assessed by the CATSYS system, while a few subjects had noticeable tremor as assessed by the Static Steadiness test.

Neuromotor function in a cohort of Danish steel workers

OBJECTIVE

With a longitudinal design to evaluate possible neuromotor impairment in a cohort of steel workers exposed to metal dust.

MATERIAL

Ninety-two employees from a steel works were examined in 1989 and 1995. Sixty were re-examined in 2003. A non-matched control group was examined in 1996 (n=19) and in 2003 (n=14). Median blood manganese in 1989, 1995 and 2003 was 149, 171 and 155 nmol/l. Median blood lead in 1989 and 2003 was 0.76 and 0.22 micromol/l. Median air concentration of manganese at the steel works was estimated to be 0.11 mg/m3 in 1970s and was 0.03 mg/m3 in 1990s. Median air concentration of lead was estimated to be 0.13 mg/m3 in 1970s and was 0.01 mg/m3 in 1990s.

METHOD

The Catsys 2000 system developed by Danish Product Development is computer-based device for measuring hand tremor, hand coordination and reaction time.

RESULTS

Over all there were no statistically significant differences in neuromotor function between the participating steel workers, non-participating steel workers and controls in 1995/1996. Only reaction time for the right hand was slower for the participating steel workers. Compared with the control group the steel workers showed a decline in the ability to perform fast precise hand pronation/supination and finger tapping from 1995 to 2005. Correlation analysis showed no associations between test results for fast hand coordination and blood manganese and lead. Only seniority was associated with deterioration of beat regulation of fast pronation/supination of the hands.

DISCUSSION

On a group basis the changes were subclinical, but they should none the less be taken seriously.

CONCLUSION

Changes of neuromotor function measured as the ability to perform fast precise pronation/supination of the hands and fast precise finger tapping was shown in this cohort of steel workers. No causal relationships could be shown.

Neuropsychological correlates of manganese exposure: A meta-analysis

The hypothesized effect of recurrent low-dose manganese (Mn) exposure on neuropsychological function is controversial because of inconsistent findings across three decades of research. We conducted a meta-analysis on 41 variables from nineteen neuropsychological studies of Mn-exposed workers. The results showed: Large effect size (ES) for biological markers of Mn and lead levels; thirteen of 26 neurocognitive measures showing a small average ES; only one of 26 tasks showed a moderate ES; and small to medium ES for confounding/competing variables such as education and aptitude. Tasks with the highest ES included clerical substitution tasks, digit span, tapping endurance, and Swedish Performance Evaluation System "Additions" reaction time, but none exceeded the ES for education or aptitude. The mean ES of dose-response relationships was zero. The data did not support a theory of preclinical ("early") neuromotor or cognitive dysfunction. Overall, the pooled data are more consistent with covariate effect than toxic effect, insofar as the pooled exposure group showed demographics less favorable to neuropsychological performance than the pooled referent groups. Future consideration of demographic and biological covariates is necessary before inferring subtle toxin-induced brain damage because neuropsychological tests are nonspecific.

Is electric arc welding linked to manganism or Parkinson's disease?

