ST. LOUIS -- A new study by researchers at Washington University in St. Louis has found safety standards to protect welders from harmful fumes may be inadequate.

Dr. Brad A. Racette, senior author of the study, said the research showed the more exposure one had to airborne manganese, the greater the progression of parkinsonism, a neurological condition that causes tremors, muscle stiffness and other movement abnormalities.

Manganese is found in materials used for welding.

Racette said when the chemical element is airborne and inhaled, it alters the part of the brain that controls movement.

The study examined nearly 900 welders at two shipyards and one heavy-machinery fabrication shop in the Midwest, the St. Louis Post-Dispatch reported.

Researchers used the Unified Parkinson's Disease Rating Scale to measure symptoms.

According to the study, a score of six or below is considered normal, while a score of 15 or higher is considered an indication of parkinsonism.

In the first evaluation, workers scored an average of 8.8, with 15 percent of them falling into the parkinsonism category, but scores increased over time.

"While that's not ideal, we're looking at long-term health effects from chronic exposure," Racette said. "Our study can't answer what safe is, but what we can say is the current government limits are far too high for worker safety."