| Rapid urbanization and industrialization in recent decades have significantly impacted ecosystems globally,and anthropogenic activities are one of the primary sources of potentially toxic metal(oids)(PTMs).Soil is a fundamental component of the environment and serves as a vital natural resource.The severe PTM pollution in soil has threatened the ecological balance of the soil and impacted animal,plant,and human health.Hence,it is significant to investigate the distribution,occurrences,and sources of PTMs in soil,which can provide theoretical reference for studying the migration and transformation mechanisms of PTMs in soil and provide technical support for the remediation and prevention of soil pollution.In this thesis,the soil sampling sites were located in the upper and lower Indus basin of Pakistan.According to the regional ecological environment survey,a total of 932 soil samples were collected from various areas(agricultural,urban,and industrial sites)at different depths.By applying a variety of techniques including Inductively coupled plasma-Mass Spectrometry(ICP-MS),X-Ray Diffraction(XRD),X-Ray Photoelectron Spectroscopy(XPS),Fourier Transform Infrared Spectroscopy(FTIR),Multi-Collector-Inductively coupled plasma-Mass Spectrometry(MC-ICP-MS),and sequential extraction protocol,the physicochemical properties,mineralogical profile of the soils and distribution characteristics of the soil PTMs were examined.Furthermore,the chemical forms and occurrences of the soil PTMs were quantitatively analyzed,and the sources of Pb contamination in soil were identified by using isotopic fingerprinting of Pb.Ultimately,the contamination status and health risks of the soil PTMs were evaluated.The main research results are as follows:(1)The soil samples were collected from four cities(Abbottabad(ABT),Haripur(HRP),Attock(ATC),and Islamabad(ISB))in Pakistan,and the physicochemical properties and mineral composition of the soils were analyzed.The result showed that the pH of the soil samples(0-50 cm)was 7.65±0.10,8.55±0.27,6.58±0.47,and 7.39±0.37,respectively.Meanwhile,the soil samples(0-100 cm)collected from agricultural(Agri),urban(Urb),and industrial(Ind)areas in Islamabad showed a predominantly alkaline composition,with average pH values of 7.61 ± 0.27,7.48 ± 0.28,and 7.56 ± 0.41,respectively.In addition,the mineralogical analysis of the soil samples from ABT,HRP,ATC,and ISB revealed that the dominant mineral phases present were silicon oxides and zeolites.(2)By analyzing the PTMs concentrations of soils from various areas in different cities,the elevated concentrations of As,Cd,Cr,Cu,Fe,Mn,Ni,Pb,Sr,and Zn were observed at ABT,HRP,ATC,and ISB in comparison to the background levels of each site.The highest concentrations of Cd(0.23 mg/kg),Cu(38.21 mg/kg),Zn(112.12 mg/kg),and Ni(42.77 mg/kg)were identified in soil samples from HRP,followed by elevated levels of As(17.06 mg/kg),Cr(376.67 mg/kg),Pb(15.14 mg/kg),and Sr(349.89 mg/kg)at ATC.The vertical distribution of these metal(loid)s showed an overall decreasing trend.Additionally,Pb concentration was evaluated in soil samples from agricultural,urban,and industrial areas.The highest concentration of Pb was found at Ind(105 mg/kg)in surface soils,followed by Agr(72 mg/kg)and Urb(47 mg/kg).The soil core(0-400 ft)samples were collected from the Peri-urban(Core 1)and Industrial(Core 2)sites of Lahore.The surface soil concentrations of Al(5783 mg/kg),As(15.65 mg/kg),Cd(3.32 mg/kg),Co(7.57 mg/kg),Cr(294 mg/kg),Pb(57.18 mg/kg),and Rb(2.37 mg/kg)were higher in core 2 as compared to core 1.(3)The occurrence of As,Cd,Cu,Cr,Fe,Mn,Ni,Pb,Sr,and Zn in soils from different areas was compared via the integrated analysis of sequential extraction protocol and spectroscopy.It was found that As at ATC was mostly found in the organic matter(12-15%)and sulfide(7-26%)fractions,followed by the residual fraction(3858%).And the residual fraction was found to be the most prevalent for Cd across all depths and locations studied(ABT:64-96%,HRP:56-90%,ATC:77-93%,ISB:4894%).According to the FTIR spectra for functional groups and elemental fine chemical states analysis,a profusion of peaks appeared in the mid-infrared region i.e.,800 to 1700 cm-1,which is indicative of the chemical composition of soil organic matter.And the fine chemical states of As and Pb were further identified to be As(Ⅲ),As2O3,As4S4,PbO2,and PbCO3.(4)The 206Pb/207Pb and 208Pb/206Pb isotopic ratios were calculated through Pb isotope analysis of the soils from Agri,Urb,and Ind site,from which the pollution sources of Pb were quantitatively analyzed.The results indicated that the average 206Pb/207Pb isotopic ratios were 1.198 at Agri,1.189 at Urb,and 1.178 at Ind.The enrichment of Pb in the soils primarily originated from anthropogenic and geogenic inputs.Specifically,the vehicular exhaust was found to be the primary source of Pb contamination at the Urb site i.e.,67%.Whereas,industrial inputs and vehicular exhaust(48%)were found responsible for Pb enrichment at the Ind site.And the geogenic input was the main source of Pb at the Agri.(5)By calculating the pollution indices,the contamination status of PTMs in the soils was evaluated,and the health risk assessment of PTMs in the soils was conducted.The results showed that the contamination degree of surface soil samples(0-10 cm)was highest in ISB(33.75),followed by ABT(25.30)and ATC(23.57).The enrichment factor indicated that the metal(loid)s enrichment Ni(2.45),Cd(1.94),and Pb(10.55)at ABT,As(2.18),and Pb(3.56)at HRP,Cr(3.52),Sr(4.37),Pb(4.13),and As(6.64)at ATC,followed by Mn(1.81),Cd(1.94),Sr(6.65),As(6.67),and Pb(8.33)at ISB.In the 0-100 ft soil samples from Core 1 and Core 2,the average EF of As,Bi,Cd,Cr,Pb and Sb was greater than 2,suggesting strong anthropogenic influence.The human health risk assessment results suggested that Cr was the major element posing noncarcinogenic health risks to children at ATC whereas the non-carcinogenic risks posed by all other PTMs were within the safe limit.Furthermore,lifetime carcinogenic risks for Ni followed by Cr and Cd were greatly exceeded at all locations and As at ATC and ISB for both age groups,but comparatively,children were found to be at a higher risk of carcinogenicity. |
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