Arc Welding, Manganese, and Manganism

The Welding Process and Generation of Manganese Fume

  1. Welding fume comes mainly from the filler metal and flux (if used); the contribution of the parent metal is relatively minor. [Hendrick, p. 470]
  2. "The concentration of metal fume to which the welder is exposed depends not only on the composition of the parent metal and the electrodes, but also on the welding process, including the current density (amperes per unit area of electrode), the wire feed rate, the arc time (which may vary from 10 to 30%), the power configuration, that is, dc or ac supply, and straight or reverse polarity. The work environment also defines the level of exposure to welding fume and includes the type and quality of exhaust ventilation and whether the welding is done outdoors, in an open building workstation, or in a confined space." [Burgess, p. 173]
  3. "The distribution by metal welded in Sweden is 64% mild steel, 22% stainless steel, 9% aluminum, and 5% all other metals." [Burgess, p. 168]
  4. Shielded Metal Arc Welding (abbreviated as SMA and also known as Manual Metal Arc Welding or MMAW): "The most common nonpressure or fusion welding process is also commonly called stick or electrode welding. . . . The percent of total electrode mass that appears as airborne fume ranges from 0.5 to 5%. Pantucek (1971) states that the "fume" generated from coated electrodes may contain iron oxides, manganese oxide, fluorides, silicon dioxide, and compounds of titanium, nickel, chromium, molybdenum, vanadium, tungsten, copper, cobalt, lead, and zinc. The manganese content of welding fume ranges from 3 to 10%." [Burgess, p. 169-171]
  5. "A significant amount of welding is done on steel. Inevitably, iron and manganese will be present in the base metals being joined and the filler wire being used, and, hence, in the fumes that workers are exposed to." [Manganese, iron, and total particulate exposures to welders]
  6. "Manganese is found in all mild steels and is always used in steel alloys to improve metallurgical properties by neutralizing the effects of sulfur and preventing the oxygen from contaminating the molten metal. To restore the manganese lost by the heat during welding, manganese up to 15% by weight can be used as flux agents in the coatings of SMAW electrodes and FCAW electrodes). Depending on the above mentioned factors, manganese generally makes up from 0.2% to 10% of the fume. However, special steels, such as Hadfield steel and 13% Mn steel, may produce higher concentrations of MnO2(s) in the welding fume." [Manganese in occupational arc welding fumes--aspects on physiochemical properties, with focus on solubility]
  7. "Since the early 1990s, concerns have increased about manganese exposure in welding fumes. Exposure arises from manganese content in the metals being welded, as well as manganese present in certain welding rods and wires. Korcynski (2000) found personal exposure levels of 0.011-4.93 mg Mn/m3 "total aerosol" in 42 Canadian welders, and 62% had manganese exposures > 0.2 mg Mn/m3. In confined space operations, Bowler et al. (2007) found personal exposures of 0.11-0.46 mg Mn/m3 respirable aerosol. Particles in welding fume are generally less than 4 um in diameter and, therefore, in the respirable size range." [ACGIH: 2013 Supplement to the 7th Edition]

