Non-residual heavy metals in Lake Nasser bed sediments, Egypt.

Abstract

ABSTRACThe Present study with the determination of concentrations of non-residual heavy metals (Iron, Manganese, Lead, Cadmium, Chromium, Copper, Nickel and Zinc) in Lake Nasser bed sediments as compared with total heavy metals contents in order to identify their environmental risk in Lake water. The analysis involves testing of sediments collected from eight sampling sites along riverine and transtion zones of Lake Nasser. Organic matter content for each of the sediment samples was also reported to study the effect of its content on the accumulation of metals in bed sediments. It was found that, the non-residual heavy metal levels (mg kg -1 ) in bed sediments were 0.11±0. 20.4, 19.9, 25.2, 38.6, 57.6, 49.3, 41.1 and 45.8% from the total content of these metals respectively. Fe-Mn oxides and organic matter seem to be the main carrier phases for the non-residual fraction of these metals. The order of non-residual metal concentrations in sediment samples was found to be Fe>Mn>Zn, Ni>Cu>Cr>Pb>Cd. In the present study, sediment quality assessment was done by calculating sediment pollution index and metal pollution index. The results of the assessment showed that, stream sediments from Lake Nasser are categorized into SPI0 natural sediments in all sites, except one site at km 403 which show SPI1 low polluted sediment. Metal pollution index highlights concentration differences between sites. Moreover, by comparing the results with sediment quality guidelines, it can be found that the Cd, Cu, Zn, Pb and Cr levels belong to the concentration below The Effect Range Low (ERL) and the toxicity to the biota in Lake Nasser was rarely occurred. It was also observed that, non-residual heavy metals were found very low compared with the agricultural land use target. This indicates that, Lake Nasser sediment can be used in amendment of agricultural land. The results of this study recommended the use of a pilot project to evaluate the characteristics of sediment for its potential use in agricultural land and to identify how sediments affect the crop yields. Some statistical applications were applied to study the behavior of the metal contents and their correlations in bed sediments.