Mercury and Water Quality Study. Impact of Gold Mining in Song Bung 4 Project Area, Central Vietnam
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- NIVA-rapport 
The aim of this study is to elucidate any impact that the mining activity in the catchment of Song Bung River has on the water quality, sediment quality, as well as for the fish and the fish flesh quality in the mainstream river and in some tributaries in the Song Bung 4 hydropower development project area. In Song Bung mainstream enhanced concentrations of mercury were found both in the water and in the sediments in the river stretch where gold dredging activity was carried out. The concentrations were however low, much lower than problem levels both in national and internationally recognized environmental quality guidelines. This also applied for the tributaries. For arsenic and all other heavy metals normally confined with mining activity, observed concentrations were all lower than levels known to give environmental or consumption concerns. In the downstream part of the tributaries no traces of cyanide pollution were detected. The concentrations of mercury and other heavy metals in fish flesh were all low, and well below the WHO standards for consumption. The sediment dredging had only moderate impact on river water turbidity. However, the dredging made large physical disturbances of river habitats in the dredged sections of the rivers. Otherwise the water quality of Song Bung River was good and was to a low degree impacted by human activities. The mercury pollution of river sediments from the gold mining was so small that it will not create problems in the planned reservoir of Song Bung 4 Hydropower plant.