- Welders exposed manganese-containing fumes as low as 0.14 milligrams per cubic meter of air exhibited neurological problems.
- The neurological signs include slow movement, difficulty with speaking and activities of daily life such as eating, mobility and writing.
- The more the exposure to manganese-containing welding fumes, the more quickly the symptoms progress over time.
Chronic exposure to manganese-containing fumes is associated with progressive neurological symptoms such as slow movement and difficulty speaking similar to Parkinson's Disease.
This was observed among welders who were exposed to airborne manganese at levels below federal occupational safety standards, suggesting that current safety standards may not adequately protect welders from the dangers of the job.
According to new research at Washington University School of Medicine in St. Louis, the more they are exposed to manganese-containing welding fumes, the faster the workers' signs and symptoms worsen.
Manganese is a key component of important industrial processes such as welding and steelmaking. At higher levels, it can cause manganism, a severe neurologic disorder with symptoms similar to Parkinson's disease, including slowness, clumsiness, tremors, mood changes, and difficulty walking and speaking.
The risk of manganism prompted the Occupational Safety and Health Administration (OSHA) to set standards limiting the amount of manganese in the air at workplaces. The safety standards have succeeded in eliminating manganism as an occupational hazard.
But the neurological signs showed up in people with an estimated exposure of only 0.14 milligrams of manganese per cubic meter of air, far below the safety standard set by OSHA at 5 milligrams per cubic meter.
"Many researchers view what's allowable as too high a level of manganese, but until now there really weren't data to prove it," said Racette, who also is executive vice chairman in the Department of Neurology. "This is the first study that shows clinically relevant health effects that are occurring at estimated exposures that are an order of magnitude lower than the OSHA limit."
Researchers studied 886 welders at three worksites- two shipyards and one heavy-machinery fabrication shop.
Each welder was asked to fill out a detailed job history questionnaire. The researchers used the questionnaire to calculate each participant's exposure by combining the exposure for specific job titles with the amount of time spent in each job.
Each participant also underwent two standardized clinical evaluations of motor function spaced a year apart, by trained neurologists. They used the Unified Parkinson's Disease Rating Scale.
The neurologists looked for signs of neurological damage such as muscle stiffness, gait instability, reduced facial expressions and slow movement.
A score of 6 or lower on the Unified Parkinson's Disease Rating Scale was considered normal, and those with scores of 15 or higher were placed in the parkinsonism category.
Parkinsonism is a set of neurological signs and symptoms similar to what is seen in Parkinson's disease.
The welders had an average score of 8.8, suggesting that 15% of the welders fell into the parkinsonism category.
The welders exposed to the highest levels of manganese showed the highest scores. This indicated that the neurological problems of workers exposed to higher manganese worsened faster than those of workers exposed to less manganese.
The welding fumes, and not the age of the workers, were responsible for the increasing scores.
Higher parkinsonism scores in welders are associated with more difficulty with activities of daily life such as eating, mobility and writing.
"This is not something we can ignore," Racette said. "I think a qualified neurologist would look at these clinical signs and say, 'There's something wrong here.' This would be having an effect on people's lives."
"We can make the workplace safer for welders," Racette said. "Reducing OSHA's allowable levels of manganese would probably make a big difference in terms of safety and help workers avoid such risks."
The findings are published in Neurology.
- Brad A. Racette et al. Dose-dependent progression of parkinsonism in manganese-exposed welders. Neurology; (2016) doi.org/10.1212/WNL.0000000000003533