Exposure to black carbon is associated with symptoms of depression: A retrospective cohort study in college students

Background: Previous studies have revealed a significant association of fine particulate matter (PM2.5) with emotional disorders. However, as a crucial component of PM2.5, little is known about the potential effect of exposure to black carbon (BC) on the symptoms of depression and anxiety. Objectives: To explore the associations of long-term exposure to BC during the past six years with the current symptoms of depression and anxiety in a group of incoming college students. Methods: This was a retrospective cohort study of incoming students in five universities of China. Symptoms of depression and anxiety during the past two weeks were measured by the Patient Health Questionnaire-2 (PHQ-2) and Generalized Anxiety Disorder Scale-2 (GAD-2), respectively. Levels of BC and other environmental factors during 2013 ∼ 2018 (six years prior to the recruitment) was obtained from public repositories and linked to individual data by home addresses. Averagely daily dose of BC exposure was estimated according to the respiratory rate. Demographic and behavioral variables were collected through a questionnaire. The associations of BC with symptoms of depression and anxiety were estimated by mixed linear models adjusting for socioeconomic and behavioral characteristics, and the principal components of multiple environmental exposures. Subgroup analysis was conducted to assess the effect modification by covariates. Overall effect of environmental mixture was evaluated by weighted quantile sum (WQS) and Bayesian kernel machine regression (BKMR). Results: A total of 20,079 participants was included in the current study. After adjustment for covariates, long-term BC exposure was significantly associated with symptoms of depression (β = 0.17, P < 0.001) but not anxiety (β = 0.07, P = 0.125). Effect modification by sex and parental educational level: BC was correlated with depressive symptoms in women (β = 0.23, P < 0.001) but not in men (β = 0.04, P = 0.581), and higher educational level was associated with decreased effect sizes of BC. Sensitivity analysis showed that the acute and short-term effects of BC on depression was consistent with its long-term exposure (β varied from 0.18 to 0.20). WQS identified BC as the primary pollutant in association with symptoms of depression but not anxiety. BKMR identified no significant interaction between BC and other exposures. Conclusion: Exposure to BC is associated with symptoms of depression but not anxiety in college students, and the relationship is modified by sex and education