Public Health

Substantial research has linked fine particulate matter (PM<2.5 μm in diameter, PM_2.5) to cardiovascular disease and dementia, however, the role of ultrafine particulate matter (PM<0.1 μm in diameter, PM_0.1), which is more readily absorbed into the bloodstream due to its smaller size, remains underexplored, especially in diverse populations.

The study included data from n = 1648 adults aged ≥65 in the ethnically diverse Kaiser Healthy Aging and Diverse Life Experiences (KHANDLE) study, and n = 746 African Americans in the Study of Healthy Aging in African-Americans (STAR). Three domains of cognitive outcomes (semantic memory, verbal episodic memory, and executive function were measured using the Spanish and English Neuropsychological Assessment Scales and Z-scored. Total PM_0.1, and the fraction of PM_0.1 from two sources (biomass combustion and wildland urban interface (WUI)), during 2000-2020 were generated using a chemical transport model and linked to geocoded residential addresses. We used linear regression to assess the association between long-term exposure to PM_0.1 (5-, 10-, and 17-year averages) and domain-specific cognitive function adjusting for age, self-reported gender, education (≤High School, Trade/College, and Graduate School), marital status (married/living as married, not married, missing), neighborhood income, and study. Effect modification by race/ethnicity was assessed using a multiplicative term, with p < 0.05 indicating significant effect modification.

No associations were observed in main effects models (Figure 1). Effect modification by race and ethnicity was observed with 5-year WUI PM_0.1 exposures across all cognitive domains (p < 0.05). Among non-Latino white participants, an IQR increase in 5-year average WUI PM_0.1 was associated with a decrease in cognition across all cognitive domains (Figure 1). Among Latino participants, an IQR increase in 5-year average total PM_0.1 was associated with decreased verbal episodic memory. Associations were attenuated or null for 10- and 17-year exposures.

Long-term WUI PM_0.1 exposure was associated with decreased cognitive function among non-Latino white participants. Wildfires are an increasing threat in California, and more research on their impact on cognition is needed.