Assessment of heavy metal pollution in river water of Hanoi, Vietnam using multivariate analyses.

Concentrations of heavy metals in water of the Nhue River (a suburban/rural river) and one of its tributaries, the To Lich River (an urban river), in Hanoi, Vietnam had been monitored, and spatial and seasonal variations in their composition were evaluated by means of principal component analysis and cluster analysis. Heavy metal concentrations in water of the two rivers were generally lower than the surface water quality standard in Vietnam, except for manganese in several sites, although they were higher than the median values in freshwater of the world by 0.42-43 times in Nhue and 0.13-32 times in To Lich. The two multivariate analyses represented that the composition of heavy metals in river water of To Lich was distinctly different from that of Nhue. It was also suggested that metal concentrations and their composition in Nhue river water would be affected by inflowing water of To Lich and wastewater discharged from the up- and middle-stream basin, and that they gradually recovered along the direction of water flow in the downstream area in rainy season.