Association between Wildfire area and PM2.5 levels on the Prevalence of Mental disorders in Thailand

• Wildfire area associated with an increased prevalence of most mental disorders. • PM2.5 level associated with schizophrenia, bipolar, depressive, and anxiety disorders. • Wildfire directly affects mental disorder prevalence, not via the PM2.5 pathway. • Since Thai wildfires are man-made, better monitoring and policies may help. Association between wildfire and health outcomes has usually been studied based on major wildfire events. However, studies on chronic wildfire activity, especially studies of the effects that mediate through particulate matter 2.5 (PM2.5), remain limited. This study aims to investigate the association between wildfire area and satellite-derived PM2.5 levels over years with the prevalence of mental disorders across Thailand. Data were obtained from secondary sources for the years 2015 to 2023, aggregated at the provincial level annually. Poisson regression models with robust standard errors, clustered by province, were employed to estimate prevalence ratios (PR). To estimate indirect effects of wildfire through PM2.5, mediation analyses were conducted for disorders that showed significant associations. The findings showed significant associations of wildfire exposure and prevalence of dementia (PR = 1.010), alcohol dependence (PR= 1.007), stimulant dependence (PR= 1.009), other substance dependence (PR= 1.008), bipolar disorder (PR= 1.008), depressive disorders (PR= 1.012), anxiety disorders (PR= 1.008), other mental disorders (PR= 1.009), and suicide attempts (PR = 1.009), with all P < 0.05 . Despite the significant correlation between wildfire exposure and PM2.5, mediation analysis revealed that wildfires exert direct effects on mental disorders, rather than through the PM2.5 pathway. In conclusion, wildfire may play an important role in the occurrence of mental disorders. Enhanced wildfire monitoring and mitigation efforts should be prioritized to potentially reduce the prevalence of mental disorders, rather than relying solely on air pollution levels for public health interventions.