Adverse Effects: Manganism

  1. In 2012, ACGIH changed the TLV-TWA for manganese and inorganic compounds to 0.02 mg/m3, as Mn, Respirable particulate matter and 0.1 mg/m3, as Mn, Inhalable particulate matter. The "TLV Basis" is "Central nervous system (CNS) impairment."  [TLVs and BEIs]
  2. "Because manganese is a paramagnetic element, magnetic resonance imaging (MRI) can identify where manganese accumulates in the brain. In humans, manganese preferentially accumulates in the globus pallidus, followed by the substantia nigra pars reticularis, the corps striatum, pineal gland, olfactory bulb, and substantia nigra pars compacta. This contrasts with PD [Parkinson Disease], where the substantia nigra pars compacta is the first site to degenerate. Also, manganism involves impairment in GABA-related pathways, whereas PD does not." [ACGIH: 2013 Supplement to the 7th Edition]
  3. "Several studies have reported resolution of T1 hyper intensities among occupationally exposed workers after removal from the source of Mn exposure. Despite improvement in their T1 imaging characteristics, clinical deficits in these workers, if present, frequently persist. This suggest while the increased T1 signal intensity is potentially reversible, there may be an exposure threshold at which the MRI changes and neurotoxic effects become permanent." [Neurological outcomes associated with low-level manganese exposure in an inception cohort of asymptomatic welding trainees]
  4. "In conclusion, this study showed that even with 8-hr TWA Mn exposures at or below the ACGIH recommendations, there were increases in T1-weighted indices in the caudate, anterior and posterior putamen, and combined basal ganglia, that were significantly related to increases in cumulative Mn exposure among asymptomatic welder apprentices. However, there were no clinical signs of neurological dysfunction related to increases in cumulative Mn exposure at these low levels and over this relatively short time period as assessed via UPDRS3 and Grooved Pegboard." [Neurological outcomes associated with low-level manganese exposure in an inception cohort of asymptomatic welding trainees]
  5. "This was a cross-sectional and nested case–control study to investigate the prevalence and phenotype of parkinsonism among 811 shipyard and fabrication welders recruited from trade unions. Two reference groups included 59 non-welder trade workers and 118 newly diagnosed, untreated idiopathic PD patients. Study subjects were examined by a movement disorders specialist using the Unified Parkinson Disease Rating Scale motor subsection 3 (UPDRS3). Parkinsonism cases were defined as welders with UPDRS3 score ≥15." [Increased risk of parkinsonism associated with welding]
  6. "The clinical phenotype of welders with parkinsonism may provide insight into the pathophysiology of welding-associated neurotoxicity. The severity of bradykinesia and rigidity in welding exposed workers was comparable to newly diagnosed PD patients. Although there were slight but significant differences in lower extremity rigidity (worse in welders) and axial signs (worse in PD patients), these differences were not sufficiently different to distinguish parkinsonism in welders from PD patients. Rest tremor and asymmetry were more common in PD patients than welders with parkinsonism." [Increased risk of parkinsonism associated with welding]
  7. "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. . . . 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." [Sequelae of fume exposure in confined space welding: a neurological and neuropsychological case series]
  8. "In patients who have had manganese intoxication, the MRI can have diagnostic value provided the scans are done within less than 6 months of cessation of exposure, whereas blood, serum or urine Mn concentrations are not very useful for neurotoxic risk assessment. Nevertheless, increased manganese levels in blood were often found in groups of workers exposed to Mn dust and fumes." [Sequelae of fume exposure in confined space welding: a neurological and neuropsychological case series]
  9. "It is a very important finding that this group of 11 clinical welders cases had MnB concentrations from 5.85 ug/L to 14.6 ug/L with a concomitant dose-dependent deterioration of neuropsychological functions (see multiple regression results) which is paralleled by significant inverse associations between neuropsychological performances and the cumulative dose of air-Mn (CEI) over a relatively short exposure period (8.1-28 months)." [Sequelae of fume exposure in confined space welding: a neurological and neuropsychological case series]
  10. "Inhalation of respirable Mn particles may via the lung alveoli lead to a rather quick systemic absorption of manganese that bypasses the hepatic homeostasis and crosses the blood/brain barrier making Mn exposure from welding fumes a greater neurotoxic risk than Mn exposure from other types of occupational exposure such as in mining, dry cell battery production and chemical manufacturing." [Sequelae of fume exposure in confined space welding: a neurological and neuropsychological case series]
  11. "Twenty-eight studies show an exposure-response relationship between Mn and neurobehavioral effects, including 11 with continuous exposure metrics and six with three or four levels of contrasted exposure. The effects of sustained low-concentration exposures to Mn are consistent with the manifestations of early manganism, i.e., consistent with parkinsonism." [Neurobehavioral Deficits and Parkinsonism in Occupations with Manganese Exposure: A Review of Methodological Issues in the Epidemiological Literature]
  1. "Neurobehavioral changes, such as performance decrements on standardized neuropsychological tests and adverse symptoms, have been consistently reported in studies of welders and other workers with known or likely sustained exposures to respirable Mn. Workers with these Mn exposures are at risk for developing neurological effects.
  2. These effects are consistent with signs of early manganism.
  3. Although some research has suggested that Mn exposures confer increased risk of PD (which might include accelerated onset or detection), and may perturb dopamine metabolism, this has not yet been established.
  4. Statistically significant adverse neurobehavioral effects have been reported at airborne concentrations below 0.2 mg/m3 Mn."

Prevention of Manganism

"The data examined here suggest that arc welding produces manganese exposures that are frequently close to or in excess of the current ACGIH TLV of 0.2 mg/m3. This may present an increased risk of neurological impairment depending on the magnitude and duration of the exposures, the individual's susceptibility, and other factors. The data suggest that local exhaust ventilation can be effective at reducing these exposures, and that in cases where it is not feasible to use it, respiratory protection is needed." [Manganese, iron, and total particulate exposures to welders]

See Parkinson Disease: No Established Occupational Causes.


Last Editied: 15 March, 2015

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