Assessment of respirable silica in ambient air of Dhaka and evaluation of human health risks

Respirable Silica (RS) is a substantial pollutant in urban air, and it is associated with severe health hazards, including lung inflammation, kidney diseases, poor lung function, and silicosis. RS levels in close proximity to occupational and emission sources are widely reported; however, ambient exposure from non-occupational sources is still not properly studied. This study examines the concentration of RS in ambient air during different seasons of the year and the diverse sources that contribute to RS concentrations in Dhaka City, Bangladesh. Ambient fine particulate matter (PM) was collected using a low-volume air sampler on Teflon filters at an average flow rate of 15.4 ± 1.36 L min⁻¹, with each sample collected continuously over 24 h to assure a representative daily exposure at five different locations. RS concentrations were quantified spectrophotometrically, with a limit of detection (LOD) of 0.05 µg m⁻³. The highest recorded concentration was 14.2 µg m⁻³, while the mean RS concentration was 3.74 ± 3.12 µg m⁻³. Seasonal patterns indicated increased RS concentrations in winter (6.28 µg m⁻³) relative to the pre-monsoon (1.97 µg m⁻³) and post-monsoon (3.74 µg m⁻³) phases. Among the five study sites, the Teacher Student Center (TSC) exhibited the highest RS concentration (7.33 µg m⁻³) due to proximity to metro-rail construction, whereas the academic building site recorded the lowest (0.95 µg m⁻³), indicating relatively cleaner air. Health risk assessments indicated an average hazard quotient (HQ) of 1.25, suggesting significant non-cancer risks, and a cancer risk of 14.2 cases per 10,000, emphasizing the urgent need to address RS exposure. These findings emphasize the substantial public health impact associated with ambient RS pollution in urban environments, urging quick regulatory and mitigation steps in rapidly rising cities such as Dhaka.