| Air pollution is a problem faced by many developing countries.Dust is a particle suspended in the air.Heavy metal elements in the air attach to dust and other small particles,which will not only harm the environment,but also pose a threat to human health.The ways of dust and heavy metals affecting human health are mainly passed through the food chain through hand mouth intake,breath inhalation and skin contact,and finally into the human body.study the pollution of heavy metals in the dust of campus on a small scale,and then to assess the health risk of minors.On the one hand,it is helpful to improve the residents understanding of heavy metals in campus dust.On the other hand,it can better determine the priority control area and screen the priority control pollutants.In this study,the main urban area of Lanzhou campus dust as the research object.7 kinds of heavy metal elements were selected to determine the content of heavy metal elements in the dust of sampling points.Firstly,the temporal and spatial characteristics of heavy metal content in dust are revealed by spatial interpolation and time series analysis.By using isoline map of population spatial distribution and spatial interpolation map of dust heavy metal content,the location relationship between cold hot spot of dust heavy metal content and population aggregation state is obtained.Secondly,the accumulation degree and spatial-temporal distribution characteristics of heavy metals in dust were analyzed by geoaccumulation index.Thirdly,the sources of heavy metals in dust were determined by correlation analysis,cluster analysis,self-organizing neural network and principal component analysis.Fourth,single factor pollution index and Nemero comprehensive pollution index were used to analyze the pollution level of heavy metals in dust.Fifth,the potential ecological risk index is used to analyze the ecological risk of heavy metal pollution in schools dust.Finally,the USEPA health risk assessment model was used to evaluate the health risks of the children and juveniles.Because this study used the dust on the surface of kindergartens,elementary schools,and middle schools as the research object,the health risk assessment system was adjusted slightly and divided into preschool groups（0 to 6 years old）and adolescents（7 to 18 years old）were evaluated for health.The results include the following six points.The first,the results show that the average content of 7 heavy metals are higher than the background value of Lanzhou City,and the over standard rate of a single sample is 100%.Ranking of spatial variation of heavy metal content in different regions showed the characteristics of Qilihe,Anning,Chengguan and Xigu.Winter is the season with the highest content of heavy metals in the year.The spatial distribution data of population and heavy metal content in dust are analyzed,and the conclusion is drawn.It is concluded that the content of Cr element in the dust is very close to the population spatial distribution,and the spatial distribution of Cu,Pb,Zn and As is locally consistent,while that of Co and Ni is not.Secondly,the Geoaccumulation index method reveals the enrichment degree of heavy metals in dust shows that:Co,Cr,Ni and As have no obvious enrichment status in the entire study area,the spatial distribution characteristics of Cu,Zn and Pb show that a wide range of slight accumulation and mid-range and moderate accumulation,there are some heavy accumulation.Third,there are two main sources of heavy metal pollution from the ground dust in the campus of the main city of Lanzhou.The first is anthropogenic sources,which account for 48.74%.and the heavy metal pollution of dust generated by transportation among man-made sources is higher than industrial production,the second is natural source accounting for 18.73%.Fourth,the single-factor pollution index and the comprehensive pollution index in the study area are the highest in winter,and the ranking of the comprehensive pollution index is Chengguan>Xigu>Anning>Qilihe.With the exception of Cu,Pb,and Zn,the single-factor pollution index in most areas of the entire study area is moderate pollution.The comprehensive pollution index in the entire study area shows a serious pollution state.There are four high-value areas in the spatial distribution,which are basically distributed in the center of each area and along the main railway line.It can be seen that the comprehensive pollution index is greatly affected by population density and transportation.Fifth,the seasonal characteristics of the potential ecological risk index are as follows.The main urban area of Lanzhou city is in the middle ecological risk in spring and summer,and gradually increases in autumn,with the highest ecological risk in winter.The high-value areas with potential ecological risks are all located in the transportation hub of Lanzhou.The potential ecological risk index of each area is in the order of Xigu>Chengguan>Qilihe>Anning.In this study,the entire study area ranged from medium ecological hazards to strong ecological hazards.Sixth,The non-carcinogenic exposures of the seven heavy metals were ranked as Zn>Cr>Pb>Cu>Ni>Co>As.The non-carcinogenic exposure of the preschool population was 7.8 times that of the adolescent population.The rankings of the exposure amount of the three exposure routes of different elements are hand-oral ingestion>skin contact>breathing and inhalation,and hand-oral ingestion is absolutely dominant.Non-carcinogenic health risks are lower in summer and winter.Children have a large non-carcinogenic health risk throughout the study area,and their high-value areas are mainly distributed near the traffic trunks in Chengguan District and Qilihe District.Adolescents are essentially free of non-carcinogenic health risks.The carcinogenic health risk value of Cr is greater than 1×10-4,and there is a carcinogenic risk.The carcinogenic risk of each region is ranked as Qilihe>Xigu>Chengguan>Anning.Tthe carcinogenic risk of As and Ni is critical and is still acceptable.Within the scope,attention should be drawn. |
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