People who work in manufacturing, welding and chemical operations and are exposed to hazardous chemicals may face a higher risk of developing amyotrophic lateral sclerosis (ALS), a new study found.

"This study shows that certain occupational settings and exposures increase one's chances of developing ALS," said first author Dr. Stephen Goutman. He's director of the Pranger ALS Clinic and associate director of the ALS Center of Excellence at University of Michigan.

Pesticides and carcinogenic compounds have been found at elevated levels in the blood of patients with ALS, the rare and deadly condition also known as Lou Gehrig's disease.

To study whether that had an impact on the development of ALS, researchers surveyed 381 patients with ALS and 272 controls. The research team analyzed self-reported occupational exposures from the participants' four most recent and longest-held jobs.

Participants who had ALS reported higher occupational exposure to metals, particulate matter, volatile organic compounds and combustion pollutants prior to diagnosis. Those whose jobs were in manufacturing and welding also had a higher ALS risk.

"We have known for some time that certain pollutants can increase ALS risk, but identifying where these exposures are occurring is important as we begin to think about strategies for ALS prevention and studying populations of individuals at high disease risk," Goutman said in a university news release.

Exposure to metals was most strongly linked to ALS. This was most common with iron and welding fume exposure.

Researchers said people in jobs with higher metal exposure, particularly in manufacturing and trade industries, are often exposed to mixtures that may also contain particulate matter. This can include silica and volatile organic compounds, such as formaldehyde.

"Some of these workers who later developed ALS may have been exposed to mixtures of metals and other chemicals without their knowledge," Goutman said. "This should lead our research to investigate these mixtures and the resulting injuries to the central nervous system, or what we refer to as the ALS exposome [lifestyle, diet and daily environmental exposures]."

The findings were published in the Interventional Archives of Occupational and Environmental Health.

ALS is progressive and fatal, beginning with muscle weakness, slurred speech and difficulty swallowing. About five to 10 in 100,000 Americans have the disease, according to the U.S. Centers for Disease Control and Prevention.

Although the U.S. Food and Drug administration has approved two medications to treat ALS, both riluzole and edaravone have been minimally effective at slowing disease progression. Patients can also get treatment that includes a mask worn over the nose to make breathing easier.

"I have spent my 30-year career on evaluating and treating individuals living with ALS," said senior study author Dr. Eva Feldman, director of the ALS Center of Excellence at Michigan and the James W. Albers Distinguished Professor of Neurology at the university's medical school.

"ALS remains a disease without an effective treatment," Feldman said in the release. "Studies such as ours are critical in identifying modifiable disease factors and populations at risk, so that we can prevent ALS from occurring in the first place."