Heavy metals in road deposited sediments and road dusts of Colombo Capital, Sri Lanka

Road deposited sediment (RDS) and road dust analyses are useful techniques to understand the heavy metal (HM) pollution in an urban area. Therefore, this study focused on the chemical characteristics of RDS and road dust in order to evaluate the pollution conditions in the Colombo Metropolitan Region (CMR) in terms of HMs. Forty six (46) RDS samples and forty eight (48) road dust samples were collected, and elemental concentrations of Zn, Cu, Pb, Fe, Mn and Cr were determined. Out of these measured elements, the most abundant element in all the samples was Fe, which is a common element in the basement lateritic soil in the area. Cu, Pb, Fe and Cr concentrations in RDS are high in industrial areas, while Zn and Mn are high in commercial areas. Except Fe, all the other element levels were higher in road dust than in RDS. Data analysis revealed that vehicle-related activities are the dominant source for the metals in the city. Zn, Cu, Mn and Fe contents were significantly higher than the background levels of the area. Statistical analysis reconfirms that road dust is more polluted than RDS in terms of Zn and Cu. According to the geoaccumulation index, road dust is moderate to strongly polluted and RDS are moderately polluted. Higher pollution conditions of road dust may be due to the resuspension of dust particles. Spatial distribution patterns show that HMs of anthropogenic origin were accumulated towards the North and Northwestern parts where the transportation related activities are centered in the CMR. However, the prevailing natural conditions such as wind direction, geomorphology and basement soil also control the level of contamination in the area.