Author(s): Huong Thi Lan Nguyen
Linked Author(s):
Keywords: Gricultural soils; Heavy metal; Selective Sequential Extraction; Leaching
Abstract: The To Lich and Kim Nguu Rivers, laden with untreated waste from industrial sources, serves as sources of water for irrigating vegetable farms. The purpose of this study is to identify the impact of waste-water irrigation on the level of heavy metals in the soils and vegetables, and to predict their potential mobility and bioavailability. Soil samples were collected from the locations of different distances from the canal. The average concentrations of the heavy metals in the soil were in the order: Zn (204 mg kg -1) >Cu (196 mg kg -1) >Cr (175 mg kg -1) >Pb (131 mg kg -1) >Ni (60 mg kg -1) >Cd (4 mg kg -1). The concentrations of all heavy metals in the study site was much higher than the background level in that area, and exceeded the permissible level of the Vietnamese standard for Cd, Cu and Pb. The concentrations of Zn, Ni and Pb in the surface soil exhibited decreased with distance from the canal. The results of selective sequential extraction procedure indicated that dominant fractions were oxide, organic and residual for Ni, Pb and Zn, organic and oxide for Cr, oxide for Cd, and organic for Cu. Leaching tests for water and acid indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order: of Cd>Ni>Cr>Pb>Cu>Zn, and in the order of: Cd>Ni>Cr>Zn>Cu>Pb for the EDTA treatment. The EDTA treatment gave higher leachability than other treatments for most metal types. By leaching with water and acid, all heavy metals were released fully from the exchangeable fraction, and some heavy metals were fully from carbonate and oxide fractions. The concentrations of Cd, Cr, Cu, Ni, Pb and Zn in the vegetables exceeded the Vietnamese standard. The transfer coefficient for the metals was in the order of: Zn>Ni>Cu>Cd=Cr>Pb.
Year: 2014