Ecological Risk,Magnetic Measurements And Source Identification Of Heavy Metals Pollution In Urban Soils And Dusts Of Old Steel And Iron Region,Northeast China

This study deals with ecological and health risks,magnetic measurement and source identification of heavy metals pollution in urban soils and dusts from a steel industrial district in Northeast China.A total of 115 topsoil and 90 road dust samples were collected to assess the pollution level and spatial distribution of the heavy metals.Evaluating the environmental releasability,bio-availability and human health risk,as well as determining the magnetic properties and monitor the degree and spatial distribution of heavy metal pollution was studied.The main results are as follows:1.The average concentration of Cr,Cd,Pb,Zn,Cu,and Ni in urban soils were69.9,0.86,45.1,213,52.3,and 33.5 mg/kg,respectively.Urban soils were moderate to highly polluted by Cd,Zn,Cu,and Pb.Pollution levels and spatial distribution of heavy metals indicated that dusts had a moderate to extremely highly potential environmental risk.The spatial distribution maps of heavy metals revealed that steel industrial district was the contamination hotspots.The health risk assessment indicated that non-carcinogenic values were below the threshold values for both adults and children in urban soils,while carcinogenic risk value of Cr for children was slightly higher than the threshold value.For dusts,children could face both carcinogenic and non-carcinogenic risk in this study area.Both PCA and CA indicated that the metal Zn and Pb originated from the traffic emission,Cd,Cr,Fe,Mn,Ni,and Sb primarily came from industrial activities,while Cu and Sn could come from the mixture of coal combustion and soil parent material.2.Sequential extraction results showed that Cd has the highest percentage of exchangeable form,whereas Cr primarily exists in residual form.The leachability of heavy metals evaluated by the toxicity characteristic leaching procedure?TCLP?test indicates that Cd,Zn,Cu,and Pb have much higher mobile than Cr.The bioavailability of heavy metals determined by ethylenediaminetetraacetic acid?EDTA?extraction decreases in the order of Pb>Cu?Zn>Cd>Cr.The order of bioaccessibility determined by US Pharmacopeia methodology?USPM?extraction is Pb=Cu>Zn>Cd>Cr.Highly significant correlation was found between amounts of EDTA-extractable Cd,Cu,Pb,and Zn and USPM-extractable metals.The result suggests that EDTA extraction can be helpful to estimate the bioaccessibility of heavy metals for human ingestion.TCLP and EDTA extraction indicated that Cd and Zn had high ecological risks and health risks.Representative urban topsoils were separated into six particle size fractions and their heavy metal contents?Cr,Cu,Cd,Pb,and Zn?were determined.The results indicated that the contents of five heavy metals in the size fractions increased with the decrease of particle size.The clay fraction of<2?m had the highest content of heavy metals.Meanwhile,the TCLP and EDTA extractable concentrations of heavy metals in the clay fraction were relatively higher than those in coarse particles,indicating that fine particles were the main carriers of potentially toxic metals in urban soils.3.Magnetic measurements of urban soils and dusts were performed.Both soils and dusts exhibited strong magnetic features.The soil?and SIRM values are significantly correlated with the contents of metals and Tomlinson pollution load index?PLI?,which indicated that?and SIRM could be served as better indicators for the pollution of heavy metals in the urban topsoil.Spatial distribution maps of?,SIRM and PLI showed the similar trendeny.X-ray diffraction?XRD?,and scanning electron microscope?SEM?equipped with an energy-dispersive X-ray spectrometer?EDS?and Curie temperature analyses indicate that the main magnetic minerals of urban topsoils are magnetite?Fe₃O₄?,hematite??-Fe₂O₃?and metallic iron.Magnetic minerals mostly occur in the pseudosingle-domain/multidomain?PSD/MD?grain size range.Magnetic particles?PMs?were separated from soils and dusts to determine the enrichment of heavy metals of them.Urban soils and road dusts were enriched with magnetic particles?MPs?ranging from 0.85%to 35.49%and 1.5%to 41.9%,respectively,which were characterized by high magnetic susceptibility??lf?and very low?fd.The regression analysis between MPs content and PLI indicated a strong positive correlation,indicating that MPs can be used as powerful proxy indicator to detect the degree of pollution.The MPs exhibited an obvious enrichment of heavy metals,while Cd had a high risk to environment.Different anthropogenic magnetic particles show different stability in the environment.MPs released heavy metal into soils,depending on their chemical form.Our results indicated that magnetic technology could be used as proxy indicator of determining the contamination degree,spatial distribution and sources of heavy meal in urban soil and dusts.