Chronic occupational exposure to manganese and neurobehavioral function

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.

The association of bone, fingernail and blood manganese with cognitive and olfactory function in Chinese workers

Occupational manganese (Mn) exposure has been associated with cognitive and olfactory dysfunction; however, few studies have incorporated cumulative biomarkers of Mn exposure such as bone Mn (BnMn). Our goal was to assess the cross-sectional association between BnMn, blood Mn (BMn), and fingernail Mn (FMn) with cognitive and olfactory function among Mn-exposed workers. A transportable in vivo neutron activation analysis (IVNAA) system was designed and utilized to assess BnMn among 60 Chinese workers. BMn and FMn were measured using inductively coupled plasma mass spectrometry. Cognitive and olfactory function was assessed using Animal and Fruit Naming tests, World Health Organization/University of California-Los Angeles Auditory Verbal Learning Test (AVLT) and the University of Pennsylvania Smell Identification Test (UPSIT). Additional data were obtained via questionnaire. Regression models adjusted for age, education, factory of employment, and smoking status (UPSIT only), were used to assess the relationship between Mn biomarkers and test scores. In adjusted models, increasing BnMn was significantly associated with decreased performance on average AVLT scores [β (95% confidence interval (CI)) = -0.65 (-1.21, -0.09)] and Animal Naming scores [β (95% CI) = -1.54 (-3.00, -0.07)]. Increasing FMn was significantly associated with reduced performance measured by the average AVLT [β (95% CI) = -0.35 (-0.70, -0.006)] and the difference in AVLT scores [β (95% CI) = -0.40 (-0.77, -0.03)]. BMn was not significantly associated with any test scores; no significant associations were observed with Fruit Naming or UPSIT tests. BnMn and FMn, but not BMn, are associated with cognitive function in Mn-exposed workers. None of the biomarkers were significantly associated with olfactory function.

Glial-neuronal signaling mechanisms underlying the neuroinflammatory effects of manganese

BACKGROUND

Exposure to increased manganese (Mn) causes inflammation and neuronal injury in the cortex and basal ganglia, resulting in neurological symptoms resembling Parkinson's disease. The mechanisms underlying neuronal death from exposure to Mn are not well understood but involve inflammatory activation of microglia and astrocytes. Expression of neurotoxic inflammatory genes in glia is highly regulated through the NF-κB pathway, but factors modulating neurotoxic glial-glial and glial-neuronal signaling by Mn are not well understood.

METHODS

We examined the role of NF-κB in Mn-induced neurotoxicity by exposing purified microglia, astrocytes (from wild-type and astrocyte-specific IKK knockout mice), and mixed glial cultures to varying Mn concentrations and then treating neurons with the conditioned media (GCM) of each cell type. We hypothesized that mixed glial cultures exposed to Mn (0-100 μM) would enhance glial activation and neuronal death compared to microglia, wild-type astrocytes, or IKK-knockout astrocytes alone or in mixed cultures.

RESULTS

Mixed glial cultures treated with 0-100 μM Mn for 24 h showed the most pronounced effect of increased expression of inflammatory genes including inducible nitric oxide synthase (Nos2), Tnf, Ccl5, Il6, Ccr2, Il1b, and the astrocyte-specific genes, C3 and Ccl2. Gene deletion of IKK2 in astrocytes dramatically reduced cytokine release in Mn-treated mixed glial cultures. Measurement of neuronal viability and apoptosis following exposure to Mn-GCM demonstrated that mixed glial cultures induced greater neuronal death than either cell type alone. Loss of IKK in astrocytes also decreased neuronal death compared to microglia alone, wild-type astrocytes, or mixed glia.

CONCLUSIONS

This suggests that astrocytes are a critical mediator of Mn neurotoxicity through enhanced expression of inflammatory cytokines and chemokines, including those most associated with a reactive phenotype such as CCL2 but not C3.

Inflammatory Activation of Microglia and Astrocytes in Manganese Neurotoxicity

Neurotoxicity due to excessive exposure to manganese (Mn) has been described as early as 1837 (Couper, Br Ann Med Pharm Vital Stat Gen Sci 1:41-42, 1837). Extensive research over the past two decades has revealed that Mn-induced neurological injury involves complex pathophysiological signaling mechanisms between neurons and glial cells. Glial cells are an important target of Mn in the brain, both for sequestration of the metal, as well as for activating inflammatory signaling pathways that damage neurons through overproduction of numerous reactive oxygen and nitrogen species and inflammatory cytokines. Understanding how these pathways are regulated in glial cells during Mn exposure is critical to determining the mechanisms underlying permanent neurological dysfunction stemming from excess exposure. The subject of this review will be to delineate mechanisms by which Mn interacts with glial cells to perturb neuronal function, with a particular emphasis on neuroinflammation and neuroinflammatory signaling between distinct populations of glial cells.

