Study On Risk Assessment Method Of Heavy Metal Compound Contaminated Sites Based On Speciation Evolution

Heavy metal elements are concomitant and co-exist in the environmental medium,and all of them are compound pollution to the polluted site.At present,however,there are few studies on simultaneous extraction of heavy metal composite pollution,and there is no unified process and standard.This topic selected the two classic extraction:BCR and Tessier extraction methods,Based on the comprehensive evaluation of recovery rate,reproducibility,identification ability of bioavailability components and differences between single extraction and simultaneous extraction,the extraction method with better simultaneous extraction effect of Pb and Cd was selected and applied to the modeling and risk assessment of geochemical disasters in Pb and Cd compound pollution sites.The results showed that the Tessier extraction method had a high average recovery rate of 99.98%for lead and cadmium,and the average coefficient of variation was 3.18%.The bioavailability analysis also showed that the method could quantify the absorption sources of Pb and Cd in plants more clearly and comprehensively.The difference between single extraction and simultaneous extraction is small,and the correlation between some fractions in different concentrations is good.Therefore,it is applied to the study of geochemical disasters in Pb-Cd compound contaminated sites.Static risk is inherent in heavy metal contaminated sites and is the final result of long-term spontaneous evolution of site risk.The occurrence of dynamic risks depends on the environmental conditions and the heavy metal content accumulated in the site,which reflects the dynamic change of on-site risks in a short period of time.The field risk assessment should take into account both static and dynamic risks,and the propensity for either risk type can lead to an incomplete risk profile.There are many reports on site risk assessment methods and case studies.However,they are mainly based on the content of heavy metals and their components in the site soil,and basically only involve static risks,with little or no consideration of dynamic site risks.Therefore,the site risk assessment is not comprehensive.This topic selection of yunnan huize lead and zinc smelter surrounding area as the research object,use the Tessier extraction method in the fraction of Pb and Cd,draw lessons from Hakanson potential ecological risk index method to quantity of toughened ideas to deal with the data,selected the Igeo and RAC two evaluation methods for Pb and Cd linear transformation of the static risk assessment,using the DGH method of nonlinear transformation of lead and cadmium dynamic risk assessment,eventually produced compound of the static,dynamic risk composite evaluation.According to the Igeo evaluation,the area was seriously polluted by the composite static pollution(class 6,50<Igeo).RAC evaluation indicated that the region had a composite static high risk(class 4,31<RAC ?50).According to the DGH model,about 4.35%?50.00%of the region has the possibility of compound dynamic risk.The content of lead and cadmium in some soils in this region has accumulated to a high level,posing high ecological risks.Measures should be taken to eliminate the hidden dangers as soon as possible.