Non-residual metal in bed sediments is the amount of metal that is not present in the silicate matrix. It includes metal adsorbed on sediment particles, complexed by and adsorbed on organic matter, and in the form of soluble salts.
Metal toxicity is dependent on its chemical form, mobility, degree of transformation, and bioavailability, which allow metal contaminants to enter the food chain. Bioaccumulation of metals by biota in surface water and by plants and
animals in terrestrial can adversely affect humans. This paper deals with the determination of concentrations of non-residual heavy metals (Iron, Manganese, Lead, Cadmium, Chromium, Copper, Nickel and Zinc) in Nasser Lake bed
sediments as compared with total heavy metal content in order to identify their environmental risk in Lake Water. The analysis involves testing of sediments collected from eight sampling sites along riverine and transition zones of Nasser
Lake. Organic matter content for each of the sediment samples is 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±0.05, 13.28±5.02, 12.52±2.89, 25.54±11.1, 24.53±11.29, 27.66±7.29, 11610±2810 and 418.87±190.91 for Cd, Cr, Pb, Ni, Cu, Zn, Fe and Mn respectively. It represents about 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 Nasser Lake 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 Nasser Lake was rarely occurred. It was also observed that, nonresidual heavy metals were found very low compared with the agricultural land use target. This indicates that, Nasser Lake sediment can be used in amendment of agricultural land. The results of this study recommended the use of a pilot project to evaluate the characteristic of sediment for its potential use in agricultural land and to identify how sediments affect the crop yields. Finally, some statistical
applications were applied to study the behavior of the metal contents and their
correlations in bed sediments.