Association between exposure to PM and black carbon and the risk of childhood leukemia in Tehran: A case-control study with critical exposure time windows.

Limited research has explored the relationship between air pollutants and childhood leukemia during critical exposure periods, and no such research has been conducted in Tehran to date. This study assessed the association between exposure to fine particulate matter and black carbon and the risk of childhood leukemia, focusing on various postnatal exposure windows. This case-control study involved 428 children aged 1-15 years diagnosed with leukemia in Tehran. Annual concentrations of PM and BC were estimated using the Gradient Boosting Machine (GBM) algorithm, integrating ground-based measurements with meteorological data and satellite-derived Aerosol Optical Depth (AOD). The relationship between pollutant exposure and the probability of developing leukemia was investigated using logistic regression models with 95 % confidence intervals. Three exposure periods were considered: the entire exposure period from birth to diagnosis, the year prior to the diagnosis, and the age range corresponding to when children were aged between two and four years. Additionally, a logistic regression model with cubic splines was used to allow for nonlinear associations. The analysis revealed that a 5.09 μg/m increase in PM. concentration (interquartile range (IQR)) was associated with an increased odds ratio for childhood leukemia of 1.10 (95 % CI: 1.05-1.15). Similarly, for each 1 μg/m increase in BC, the OR was 1.14 (95 % CI: 0.99-2.20). The findings showed that with each increase of IQR in the PM concentration in the year before diagnosis, the OR was 1.12 (95 % CI: 1.01-1.11) for childhood leukemia, while for BC, the OR was 1.16 (95 % CI: 1.00-2.15). Cubic spline analysis suggested a potentially non-linear association between PM and BC concentrations and the risk of childhood leukemia, with an increasing trend observed at higher exposure levels. These results demonstrate a significant relationship between the incidence of leukemia in children and residential exposures to either PM or BC.