Fractionation and biotoxicity of heavy metals in urban dusts collected from Hong Kong and London

Samples of urban dusts, road site dusts and car park dusts, were collected at two selected sites each in Hong Kong and London. Sequential extraction was used to characterise the chemical compositions of these urban dusts. Copper, lead, zinc, pH, electrical conductivity and organic content were measured. Biotoxicity tests of urban dusts were conducted on higher plants (Brassica chinensis and Lolium perenne), a dinoflagellate green alga (Dunaliella tertiolecta) and luminescent bacteria (Photobacterium phosphoreum). A significant correlation was found between total lead (r = -0.70, p < 0.01) and zinc (r = -0.74, p < 0.05), and the 20min - EC₅₀ using P. phosphoreum. In addition, there was a significant correlation (r = -0.72, p < 0.01) between the exchangeable lead content in dust and the 48 h-EC₃₀ using D. tertiolecta. No specific trend was obtained for higher plants. Total lead and zinc contents were higher in dusts from London while the percentage of exchangeable fraction of metal contents was higher in those from Hong Kong.