Research And Application Of Traceable Risk Assessment Methods Of Heavy Metals In Contaminated Sites Based On Speciation Simulation

With the sustainable and rapid development of economy,many cities have undergone industrial restructuring.Contaminated industries in cities are forced to be shut down and relocated,resulting in a large number of industrial legacy and abandoned sites.This kind of heavily polluted and high-risk site will not only affect the water and soil of the local environment,but also harm human health when it is redeveloped and utilized.In order to clarify pollution situation of contaminated sites,it is necessary to carry out environmental investigation and human health risk assessment.In recent years,heavy metal pollution in soil and groundwater has attracted more and more attention due to its extensive sources,diverse forms,complex migration and difficult restoration.The primary task to solve the problem of heavy metal pollution is to find out its pollution status and characteristics of pollutant,identify the source of pollution and control it at source.The heavy metal contents of As,Cd,Cr,Hg,Ni,Zn and Pd were measured in electroplating plant,dyeing plant and landfill in Suzhou,Jiangsu Province.Kriging spatial interpolation,Positive matrix factorization(PMF),Principal component analysis(PCA),Principal component multiple linear regression analysis(PCA-MLR),chemical equilibrium morphology simulation and fuzzy comprehensive evaluation method were used to carry out the research,and the weight of heavy metal intake dose was optimized.At the same time,a comprehensive evaluation of heavy metals in water and soil of the study area based on health risk model and ecological risk model was carried out to establish a research method for heavy metal pollution and environmental assessment.(1)A health risk assessment method based on spatial interpolation and source analytic traceability was proposed to evaluate the potential harm of soil heavy metals to human health.The optimized spatial interpolation method provides global data for pollution allocation and introduces quantified source contributions into health risk assessment.The linear fitting results show that ordinary Kriging is superior to inverse distance weighting method in spatial interpolation.PMF extracts five pollution sources:traffic,natural,agricultural,atmospheric deposition and industrial sources.The carcinogenic risk of As and Cr exceeds 1.0E-04,posing a potential risk to human health.In addition,the high carcinogenic risk index and the non-carcinogenic risk index were derived from industry and agriculture respectively,and the risks were 3.5E-01 and 2.6E-04,respectively.This method can quantify the health risk contribution of spatially related sources and propose effective environmental risk countermeasures for similar polluted areas.(2)An integrated risk assessment method of source identification for heavy metal based on spatial interpolation was established by combining source analysis with human health risk model.Principal component analysis(PCA)and positive matrix decomposition(PMF)models were used to comprehensively identify and classify potential sources of heavy metals.The integrated results were incorporated into human health risk model to assess the potential non-carcinogenic and carcinogenic risk of soil heavy metals.Taking Suzhou city as an example,the empirical study is carried out.The results showed that the concentrations of Cd and Hg were 239.6%and 415.9%,respectively,higher than the background values.Source contributed human health risk index of As accounted for 76.9%of non-carcinogenic risk from agricultural pollution sources.The non-carcinogenic health risk index for adults and children was 0.308 and 1.00 respectively,indicating a threat to children’s health.The health risk assessment based on source contribution showed that industrial activities contributed the most to the health risk of soil heavy metals.This study will provide new ideas for the treatment of multi-source soil heavy metal pollution,and also have certain reference value for the improvement of risk assessment system.(3)A comprehensive risk assessment method for human health was proposed based on screening of primary targeted metal and simulation of chemical morphological evolution.The targeted heavy metals selected by traditional health risk assessment methods were introduced into chemical equilibrium simulation to obtain their morphological distribution and corresponding risks.According to the risk assessment results of the morphologic evolution of the targeted heavy metal,a remediation method was proposed to effectively and rapidly reduce the risk level of the targeted metal by adding acid and alkali substances to change the pH value of the soil environment.A dye plant in Suzhou City,Jiangsu Province was taken as an example for research.The results of the classical health risk assessment showed that the regional children’s health risk index exceeded the tolerance value of 1,and Cr accounted for 61%of the high risk levels.The results showed that CrO42-and CaCrO4 had the highest risk index.The change of pH value could affect the proportion of CrO42-and CaCrO4 in Cr6+ ion forms,which may indirectly change the risk level.It is suggested to reduce regional human health risk quickly by adjusting soil pH value.(4)A health risk assessment method based on PMF source contribution rate combined with grid spatial interpolation is proposed.Taking an industrial park in Suzhou as the study area,the source of heavy metals was quantitatively analyzed by using positive definite matrix model,and the spatial distribution of heavy metals was discussed by using grid spatial scale.PMF identified four pollution sources of heavy metals in soil,among which industrial activities(33.5%)contributed the most to heavy metals,followed by soil parent materials(30.8%)and agricultural activities(19.7%).The targeted metals were screened out through potential ecological risk assessment,and 13 kinds of zinc ion chemical speciation were simulated by PHREEQC,geochemical software.The high-risk zinc species were determined through health risk assessment model,in which the carcinogenic index of Zn2S32-for adults was 2.01E-04,and the non-carcinogenic risk index for children was 1.31.Adults and children accounted for 61.5%and 58.5%,respectively.The proposed method can provide reference for the decision of soil heavy metal pollution and remediation of specific heavy metals in polluted areas.(5)A weighted human health risk assessment method combining fuzzy comprehensive evaluation and chemical equilibrium simulation was proposed.The potential toxicity and speciation characteristics of cadmium(Cd)in groundwater were studied by using this method.Visual MINTEQ was used to study the concentration and activity of 15 Cd(Ⅱ)ions to modify the average daily dose of Cd(Ⅱ)ions by fuzzy entropy weight method in the health risk model.Both carcinogenic and non-carcinogenic health risk of Cd(Ⅱ)species for adults and children were conducted.The health risk assessment revealed that metal species of Cd2+ and CdCl+posed carcinogenic risk to adults.The carcinogenic risk of Cd2+with the value 8.03E-04 and 5.43E-04 for adults and children demonstrated high carcinogenicity,respectively.Non-carcinogenic risk values for Cd(Ⅱ)ion species were all less than 1 except for Cd2+.It was noteworthy that the non-carcinogenic risk index of Cd2+ and CdCl+ were slightly higher than those after weight assignment.In addition,conventional risk assessment may overestimate or underestimate the risk level of Cd(Ⅱ)speciation,and the health risk of Cd(Ⅱ))speciation in groundwater mainly depends on the pH value,which is the influence factor related to the metal species.Nemero index in Cd(Ⅱ)form showed that light pollution accounted for 13.33%of the sampling area.Therefore,Cd2+and CdCl+ were identified as the targeted speciation of pollution assessment by this method.This strategy provided a solution of correlation degree optimization for groundwater health risk assessment and a reference for the administration to manage groundwater pollution.