Decreased brain volumes in manganese-exposed welders

BACKGROUND

A great deal of research has been devoted to identifying subclinical functional brain abnormalities in manganese (Mn)-exposed welders. However, no previous study has investigated morphological brain abnormalities, such as changes in brain volume, in welders. This study evaluates morphological changes in brain volume among welders, and investigates the relationship between structural brain abnormalities and subclinical dysfunction in this population.

METHODS

We used voxel-based morphometry (VBM) to assess differences in gray and white matter brain volumes between 40 welders with chronic Mn exposure and 26 age-matched control subjects. Correlation analyses were used to investigate the relationship between brain volume changes and decreased performance on neurobehavioral tests.

RESULTS

Brain volumes in the globus pallidus and cerebellar regions were significantly diminished in welders with chronic Mn exposure compared to controls (FDR-corrected P<0.05). These changes in brain volume were negatively correlated with cognitive performance and grooved pegboard scores.

CONCLUSION

There are measurable brain volume reductions in the globus pallidus and cerebellum of welders chronically exposed to Mn, and these volume reductions correlate with cognitive and motor neurobehavioral deficits. Our findings therefore indicate that volumetric measurement could be a useful subclinical marker among welders that show no signs of manganism.

Occupational neurotoxic diseases in taiwan

Occupational neurotoxic diseases have become increasingly common in Taiwan due to industrialization. Over the past 40 years, Taiwan has transformed from an agricultural society to an industrial society. The most common neurotoxic diseases also changed from organophosphate poisoning to heavy metal intoxication, and then to organic solvent and semiconductor agent poisoning. The nervous system is particularly vulnerable to toxic agents because of its high metabolic rate. Neurological manifestations may be transient or permanent, and may range from cognitive dysfunction, cerebellar ataxia, Parkinsonism, sensorimotor neuropathy and autonomic dysfunction to neuromuscular junction disorders. This study attempts to provide a review of the major outbreaks of occupational neurotoxins from 1968 to 2012. A total of 16 occupational neurotoxins, including organophosphates, toxic gases, heavy metals, organic solvents, and other toxic chemicals, were reviewed. Peer-reviewed articles related to the electrophysiology, neuroimaging, treatment and long-term follow up of these neurotoxic diseases were also obtained. The heavy metals involved consisted of lead, manganese, organic tin, mercury, arsenic, and thallium. The organic solvents included n-hexane, toluene, mixed solvents and carbon disulfide. Toxic gases such as carbon monoxide, and hydrogen sulfide were also included, along with toxic chemicals including polychlorinated biphenyls, tetramethylammonium hydroxide, organophosphates, and dimethylamine borane. In addition we attempted to correlate these events to the timeline of industrial development in Taiwan. By researching this topic, the hope is that it may help other developing countries to improve industrial hygiene and promote occupational safety and health care during the process of industrialization.

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.

Bone manganese as a biomarker of manganese exposure: a feasibility study

BACKGROUND

There is a need for a diagnostic tool with the ability to measure cumulative exposure to manganese (Mn) in the workplace. Measuring bone Mn levels with in vivo neutron activation analysis (IVNAA) could serve as a biomarker of past exposure. Bone Mn levels of welders were measured and compared to the levels found in subjects without exposure to the element.

METHOD

Forty subjects (30 welders and 10 controls) were recruited. An occupational history was obtained and subjects underwent IVNAA bone Mn measurements.

RESULTS

The mean bone Mn levels were (2.9 +/- 0.4) and (0.1 +/- 0.7) microg Mn/g Ca for welders and controls, respectively (P < 0.05).

CONCLUSIONS

This project, the first of its kind, reports differences in bone Mn between Mn-exposed welders and non-occupationally exposed subjects. It appears that bone Mn levels do reflect differences in the occupational exposure of welders.

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.

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.

