Metal interactions in contaminated freshwater sediments from the fly river floodplain, Papua New Guinea

Field data for sediment pH, Eh, sulphur and organic matter were analysed to determine their relationship with measured dissolved and particulate metals from sites in the Fly River affected by mine-derived wastes. The above-background concentrations of dissolved metals correspond to various concentration groups as demonstrated by copper for background (< 70 mg/kg), moderate (70-500mg/kg) and severe (> 500mg/kg), respectively. Dissolved Cu (r = 0.7431, p < 0.0005) and Mo (r = 0.7133,/> < 0.0005) were significantly correlated with their sediment component. Dissolved Al, Cd, Cu and Mo were positively correlated with sediment pH. Significant negative correlation between dissolved copper and sediment (SOM) organic matter (r = -0.3821, p < 0.05), and positive correlation with dissolved Al (r = 0.9358, p < 0.0005) suggest that dissolved Cu is present as a complex with either organic matter, Al/Fe oxyhydroxides, or oxyhydroxide-organic matter colloids. Significant interrelations between dissolved Al, Cu and Mo with organic matter and the ratio of Fe/SOM also suggests that sediment physico-chemical characteristics are important in the processes occurring in the Fly River floodplain sediments. These processes appear to be responsible for the significantly increased metal concentration in the water column.