| In this study,geochemical characteristics of heavy metals in various environmental media from Xining(includling street dust,urban topsoil,river water and river sediment)were as the main objects of the study.The physiochemical characteristics and elment compositions of water and sediment samples(35 samples respectively)collected from the Xining section of Huangshui river,urban topsoil(5 composite samples)and street dust samples(204 samples)from Xining urban area were studied detailly.AAS(atomic absorption spectrophotometer)and X-Ray fluorescence spectrometer were used to determine the concentrations of heavy metals in water,sediment,soil and dust samples.The modified BCR sequential extraction procedure was used to analyze the speciation of metals in sediment,soil and dust samples.The environmental quality of all mediums and risk were assessed by different methods.And the heavy metals sources were identified by using multivariate statisctical method.The main conclusions were gotten as following.1.Physichemical characteristics of the environmental media from Xining city.1)Water in Xining section of Huangshui river:The average values of pH,conductivity,total bacterial count,dissolved oxygen,turbidity and soluble ion concentration of suspended solids were 7.14,553.29(?s/cm),12×103,4.37(mg/L),338.97(NTU)and 280.5(mg/L),respectively.The concentrations of anion and cation showed that thewater was S042-Cl-—Ca2+ form.2)Sediments in Xining section of Huangshui river:The mean pH of sediments was 8.54,showing strongly alkaline.The average conductivity of sediment was 342.08?s/cm.The low-frequency magnetic susceptibility,high-frequency magneticsusceptibility and frequency of susceptibility was 74.33×10-8 m3/mg,73.20×10-8 m3/mg and 1.67%,respectively.Silt is the main particle in the sediments.The average content of calcium carbonate and organic matter content were 7%and 26.7%,respectively.3)Urban topsoil in Xining:The topsoil in Xining was alkaline soil with the pH of 8.08.The average conductivity of soil was 8.54 ?s/cm.The low-frequency magnetic susceptibility,high-frequency magnetic susceptibility and frequency of susceptibility was 87.30×10-8 m3/mg,83.72×10-8 m3/mg and 4.04%,respectively.Clay was in the main particle in topsoil.The order of calcium carbonate in five areas was:City center>North>Nouth>West>East,with the mean content of calcium carbonate of 20.3%.The average content of organic matter content was 4.7%,and with the following sequence:City center>South>Story>East>North.4)Street dusts in Xining:The street dust in Xining city was strongly alkaline with the pH of 9.05.The average conductivity of soil was 872.03 ?s/cm.The low-frequency magnetic susceptibility,high-frequency magnetic susceptibility and frequency of susceptibility of street dusts was 325.60×10-8m3/mg,321.65×10-8 m3/mg and 1.38%,respectively.Sand was the main particle in dusts.The average content of calcium carbonate was 20.6%,and with the following sequence:West>South? City center>North>East.The order of organic matter content in five study areas was:City center>East>North>West>South,with the mean content of organic matter of 3.2%.2.The average content level of heavy metal in different environmental mediums from Xining.1)Water in Xining section of Huangshui river:In the analyzed heavy metals,Pb and Cr don't meet the plan requirements of Huangshui basin eliminating worse than Grade V water from protecting environment "the twelfth five-year" project indicators.2)Sediments in Xining section of Huangshui river:The mean contents of Co,Cr,Pb and Zn in original samples were respectively 2.1,6.0,1.1 and 1.0 times the background values of Qinghai soil.The mean contents of Co,Cr,Pb and V in smaller than 100 ?m samples were respectively 9.1,3.3,1.2 and 1.1 times the background values of Qinghai soil,whereas the mean contents for other heavy metals don't exceed the background values of Qinghai soil.3)Urban topsoil in Xining:As and Ni were less than the background values of Qinghai soil and other heavy metals were polluted in different degrees,especially for Co and Cr,which are respectively 3.7 and 2.8 times the background values.The mean contents of Co,Cr,Cu,Pb and V in smaller than 100 ?m samples were less than 100 ?m were respectively 4.1,1.9,1.1,1.6 and 1.1 times the background values.4)Street dust:The average contents of Ba,Co,Cr,Cu,Pb and Zn in the bulk dust samples were respectively 1.2,6.3,7.0,1.8,2.2 and 1.6 times the background values.The contents of Co,Cr,Cu,Pb and Zn smaller than 100 ?m samples were 4.9,8.2,1.8,2.5 and 1.4 times the background values.3.The speciations of heavy metals in the different environmental mediums from Xining.1)The speciations of heavy metals in the water from Xining section of Huangshui river have the same variation trend,and the contents of both particulate form for Cu and dissolved form for Pb show gradual rising trend from upstream to downstream.However,Cr,Ni and Zn show the downward trend from upstream to downstream.The dissolved form contents of Co shows the gradual decreasing tendency from upstream to downstream,whereas particulate form is opposite.2)The proportion of the unsteady state for heavy metals in sediment was Pb>Cu>Zn>Ni>Co>Mn>As>Cr>V,the unsteady state contents of Pb,Cu,Zn and Ni account for more than 60%of the total content,which can easily cause secondary pollution with a higher risk to the environment.However,V shows the steady state occupies 72.5%,which migrates and transforms difficultly with a lower potential hazards to the environment.3)The proportion of the unsteady state for heavy metals in urban topsoil soil was Pb>Mn>Cu>Zn>Co>Ni>Cr>V?As.The unsteady state contents of Pb,Mn,Cu,Zn and Co account for more than 64%of the total content,which can easily cause secondary pollution