Spatial-Heterogeneity And Pollution Risk Assessment Study Of Heavy Metals(Cd、Pb) In Road Dust In Harbin

With the rapid socio-economic development of the country,the acceleration of urbanisation and the demand for high quality development,the problem of urban environmental pollution has become an important factor hindering and affecting urban development.Industrial production,transportation and human production and living can increase the content of heavy metals in the urban environment,thus leading to an increasingly serious problem of heavy metal pollution,which directly or indirectly affects the quality of the urban environment and human health.As one of the important manufacturing bases in China,Harbin City has a large population base in its main urban area,and the problem of heavy metal pollution is prominent.Therefore,this paper took road dust in the main urban area of Harbin as the research object,determined the content of heavy metals(Cd and Pb)of the dust of the study area,studied the spatial heterogeneity of heavy metals by means of geostatistical theory and GIS spatial means,explored the factors affecting the spatial distribution of heavy metal content by using Geo-detector,the pollution status was evaluated using three methods: fuzzy mathematical integrated evaluation,potential ecological risk index and health risk evaluation.The main conclusions are as follows:(1)There was variability in the pollution status of the heavy metal elements Cd and Pb in dust in Harbin,with mean values of 0.954 mg/kg and 80.609 mg/kg respectively.referring to the Soil Environmental Quality Standard(GB15618-2018),this study compared the actual measured values of heavy metals with the risk screening values in this standard,and the study showed that the exceedance rate of Pb was 4.71% and Cd was90.59%.The coefficients of variation for Cd and Pb were 39.41% and 27.66% respectively,both of which belonged to medium spatial variation,indicating that their contents had a large dispersion among sample points and were significantly affected by human perturbation.(2)The analysis of the Global Moran’s I and Anselin Local Moran’s I of dust heavy metal content showed that the standardized Z value of Pb was higher than 1.96 with probability P less than 0.05,which was spatially moderate correlation,and the Z value of Cd was 1.941 with P greater than 0.05,which was spatially weak correlation,and the high value areas of the two heavy metals were mainly distributed in Nangang District.The results of the semi-variance variance function simulation showed that the nugget factor of Pb and Cd were 71.9% and 84.1%,respectively,indicating that the variation of Pb content was jointly determined by structural and human disturbance factors,while the spatial variability of Cd was dominated by random variation.The results also indicated that the optimal theoretical model for Cd was a spherical model,while the optimal theoretical model for Pb was an exponential model.(3)The optimal spatial interpolation model selected for comparison was empirical Bayesian kriging interpolation,which showed some spatial heterogeneity,with both high in the east and low in the west,but a cluster-like distribution for Cd and a strip-like distribution for Pb.The enrichment of the two heavy metals was significant in Nangang and Daowai districts.The estimated probability of exceeding the Cd standard according to the soil environmental quality standard showed that the estimated probability [Cd≥0.6mg/kg] has reached more than 90%,especially in the northeastern part of the study area,where there was a high potential risk.(4)The results of the Geo-detector ’s differentiation and factor detection showed that the spatial distribution of population,urban GDP,distance from settlements and road network density were the main factors affecting the spatial variation of Cd content;while urban GDP,distance from water systems,spatial distribution of population and distance from settlements were the main factors affecting Pb.The interactive effect of each factor on the content of heavy metals was greater than the single factor effect,and was linearly enhanced.(5)The results of the comprehensive fuzzy mathematical evaluation showed that most of the surface dust in Harbin was lightly polluted at level II,accounting for 82% of the total number of sample sites,and the number of sample sites with heavy pollution at level III accounted for 14% of the total,and the urban environment was at risk of pollution.The potential ecological risk results showed that the E value of the potential ecological risk factor for Cd was 357.76,which was at a very high ecological risk level,and the E value of Pb was 15.81,which was at a low ecological risk level.The integrated potential ecological hazard index RI for the study area was 373.37,indicating that the study area was at a high ecological risk level.The results of the health risk evaluation showed that although the levels of both Cd and Pb did not reach the hazard values for non-carcinogenic and carcinogenic risks,the highest exposure to heavy metals was found under the handoral intake route,especially in children.In terms of spatial distribution,the spatial distribution map of dust heavy metal RI values,the spatial distribution map of fuzzy mathematical comprehensive evaluation grading and the distribution map of noncarcinogenic and carcinogenic hazard indices all showed similar pattern characteristics,i.e.the distribution of high values was mainly concentrated in Nangang District and Daowai District.