Dose–effect relationships between manganese exposure and neurological, neuropsychological and pulmonary function in confined space bridge welders

Abstract

Background: Although adverse neuropsychological and neurological health effects are well known among workers with high manganese (Mn) exposures in mining, ore-processing and ferroalloy production, the risks among welders with lower exposures are less well understood. Methods: Confined space welding in construction of a new span of the San Francisco-Oakland Bay Bridge without adequate protection was studied using a multidisciplinary method to identify the dose-effect relationship between adverse health effects and Mn in air or whole blood. Bridge welders (n = 43) with little or no personal protection equipment and exposed to a welding fume containing Mn, were administered neurological, neuropsychological, neurophysiological and pulmonary tests. Outcome variables were analysed in relation to whole blood Mn (MnB) and a Cumulative Exposure Index (CEI) based on Mn-air, duration and type of welding. Welders performed a mean of 16.5 months of welding on the bridge, were on average 43.8 years of age and had on average 12.6 years of education. Results: The mean time weighted average of Mn-air ranged from 0.11-0.46 mg/m 3 (55% .0.20 mg/m 3 ). MnB .10 mg/l was found in 43% of the workers, but the concentrations of Mn in urine, lead in blood and copper and iron in plasma were normal. Forced expiratory volume at 1s: forced vital capacity ratios (FEV 1 / FVC) were found to be abnormal in 33.3% of the welders after about 1.5 years of welding at the bridge. Mean scores of bradykinesia and Unified Parkinson Disease Rating Scale exceeded 4 and 6, respectively. Computer assisted tremor analysis system hand tremor and body sway tests, and University of Pennsylvania Smell Identification Test showed impairment in 38.5/61.5, 51.4 and 88% of the welders, respectively. Significant inverse dose-effect relationships with CEI and/or MnB were found for IQ (p(0.05), executive function (p(0.03), sustaining concentration and sequencing (p(0.04), verbal learning (p(0.01), working (p(0.04) and immediate memory (p(0.02), even when adjusted for demographics and years of welding before Bay Bridge. Symptoms reported by the welders while working were: tremors (41.9%); numbness (60.5%); excessive fatigue (65.1%); sleep disturbance (79.1%); sexual dysfunction (58.1%); toxic hallucinations (18.6%); depression (53.5%); and anxiety (39.5%). Dose-effect associations between CEI and sexual function (p,0.05), fatigue (p,0.05), depression (p,0.01) and headache (p,0.05) were statistically significant. Conclusions: Confined space welding was shown to be associated with neurological, neuropsychological and pulmonary adverse health effects. A careful enquiry of occupational histories is recommended for all welders presenting with neurological or pulmonary complaints, and a more stringent prevention strategy should be considered for Mn exposure due to inhalation of welding fume.

Levels and predictors of airborne and internal exposure to manganese and iron among welders

“…Increased concentrations of MnB have been frequently observed in exposed vs non-exposed workers, for example in welders 21 and in smelter workers. 25,26 We determined about 10 mg/l as median MnB in German welders that was similar to the average concentration reported for US welders in bridge building 27 but lower than in Korean welders (15.5 mg/l). 28 A lower average concentration of 8.6 mg/l in Russian welders might be explained by a longer time lag between shift exposure and blood sampling.…”

Protective effects of dietary fibre against manganese-induced neurobehavioral aberrations in rats

“…Bouchard et al (9) conducted a followup study of alloy workers and concluded that Mn cumulative exposure could lead to learning and memory defi cits. In spite of the criticism due to certain biases pointed out in the above mentioned reports, the fact remains that Bowler et al (8) confi rmed the correlation between abnormal neuropsychological fi ndings and Mn exposure in welders in a dose-related manner.…”

Neurobehavioral testing in human risk assessment

“…Mergler et al (1999) found a correlation between blood manganese and coordinated movements, learning, and recall. Bowler et al (2007) found a correlation between blood manganese and measures of executive function, memory, sustained concentration and sequencing, verbal learning, cognitive flexibility, visuospatial constructional ability, and visual contrast sensitivity.…”

“…Park et al (2006) found an association between exposure and the Rey-Osterrieth Complex Figure task, a working memory Index, Stroop Color Word, and Auditory Consonant Trigrams. Bowler et al (2007) later reported a correlation between exposure and tests of executive function, memory, sustained concentration and sequencing, verbal learning in the same population.…”