Abstract

Environmental mobility and geochemical partitioning of iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni) and molybdenum (Mo) were examined in sediments collected from the whole old Nakagawa river (NR), Tokyo, Japan. A combined 6- step sequential extraction procedure was employed for the partitioning of the metals and the concentrations were measured in the liquid extracts by atomic absorption spectrophotometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). The observed order of potential mobility of metals in the aquatic system of NR was: Ni > Co > Mo > Mn > Fe. The association of Co, Ni and Mo (26.6-30.5; 23.2-38.5 and 19.0-40.1% of total, respectively) were found highest with amorphous Fe oxyhydroxide phase, and the maximum fraction of Fe and Mn were in silicates and residual phase. The normalization of the concentrations of metals using Al as a conservative element confirmed that most of the sampling stations of NR were enriched with Ni, Mo and Mn. Geoaccumulation index (I_geo) values for most of the sites have higher for Ni and Mo. Environmental risk of metals were also evaluated by using risk assessment code (RAC) and found medium risk for Ni, Mo, Co and Mn.

Key words: Mobility, partitioning, pollution, metals, sediment.