Manganese and its inorganic compounds are widely used in many industries and have been accepted as occupational neurotoxins that have caused a distinct and disabling clinical entity, manganism, in several types of work, notably where exposure is by way of dust. There is inconclusive and inconsistent evidence that, in these occupations, subclinical neurological effects, detectable only by neurobehavioural studies, may be caused by low doses. This has prompted a re-evaluation of occupational exposure limits. Some countries, including the UK, already demand much higher levels of protection against exposure than 5 years ago. Welding is the most common source of occupational exposure as manganese is an essential component of steel and so its compounds are inevitable components of fume emitted from steel welding processes. There it is found in respirable particles, often as complex oxides (spinels), sometimes within a core protected by a silicon oxide shell - as distinct from the much simpler form of particle formed by disintegration in processes such as mining and ore milling where manganism has been diagnosed convincingly. Millions of workers are at risk of exposure to manganese-containing compounds in fumes from electric arc welding of steel. In recent years it has been asserted that neurological and neurobehavioural disorders may develop consequent to exposure to steel welding fumes and that employment as a welder is associated with the unusually early onset of Parkinson's disease. Causal relationships have been postulated. Welders have been recorded as having been exposed to high levels of manganese-containing fume, especially where they have worked in confined, unventilated spaces, although this appears from limited data to be the exception rather than the rule. Even then the dose received is generally less than in mining or ore crushing. When care is taken to exclude exposures from hardfacing and burning and cutting arc processes, where manganese may form a high percentage of the fume, manganese compounds usually form a relatively low percentage of the composition of welding fume particles, <2.0%, much outweighed by iron. Although these manganese-compound-containing welding fume particles are insoluble in water, the manganese compounds in particles that are retained in the alveoli may be absorbed, at least in part. Manganese concentrations in biological material samples in some exposed groups reflect this relative to unexposed workers. Some of the transfer systems for absorption and transport, including across the blood-brain barrier, are used in competition with iron which is present in abundance in welding fume. This may reduce absorption of manganese in welders and thus reduce the opportunity for sufficient doses to cause neurotoxicological consequences. Scrutiny of the literature covering the last 40 years has revealed only five cases that meet sufficient criteria for manganism to just cross the diagnostic threshold, and even then they carry a degree of doubt with them. This low incidence alone gives notice that welders have not been and are not at high risk of clinically apparent damage from exposure to manganese. If this needs to be further emphasised, there is the fact that the literature contains no confirmed cases of manganism in welders. Assertions of abnormal results in neurobehavioural studies of welders have raised the possibility of there being a subclinical form of manganism with loss of fine motor control as one of its features. While observations of such changes in workers in other industries have caused regulators in some countries to apply more stringent controls of exposure, as yet the results lack convincing consistency and there is no indication of any dose-effect relationship. If welding fume can have these motor effects it would be a heavy and perhaps career-ending blow to those affected. It would not be prudent to dismiss the warnings sounded by the results of studies of welders, no matter how flawed these investigations are, but wiser and better to act with vigour to reduce exposure and monitor the effectiveness of this additional protection whilst conducting high quality research to allow sound conclusions to be drawn as to whether there actually is a subclinical disorder. Idiopathic Parkinson's disease is a common disorder affecting 1-2% of those in the general population aged >65 years. It has been suggested, on flawed and contested evidence, not that welding causes the disease but rather that employment as a welder carries with it the risk of developing this disease at a younger age than if that trade had not been followed. Manganese in welding fume has been nominated as the neurotoxin. This may be biologically feasible if manganese destroys insufficient receptor cells to produce clinical manganism but sufficient to enhance the effects of a reduced supply of dopamine to give the manifestations of already developing idiopathic Parkinson's disease earlier in the course of destruction of the substantia nigra than if all receptors were intact.

Postnatal manganese exposure attenuates cocaine-induced locomotor activity and reduces dopamine transporters in adult male rats

In the present study, we examined whether exposing rats to manganese (Mn) during the preweanling period would affect basal or cocaine-induced locomotor activity in adulthood and reduce the number of striatal dopamine transporter binding sites. On postnatal day (PD) 1-21, rats were given oral supplements of vehicle or Mn chloride (250 or 750 microg/day). Striatal Mn and iron (Fe) accumulation as well as serum Fe levels were measured on PD 14, PD 21, and PD 90. Throughout the dosing period, rats were evaluated on standard measures of sensory and motor development. During adulthood, the basal and cocaine-induced locomotor activity of vehicle- and Mn-exposed rats was assessed using automated testing chambers. After completion of behavioral testing, striatal dopamine transporter binding sites were measured using [(3)H]GBR 12935. Results showed that early Mn exposure enhanced striatal Mn accumulation on PD 14 and PD 21, while depressing serum Fe levels on PD 21. Exposure to Mn on PD 1-21 did not affect striatal or serum Mn or Fe levels on PD 90. During the second postnatal week, Mn-exposed rat pups performed more poorly than controls on a negative geotaxis task, however basal motor activity of preweanling rat pups was not affected by Mn treatment. When tested in adulthood, basal locomotor activity of vehicle- and Mn-exposed rats also did not differ. In contrast, adult rats previously exposed to 750 microg/day Mn showed an enhanced locomotor response when challenged with 10 mg/kg cocaine. A different pattern of results occurred after treatment with a higher dose of the psychostimulant, because Mn-exposed rats showed an attenuated locomotor response when given 20 mg/kg cocaine. Importantly, Mn-exposed rats exhibited long-term reductions in striatal dopamine transporter binding sites. Considered together, these results indicate that postnatal Mn exposure has long-term behavioral and neurochemical effects that can persist into adulthood.

