ASSESSMENT OF TRACE METAL CONTAMINATION IN URBAN SURFACE ENVIRONMENT

This study was concerned with the concentration and distribution of a selected group of elements (Ca, Co, Cu, Cr, Fe, Mg, Mn, Ni, Pb, V and Zn) in Hong Kong urban deposits, represented by the roadside surface sediments (RRS), gully sediments (RGS) and vehicular tunnel-ceiling dusts (TCD). The particle size distributions, pH and total C and S contents of each sample were analyzed to guide interpretation of the elemental variations. Among the urban deposits, TCD had the highest fine-size fraction (< 63 µm) and total S contents, but the lowest pH values, while the physicochemical characteristics of RSS and RGS were similar to each other. The Ca, Co, Cr, Fe, Ni and V concentrations in different urban deposits were comparable. The ^208/207Pb vs ^206/207Pb plots showed a linear trend suggesting potential mixing of highly radiogenic (geogenic) and less radiogenic (anthropogenic) sources. Furthermore, the range of variation in Pb-isotope composition in the urban deposits suggested that possible geogenic contribution was the highest in RGS and the lowest in TCD.

The level of trace metal (Co, Cr, Cu, Ni, Pb and Zn) contamination in the urban deposits was estimated by using geo-accumulation index (Igeo). The relative order of trace metal contamination (Cu ≥ Zn > Cr ~ Ni ~ Pb > Co) changing from extremely- to moderately-contaminated was comparable in all urban settings. The level of Cu and Pb contamination was, however, the most severe in TCD compared to the RSS and RGS, while the Zn contamination was the highest in RSS. Potential ecological risk of trace metals in the urban deposits was also assessed by utilizing their potential ecological risk index. Potential ecological risk of Cu and Pb were the most distressing. Overall, trace metal contamination in RGS, RSS and TCD was found to pose low-, moderate- and considerable-risk, respectively, to the urban environment of Hong Kong.