BCR Sequential Extraction and AAS Analysis of Selected Heavy Metals in Street Sediments of Some Cities of Heavy Motor Traffic and Industrialization in Sri Lanka

Abstract

Topsoil and street-deposited sediments in urban areas are sinks for potentially toxic metals.Heavy metals are considered as serious inorganic pollutants due to their toxic effects onliving organisms having a high accumulation and slow removal rate. Vehicle emissions,industrial discharges and other anthropogeni c activities are the sources of heavy metals suchas cadmium (Cd), lead (Pb), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), and zinc(Zn) in roadside sediments in urban areas. Though the common practice is to report the totalmetal content of polluted soil sample, it does not accurately reflect the metal mobility in theenvironment, bioavailability or the level of environmental hazard of the metal. Conversely,modified BCR (European Community Bureau of Reference) sequential extraction procedurepermits the fractionation of heavy metals based on the chemical association of different metalpollutants in soil.

In this study, street surface sediment and dust deposition on roadside tree leaves werecollected from Pettah, Borella, Nugegoda, Katunayake, and Makandura areas and sedimentsof a vehicle washing station at Negombo was also collected. According to the BCRprocedure, four fractions (water and acid soluble, reducible, oxidisable, residual) wereseparated from each sample and analysed by flame atomic absorption spectroscopy (FAAS)using standard addition method. Metal contents in total extracts were also analysed by FAASand compared with the total sum of four BCR fractions obtained for each metal ion.

The total mean contents of Pb, Cr, Ni, Cu, and Zn were calculated for each fraction for all sixlocations. Heavy metals, Cd and Co were not detected. Out of five heavy metals underinvestigation, only Cr in the bioavailable or potentially bio available fraction exceeded therecommended level that caused risks on human health, according to the New York statedepartment of environmental conservation (NYS DEC 2007). Significant levels of Ni and Pbwere detected in the sediment samples from Nugegoda and Katunayake, Nugegoda andvehicle washing station at Negombo, respectively. Through continuous industrialization andheavy motor traffic, both Ni and Pb contents in these locations could soon surpass the levelsof unrestricted residential use recommended by NYS DEC 2007.