Rationale: Wildfire smoke is recognized by the US Environmental Protection Agency as a major source of particulate matter under 2.5 microns diameter (PM2.5 ) emissions which is expected to increase in the future because of climate change. There is an abundance of epidemiologic and mechanistic data supporting the link between poor air quality and respiratory health, but the biological basis for effects on mental health is not well understood. We hypothesized that early-life inhalation of PM2.5 derived from wildfires can contribute to increased behavioral abnormalities and anxiety with maturation. To test this hypothesis, we investigated parameters of sleep, activity, and cortisol in an outdoor colony of rhesus macaque monkeys that were exposed to ambient wildfire smoke during infancy.
Methods: Adult female monkeys were born and reared in an outdoor environment within three months prior to the Trinity and Humboldt County summer wildfires in 2008, which produced significant episodes of PM2.5 within one mile of the California National Primate Research Center. Controls for the study were female monkeys born in 2009 that were not exposed to wildfire smoke during infancy. Quantitative tracking data for activity and sleep were obtained using CamNtech Actiwatch monitors that were recorded every 30 seconds for one week. Activity monitors were worn by monkeys using 3D-printed collars; all animals remained housed in large social groups in half-acre field cages during data collection (n=5 for 2008 and n=7 for 2009). Serum cortisol levels were measured in historical samples from infant monkeys following the wildfire event in 2008 and 2009 animals.
Results: Adult female monkeys that were exposed to wildfire smoke as infants in 2008 showed significantly reduced sleep duration compared to controls. The average daily sleep duration for control animals was 555.7 minutes. The average daily sleep duration for wildfire smoke-exposed animals was 464.8 minutes. representing a 16% reduction in sleep per day. Comparatively, wildfire smoke-exposed animals also showed significantly increased activity levels normalized to body weight relative to controls. Wildfire smoke-exposed animals showed significant evidence of cortisol dysregulation compared to control counterparts. Body weight for adult wildfire smoke-exposed animals was also reduced relative to controls.
Conclusion: Our results demonstrate that early-life wildfire smoke exposure is associated with disturbances in sleep, activity, and cortisol levels compared to controls. Collectively, these findings suggest wildfire smoke exposure may promote neurobehavioral dysregulation, possibly through altered circadian rhythms.