Distribution, source identification and risk assessment of selected metals in sediments from freshwater lake

摘要

This study is based on the assessment of distribution,source apportionment and risk assessment of selected metals in freshly deposited sediments from freshwater lake,Pakistan.Composite sediments were collected and processed to assess Ca(NO_3)_2-extractable and acid-extractable levels of the metals in the sediments using flame atomic absorption spectrophotometry.Enrichment factors(EF),geoaccumulation indices(I_(geo)),contamination factors(C_f) and degree of contamination(C_(deg)) were computed to estimate the degree of contamination.The potential ecological risk was assessed using sediment quality guidelines and mean-ERM-quotient(m-ERM-Q).On the average basis,acid-extractable metals followed the decreasing concentration order:Ca>Mg>Fe>K>Mn>Na>Sr>Zn>Pb>Cr>Co>Cu>-Li>Cd,whereas,the Ca(NO_3)_2-extractable levels were:Na>Ph>Cd>Sr>Co>Cr>K>Mg>-Cu>Zn>Li>Ca>Fe>Mn.The highest Ca(NO_3)_2 extractable concentrations were observed for Na,Pb and Cd,while that of Ca,Fe and Mn were the least.EF showed very high and extremely high enrichment of Pb and Cd,respectively,while Ca,Co,Cr,Li,Mg,Mn,Sr and Zn manifested moderate enrichment:the I_(geo) results revealed moderate to strong and strong to extreme pollution for Pb and Cd,respectively;and the C_f study showed moderate,considerable and very high contamination by Co,Pb and Cd,respectively.The C_(deg) revealed very high degree of contamination in the sediments as a whole.Principal component analysis(PCA) and cluster analysis(CA) showed considerable anthropogenic contributions of Cd,Pb,Co,Mn,K,Zn and Li in the sediments.Measured levels of Cd and Pb exceeded ERL values,manifesting occasional adverse biological effects to the dwelling biota.Moreover,the mERM-Q study manifested 21%probability of toxicity in the sediments.