Cognitive function in a cohort of Danish steel workers

OBJECTIVE

The aim of this study was to evaluate the level of possible cognitive impairment in a cohort of steel workers occupationally exposed to manganese and lead.

MATERIAL

Ninety-two employees from an electro-steel works were examined in 1989 and 1995. Fifty-three were re-examined in 2003. Median age of the participants was 53 years, median duration of employment was 24 years, median blood manganese in 1989 and 1995 was 148 and 171 nmol/l, respectively, and median blood lead in 1989 was 0.79 micromol/l. Non-participants were comparable with participants, although they had a higher level of blood manganese in 1989 (186 nmol/l) and 1995 (186 nmol/l). Manganese level in the air was estimated below 1.9 mg/m3 in the 1970s. In the 1990s, manganese level in the air was below 0.28 mg/m3 in the majority of measurements.

METHOD

Cognitive function was examined with the Cognitive Function Scanner, a computer-based neuropsychological test battery. From a published set of norms a subgroup (n=106) matched for gender, age and social status was extracted and used for comparison.

RESULTS

Learning and memory, visuomotor and visuospatial function, concentration, attention, perception and vigilance were examined. Despite many statistically significant differences between the groups, it was not possible to interpret the results for the steel workers as being better or worse. In a visuomotor subtest, the pen-to-point test, the steel workers were much less accurate than the comparison group. This could be the result of an impaired ability to make fast accurate movements. There were no associations between pen-to-point test results and duration of employment or blood levels of manganese and lead.

CONCLUSION

Intellectual impairment could not be shown with the Cognitive Function Scanner in this cohort of low to moderate manganese and lead exposed steel workers. A slight subclinical impairment of the visuomotor function was possibly found.

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.

Sequelae of fume exposure in confined space welding: a neurological and neuropsychological case series

Welding fume contains manganese (Mn) which is known to be bio-available to and neurotoxic for the central nervous system. Although an essential metal, Mn overexposure may cause manganism, a parkinsonian syndrome. The present welder study sought to improve the clinical portrait of manganism and to determine dose-effect relationships. The welders were employed in the construction of the new Bay Bridge (San Francisco) and welded in confined spaces for up to 2 years with minimal protection and poor ventilation. Neurological, neuropsychological, neurophysiological, and pulmonary examinations were given to 49 welders. Clinical cases were selected on the basis of apriori defined criteria pertaining to welding history and neurological/neuropsychological features. Among the 43 eligible welders, 11 cases of manganism were identified presenting with the following symptoms: sleep disturbance, mood changes, bradykinesia, headaches, sexual dysfunction, olfaction loss, muscular rigidity, tremors, hallucinations, slurred speech, postural instability, monotonous voice, and facial masking. Significant associations between outcome variables and cumulative exposure index (CEI) or blood Mn (MnB) were obtained with CEI for variables implicating attention and concentration, working and immediate memory, cognitive flexibility, and verbal learning; and with MnB for executive function, cognitive flexibility, visuo-spatial construction ability, and visual contrast sensitivity. This study strongly suggests that neuropsychological features contribute in a dose-effect related way to the portrait of manganism usually characterized by tremor, loss in balance, diminished cognitive performance, and signs and symptoms of parkinsonism.

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.

[18F]FDOPA PET and clinical features in parkinsonism due to manganism

Manganese exposure reportedly causes a clinically and pathophysiologically distinct syndrome from idiopathic Parkinson's disease (PD). We describe the clinical features and results of positron emission tomography with 6-[18F]fluorodopa ([18F]FDOPA PET) of a patient with parkinsonism occurring in the setting of elevated blood manganese. The patient developed parkinsonism associated with elevated serum manganese from hepatic dysfunction. [18F]FDOPA PET demonstrated relatively symmetric and severely reduced [18F]FDOPA levels in the posterior putamen compared to controls. The globus pallidum interna had increased signal on T1-weighted magnetic resonance imaging (MRI) images. We conclude that elevated manganese exposure may be associated with reduced striatal [18F]FDOPA uptake, and MRI may reveal selective abnormality within the internal segment of the pallidum. This case suggests that the clinical and pathophysiological features of manganese-associated parkinsonism may overlap with that of PD.

