Long-term exposure to manganese in welding fumes may affect welders' brains over time, according to a new, small study described in the National Institutes of Health’s MedLine Plus website.

In the study, which appears online in the journal Neurology, welders who worked at shipyards and a metal fabrication plant and had an average of 30,000 hours of lifetime welding exposure had manganese levels that were twice the upper limits of normal.

Compared to the non-welders included in the study, the welders had mild movement disorders and an average 11.7 percent reduction in a marker of the neurotransmitter dopamine in the same area of the brain affected by Parkinson's disease. Dopamine helps nerve cells communicate.

Although previous studies suggested a link between manganese and neurological disorders – including Parkinson’s disease-like symptoms, one expert cautioned against drawing conclusions from the latest study.

"The dopaminergic reductions [observed] were not as dramatic as those seen in Parkinson's disease patients, nor was the nature of the reduction exactly like that typically seen in Parkinson's," said Dr. Michael Pourfar, director of the division of movement disorders at North Shore-LIJ Health System, Great Neck, NY. He said the findings suggest an association with dopamine function.

"That is to say, exposure to manganese may affect dopamine function and cause a parkinsonian syndrome but it does not clearly cause the same classic Parkinson's that most people are familiar with," Pourfar said. "The number of subjects in the study was relatively small and prior PET studies have not consistently demonstrated the same findings, so many questions remain about the nature of the association between manganese and parkinsonism.” Still, study author Dr. Brad A. Racette of the Washington University School of Medicine in St. Louis said that, with more than a million welders in the U.S., a proven link between neurotoxic effects and manganese fumes “would have a substantial public health impact for the U.S. workforce and economy.”