Assessment Model For Heavy Metal Pollution In Sediment Based On Blind Theory

The risk assessment system for heavy metal in sediment was a large system，in whichthe information was usually random, fuzzy, gray and uncertain. The existence of theseuncertainties made traditional deterministic assessment or some assessments for singleuncertainty can not accurately predict the real result and they also can not objectively reflectthe real heavy metal pollution. On the basis of the characteristics of the coexistence ofmultiple uncertainties, blind theory was introduced to the pollution assessment system toreduce the uncertainties in the assessment process.A model of index of geoaccumulation based on blind theory was established in thispaper. With the concentrations of contaminants in the sediment and their values in thegeochemical background as blind numbers, the pollution degrees of heavy metals wereobtained by using reliability analysis model BM of blind numbers and calculating themembership grade. The introduction of blind theory can provide a new way of thinking foruncertainty study in the assessment of heavy metal pollution.Firstly, this paper summarized the evaluation of various methods of heavy metal insediment, and compared these methods. The application in the environmental assessment ofuncertainty theory and various mathematic for uncertainty are reviewed in this study.Secondly, an assessment model for heavy metal in sediment based on blind theory wasestablished. Finally, the evaluation model was applied to assess the heavy metal pollution insediment from Dongting Lake. The results showed that the pollution level of Cr may be level1or level2with the credibility of0.969and0.031respectively. The pollution level of Cu maybe level0, level1, level2or level3, with the credibility of0.152,0.707,0.058and0.083respectively. The pollution level of Zn may be level0, level1or level2, with the credibilityof0.474,0.443and0.083respectively. The pollution level of Pb may be level0or level1with the credibility of0.583and0.417respectively. The pollution level of Cd may be any oneof0to6with the credibility of0.203,0.048,0.123,0.239,0.275,0.030and0.083sequentially.The pollution level of Hg may be any one of0to3with the credibility of0.231,0.292,0.305and0.167sequentially. The pollution level of As may be level0or level1with the credibilityof0.415and0.585respectively. The order of the geoaccumulation degrees in these metalswas Cd﹥Cr=Cu=Zn=Hg=As﹥Pb. Cd was considered the primary important polluting factorin Doting Lake. Both the possible ranges and their credible degrees of indexes ofgeoaccumulation of heavy metals can be calculated in this model, thus the possibilities of pollution of heavy metals can be quantitatively calculated. The model reduced the drawbacksof the certain assessment efficiently, and conveyed information about degree of enrichmentmore factually and objectively.