A Meta-Analysis of the Neuropsychological Effects of Occupational Exposure to Manganese

This article reports a meta-analysis of 25 samples in 20 peer-reviewed published neuropsychological studies of the cognitive, psychological, motor, and sensory/perceptual effects of exposure to manganese. These studies included 1,410 exposed participants and 1,322 controls, for a total N = 2,732. Studies were excluded from this analysis if they were unpublished, had uncodeable data, were based on fewer than four participants, failed to have a comparison group, or reported on manganese effects other than cognitive or sensory/motor (e.g., liver functioning). Because the independent variables defining manganese exposure varied across studies, effect sizes were calculated for exposed versus non-exposed workers. Dose-response relations were considered for measures of manganese levels in air/dust (84% of studies reported), blood (MnB; 76% reported), urine (MnU; 52% reported), and hair samples (4% reported). Level of exposure was also estimated by reported years of exposure (M = 13.1 years). Cohen's d statistic yielded a statistically significant weighted mean effect size of - .17, p < .0001 for manganese exposure. However, an effect this small is typically undetectable when evaluating individuals because it is smaller (about 1/6 SD) than the confidence intervals of most neuropsychological measures. Because the effect is so slight and the overlap so great between exposed and unexposed participants (87%), the error rate would exceed the hit rate if causal conclusions were rendered for occupational exposure to manganese as the source of an individual's cognitive, sensory, or motor impairments based on neuropsychological testing or symptom reports.

Manganese exposure: neuropsychological and neurological symptoms and effects in welders

Manganese exposure reportedly may have an adverse effect on CNS function and mood. Sixty-two welders with clinical histories of exposure to manganese were compared to 46 matched regional controls chosen at random from a telephone directory. The following tests were given: Wechsler Adult Intelligence Scale (WAIS-III), Wechsler Memory Scale (WMS-III), Boston Naming, WRAT-3, Cancellation H, Trail Making Tests A and B, Auditory Consonant Trigrams, Stroop, Rey-Osterreith, Animal Naming, Controlled Oral Word Association (COWAT), Test of Memory Malingering, Rey 15-item, Fingertapping, Grooved Pegboard, Dynamometer, Visual Attention Test, Lanthony d-15 Color Vision, Vistech Contrast Sensitivity, and Schirmer strips. The controls were administered a shorter battery of tests and the Rey-Osterreith, Animal Naming and some of the subtests of the WAIS-III, WMS-III were not administered. Mood tests, given to both groups, included the Symptom Checklist-40, Symptom Checklist-90-R, Profile of Mood Scale, Beck Depression Inventory II, and Beck Anxiety Inventory. Forty-seven welders and 42 controls were retained for statistical analysis after appropriate exclusions. Results showed a high rate of symptom prevalence and pronounced deficits in motor skills, visuomotor tracking speed and information processing, working memory, verbal skills (COWAT), delayed memory, and visuospatial skills. Neurological examinations compared to neuropsychological test results suggest that neuropsychologists obtain significantly more mood symptoms overall. Odds ratios indicate highly elevated risk for neuropsychological and neurological symptomatology of manganism. Mood disturbances including anxiety, depression, confusion, and impaired vision showed very high odds ratios. Neurological exams and neuropsychological tests exhibit complementarity and differences, though neuropsychological methods may be more sensitive in detecting early signs of manganism. The present study corroborates the findings of our previous study in another group of welders.

Pharmacokinetic and pharmacodynamic factors that can affect sensitivity to neurotoxic sequelae in elderly individuals

