Assessment of trace metal contamination and exchange between water and sediment systems in the To Lich River in inner Hanoi, Vietnam

The To Lich River (TLR), which receives considerable amounts of wastewater from the inner city of Hanoi, is used for irrigation purposes by areas further downstream. The marked increase in urbanization in recent decades has meant that considerable amounts of untreated and/or partially treated wastewater from industry and households have been discharged into the river, causing serious environmental problems. Trace metal concentrations in surface waters and in different sediment layers were analyzed at nine sample sites along the TLR. The enrichment factor, geo-accumulation index (I _geo), cluster analysis, and quality guidelines were used to assess the current status and potential risks arising from trace metal contamination. The Mn concentration in surface water exceeded the irrigation water standards at seven of the nine sites, and I _geo values indicated that Cd was the most abundant trace metal in sediments at six of the nine sites. Sediments at all sites contained levels of trace metals that exceeded the maximum permissible concentrations of potentially toxic trace metals for crops, and all sediments were considered to be toxic to aquatic life. Cluster analysis revealed that TLR sediments could clearly be divided into three groups based on the degree of contamination. Accumulation of trace metals in sediments was in order of Cr > Cu > Ni > Zn > Pb > As > Mn.