with a higher risk to the environment.However,the unsteady state contents of Cr,As and V were more than 65%with a relatively lower potential hazards to the environment.4)The proportion of the unsteady state for heavy metals in street dust was Pb>Zn>Cu>Cd>Mn?Ni>Co>Cr>V>As.Except steady contents of Cr,V and Ar were higher,the unsteady contents of other elements were more than 72%and unsteady contents of Pb and Zn occupied more than 90%,which migrate and transform easily in the environment to cause secondary pollution.4.Source characteristics1)The sources of total metal elements in the water,Pb,Co and Cu mainly originated from industrial source,Zn?Mn and Cr mainly from domestic source and Ni from nature.2)In river sediment,Ni,V,Cu,Zn and As in the bulk samples were mainly affected by the nature factor,As and Cu were also impacted by agricultural activities.Ba,Mn and Cr were mainly due to the impact of many factors,such as sanitary waste water and urban surface runoff.Pb and Co were influenced seriously by industrial waste water.In smaller than 100 ?m samples,As,Cu,Ni,Pb and V were impacted by the compound source.Ba,Mn,Zn and Cr were affected by both nature and human sources.Co was seriously impacted by waste water.3)The bulk samples of urban top soil,As,V and Ni belong to nature.Zn and Pb were mainly orginate from traffic source.Ba,Mn,Co,Cu and Cr were probably related to human activities and traffic.In less than 100 pm samples,Mn,Ba and V mainly due to the impact of parent material.Mn and V were also influenced by industrial activities.As,Co,Cr,Cu,Ni,Pb and Zn were mainly effected by transportation and industry.4)The sources of heavy metals in street dust in Xining are very complex.Nature factor predominate sources for some elements and human factor plays a dominant role in some elements,whereas industrial location occupies the leading position.5.Contamination levels of heavy metals in various environmental media.1)Rivers waterBased on comprehensive water quality model,the average comprehensive water quality of Huangshui River monitoring sections were IV class.According to Nemerow synthetic pollution index,the pollution grade of heavy metals was class five which is heavily polluted.Health risk assessment results show that,the non-carcinogenic risk maximum value of Pb,Cu,Mn and Zn are lower than the maximum acceptable risk level that ICRP recommended.The order of carcinogenic risk by Cr,Niand Co is:Cr>Ni>Co.Cr is the main carcinogenic substance.The carcinogenic risk of original water sample is higher than maximum acceptable risk level that ICRP recommended.2)River SedimentsPollution evaluation results showed that:the overall pollution levels under the small size conditions were higher than that in the original sample.The contamination of Co,Cr and Pb in different particle diameter conditions was more serious than other elements.Ecological risk assessment results showed that the potential ecological risk index(RI)of various heavy metals in original sediments sample and sample that particle size less than 100 ?m belonged to the medium risk.Of which the single risk factor index(Eri)of Co,Pb and Cr in these samples is relatively high.3)City surface soilPollution evaluation results showed that:the overall pollution levels of sample that particle size less than 100 ?m was lower than that of original sample.Co and Cr pollution was more serious than other elements.The city zoning evaluation results of original soil samples in Xining showed:East>West>South>North>City center.The city zoning evaluation results of samples that particle size less than 100 ?m was:City center>South>East>West>North.Ecological risk assessment results showed that:the potential ecological risk index(RI)in different areas is different,and showed a slight risk status.The order of potential ecological index was City center>West>South>East>North in original sample,and North>South>East>West>City center in sample that particle size less than 100 ?m sample.Under two conditions,the single risk factor index(Er1)of Co,Pb and Cu was relatively high.4)Street dustPollution evaluation results showed that:the pollution levels of same heavy metals in different particle size were different.The pollution levels of different heavy metals in the same particle size were different.Of which Cr and Co pollution was the most serious.The city zoning evaluation results were North>West>East>City Center>South in original samples,sand West>North>City center>East>South in samples that particle diameter less than 100 ?m,respectively.Ecological risk assessment results showed that:the average potential ecological risk index(RI)of heavy metal in original street dust sample and sample that particle size less than 100 ?m of Xining belong to medium risk,and was North>West>City center>East>South in order.The ecological risk index of Pb and Cu Co,Cr was dominant.Health risk assessment results showed that:the heavy metals of original street dust sample and sample that particle size less than 100 ?m in Xining has different exposured dose in different ways,but the order of them were both in hand to mouth>skin contact>inhalation.The non-carcinogenic risk in children is higher than that in adult.The non-carcinogenic risk of original sample in children and adult from large to small were:North>West>East>City center>South.The non-carcinogenic risk in children is higher than that in adult.The non-carcinogenic risk of samples that particle size less than 100 ?m in children and adult from large to small were as follows:East>West>North>City center>South.Carcinogenic risks from large to small was in the order of Cr>Co>As>Ni.Carcinogenic risk of Cr was slightly higher thanl0-6,which should be brought to the attention. |
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