Heavy metals in the bed and suspended sediments of Anyang River, Korea: Implications for water quality

The objective of this study is to compare Anyang River bed sediments with water chemical composition and to assess the anthropogenic chemical inputs into the river system. Eight sampling locations were chosen along the river channel. Bed and suspended river sediments and water samples were collected, and analyzed for their chemical and physical composition. Data revealed that trace element concentrations in the river water were generally below world average, except for As, Mn, Ni and Cr. Among the three phases: water, bed and suspended sediment, more than 99% of the trace elements was associated with the bed sediment. Concentrations of trace elements in the sediment were a function a particle size distribution and organic content. The calculated degrees of enrichment based on the least influenced sample (ASD 1) indicated the river sediments were enriched with respect to background. The enrichment factors for Pb, Zn and As were relatively lower than for Cr, Co, Ni and Zn. The difference in the enrichment seems to reflect the human activities influence in the basin, and specially for Cd. Speciation of the elements in the five different chemical forms in the sediment by sequential extraction indicated that the reducible fraction was predominant for Fe, Zinc and Cu showed an irregular variation among the different fractions; whereas, Cd and Pb were more regular. Zinc and Cu highly existed mostly in exchangeable forms. Acid soluble and reducible forms were also important for most metals. The speciation implies that the metals associated with the sediment are subject to release into water bodies as goechemical variables ( pH and Eh) change. Currently, the introduced metals are deposited near the source area and are mostly associated with the sediment, implying that the river bed sediment acts mainly as a sink, rather than a pool. The accumulated and enriched toxic trace elements can pose a potential pollution of river water.