Apportionment Of Heavy Metals In Soil Using UNMIX Model

The content of heavy metals in the soil is affected by both human and natural factors.Once the concentration exceeds the standard,it will pose a great threat to human health.It is of great significance to analyze the source and contribution of heavy metal content in the soil to control soil pollution.In this study,the UNMIX model was selected as the source apportionment tool to directly analyze the receptor data and obtain information on the source of pollution.Through analysis of the synthetic datasets,the effectiveness of UNMIX model is focused in the source apportionment of soil heavy metal.Simultaneously,the Pearl River Delta as the study area was used the model to identify the source and contribution of pollutants.(1)The synthetic datasets contains 400 sampling points and 8 heavy metals with agriculture,sewage irrigation,atmospheric deposition,and soil parent material as the main pollution sources.Each type of pollution source has a spatial distribution characteristic.The UNMIX model verification results show that the number of pollution sources and heavy metal content in the source composition table are consistent with the set conditions in the data,the contribution value contains the same receptor pollution information as the synthetic datasets,and the contribution rate was also consistent with the set conditions.Pearson test,linear fitting,concentration fitting and spatial distribution comparison results all show that the analytical results of the UNMIX model are consistent with the simulation conditions.This shows that the UNMIX model is suitable for the sources apportionment of soil heavy metal.(2)Based on the original synthetic datasets,through analyzing data with different sample sizes,the impact of sample size on UNMIX analysis results was studied.The results show that all sample sizes could resolve the pollution sources consistent with the simulated information,but when the sample size decreases,the contribution ratio of each source to the concentration of heavy metals fluctuates to a certain extent,and the spatial distribution information of the pollution sources is imprecise.Correlation and fitting tests showed that the source composition and contribution value of each sample size were consistent with the synthetic datasets.This shows that when the data meets the conditions of the UNMIX model,even if the sample of the recipient is small,a more reasonable interpretation of the sample information can be made,but the accuracy of identifying the pollution source is reduced.(3)Taking the Pearl River Delta as the research area,a total of 227 surface soil samples were collected,and the UNMIX model was used to apportionment the source of Cd、Hg、Cr、As、Cu、Zn、Ni、Pb as the research indicators.As a result,4 types of pollution sources were obtained.Source types and their contribution rates are: Source 1 represents the source of pollution caused by fuel combustion and waste disposal,with a contribution rate of 8.77%;Source 2 may be related to natural factors,with a contribution rate of 14.64%;Source 3 is affected by local background values,with a contribution rate of 39.28%;Source 4 is a composite source of industrial traffic pollution,with a contribution rate of 37.3%.This result is similar to previous studies on the Pearl River Delta,and it also shows that the UNMIX model has good applicability in the study of actual soil heavy metals.