Methodological Problems in the Neuropsychological Assessment of Effects of Exposure to Welding Fumes and Manganese

Recently, Kaiser (2003) raised concerns over the increase in brain damage claims reportedly due to exposure to welding fumes. In the present article, we discuss methodological problems in conducting neuropsychological research on the effects of welding exposure, using a recent paper by Bowler et al. (2003) as an example to illustrate problems common in the neurotoxicity literature. Our analysis highlights difficulties in conducting such quasi-experimental investigations, including subject selection bias, litigation effects on symptom report and neuropsychological test performance, response bias, and scientifically inadequate casual reasoning.

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.

Behavioral impairments in acute and chronic manganese poisoning in white rats

Single p.o. doses of manganese chloride (MnCl2 x 4H2O; 50 mg/kg) induced significant and reversible decreases in total activity in white rats, along with worsening of the acquisition of an avoidance reaction in response to unconditioned and conditioned stimuli, increases in the latent period of conditioned reflex activity, and a temporary worsening of the learning process. Chronic manganese poisoning (daily p.o. manganese chloride at 20 or 50 mg/kg for one month) led to significant impairment of learning processes in a multipath maze but had no significant effect on reproduction of previously acquired stereotypical behavior.

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.

Potential health effects of gasoline and its constituents: A review of current literature (1990-1997) on toxicological data

We reviewed toxicological studies, both experimental and epidemiological, that appeared in international literature in the period 1990-1997 and included both leaded and unleaded gasolines as well as their components and additives. The aim of this overview was to select, arrange, and present references of scientific papers published during the period under consideration and to summarize the data in order to give a comprehensive picture of the results of toxicological studies performed in laboratory animals (including carcinogenic, teratogenic, or embryotoxic activity), mutagenicity and genotoxic aspects in mammalian and bacterial systems, and epidemiological results obtained in humans in relation to gasoline exposure. This paper draws attention to the inherent difficulties in assessing with precision any potential adverse effects on health, that is, the risk of possible damage to man and his environment from gasoline. The difficulty of risk assessment still exists despite the fact that the studies examined are definitely more technically valid than those of earlier years. The uncertainty in overall risk determination from gasoline exposure also derives from the conflicting results of different studies, from the lack of a correct scientific approach in some studies, from the variable characteristics of the different gasoline mixtures, and from the difficulties of correctly handling potentially confounding variables related to lifestyle (e.g., cigarette smoking, drug use) or to preexisting pathological conditions. In this respect, this paper highlights the need for accurately assessing the conclusive explanations reported in scientific papers so as to avoid the spread of inaccurate or misleading information on gasoline toxicity in nonscientific papers and in mass-media messages.

The effect of manganese-induced hypercholesterolemia on learning in rats

Since the exact mechanism of manganese (Mn)-induced learning disability is not known, we investigated the role of elevated cholesterol in rats exposed daily to 357 and 714 micrograms Mn/kg for 39 d. Significant Mn accumulation was accompanied by increased cholesterol content in the hippocampal region of Mn-treated rats. The learning, which is based on the time needed to reach food placed at the exit of a T-maze after a 1-d training period, was significantly slower in exposed rats than in unexposed rats. The rats receiving 357 and 714 micrograms Mn/kg reached the food in 104.5 +/- 13.8 and 113.3 +/- 25.7 s, respectively, on d 30, whereas their untreated counterparts reached the food in 28.7 +/- 11.4 s. This delay was completely corrected to 29.3 +/- 7.8 and 30.7 +/- 6.0 s in rats with coadministration of an inhibitor of cholesterol biosynthesis with 357 and 714 micrograms/kg of Mn. The correction of impaired learning was associated with the normalization of hippocampal cholesterol, but the Mn level in this region of the brain was not influenced in rats treated with a drug that inhibits cholesterol biosynthesis. These results suggested that Mn-induced hypercholesterolemia is involved in Mn-dependent learning disability.

Meta-analytic comparison of the components of visual cognition in Parkinson's disease

Controversy surrounds the presence of deficits of visual cognition in Parkinson's Disease. This literature has been seriously undermined by a number of methodological and theoretical faults that make interpretation of this hypothesis difficult. This review proposes a structure of visual cognition composed of 13 aspects. A meta-analysis of these components on 70 studies that used standardised neuropsychological tests and an appropriate normal control group indicates that the PD subjects are significantly compromised on tests of attention and concentration, complex visuospatial functions, and multifactorial spatial functions. More detailed analysis of the basic components of visual cognition was not undertaken due to low statistical power; hence, it remains unclear whether these subjects have primary visual processing deficits in association with their higher order deficits. The observed deficits may be interpreted as being a consequence of either undetermined lower level visual cognitive deficits or a compromise in executive functioning.

