Street dust bound PAHs, carbon and heavy metals in Guwahati city - Seasonality, toxicity and sources

Street dust is an indicator of pollution status of a city area. We present comprehensive assessment of USEPA's priority 16 Polycyclic Aromatic Hydrocarbons (PAHs), carbon and heavy metals in street dust of Guwahati, a fast growing city of the Brahmaputra Valley. On assessment of different representative landuse classes, the concentrations of PAHs were found to decrease spatially in the order of industrial, commercial, institutional, residential and forest site. The profile of PAHs was dominated by 2- and 4-ring compounds and the carcinogenic PAHs (CPAHs) were found to be in the range of 16-55% of ∑PAHs. The mean toxicity in terms of Benzo(a)pyrene equivalent (BaPq) concentrations varied seasonally, which was found to be maximum during pre-monsoon. Principal Component Analysis, diagnostic ratios and correlations of PAHs with heavy metal implied that the PAHs originated mainly from coal and wood burning, and vehicular emission. Seasonality in sources of PAHs with respect to the diagnostic ratios was discovered and signatory influence of local sources was found during the pre-monsoon. The correlations of black carbon (BC) and organic carbon (OC) with PAHs were found to show seasonality.