DISTRIBUTION AND TRANSLOCATION OF HEAVY METALS IN SOIL IRRIGATED WITH TREATED WASTEWATER IN BRAUNSCHWEIG

Abstract

The study to investigate the distribution and translocation of heavy metals in the wastewater irrigated soils in Braunschweig has been carried out. The wastewater used for irrigation was the previously treated domestic and industrial wastewater from Braunschweig. The soil samples were taken from the Steinhof wastewater treatment plant (WWTP) area in the northwest of Braunschweig, Germany. The non-irrigated soil was also analyzed as a comparison. The soil fraction > 2 mm was excluded from analysis through sieving. All soil samples were analyzed for the pH values in 0.01M CaCl2 solution, grain size distribution (using wet sieving and settling methods), and the concentration of their aqua regia (3:1, v/v, HCl 32% to HNO3 65%) extractable elements. The concentration of aqua regia extractable elements was analyzed using ICP/OES instrument. The pH values of soil samples ranged from 4.9 to 6.8. The soil samples are dominated by sand fraction with the content in the range of 75 � 97%. The concentrations of heavy metals in the top soils of irrigated areas are generally higher than the concentrations of heavy metal in the reference areas, indicating the heavy metals enrichment on top soils due to the long term application of wastewater. There is a linear correlation between heavy metals (Al, Fe and Zn) and silt fraction. A second-order correlation was found between aqua regia extractable elements (Cd, Cu, Pb and Zn) and the organic content of the soil. There is also a linear correlation between inter-element such as Fe versus Al, Al versus Zn, Zn versus Pb, Sr, P and Ca and for P versus Ca and Pb. The enrichment factors (EFs) of some heavy metals calculated using Al as the normalizing element revealed that the EFs of heavy metal in soil samples are higher than those of the references. This indicated that the long-term application of wastewater has elevated the concentration of heavy metals in the soil