Exposure to pesticide HCB may raise risk of ALS, new study finds

Higher blood levels of the pollutant hexachlorobenzene (HCB), once widely used as a pesticide and later restricted in many countries due to concerns about toxicity, may increase the risk of developing amyotrophic lateral sclerosis (ALS), according to data from people living in two cities in Denmark.

In contrast, most of the other persistent organic pollutants analyzed showed no consistent link to ALS, and many findings were not statistically significant.

Recommended Reading

April 13, 2026 News by Marisa Wexler, MS

Scientists identify blood markers that may predict ALS progression

Study examines pollutants in blood samples before ALS diagnosis

The study, “Associations between pre-disease biomarkers of persistent organic pollutants and amyotrophic lateral sclerosis risk in four European cohorts,” was published in Environmental Research. It was led by researchers at the Harvard T.H. Chan School of Public Health in Boston, working with scientists at the Danish Cancer Institute of the Danish Cancer Society, and the Finnish Institute for Health and Welfare.

ALS is thought to develop from a combination of genetic and environmental factors, including exposure to pesticides used in agriculture and that can be present in food. Earlier studies suggested that some persistent organic pollutants may be associated with greater odds of developing ALS, and one recent study also linked higher exposure to shorter survival. However, many of those studies were retrospective or cross-sectional.

In this study, the researchers measured levels of persistent organic pollutants in blood samples collected before people developed symptoms of ALS. Persistent organic pollutants can stay in the environment for long periods, and measuring them in the blood can provide an estimate of long-term exposure.

The researchers used the Danish Diet, Cancer and Health study (Danish EPIC), which contains long-term data from 57,053 people ages 50 to 64 living in Copenhagen and Aarhus, two Danish cities. Among them, 166 people went on to develop ALS.

Researchers compare pollutant levels in people with and without ALS

The scientists looked at blood levels of several pollutants in these patients before they were diagnosed and compared them with 334 individuals who did not develop the disease. They examined levels of 25 regulated chemicals, including 13 polychlorinated biphenyls used in industry and electronics, nine organochlorine pesticides, and three polybrominated diphenyl ethers used as flame retardants in many industries.

Across the pollutants analyzed, most showed no consistent link to ALS. Some appeared to be associated with a lower risk at higher exposure levels, but many of these findings were not statistically significant.

However, when adjusting for the presence of other pollutants, higher levels of hexachlorobenzene (HCB) in the blood were associated with a higher risk of developing ALS. HCB is a type of pesticide that was historically used to prevent fungal growth.

“Our study suggested elevated risk of ALS among those highly exposed to HCB when adjusting for co-pollutants,” the researchers wrote. They also noted that at very high levels of some persistent organic pollutants, the risk of ALS appeared to increase, but there were very few people in these groups to draw definite conclusions.

To strengthen their findings, the team combined their results with data from three similar studies conducted in Finland. This combined analysis showed patterns mostly consistent with the Danish study, though the association between HCB and ALS did not reach statistical significance in the combined analysis.