Content, distribution and fate of 33 elements in sediments of rivers receiving wastewater in Hanoi, Vietnam

Untreated industrial and domestic wastewater from Hanoi city is discharged into rivers that supply water for various agricultural and aquacultural food production systems. The aim of this study was to assess the content, distribution and fate of 33 elements in the sediment and pore water of the main wastewater receiving rivers. The sediment was polluted with potentially toxic elements (PTEs) with maximum concentrations of 73 As, 427 Cd, 281 Cr, 240 Cu, 218 Ni, 363 Pb, 12.5 Sb and 1240 Zn mg kg ^-1 d.w. Observed distribution coefficients (log ₁₀ K _d,obs) were calculated as the ratio between sediment (mg kg ^-1 d.w.) and pore water (mg L ^-1) concentrations. Maxima log ₁₀ K _d,obs were >4.26 Cd, >6.60 Cu, 4.78 Ni, 7.01 Pb and 6.62 Zn. The high values show a strong PTE retention and indicate the importance of both sorption and precipitation as retention mechanisms. Sulphide precipitation was a likely mechanism due to highly reduced conditions.