Research On The Potential Ecological Risks Of Heavy Metal Pollution In The Surface Sediments Of Xiaoyao Bay In Dalian

In the study, the contaminated degree and the potential ecological risks of heavy metals, such as Cr, Cu, Pb, Zn, Cd and Hg, in the surface sediments of Xiaoyao Bay in Dalian were evaluated with the potential ecological risk indexing method. Furthermore, through geographical spatial analysis by ArcGIS, the distribution of heavy metals was characterized.The potential ecological risk indexing method proposed by Hakanson in 1980 is an effective standard way to divide pollution degrees in sediments and to assess potential ecological risks in the corresponding aquatic environment. Mass fraction of limited pollutants (e.g., heavy metals) in sediment samples is determined and then the value of ecological risk index is calculated, based on which the mass fractions, specie numbers, toxicity levels and aquatic sensitivity of heavy metal pollution in surface sediments will be indicated. In the process, toxicities, susceptivity, transport and transformation of heavy metals in sediments are considered, and the difference among the various regions and sources are eliminated by comparing analysis results of heavy metals with their background values, thus the method is very suitable to assess the various-source sediments from large areas. Therefore, relative to the method of single factor pollution index, the potential ecological risk indexing method used in the study not only can synthetically access the contaminated degree and characteristic of heavy metals, but also help develope and protect the ecological environment in coastal areas.The study indicated as follows:(1) Based on the analysis of single factor pollution index, the inorganic nitrogen and pH were the main contaminative factors in the seawater of the studied area. The pH of the surface water in the sampling site 9 was over standard, and the corresponding single factor pollution index was 1.39. The inorganic nitrogen in the bottom water of the site 11 was exceeding standard and the corresponding single factor pollution index was 1.49. Thus, the total over-standard rate was calculated to be 3.33%, which indicated that the seawater quality was according with the second level.(2) According to the analysis of single factor pollution index, the main contaminative factor in the sediments of the studied area was oils. Heavy metals were not exceeding standard, the over-standard rate was 22.2% for the the sampling sites, showing the quality of the studied sediments accorded with the standard of the second kind.(3) The potential ecological risk indexing method was employed to assess the contamination of heavy metals. The contaminated degrees of heavy metals were shown as follows:Cd＞Cu＞Pb＞Hg=Cr＞Zn. The potential ecological risk grades of heavy metals were:Cd＞Hg＞Cu＞Pb＞Cr＞Zn.(4) The ArcGIS was used to spatially characterize the contaminated degrees and the potential ecological risks of heavy metals, and the results indicated that the order of their contaminated degrees in every sampling sites was as follows:P5＞P1＞P6＞P13＞P15＞P9＞P12＞Pn＞P7. And the distribution of their potential ecological risks was:P1＞P5＞P6＞P15＞P13＞P9＞P11＞P12＞P7. Thus, the above two orders were similar.(5) The moderate levels of the Cd contaminated degrees and Cd and Hg potential ecological risk index possibly attributed to inlet of waste water to Xiaoyao Bay. And the tideway in the bay might result in the similar orders of the contaminated degrees and the potential ecological risks.In conclusion, the study first employed the potential ecological risk indexing method to assess the contaminated characteristics and degrees of heavy metals in Xiaoyao Bay, used ArcGIS to spatially characterize the contaminated degrees and the potential ecological risks, and proposed some advice for the sustainable development and protection of the coastal sea area.