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

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. 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. 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. This study in Tehran found significant effects of BC exposure on daily mortality for cardiovascular, ischemic heart disease, cerebrovascular disease.