Welders Lose Sense Of Smell

PHILADELPHIA, Oct. 12 -- Exposure to hazardous fumes and aerosolized heavy metals may put welders at risk of losing olfactory abilities, researchers here said.

In a case-control study of 43 professional welders, the workers were significantly less able to identify different odors than were individually matched controls, according to Richard Doty, Ph.D., of the University of Pennsylvania and colleagues.

However, only three of the welders had a complete loss of smell, the researchers reported in the Sept. 18 issue of Neurology.

The 43 welders had worked for between six and 28 months on the San Francisco/Oakland Bay Bridge, often in confined spaces without adequate respiratory protection, they said.

While loss of smell is often regarded as trivial, "this important sense not only determines the flavors of foods and beverages, but serves as an early warning system for the detection of fire, dangerous fumes, leaking gas, spoiled foods, and polluted environments," Dr. Doty said.

The workers were assessed on behalf of their employer as part of a State and Federal Workers' Compensation administrative mandate, the researchers said.

To measure olfactory ability, the researchers used the University of Pennsylvania Smell Identification Test, a 40-item "scratch-and-sniff" battery of odors that test-takers identify using multiple choice.

The test was developed by Dr. Doty and colleagues at the University of Pennsylvania Smell & Taste Center and is currently marketed by Sensonics, Inc., of Haddon Heights, NJ.

The researchers also tested for blood levels of manganese, iron, copper, and lead - common constituents of welding fumes -- and administered a battery of neurologic and neuropsychological tests.

The study found that:

• On average, the welders had lower scores on the smell test than controls. The average score for welders was 29.62, compared with 36.90 for the controls, a difference that was significant at P<0.001.
• On an individual basis, 88% of the welders did worse on the smell test than their controls.
• Mild, moderate, or severe microsmia was seen in 30.2%, 18.6%, and 16.3% of the welders, respectively, but only 7% had a complete loss of smell.

There was no correlation between olfactory status and results on any of the neurologic and neuropsychological tests.

Of the 37 welders for whom blood test data were available, 15 had elevated levels of manganese, two had elevated levels of iron, and none had elevated levels of lead or copper, the researchers found.

There were no significant correlations between any of the metals and scores on the smell test, Dr. Doty and colleagues said, although the average scores for those in the highest and lowest tertiles of manganese differed significantly (at P=0.038).

Paradoxically, those with the highest levels of manganese did better on the smell test than those with less of the metal in their blood, Dr. Doty and colleagues found.

"The basis of the smell loss of the welders in this study is not entirely clear," the researchers said, but the "most likely hypothesis" is that airborne metals somehow damage the olfactory epithelium.