Early-life exposure to agents that modulate neurologic function can have long-lasting effects well into the geriatric period. Many other factors can affect neurologic function and susceptibility to neurotoxicants in elderly individuals. In this review we highlight pharmacokinetic and pharmacodynamic factors that may increase geriatric susceptibility to these agents. There is a decreasing trend in hepatic metabolizing capacity with advancing years that can affect the ability to clear therapeutic drugs and environmental chemicals. This factor combined with decreased renal clearance causes prolonged retention of numerous drugs in elderly individuals. A geriatric pharmacokinetic database was developed to analyze changes in drug clearance with advancing age. This analysis shows that the half-life of drugs processed by hepatic cytochrome P450 enzymes or via renal elimination is typically 50-75% longer in those older than 65 than in young adults. Liver and kidney diseases are more common in elderly individuals and can further decrease the clearance function of these organs. Polypharmacy, the administration of numerous drugs to a single patient, is very common in elderly individuals and increases the risks for drug interaction and side effects. With advancing age the nervous system undergoes a variety of changes, including neuronal loss, altered neurotransmitter and receptor levels, and decreased adaptability to changes induced by xenobiotics. These changes in the central nervous system can make elderly individuals more susceptible to neurologic dysfunction when confronted with single pharmacologic agents, polypharmacy, or environmental toxicants. The many factors that affect elderly responses to neuroactive agents make environmental risk assessment for this age group a special concern and present a unique challenge.

Economic implications of manganese neurotoxicity

Manganese neurotoxicity is linked primarily to inhalation exposure, and its clinical features are almost totally based on high doses, such as those experienced by miners. Manifestations of lower level exposures can take two forms. One is the appearance of neurobehavioral deficits. A second, equally subtle, form is as a promoter, borrowing the term used in carcinogenesis, of neurodegenerative disease. Such low-level environmental exposures may be more potent than expected if they occur as ultrafine particles able to penetrate directly into the brain. The neurological disorder linked most closely to manganese is Parkinson's disease (PD). Although most observers recognize that the features of manganese-induced parkinsonism differ from those of idiopathic PD, they overlap considerably. The overlaps should be expected because the underlying lesions, although distinguishable, are closely linked because they belong to structures with complex interdependent circuitry. Such interdependence makes it feasible to undertake an analysis of how manganese neurotoxicity might elevate the risks of PD. A relatively small increment in risk, expressed as a leftward shift in the age prevalence of PD, incurs significant economic costs.

Manganese exposure and age: neurobehavioral performance among alloy production workers

Manganese (Mn) is associated with neurotoxic effects under certain conditions of exposure. A recent study on environmental Mn exposure showed an Mn×age interaction for several neurobehavioral functions. The objective of the present study was to examine the neurobehavioral test results in relation to age and Mn exposure, using an existing data set on 74 workers from an Mn alloy production plant and referents pair-matched for age (±3 years), educational level (±2 years), number of children, and smoking status. The pair differences between Mn-exposed workers and referents increased significantly with age for scores on Delayed Word Recall, Trail Making B, Cancellation H, Nine-Hole Hand Steadiness Test, and Vibratometer. These results suggest that for certain neurobehavioral functions, and in particular for information processing, Mn-related deficits increase with age. This outcome could not be explained by higher cumulative Mn exposure.

Manganese-induced parkinsonism and Parkinson's disease

It has long been appreciated that manganese exposure can cause neurotoxicity and a neurologic syndrome that resembles Parkinson's disease (PD). Current evidence indicates that manganese-induced parkinsonism can be differentiated from PD because of its predilection to accumulate in and damage the pallidum and striatum rather than the SNc. The clinical syndrome, response to levodopa, imaging studies with MRI and PET, and pathologic features all help to distinguish these two conditions and permit the correct diagnosis to be established. This is of particular relevance in differentiating patients with parkinsonism due to manganese intoxication from patients with idiopathic PD who have incidental manganese exposure.

Determination of an occupational exposure guideline for manganese using the benchmark method

An occupational risk assessment for manganese (Mn) was performed based on benchmark dose analysis of data from two epidemiological studies providing dose-response information regarding the potential neurological effects of exposure to airborne Mn below the current Occupational Safety and Health Administration (OSHA) Permissible Exposure Level (PEL) of 5 mg Mn/m3. Based on a review of the scientific evidence regarding the toxicity of Mn, it was determined that the most appropriate measure of exposure to airborne Mn for the subclinical effects measured in these studies is recent (rather than historical or cumulative) concentration of Mn in respirable (rather than total) particulate. For each of the studies analyzed, the individual exposure and response data from the original study had been made available by the investigators. From these two studies benchmark concentrations calculated for eight endpoints ranged from 0.09 to 0.27 mg Mn/m3. From our evaluation of these results, and considering the fact that the subtle, subclinical effects represented by the neurological endpoints tested in these studies do not represent material impairment, we believe an appropriate occupational exposure guideline for manganese would be in the range of 0.1 to 0.3 mg Mn/m3, based on the respirable particulate fraction only, and expressed as an 8-hour time-weighted average.

