Five toxic chemicals in air may raise, by 3 to 6 times, risk of ALS

Chemicals studied used in dyes, batteries, solvents, steel, and rubber

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Exposure to certain toxic airborne chemicals used in industry significantly increases — by up to six times — the odds of developing amyotrophic lateral sclerosis (ALS), a study suggests.

Findings underscore the importance of surveillance programs testing exposure to these airborne pollutants, especially among populations at risk.

The study, “Exposure to ambient air toxicants and the risk of amyotrophic lateral sclerosis (ALS): A matched case control study,” was published in the journal Environmental Research.

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Specific chemicals carried on air spotted as possible ALS risk factors

Almost anyone can be exposed to some level of toxic chemicals, such as heavy metals and pesticides, outdoors, at home, or at work. Besides being breathed in, these chemicals enter the body through foods and water, or be absorbed through the skin.

It is thought that ALS arises from a combination of genetic and environmental factors, and that breathing in airborne toxic chemicals may place people at a higher risk of developing the disease.

Researchers in the U.S. set out to add to evidence of this link by comparing exposure to 34 toxic chemicals in 267 people diagnosed with ALS and, as controls, 267 healthy individuals of the same age and sex who lived in the same county.

Nearly two-thirds of patients (62.6%) were men, and the group’s average age at diagnosis was 61.4. Most of these patients (84.3%) were diagnosed after 2011.

Data on toxic chemicals came from the U.S. Environmental Protection Agency’s 2011 National Air Toxics Assessment, which provided models of air concentrations that year for about 180 compounds. This was matched to each person’s ZIP code.

Results showed that exposure to at least one of five compounds was associated with the likelihood of developing ALS, with the 25% of people with the highest levels of exposure being significantly more likely to have the disease than the 25% with the lowest levels.

These compounds were cadmium, a heavy metal used in batteries, solar cells, and pigments; carbon disulfide, used in many industries to make rubber and other materials; 2,4-dinitrotoluene, an aromatic solvent used to produce polyurethane, explosives, and dyes; an organic/chlorinated solvent named vinyl chloride; and cyanide, widely used in steel and chemical industries.

The link between ALS and exposure to these five compounds then was examined, taking into account smoking and education levels, which also are thought to impact ALS risk.

Cyanide exposure raised risk by 4.3 times, vinyl chloride by 6 times

A higher exposure to cadmium or carbon disulfide increased the likelihood of developing ALS by about three times, compared with the lowest-exposure group, data showed. In addition, cyanide increased risk by 4.3 times, 2,4-dinitrotoluene by 5.5 times, and vinyl chloride by six times.

“When examining each compound individually, ALS cases compared to controls were exposed to higher levels of 2,4-dinitrotoluene, vinyl chloride, carbon disulfide, cadmium, and cyanide and this was independently associated with increased ALS risk,” the researchers wrote.

In contrast, exposure to selenium, another heavy metal, linked with lower odds of developing ALS.  “But this evidence was relatively weak,” they noted.

An analysis by chemical groups also tied exposure to higher levels of chlorinated solvents (a class of chemicals used as paint thinners or in dry cleaning) with 2.62 times higher odds of developing ALS, after accounting for smoking and education.

Overall, the study “provides evidence of an increased ALS risk in cases compared to controls for several neurotoxic compounds, underscoring the importance of ongoing surveillance of potential exposures for at-risk populations,” the researchers wrote.

Measuring only 2011 levels of these pollutants to determine ALS risk, particularly in people already diagnosed at that time, was pointed out as a study limitation.

“Future studies with larger sample sizes that are able to link residences over time are warranted to determine if these relationships of ambient toxicants with ALS can be confirmed,” the team concluded.