| City is the most populated place with intensive human activities,and its environmental quality is closely related to human health.Street dust,as an important medium of pollutants,can bring direct or indirect risks to urban ecosystem and human health.Baiyin City is one of the typical mine-based cities in northwestern China.For a long time,heavy metal pollution caused by non-ferrous metal smelting has become the main environmental problem of Baiyin City.Therefore,we collected 174 street dust samples in different seasons of 2013 from Baiyin City,and measured their magnetic properties and heavy metal assemblages.Using some software?e.g.Origin,ArcGIS?,the temporal and spatial distributions of magnetic properties and the contents of heavy metal elements of street dust samples in Baiyin were analyzed.Based on multivariate statistical methods,the relationship between magnetic parameters and heavy metals were analyzed,and the spatial distribution of heavy metal pollution sources was explored.The main conclusions are as follows:The magnetic susceptibility of street dust samples in Baiyin is generally high,with a seasonal variation characteristic of December(329.82×10-8 m3/kg)>October(284.62×10-8 m3/kg)>March(245.98×10-8 m3/kg)>July(149.24×10-8 m3/kg).The main magnetic minerals are low-coercivity magnetite and maghemite with coarse pseudo single domain and multi-domain.The spatial distribution of magnetic mineral contents of street dust samples of Binyin in four seasons is roughly consistent with high values in the industrial district and the stripe traffic area,and low values in the other regions?commercial district and new district?.The heavy metal concentrations of street dust samples of Baiyin are high,with different degrees of enrichment and certain seasonal changes.The Fe element values are similar to the background,while other elements?Cu,Pb,Zn,As?accumulate obviously,especially Cu and Zn elements.For different seasons,the spatial distribution characteristics of heavy metals vary slightly.In general,the heavy metal concentrations of street dust samples near the lead and zinc smelter in the northeast of Binyin is the highest,and decrease with increasing distance from the smelter plant.The traffic zones in the south and north of Bainyin are other high value areas,while the commercial district and new district are low value areas.Enrichment factor suggests that Cu,Pb,Zn,As elements are affected and disturbed seriously by human activities.The pollution load index?PLI?reveals that heavy metal pollution of street dust in Baiyin is more serious in March,October and December than in July.The heavy metal pollution in the industrial area is more serious than in the traffic area,the commercial district and the new district.Additionally,the PLI values of street dust samples of Jianshe Road are also high.The street dust of Baiyin is generally affected by the heavy metal pollution with a certain seasonal variation and a significant difference in spatial distribution.There are significantly positive correlations between magnetism parameters(?lf,?ARM,SIRM,SOFT,HIRM)and pollution load index?PLI?.The spatial distribution of magnetism parameters,heavy metals and PLI values is consistent.The cluster analysis and factor analysis results indicate that ferrimagnetic minerals and heavy metals mainly come from industrial pollution and traffic pollution.The magnetic mineral content parameters(?lf,?ARM,SIRM,SOFT,HIRM)can effectively monitor urban heavy metal pollution condition and delimit pollution areas.Compared with the domestic comprehensive cities,the magnetic mineral content in street dust samples of Baiyin is relatively low,which may be related to small city size and low population density.Different functional zones of Baiyin have a relative consistent pollution source.Furthermore,the strong magnetic minerals are predominately contributed by industrial pollution,and the spatial difference of pollution degrees is great in Baiyin. |
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