Geochemical Speciation and Enrichment of Toxic Heavy Metals in Nile Sediments and Soils in El-Tebbin Area, Egypt

Abstract

The present study was carried out to determine the status of pollution of water, soil and Nile sediments in El Tebbin area. Water, soil and Nile sediments samples were analyzed and classified both in terms of chemical parameters and spatial distribution as well as statistical analysis. In this study, we gave a special attention to the binding of some heavy metals to the main fractions in soils, using five-step sequential extraction procedures. Mapping was made using topographic map; Global positioning system (GPS) and ArcGIS (9.2). Chemical analyses were carried out for the samples collected from different locations using the standard procedures recommended by APAH-1994 and a flame atomic absorption spectrometer. Physical and chemical properties of surface water at El Tebbin area were quantified and evaluated for drinking, irrigation and industrial purposes. Different standard limits were used (WHO, EU and FAO) as well as numerical methods (WQI). The studied water at El Tebbin area was found to be unfit for drinking till simple and primary treatment. Water canals are suitable for major crops with minor degree of threat while Nile water is excellent for irrigation. All water samples require treatment for specific industries. Generally the studied samples showed no heavy metals pollution. Generally, spatial distribution of pH, EC and CaCO3 for soil showed that, the highest values are recorded eastward. Soil organic matter shows the highest values at the central pats of El Tebbin area with dense agricultural activities. Three approaches were employed to evaluate degree of soil pollution along El Tbbin area, based on one step digestion of eight metals (Co, Zn, Cd, Pb, Ni, Cu, Cr and Fe): 1) Comparison with the background value, (2) single pollution indices and (3) integrated pollution indices. Two groups of soil were classified according to Heavy metals concentrations: a- Low potential concentration group including Zn, Cd, Pb, Cu and Cr. b- Considerable concentrations potential group is represented by Co and Ni. With respect the Nile sediments, generally physiochemical parameters as well as heavy metals area depleted in most of river bank sediments comparing with soil samples, this is controlled by two factors; the textural characteristics and the anthropogenic influence, soil is finer and more subjected to anthropogenic activities. River bank sediments show no heavy metals contamination; all concentrations are lower than or flocculated within standard permissible limits. Pollution indices indicated that, the Nile sediment uncontaminated and needn't to drastic rectification measures. Another important approach identifying different forms of metals is speciation, sequential extraction scheme were applied for Co, Zn, Cd, Pb, Ni, Cu and Fe. The Co and Ni distributions in the soil were strongly associated with residual fraction, characterized by stable chemical bonds. The residual phase represents metals largely embedded in the crystal lattice of the sediment fraction and should not be available for remobilization or dissociation except under very hard condition. The non-residual metals, under favorable conditions they can be released to pollute the environment.