Samir A. El-Gendi ; A. Sh. A. Osman and M.H. Abdel- Aal( 2016). Environmental assessment of some heavy metals in Khor Garf- Hussin sediments (Nasser lake, Aswan, Egypt)., Zn
Egypt . J. of Appl. Sci., 31 (10) 248 -258
Abstract: Lake Nasser and its khors is considered the sole source of surface fresh water reservoir and provide more than 95% of the Egyptian fresh water budget. Therefore, water pollution control is clearly one of the most critical challenges. In the present study, six heavy metals in the Khor Garf –Hussin sediments were sequentially fractionated using Tessier et al (1979) method as well as two risk assessment codes were applied to evaluate potential ecological risks of that metals .The results showed that the abundance of the tested metals was in the order of Fe (15322.36)>Mn (306.12) >Zn (40.69) >Ni (37.22) > Cu (26.42)> Pb (12.41μgg-1). It is cleared that the content of the tested metals were below the threshold values for stream sediment composition reported by (Aston and Thornton ,1977).Fractionation results showed that the order of abundance of the tested metals in exchangeable fraction were Cu , Pb , Ni , Mn , Zn and Fe , comprising 9.09, 5.11, 4.58 , 2.74 , 2.20 and 0.01% of sum of their fractions, respectively. Meanwhile , Ni followed by Cu and Pb were the most abundant metals associated with carbonate fraction , comprising 24.28% , 15.78% and 8.26% of their sums , respectively . These results suggested that Ni, Cu, and Pb may exist in sediment as carbonate minerals. The data also, showed that the majority of the tested metals were associated with the reducible fraction. The order of abundance were Pb (35.28%), Zn(28.11 %),Ni(22.78%),Cu (20.02%), Mn (16.80%), and Fe (2.17%). This could be due to the fact that this fraction constitute a significant sink for heavy metals in aquatic system. Also ,the data showed that Mn , Pb and Cu were the most abundant metals in organic bounded fraction, comprising 17.73% ,15.51%,and12.48%,respectively. Moreover, the results of all the tested metals were predominant associated with residual fraction, Fe was the most abundant metal in residual fraction , constituting 97.30% of the sum of its fractions, followed in decreasing order by Mn( 59.18%) , Zn (55.71%) . Cu (42.62%),Ni (37.06%), and Pb (35.84%), suggesting that the majority of the tested metals exist mainly as silicate.
According to Risk Assessment Code, the present data indicated that Fe, Mn and Zn showing low risk for aquatic environment. Ni followed by Cu and Pb showed medium risk .On the same connection, the calculated contamination factor confirmed that sediments of Khor- Gurf Hussin are free from contamination with the tested metals. Therefore, It’s imperative on Egyptian government to quantify the pressures caused by human activities in and around lake Nasser reservoir.
Keywords: (Environmental indicators - sediments , lake Nasser , sequential fractionation)