Nervous system effects of occupational manganese exposure on South African manganese mineworkers

Occupational exposure to airborne manganese dust has been shown to produce adverse effects on the central nervous system. Four hundred and eighty-nine blue and white collar manganese mineworkers from South Africa were studied cross-sectionally to investigate the nervous system effects of medium to low occupational manganese exposures. The different facilities included underground mines, surface processing plants, and office locations. A job exposure matrix was constructed using routine occupational hygiene data. Exposure variables included years of service, a cumulative exposure index (CEI) and average intensity of exposure (AINT) across all jobs, and blood manganese. Endpoints included items from the Q16, WHO-NCTB, SPES, and Luria-Nebraska test batteries, and a brief clinical examination. Potential confounders and effect modifiers included age, level of education, past medical history including previous head injury, previous neurotoxic job exposures, tobacco use, alcohol use and home language. Associations were evaluated by multiple linear and logistic regression modeling. Average exposure intensity across all jobs was 0.21mg/m(3) manganese dust. Multivariate analyses showed that none of the symptom nor test results were associated with any measure of exposure including blood manganese, after adjustment for confounders. This relatively large null study indicates that manganese miners exposed on average across all jobs to MnO(2) at levels near the American Conference of Governmental Industrial Hygienists Threshold Limit Value (ACGIH TLV) are unlikely to have a subclinical neurotoxicity problem.

Neurologic effects of manganese in humans: a review

Manganese, which enters the body primarily via inhalation, can damage the nervous system and respiratory tract, as well as have other adverse effects. Occupational exposures occur mainly in mining, alloy production, processing, ferro-manganese operations, welding, and work with agrochemicals. Among the neurologic effects is an irreversible parkinsonian-like syndrome. An estimated 500,000 to 1.5 million people in the United States have Parkinson's disease, and physicians need to consider manganese exposure in its differential diagnosis. Since 1837, there have been many reports of cases and case series describing manganese toxicity. More recently, there have been epidemiologic studies of its adverse effects on health. Occupational medicine physicians can play critical roles in preventing the adverse health effects of manganese.

Neurological effects in workers exposed to manganese

The purpose of this study was to examine the effects on the nervous system in enamels-production workers who have low levels of and long exposure to manganese (Mn). The study included 138 Mn-exposed workers and 137 controls who received questionnaires on symptoms, a battery of psychological tests, and assessments of blood concentrations of metal. The exposure levels to airborne Mn concentrations were determined by personal and stationary samplings. The mean duration exposure to Mn was 19.87 years (SD +/- 9). The workers exposed to Mn reported more nonspecific subjective complaints than the control group. No effect of Mn exposure was indicated by the results of any of the neuropsychological tests. The Mn workers did not have higher concentrations of Mn in blood than the controls. Exposures of workers currently working with Mn averaged 57 micrograms/m3 respirable (personal samplings) and 12 g/m3 (stationary samplings). In conclusion, long exposure to low levels of Mn (approximately 200 micrograms/m3), as induced in our study, showed no significant disturbance of neurological performance.

Factors associated to hypermanganesemia in patients receiving home parenteral nutrition

BACKGROUND

Home parenteral nutrition (HPN) patients often present hypermanganesamia.

AIM

To examine which factors may be associated to hypermanganesemia in HPN patients.

METHODS

Plasma manganese (Mn), liver function tests, C-reactive protein concentrations, erythrocyte sedimentation rate (ESR), tumor necrosis factor-alpha (TNF- alpha), interleukin-6, soluble receptors of interleukin-2, and blood neopterin concentrations were determined in 21 HPN patients and 10 healthy controls. Brain magnetic resonance imaging (MRI) and careful neurologic clinical examination were performed in 11 patients.

RESULTS

Mn concentration was higher in HPN patients than controls (1.96+/-1.1 vs 0.81+/- 0.4 microg/L;P<0.001) and positively correlated to the amount of parenteral nutrition (PN) supply, transaminases and alkaline phosphatase (r=0.53, P<0.0001) concentrations, as well as to ESR (r=0.61, P<0.0001), TNF- alpha and blood neopterin. The amount of calories provided by PN was positively correlated to inflammatory markers and liver parameters. All patients investigated by MRI showed hyperintense basal ganglia on T1-weighted images suggesting brain Mn deposition. Only one had slight clinical extrapyramidal symptoms.

