Relationship between ambient black carbon and daily mortality in Tehran, Iran: a distributed lag nonlinear time series analysis

Purpose: The aim of the present study was to investigate the effect of short-term exposure to ambient black carbon (BC) on daily cause-specific mortality, including mortality due to respiratory, cardiovascular, ischemic heart and cerebrovascular diseases in Tehran, Iran. Materials and methods: Daily non-accidental death counts, meteorological data and hourly concentrations of air pollutants from 2014 to 2017 were collected in Tehran. A distributed lag non-linear model was used to assess the association between exposure to BC and daily mortality. Results: The mean daily BC concentration during the study period was 3.96 ± 1.19 µg/m3. The results indicated that BC was significantly associated with cardiovascular, ischemic heart disease, and cerebrovascular mortality, but not with respiratory mortality. In first model, each 10 µg/m3 increase in at lag 3, lag 4 and lag 5 were associated with cardiovascular mortality in 16�65 year age group with the relative risks (RRs) of 1.17 (95 CI: 1.02�1.33), 1.17 (95 CI: 1.04�1.31) and 1.12 (95 CI: 1.02�1.24), respectively. The highest mortality rate per 10 µg/m3 increase in exposure was found for ischemic heart diseases with RR of 3.98 (95 CI: 1.04�1.81, lag 01) for 16�65 age group. Cerebrovascular mortality was associated with 10 µg/m3 increases in non-cumulative exposure with RR of 1.17 (95 1.009�1.35, lag 5) in the age group � 65 years. In the second model for a 10 µg/m3 increase in BC, cardiovascular mortality at specific lag days (5 and 6 days) in the age group � 16 years were associated with RR of 1.34 (95 CI 1.08�1.66) and 1.35(95 CI 1.02�1.77), respectively. Conclusions: This study in Tehran found significant effects of BC exposure on daily mortality for cardiovascular, ischemic heart disease, cerebrovascular disease. © 2021, Springer Nature Switzerland AG.