Agriculture Work and Exposure to Pollutants May Raise ALS Risk

Agriculture and other areas that expose people to pesticides, paint solvents, electromagnetic fields, and heavy metals may increase their odds of developing amyotrophic lateral sclerosis (ALS), a population-based study from Italy shows.

But larger studies are needed to confirm these findings, its researchers wrote, as only some risk factors reached statistical significance for an association with ALS.

The study, “Environmental and Occupational Risk Factors of Amyotrophic Lateral Sclerosis: A Population-Based Case-Control Study,” was published in the International Journal of Environmental Research and Public Health.

Despite advances in understanding the genetic causes of ALS, far less is known about environmental and occupational risk factors predisposing an individual to this progressive neurological disease.

Epidemiological studies have shown associations between ALS and a large number of risk factors, including the use of herbicides, exposure to environmental pollution and to heavy metals, and working with silica. But evidence for each of these factors is inconsistent, and none has been identified as a definite cause of the disease.

Researchers conducted a population-based study, targeting three provinces of northern and one of southern Italy, to assess occupational and environmental risk factors that might contribute to ALS.

Their study included 95  people with ALS from Modena, Novara, Reggio Emilia, and from Catania in Sicily, and 135 people without ALS, matched to patients by sex, age, and province of residence, who served as a control group.

Participants were asked to fill out questionnaires reporting factors such as their occupational sector and type of job, educational status, and whether they had served in the military. Exposure to metals, pesticides, chemicals, and electromagnetic fields was also examined, as were factors unique to their place of residence.

ALS risk was then estimated using statistical models adjusted for sex, age, and education level.

Results showed that working in agriculture, with its use of pesticides, increased the odds of developing ALS by 2.1 times, whereas activities in the manufacturing sector were linked with 1.48 times greater chance of ALS compared with the service sector.

Only a history of agriculture work was significantly associated with an ALS likelihood, particularly among those with long-time farm work — disease odds for those in this field for more than 10 years were 2.7 times higher.

“Conversely, residential use of pesticides showed no such association in our study with ALS risk,” whether pesticides were used in the home on plants, insects or animals, the study noted.

Working in armed forces or as a welder also seemed to increase ALS risk, but results did not reach statistical significance.

Among other toxic agents (beyond pesticides), the team found that contact with metals and metalloids (such as mercury, lead, or selenium), chemicals and solvents (such as paint thinners or paint removers), and electromagnetic fields also showed a somewhat higher risk of ALS. But only exposure to lead and paint remover were significantly associated with disease risk.

People living in the countryside or on a farm were also seen to be at a somewhat higher risk. Those who lived at any point near water — a river, lake, sea, or even a small pond — or near overhead power lines were also more likely to develop ALS.

These results were replicated when the team excluded from its analysis people with a family history of ALS — found in five patients and two controls — and when the data was examined by sex and study area.

Men working in the agricultural sector and living in the countryside, overall, were at greater ALS risk than were women under similar conditions. But women were seen to be at greater risk than men when exposed to electromagnetic fields or living near water bodies.

While the researchers did not take water samples to evaluate for contamination, they believe that the increased risk is due to the presence of cyanobacteria in water sources. Such bacteria, often called blue-green algae, can release a neurotoxic molecule into the water, contaminating edible plants.

Overall, this study “did not detect an association between occupational history in the service sector and ALS risk, while both agricultural and manufacturing sectors showed a somewhat increased risk,” a finding seen in prior studies, the researchers wrote.

“In particular, having an occupation in the agricultural sector, especially with a long duration of the working activity as well as occupational exposure to some chemicals, such as heavy metals and selenium, might increase ALS risk,” they added.