CONCLUSION

In HPN patients, sustained inflammation may facilitate hypermanganesemia through 1. cholestatic liver disease and thereby decreased Mn biliary excretion, 2. high nutritional requirements (responsible for increased Mn supply), and/or 3. modified Mn metabolism or body distribution. Neurologic complications appeared marginal whereas Mn brain deposition seems frequent.

Validation of a portable instrument for assessing tremor severity in epidemiologic field studies

BACKGROUND

An important part of epidemiologic and genetic studies of essential tremor (ET) is an assessment of tremor severity. Clinical rating scales are semiquantitative and computerized tremor analysis, available at tertiary medical centers, is not transportable into the field. As part of an epidemiologic study, we modified the Klove-Matthews Motor Steadiness Battery, collecting objective quantitative data on tremor severity in patients with ET and control subjects.

OBJECTIVE

To describe the modified Klove-Matthews Motor Steadiness Battery, validate this test battery against several other measures of tremor severity, demonstrate test-retest reliability, and provide standard reference values for normal control subjects and patients with ET who undergo this test battery.

METHODS

Patients with ET and control subjects, ascertained from both a clinic and a community, underwent a standardized evaluation including a demographic and medical questionnaire, tremor disability questionnaire, videotaped tremor examination, performance-based test, modified Klove-Matthews Motor Steadiness Battery (Groove-Type Steadiness Tester [GTST] and Nine-Hole Steadiness Tester [NHST]), and quantitative computerized tremor analysis.

RESULTS

There were 19 patients with ET and 28 control subjects. NHST and GTST total scores were correlated significantly with the tremor disability questionnaire score (r = 0.63, p = 0.001 and r = 0.49, p = 0.016), total tremor score (tremor examination, r = 0.68, p<0.001 and r = 0.41, p = 0.005), performance-based test score (r = 0.81, p<0.001 and r = 0.65, p = 0.001), and quantitative computerized tremor analysis results (for example, spiral drawing, r = 0.62, p = 0.01 and r = 0.58, p = 0.019). Test-retest reliability was generally high (r = 0.79-0.94, p<0.001).

CONCLUSION

The modified Klove-Matthews Motor Steadiness Battery provides a reliable and valid means to collect objective quantitative data on tremor severity. Rapidity of administration and ease of transport make it a potentially useful tool in epidemiologic and genetic field studies.

Manganese

Manganese is a very hard, brittle metal, which is used to increase the strength of steel alloys. Absorption from the gastrointestinal tract occurs in the divalent and tetravalent forms. Permanganates, which are strong oxidizing agents, have a +7 valence. The principal organomanganese compound is the anti-knock additive, methylcyclopentadienyl manganese tricarbonyl. Manganese is a ubiquitous constituent of the environment comprising about 0.1% of the earth's crust. For the general population, food is the most important source of manganese with daily intake ranging from 2-9 mg Mn. Combustion of gasoline containing methylcyclopentadienyl manganese tricarbonyl releases submicron particles of Mn3O4 that are potentially respirable. Biomagnification of manganese in the food chain probably does not occur. The lungs and gastrointestinal tract absorb some manganese, but the relative amounts absorbed from each site are not known. Homeostatic mechanisms limit the absorption of manganese from the gastrointestinal tract. Elimination of manganese occurs primarily by excretion into the bile. Animal studies indicate that manganese is an essential co-factor for enzymes, such as hexokinase, superoxide dismutase, and xanthine oxidase. However, no case of manganese deficiency in humans has been identified. Manganism is a central nervous system disease first described in the 1800s following exposure to high concentrations of manganese oxides. Manganese madness was the term used to describe the initial psychiatric syndrome (compulsive behavior, emotional lability, hallucinations). More commonly, these workers developed a Parkinson's-like syndrome. Currently, the risks of exposure to low concentrations of manganese in the industrial and in the environmental settings (e.g., methylcyclopentadienyl manganese tricarbonyl in gasoline) are being evaluated with regards to the development of subclinical neuropsychological changes. The American Conference of Governmental and Industrial Hygienists recently lowered the TLV-TWA for manganese compounds and inorganic manganese compounds to 0.2 mg Mn/m3.