Enrichment Characteristics And Risk Assessment Of Dust Pollutants In Bus Stations In The Plateau Area Of ??the Loess Plateau

Bus is an extremely important transport vehical in the city,and it bears the heavy responsibility of urban population flow,Especially under the advocacy of the concept of"green travel",the relatively environmentally form not only reduces pollution but also saves resources,which has become the most important way of daily travel for the majority of small and medium-sized urban residents ici China or the world.Especially in Qingyang,a typical small and medium-sized city in the arid and semi-arid Loess Plateau tableland area of Northwest China,by bus is almost an inevitable choice for Qingyang citizens' daily commute to school or work.But up to mow,at home and abroad,health hazard study of bus stop dust to commuter is very little.And to provide some scientific data and resources,for the prevcntion and control of environmental pollution,in Qingyang city and the other city in Loess Plateau tableland area of Northwest China,it is urgent to find out the law and characteristic of content,spatial distribution,ecological and health risks of the main pollutants(Such as harmful elements and polycyclic aromatic hydrocarbons,etc.)in bus stop dust.In this paper,an in-depth study was conducted on the pollution of harmful elements(HEs)and polycyclic aromatic hydrocarbons(PAHs)in Qingyang bus stop dust,and the health hazard to the five major groups of people who take bus every day was evaluated in detail.For the first time,the surface dust was collected from 126 bus stops on 14 bus routes in Qingyang urban area.The physical and chemical properties[pH value(dust:water=1:50),carbon black(Determination by the Elelentar Vairo ? analyzer after l mol L-1 HCI treatment),organic carbon,magnetization,particle size,etc.]and larger harm main pollutants to organisms were analyzed in detail.The pollution included 12 HEs(Determination As,Hg,Cd content by atomic fluorescence after microwave digestion,determination the other 9 kinds of HEs content by X-ray fluorescence spectrometry)and 16 kinds of PAHs(Determination by high performance liquid chromatography after n-hexane:methylene chloride=1:1 volume mixture soxhlet extraction and purification).In addition,the pollution level of harmful pollutants were evaluated by various methods to comprehensive treatment.The main sources of pollutants were analyzed qualitatively and quantitatively,and the risks of ecological environment and public health were characterized accurately and meticulously.In order to better protect of living environment of Qingyang city,according to the actual pollution of the bus stop dust in Qingyang,combined with the truth of surrounding population,traffic congestion,production and living around every bus stop,the government not only may formulate the corresponding policy of environmental management and planning,but also reasonably plan bus stop number and its layout,and the bus lines numlber and its design.The authorities may further appropriate pollutants emission reduction policies and its control measures.In addition,the assessment results not Only have important reference value for understanding the current situation of street dust pollution and risk in Qingyang city,but also have extremely important reference significance for similar cities to preestimate their current situation of street dust pollution and risk.As well as the authorities may be taken the policies and leasures of reduction emission and pollutant control actions.The main results and conclusions of the research were as follow:(1)The average contents of Cd,Cu,Hg,Pb,Zn,Ba,Sr and Co in bus stop dust are higher than the background values of Gansu soil,which are 5.4,1.4,10.0,2.4,1.9,1.4,1.6 and 2.2 times of the background values of Gansu soil,respectively.While the average contents of Mn,As,Cr and Ni are lower than the background values of Gansu soil.The results of geoaccumulation index showed that Cd and Hg were moderate pollution,Pb,Zn,Co and Sr were near moderate pollution.The results of Nemero synthesis pollution index showed that 124 bus stops were heavily polluted.The content of Cu,As,Ni,Hg,Pb,Cd,Co is also lower than screening and control value of the second type land for road and traffic facilities in the GB36600-2018,respectively.Cd and Hg had great ecological hazard.The ecological hazard of HEs in 123 bus stop dust was above moderate level,while 46 bus stops dust showed severe ecological risk.