Distribution,Source,and Risk Assessment Of Potentially Toxic Metal(oid)s In Urban Dust Based On Spectroscopic Characterization And Integrated Multi-Model Analyses

Over the past few decades,the unprecedented pace of urbanization and industrialization has given rise to numerous urban environmental problems.Atmosphere is an important environmental element for the living of earth.However,enormous pollutants discharged from anthropogenic activities have led to the serious decline in air quality,which has attracted worldwide concerns about atmospheric pollution.The tiny particulates emerging from anthropogenic activities are prone to remain suspended in ambient air or settled on terrestrial surfaces.Ambient particulate matter and settled dust could be a substantial sink of potentially toxic metal（oid）s（PTM）s,which can cause severe damage to human health by further inhalation and skin contact.Hence,it is of great significance to investigate the distribution,sources,and formation mechanism of PTMs in urban atmospheric particulate matters and dusts.In the thesis,the study area is located at Lahore,the second largest populous city of Pakistan.The total of all collected samples comprised indoor dust samples from 40 schools,113 aerosol particulate matter（PM）from different functional areas,and 140 road dust samples.Combined with interdisciplinary theories of element geochemistry,atmospheric chemistry,spectroscopy,environmental science,etc.,a variety of techniques including Inductively coupled plasma-Mass Spectrometry（ICP-MS）,XRay Diffraction（XRD）,X-Ray Photoelectron Spectroscopy（XPS）,and Scanning Electron Microscope-Energy Dispersive X-Ray Spectrometry/Backscattered electron image（SEM-EDS/BSE）were applied to analyze the morpho-chemical characteristics of collected samples.The distribution and variation characteristics of PTMs in the urban dust particulates from various functional areas were comprehensively elucidated,with the major sources of these PTMs identified.Furthermore,integrated multi-model analyses were conducted to characterize the pollution levels,source apportionment,ecological and health risks of PTMs.The main research results are as follows:（1）The chemical speciation,mineralogical,and morphological characteristics of the urban dust particulates from different areas of Lahore,Pakistan were explored.The results showed that the major mineral components of school indoor dusts were aluminum silicates and iron oxide minerals.Likewise,the mineralogical composition of PM also comprised quartz（SiO₂）,calcite（CaCO3）,and pyrite（FeS₂）with small fractions of metal-associated minerals like zeolite（Aluminum Silicates）,berlinite（AlPO₄）,and zinc sulfate（ZnSO₄）.Compared with atmospheric particulate matters,the morphological characteristics of PM and school indoor dust showed small-sized and numerous-shaped.Moreover,the XPS spectra substantiated chemical species of As from school dusts and PM comprised As₂S₃,As₂O₃,and As₂O₅,and Pb,Sr,and Zn were mainly existed as Pb²⁺,Sr²⁺,and Zn²⁺.（2）The distribution characteristics of PTMs in the urban dust particulates from different functional areas of Lahore were comparatively studied.The results showed that the mean concentrations（mgkg-1）of As,Cd,Cr,Cu,Ge,Mo,Ni,Pb,Sb,Sn,Sr,V,and Zn from school dust were 7.5,5.17,193,116.2,0.175,1.43,53.6,230,0.26,3.28,194,36.7,and 1053,respectively.In case of PM10,the concentrations（ngm-3）of Cd（2.85）,Cu（75.29）,Cr（12.94）,Fe（712.94）,Ni（14.07）,and Zn（1220）were found much higher in industrial area（IndAr）as compared to other areas.While Pb was found highest in heavy transport running area（HTV）（34.45）,followed by agricultural area（AgAr）（20.82）and light transport running area（LTV）（14.62）.The mean concentrations（mg kg-1）of As（12.0）,Cd（2.1）,Cr（55.6）,Hg（21.9）,Ni（18.9）,Mn（351.5）,Mo（606.2）,and Zn（98.6）in the road dusts were found relatively higher.（3）By performing correlation and PCA analyses,the pollution sources of PTMs in urban dust particulates in the study area were identified.There were significant correlations found among As with Sn（0.53）,V（0.92）,Mo and Sb（0.65）;Zn with Ni（0.72）,Cu（0.58）,and Cd（0.55）;Ni with Cu（0.72）.The primary clusters were found for Sn-Sb-Mo,Cu-Ni,and Zn-Sr,while the principal components were among As-CuMo-Ni-Sb-Sn-V and Cd-Ni-Sr-Zn.These statistical analyses were cumulatively indicating the PTMs in PM and school indoor dusts of Lahore were mainly derived from industrial,agricultural,vehicular emissions.However,in case of road dust,multivariate analyses showed one sub-group of PTMs like Al,Mo,Hg,As,V and Sr may come from natural processes while other sub-group of PTMs like Cd,Cu,Ni,Mn,Cr,Sb,Co,Pb,and Zn sourced from anthropogenic activities especially related to exhaustive and non-exhaustive emission of vehicles.（4）The pollution level of PTMs in the urban dust particulates was evaluated.The geo-accumulation index（Igeo）and enrichment factor（EF）indicated that school dust was heavy to extreme pollution levels of Cd（Igeo=4.92）,moderate to heavy pollution of Zn（Igeo=3.22）and Pb（Igeo=2.78）.In case of PM,Cd,Cr,and Ni were the prominent polluted PTMs.It was further implied that IndAr followed by HTV and LTV were predominantly polluted areas.Additionally,the road dust of Lahore was extremely polluted with Hg（Igeo=4.98,EF=158）and Mo（Igeo=7.08,EF=752）.（5）The potential ecological risks and human health risk assessment of PTMs in the urban dust particulates from the study area were comprehensively estimated.It was found that the potential ecological risks of Cd（Eri=1287）in school indoor dust.Furthermore,there were no significant non-cancerous risks for children with the highest hazardous index of Cr in industrial（4.61E-01）and Pb in roadside（4.30E-01）and residential（2.26E-01）area schools.The non-cancerous risks of PTMs in PM from different study areas followed the descending order of IndAr>HTV>LTV>AgAr>nCgAr>GBS>AP>CgAr>FS>CM,for both children and adults.For carcinogenic risk,Cr was most prominent PTM in the urban dust particulates in all study areas.