Maryse Bouchard

Manganese exposure and the neuropsychological effect on children and adolescents: a review

OBJECTIVES Manganese (Mn) is an essential element, but overexposure can have neurotoxic effects. METHODS In this article, we review and summarize studies on exposure to Mn and nervous system impairments in children. RESULTS We identified 12 original articles published between 1977 and 2007. Overexposure to Mn was suspected to occur through diverse sources: infant milk formula, drinking water, industrial pollution, and mining wastes. The most common bioindicator of exposure to Mn was hair Mn content, but some studies measured Mn in blood, urine, or dentin; one study on prenatal exposure measured Mn content in cord blood. Most studies indicate that higher postnatal exposure to Mn is associated with poorer cognitive functions and hyperactive behavior. CONCLUSIONS The limitations of the existing studies are numerous: most were cross-sectional, had a modest sample size, and lacked adjustment for important confounders. Future investigations should be performed on a larger sample size and include a more detailed exposure assessment, addressing multiple sources of exposure such as food, water, and airborne particulates.

Manganese cumulative exposure and symptoms : A follow-up study of alloy workers

Long-term exposure to manganese (Mn) particulates through inhalation can be neurotoxic, with deficits in neuromotor and cognitive domains. Mn-exposed individuals also report symptoms, including fatigue, mood changes, irritability, concentration difficulties, and sweating in the absence of physical effort. The long-term course of Mn-related symptoms after cessation of exposure has never been examined. Male workers from a Mn-alloy production plant participated in a study on nervous system functions (initial examination), and were followed-up 14 years after plant closure. The relation between self-reported symptoms and Mn cumulative exposure index (CEI) was examined among 71 Mn-alloy workers and 71 referents. Symptoms from the questionnaire were grouped into categories, and the reported frequency was compared between referents and Mn-alloy workers in each Mn CEI tertile using General Linear Models, controlling for age, education, and alcohol consumption. A gradual increase in symptoms frequency was observed for complaints related to hearing and movement control both at initial and follow-up examination, and fatigue and autonomic nervous system only at initial examination. In addition, an exposure-effect relation was apparent for symptoms related to memory, concentration and balance reported at both examinations, with Mn-workers in the highest CEI tertile reporting the highest level of symptomatology. Sleeping complaints were not associated with exposure to Mn, while musculoskeletal pain and muscular weakness were reported more often by Mn-workers than referents but were not clearly related to CEI. The findings suggest that former Mn-alloy workers continue to perceive symptoms many years after cessation of exposure. Despite the limitations of self-reported symptoms, subjective complaints are an important part of a health assessment since they relate directly to perceived health status and day-to-day functioning.

Past Occupational Exposure to Airborne Manganese in a Manganese Alloy Plant

A retrospective exposure assessment of a group of manganese (Mn) alloy workers was performed in conjunction with a 2004 follow-up study, 14 years after cessation of exposure, to evaluate the long-term effects of occupational Mn exposure on neurobehavioral functions. The ferro- and silico-Mn alloy plant opened in 1973 and closed in 1991. The airborne total Mn (TMn) exposures for job groupings were established using personal sampling data from a 1991 industrial hygiene survey. Historical short-term total dust (TDust) data were used to estimate past TDust exposure for job groupings and plant areas. Relationships between Mn content and TDust from the 1991 survey, supported by sparse historical data, were used to estimate TMn content in the historical TDust data. Results showed past personal TDust exposure levels much higher than those found in 1991. Changes in TDust levels and corresponding TMn levels were a function of changes in ventilation, work practices, and operations, not of product (ferro- or silico-Mn). Relationships between TMn and respirable Mn (RMn) from area sampling in 1991 were used to estimate RMn exposure for the job groups. Work histories for 112 workers were developed from payroll records, questionnaires, and interviews and combined with Mn exposure estimates to develop cumulative exposure indices (CEIs). The TMn CEI ranged from 0.27 mg/m 3 × years to 100.24 mg/m 3 × years, with an AM of 24.40 mg/m 3 × years and a GM of 14.06 mg/m 3 × years. The RMn CEI had an AM of 2.95 mg/m 3 × years and a GM of 1.78 mg/m 3 × years with a range of 0.05–12.03 mg/m 3 × years. Overall average TMn exposure intensity, the TMn CEI divided by time worked in years for each worker, had an AM of 1.6 mg Mn/m 3 , a GM of 1.0 mg Mn/m 3 , range 0.02–6.2 6 mg Mn/m 3 . The results of the 2004 follow-up study showed several concentration-response relationships between TMn CEI and neurobehavioral outcomes, which suggest that increase in cumulative TMn exposure level has long-term consequences on the nervous system.

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.

Neuropsychiatric symptoms, omega-3, and mercury exposure in freshwater fish-eaters.

Mercury is a neurotoxin, absorbed primarily through fish consumption. However, the nutritional benefit from omega-3 fatty acids (n-3 FA) may offset the deleterious effects of mercury. Increased n-3 FA have been associated with lower rates of mood disorders. The authors examined neuropsychiatric symptoms among 243 freshwater fish-eaters, with low serum n-3 FA (median = 0.11 mg/mL) and low mercury exposure (median in blood and hair = 2.22 and 0.54 μg/g). They assessed neuropsychiatric symptoms with the Brief Symptom Inventory. The results did not show the expected inverse association between serum n-3 FA and neuropsychiatric symptoms. For men who consumed more than 130 g of alcohol per week, the authors observed a positive association between serum n-3 FA and neuropsychiatric symptoms, possibly reflecting an alcohol-related release of n-3 FA from membranes into blood. They observed a positive relation between hair mercury and neuropsychiatric symptoms solely for women, suggesting that men may respond differently to mercury.