| Soil heavy metal pollution has always been a hot issue in soil science research,while a reasonable soil heavy metal risk assessment is a premise of controlling soil heavy metal pollution.In the process of soil heavy metal pollution assessment,the ecological and health risk assessment of soil heavy metals is often hindered by the limited spatial coverage of the sampling area and fluctuation of the detection data,which resulted in high uncertainty of the evaluation results.The analysis on the statistical characteristics of soil heavy metal distribution will enable a determination of pollution levels based on probability,which can guide the establishment of effective strategies for risk control,pollution remediation,and site management.In this study,Monte-Carlo-Hakanson probability evaluation model and Monte-Carlo probabilistic health risk assessment model were constructed by combining Monte-Carlo simulation statistical method and Arc GIS spatial interpolation method,combined with Hakanson potential ecological risk index method and health risk evaluation model,respectively.A regional ecological and health risk assessment of eight heavy metals(Cd,Hg,As,Pb,Cr,Cu,Ni and Zn)in agriculture soils in a small watershed in Yunnan Province was carried out,and the content and pollution probability of eight heavy metals in the region were interpolated by Arc GIS interpolation.The conclusions are as follows:(1)The probabilistic ecological risk assessment of the study area was carried out by Monte-Carlo-Hakanson probability evaluation model,and severity of the contamination in the area was determined from the three indicators of pollution coefficient C_f~i,risk index E_r~i and environmental risk comprehensive index RI,and the contribution of each heavy metal pollution degree in the area was characterized by sensitivity analysis.The results have shown that metal Cd and Cu are the most polluted in the region,and from the probabilistic results,the probability of metal Cd being in a very heavy pollution level is close to 70%,and the probability of being at a very high risk is more than 50%.Among the eight metals,only metal Cd belongs to the high-risk level,and its sensitivity ratio reaches 0.99.RI results show that the probability of high ecological risk of the site has reached 40%,which should attract the attention of relevant departments.It is worth noting that the pollution level of metal Cu after Monte-Carlo simulation is different from the pollution level obtained by the mean value,and it can be considered that Monte-Carlo simulation can make up for the error caused by insufficient sample data and increase the accuracy of ecological risk assessment.(2)Based on the pollution of eight heavy metals in the study area,the content of these eight heavy metals and the probability of pollution coefficient C_f~i were spatially interpolated.Comparing the interpolation results of the ordinary kriging interpolation method and the IDW inverse distance weighted interpolation method for each heavy metal content,and it was found that IDW inverse distance weighted interpolation method was more suitable for this study area.Therefore,the IDW inverse distance weighted interpolation method was used to spatially interpolate the probability of C_f~i of each heavy metal pollution coefficient.Comparing the content interpolation results with the probability interpolation results,it was found that the probability interpolation results were more in line with the actual situation of the region.And the simple source identification was carried out through the probabilistic interpolation results:Cd,As,Pb,Cr,Cu,Ni and Zn are closely related to historical Cd hazardous wastes.Cd,Hg,As,Pb,Cu Ni and Zn are closely related to domestic waste treatment plants.Hg is closely related to livestock farms.Cd,Hg,Pb Cu and Ni are closely related to contamination in historic Cu mining areas.(3)The Monte-Carlo health risk assessment model was used to conduct probabilistic health risk assessment for children and adults in the study area,and Monte-Carlo simulation was introduced in the exposure evaluation stage to compare the exposure of the two groups and three different exposure methods in the exposure evaluation.Non-carcinogenic and carcinogenic risks were assessed in the risk characterisation,and probabilities of non-carcinogenic and carcinogenic risks were obtained for each heavy metal.During the exposure assessment process,it was found that children were exposed at much higher levels than adults.During the risk characterization stage,it was found that the non-carcinogenic risk of each metal in adults was within 1%,but the probability of Hg and Cr having non-carcinogenic risk in children was 10%and 15%,respectively.All metals are 30 times more likely to be non-carcinogenic in children than adults,and Hg and Cr are more harmful in children.Among several metals that pose carcinogenic risk,the risk caused by metal Pb requires attention,and its probability of carcinogenic risk in adults and children is close to 100%.Among the metals that pose non-carcinogenic risk,Hg and Cd have the greatest impact on non-carcinogenic risk in adults,and Hg and Cr have the greatest impact on non-carcinogenic risk in children.In this study,the mathematical statistical method and the spatial interpolation method are combined and applied to regional risk assessment,which not only broadens the application of probability method at the theoretical level,but also realizes spatial probability interpolation.It also provides a new method for risk assessment at the practical application level,while Monte-Carlo simulation can avoid the randomness in the risk assessment process to a certain extent and provide more accurate results. |
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