Study On Occurrence Of Heavy Metals In Intertidal Sediments Of The Yellow River

With the rapid development of the economy in Yellow River Delta, heavy metal pollution in the intertidal zone of Yellow River Delta becomes more and more severe. Sediments, as the convergence and source of heavy metal pollution, is the main gathering place for heavy metals in the water. This study chooses the samples sediments of the intertidal zone of Yellow River Delta in three periods of a year and extracts and analyzes speciation of seven heavy metals including As, Cd, Cr, C u, N i, Pb and Zn. It also appraises the risk of heavy metal through Hakanson potential ecological risk evaluation method, sediment quality guidelines risk evaluation method, risk assessment code method and P value method which is also called the ratio of the second phase and the primary phase. This paper aimed at providing scientific evidence for developing the resources of the Yellow River Delta, formulating anti-pollution measures and planning and governing the river basin. The results show that the amount of heavy metal and the contents of speciation changes with time. In terms of the variation trend of heavy metal total amount, As and Cr show a downtrend on the whole, Cd a nd Zn show an uptrend on the whole, C u and N i generally decrease at first and then increase, while Pb increases first and then decreases. Four speciation of heavy metals including Cd and Pb changes drastically and the ratio of speciation of As,Cr,C u,N i and Zn is relatively stable.This paper makes a comparison on the degrees of risk of seven heavy metals by four different heavy metal risk assessment methods, of which the advantages and disadvantages are also pointed out. It is observed from the heavy metal risk assessment results that, according to Hakanson potential ecological risk assessment and analysis, Cd tops the list among all the seven heavy metals of three periods; in the assessment and analysis by sediment quality guidelines, As, Cr, C u, Ni and Pb show varying degrees of middle level pollution, while Cd and Zn show no pollution; according to the assessment by RAC, Cd and Zn have greater risk, and Cu, As, Ni, Pb and Cr have different degrees of mild risk; and P value method indicates that Cd and Pb are more risky. Comprehensive analysis can be obtained that t he current situation of heavy metal pollution is not optimistic, especially the pollution of Cd is the most serious, and the pollution of Pb and Zn is also not allow to ignore. It is of great realistic significance for seeking the source of heavy metal, evaluating the current situation of pollution, predicting its impact on ecological system and also protecting the river environment.