Reversibility of manganese-induced learning defect in rats

In this study the mechanism by which manganese (Mn) induces learning defect and its reversibility has been investigated in rats. Female albino rats were dosed orally with 357 micrograms Mn/kg body weight for 15 or 30 days. Attempts were made to correct the Mn-induced learning defect by (1) co-administration of mevinolin and Mn for 30 days; (2) administration of mevinolin for 15 days after 15 days of dosing with Mn, and (3) by withdrawal of Mn treatment (15 days dosing with Mn followed by 15 days without Mn). Mevinolin was given orally at 235.7 micrograms/kg body weight. Significant increases in the Mn and cholesterol levels in the hippocampus were accompanied by an obvious slowness in learning of rats exposed to Mn. After one training period (day 29) the time required to reach the exit of a T-maze was 104.5 +/- 13.8 sec for rats dosed with Mn for 30 days, whereas that of the controls was 28.7 +/- 11.4 sec on day 30. This delay was completely corrected (to 30.7 +/- 6.0 sec) in rats co-administered mevinolin (an inhibitor of cholesterol biosynthesis) with Mn. Withdrawal of Mn, with or without inhibiting the cholesterol biosynthesis, also corrected the Mn-induced learning defect. These results suggest that Mn toxicity produces learning disability by increasing cholesterol biosynthesis and this reversible disability in learning can be corrected by withdrawal of Mn exposure.

Environmental and occupational exposure to manganese: a multimedia assessment

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic additive used in Canada since 1976 as an anti-knock agent in unleaded gasoline. Its combustion leads to the emission of Mn oxides, especially Mn3O4. Since no study has assessed the potential risk of chronic exposure to low concentrations resulting from these emissions, the present investigation was undertaken to assess the level of environmental and occupational exposure of the human population. The multimedia exposure of two groups of workers (garage mechanics and blue-collar workers) potentially exposed to different levels of Mn from the combustion of MMT was assessed using personal air samplers, a dietary compilation, water samples at their places of residence, an epidemiological questionnaire and blood and hair samples. Results show that garage mechanics were exposed on average to higher atmospheric Mn at work (0.42 microgram/m3) than the blue-collar workers (0.04 microgram/m3). However, the contribution of atmospheric Mn to the total absorbed dose was less than 1%, and well below the standards established for occupational or environmental exposure; food contributes more than 95% of the multimedia dose. The average whole blood Mn concentrations were similar for the two groups (0.67-0.76 microgram/100 ml) and fall within the normal adult range. The average hair Mn concentrations were significantly higher for the garage mechanics (0.66 microgram/g) than for the blue-collar workers (0.39 microgram/g). The contribution of exogenous Mn versus endogenous Mn is questioned. As judged by the governmental standards or criteria for occupational and non-occupational environments, the current Mn levels in food, water and air may not cause any problems for the workers.

A meta-analysis of the relative sensitivity of neuropsychological screening tests

The National Institute of Mental Health recently formed a committee of experts which published a proposal for a lengthy neuropsychological test battery judged most apt to detect diffuse brain damage while covering a wide range of cognitive abilities. The purposes of the present study were (1) to assemble empirical evidence of the existence of statistically significantly sensitive screening tests across an equivalently wide range of functional domains, and (2) to present this evidence systematically, in such a manner as to help clinicians select subsets of screening tests manifesting greatest sensitivity to diffuse brain damage. It was found that in certain functional domains (speed of processing, problem solving, executive functions), marked differences in sensitivity occurred. Brief tests just as sensitive as time-consuming tests were also identified. The reader is cautioned about possible extraneous sources of the differences obtained (test and group selection bias, test reliability, test difficulty, procedural effects, Type I error). Nevertheless, it was concluded that a brief highly sensitive and functionally wide-ranging neuropsychological test battery for screening cases of putative diffuse brain dysfunction can be assembled.

Manganese encephalopathy: utility of early magnetic resonance imaging

The use of magnetic resonance imaging (MRI) provides visual evidence of cerebral deposits of paramagnetic metals. The usefulness of MRI is described in connection with the manganese poisoning of a 44 year old arc welder who had been engaged in the repair and recycling of railroad track made of manganese steel alloy.