Welding fumes are composed of metals and most fumes contain a small percentage of manganese. There is a concern by workers, employers, and health professionals about potential neurological effects associated with exposure to manganese in welding fumes.
NIOSH has been conducting research and reviewing the published scientific literature to assess this problem. Manganese is an essential nutrient. A healthy person with normal liver and kidney function can excrete excess dietary manganese. Inhaled manganese is of greater concern because it bypasses the body’s normal defense mechanisms. This can lead to manganese accumulation and adverse health effects including damage to the lungs, liver, kidney and central nervous system.
Male workers exposed to manganese also have a higher risk of fertility problems. Prolonged exposure to high manganese concentrations (>1 mg/m3) in air may lead to a Parkinsonian syndrome known as “manganism.”
Chronic exposure to the manganese-containing pesticide, maneb, is also reported to cause Parkinson-like symptoms. Parkinson-like symptoms may include tremors, slowness of movement, muscle rigidity, and poor balance.
Recent studies indicate neurological and neurobehavioral deficits may occur when workers are exposed to low levels of manganese (<0.2 mg/m3) in welding fumes. These effects include changes in mood and short-term memory, altered reaction time, and reduced hand-eye coordination.
NIOSH is currently reviewing its Recommended Exposure Limit (REL) for manganese as a result of these studies. A comprehensive review of the available scientific literature is in development and will be made available for public review.
Neurological and Neurobehavioral Effects
Numerous studies indicate that welders may be at increased risk of neurological and neurobehavioral health effects when exposed to metals such as lead, iron and manganese. Carbon monoxide, heat and stress can also contribute to neurological impairments in welders. Some studies indicate that welders exposed to low levels of manganese (<0.2 mg/m3 ) perform more poorly on tests of brain function and motor skills. These effects include changes in mood and short-term memory, altered reaction time, and reduced hand-eye coordination. It is not known if these findings have clinical significance.