Study Finds Link Between Particulate Matter Composition, ALS Aggravation

A study published in Environmental Epidemiology found that fine particulate matter (PM_2.5) composition could have a direct effect on amyotrophic lateral sclerosis (ALS), with organic matter (OM) having a significant association with disease aggravation. The aim of the study was to assess whether year-long exposures to relatively medium to low concentrations of PM_2.5 differ in their association with ALS aggravation.

The study used data from the New York Department of Health Statewide Planning and Research Cooperative System, in which patients with ALS were identified between 2000 and 2014 by checking hospital discharge records for their first ALS hospitalization. The data set also held information on age, sex, and residential address to properly assess county-level exposure.

Annual PM_2.5 black carbon, nitrate, sulfate, OM, sea salt, and soil mass concentrations were predicted by an air pollution prediction model. The total mass of PM_2.5 in 1 area was estimated from satellite retrievals. Investigators predicted the annual concentrations in a county subdivision, then calculated an overall county average that weighted the county subdivisions with larger populations more heavily.

In 62 New York state counties, there was an annual mean (SD) of 6.0 (9.6) first ALS hospitalizations per county, with 5655 first ALS hospitalizations from 2000 to 2014. The mean age at first hospitalization was 64.3 (13.5) years.

OM and sulfate had the highest mean mass concentrations in the state, with 35% and 31% of total PM_2.5 mass, respectively, whereas sea salt had the lowest with 3% of total PM_2.5 mass. Sulfate and soil concentrations in the air had a downward pattern over time; OM, nitrate, and sea salt also decreased gradually over time.

The researchers found that a 1-SD increase in OM concentration was associated with a 17% (rate ratio [RR], 1.17; 95% CI, 1.11-1.24) increase in the annual ALS first hospitalization rate and a 1-SD increase in sea salt with a 6% increase (RR, 1.06; 95% CI, 1.01-1.11). There was an inverse correlation between soil (RR, 0.91; 95% CI, 0.86-0.97) or black carbon (RR, 0.94; 95% CI, 0.89-0.99) and first hospitalization for ALS.

There were some limitations to this study. Because the data included only information on hospitalizations, the investigators lacked any data on noncases that would allow an individual-level time-to-event analysis. The analysis was limited to the county level. The study used predicted PM_2.5 exposure rather than measured exposure, and some exposure measurement error is expected. A county-wide average may not reflect population exposure for components adequately. The PM_2.5 components in this study do not encompass all possible components.

OM’s total particulate mass was analyzed, but OM is a mixture and includes multiple chemical compounds. First hospitalization data are also likely to miss aggravation if patients are not hospitalized as disease symptoms worsen.

The researchers concluded that there were positive associations of some PM_2.5 chemical components with ALS, with a specific association between OM and disease aggravation in ALS.

“This information can be useful in identifying relevant pollution sources for targeted regulations and in studies of PM_2.5 toxicity and ALS pathology,” the authors wrote.

References

Nunez Y, Boehme AK, Goldsmith J, et al. PM_2.5 composition and disease aggravation in amyotrophic lateral sclerosis. Environ Epidemiol. 2022;6:e204. doi:10.1097/EE90000000000000204