| Railway transportation is one of the most important sources of heavy metals contamination.At present,there are increasing number of researches about environmental iusses caused by railway.Development of railway transportation in China is rapid,therefore,to analyze impact of railway transportation on environmentl is necessary.Japan's railway system is well developed.Total length of railway transportation routes in Japan is more than 20000km and covers almost every cities and towns.Thus,analysis on heavy metals originated from railway in Japan has direct reference value for railway development in China.In this research,soil and road dust samples were collected near 6 Japanese railways.Twenty-four kinds of metals(Li,Na,Mg,Al,K,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Ga,As,Sr,Rb,Se,Mo,Cd,Sn,Ba,Pb and Bi)were selected as analysis targets.The total concentration and bioavailability of heavy metal were measured.Characteristics of spatial distribution and factors affecting distribution were analyzed.At the same time,artificial neural network was applied to predicate heavy metal concentration in soil near railway.Correlation analysis,principal component analysis,cluster analysis,Pb stable isotope analysis and kriging interpolation analysis were applied to investigate potential sources of heavy metals in soil in vicinity of railway.Comprehensive pollution index,index of geoaccumulation,potential ecological risk index and health risk appraisal were applied to evaluate influence of heavy metals from railway on ecology and human health.The main conclusions were as follow:1.Concentrations of some heavy metals in soil along railways exceeded background value in Japan.Highest mean concentration of Cu and Pb near 6 railways was 39.9 times and 84.2 times higher than background value,respectively.Coefficient of variation of Cu was from 16.0%to 175%,and that of Pb was from 18.3%to 275%,indicating concentration of these two heavy metals were affect by anthropogenic factors.Besides these two elements,there were other elements in soil near railway had higher concentration than background value.Results of extraction experiment showed most elements in soil near railway has low bioavaliability.2.Enrichment factor analysis showed that serious pollution always occurred in samples collected in 20m to railway.With distance to railway increasing,pollution level reduced.In all samples from 6 railways,pollution level of Zn was at least moderately polluted.Cu's pollution level was the second highest.EFs of Pb in samples from Shuigon line and Sobu line were>2.In samples from Echigo line,Chuo line,Muroran line and Hachigo line,there 87.2%,81.9%,38.1%and 61.95%samples' EFs were above 2,respectively.3.Distribution of heavy metal concentrations in soil was variable among different railways.In soil near Shuigon line and Hachigo line,distribution of heavy metal content was uniform.In soil near other railway,concentration of some elements had negative relation with distance to railway.Several factors,like frequency of railway,type of locomotive,cargo trains,pH of soil and wind,had effect on distribution of heavy metals in soil near railway.4.Accuracy of training of BP artificial neural network prediction module of heavy metals concentration along railways was high except Cd in samples from Sobu line.Accuracy of BP artificial neural network prediction module of Cu,Zn,Mn,Cd,Sn and Pb was high,suggesting concentration of these elements had significant relation with railway operation.5.Results of potential pollution soureces analysis showed that Cu,Zn,Sn and Pb in soil were mainly orginated from railway operation,additionally,automobile affected concentration of these elements in soil.Corelation analysis revealed that along diesel driven railway all elements had significant relationship with each other,except along Hachigo line.In samples collected from 3 electricity driven railways,Cu,Zn,Se,Sn,Pb and Bi showed significant relationship with each other,indicating these 6 elements may originated from railway.Principal component analysis showed in soil near diesel driven railways,Fe,Cu,Zn,Mn,Cd and Pb has significant correlation with each other,therefore these heavy metals may originate from railway.In soil near electricity driven railways,content of Cu,Zn,Sn and Pb was affected both by railway and automobile operation,and Cr mainly originated from railway.Cluster analysis revealed that Fe,Cu,Zn,Mn and Pb had strong relationship with each other in soils along 3 diesel driven railways,this result suggested these elements may have similar source.Concentration of Cu,Zn,Sn and Pb showed strong relationship with each other in soils along electricity railways.Pb stable isotope analysis showed that both railway and automobile influenced content of Pb in soil.Geographic analysis found that Cu,Zn,Sn and Pb had high concentration in area close to railway,indicating these elements mainly emitted from railway.6.Comprehensive pollution index analysis revealed there was heavy metal pollution in soils in this study.Mean IPI of Muroran line,Sobu line and Chuo line was above 3,which meant serious heavy metal pollution in soil along these 3 railways.Index of geoaccumulation analysis showed pollution of Zn was most serious following by Cu.High value of Igeo mainly occurred in samples collected within 20 meters from railway.7.In this study,heavy metal in soil collected near railway had high ecological risk.Heavy metal near Sobu line had the highest ecological risk.Samples from Chuo line was following.Cd had the highest potential ecological risk.In health risk analysis,non-carcinogenic risk index of all heavy metals in this study was below 1,suggesting non-carinogenic risk of heavy metals in soil near railway could be ignore.Carinogenic risk index of heavy metals was below 5.0×10-5,except Cr.High carinogenic risk index of Cr resulted in high comprehensive carinogenic risk index,indicating heavy metals in soil near railway had high carinogenic risk. |
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