(2)Sixteen polycyclic aromatic hydrocarbons(?16PAHs)were detected from most bus stops dust samples in Qingyang.?16PAHs had an average of 3.0 mg kg-1,while the maximum value was 22.6 times than the minimum value.Compared with GB36600-2018,only a few bus stops dust had higher BaP content than the risk screening value of soil pollution on construction land in the standard.Compared with the Canadian soil standard,the pollution degree of Pyr,BkF and DA were moderate level,while the pollution degree of Phe and Bap were serious pollution.Compared with the Dutch soil standard,the content of Ant,BaA,BkF,BaP and IP in bus stop dust had exceeded the standard,their range was 0.8%?78.6%,while the maximum value over the standard ranges was 1.3 to 404.0 times.The average value of the ?16PAHs total toxic equivalent concentration(4020 ?g kg-1)was also very large.?16PAHs in 103 bus stops dust had exceeded the effect range low,which had greater ecological risk,11 PAHs had higher ecological risk.(3)The non-carcinogenic risk of 12 HEs in bus stop dust was varied from the crowd.the order of Ba,Sr,Co,Cu,Ni and Zn was significantly different for the 5 groups of people(office worker,grade junior primary school students,grade senior primary school students,senior high school students,junior high school students),while Cr,As,Cd,Pb and Mn were larger hazard for the 5 groups people.The total risk of 12 HEs is lower than the human body acceptable limit.As.Ni.Cd and Co in bus stop dust was very little.For office worker,the average carcinogenic risk of Cr in some bus stops dust was 2.2 times than human body acceptable lower limit(1.0 E-6).For 5 groups of people,the carcinogenic risk of Cr was also the highest,which needed some attention.For the other 3 groups ofstudent,the carcinogenic risk was very small.(4)For 5 groups of people,the non-carcinogcnic risks of Nap,Acy,Ace.Flu,Ant.Phe,Fla.Pyr and BP was also far less than the lower limit(0.1),respectively.The carcinogenic risks of BaA,Chr,BkF,IP,BaP and DA was very small.For office worker,the carcinogenic risk of BbF was 1.1 times than 1.0 E-6.For 4 groups of student,the comprehensive risk of 7 carcinogenic PAHs is less than 1.0 E-6.While the carcinogenic risk for office worker was 1.2 times higher than 1.0 E-6,which needs further attention.(5)For 5 groups of people.the total carcinogenic risk order of 5 HEs and 7 PAHs in bus stop dust was as follow:office worker>grade junior primary school students>grade senior primary school students>junior high school students>senior high school students.The total carcinogenic risk of pollutants in all 126 bus stops dust in Qingyang city was 3.85,1.52,1.14,1.07 times than the 1.0 E-6 for office worker,grade junior primary school students,grade senior primary school students,junior high school students,respectively.The carcinogenic risk to senior high school students is lower than the 1.0 E-6.The total non-carcinogenic risk order of 12 HEs and 9 PAHs in bus stop dust was as follow:office worker>grade junior primary school students>grade senior primary school students>senior high school students>junior high school students,and their non-carcinogenic risk is very small.(6)The comprehensive analysis of PCA-MLR showed that the main sources of HEs was traffic source,mixed source of natural and man-made sources,construction and decoration source,unknown source,their contribution rate was 35.8%,26.0%,23.0%,15.2%,respectively.And that the main sources of PAHs was petroleum,biomass,fuel oil,coal and unknown sources,their contribution rate was 28.7%,18.0%,4.2%,46.0%,3.1%,respectively.The innovation of the paper choose typical representative city in Loess Plateau tableland area.It takes Qingyang city as an exanple.The risk of PAHs and HEs to people and environment were described in detail.Especially for the main group of people by bus,it has carried on the detailed and accurate health hazard evaluation.Moreover,it takes 12 HEs and 16 PAHs as a whole to analyze their comprehensive health hazards to people.Finally,the sources of pollutants in bus stop dust were analyzed by factor analysis,cluster analysis,and PCA-MLR analysis.The results showed that the distribution of pollutants in bus stop dlst had extremely significant diversity.To relieve the traffic congestion,and the people and traffic density,it is suggested to expand the urban development space and to stagger the bus stops in the densely areas in Qingyang city north and center,such as population,commerce and traffic.In addition,the residents of "villages within cities" should reduce the proportion of coal and fuel oil,and promote to use electric energy,natural gas or clean renewable energy,such as solar energy etc.It can reduce fundamentallx;the emission of pollutants,and realize the development of environment-friendly economy and society with the sustainable concept.