Source,exposure characteristics and its environmental effect of heavy metals in urban surface dust

Surface dust is the "source","sink" carrier of heavy metals in urban environments,which has a close relationship with the environmental quality and human health.Heavy metal geochemistry characteristics in urban surface dust were analyzed,and an overview of heavy metal geochemical behavior of surface dust in domestic and abroad was generalized,including source of heavy metals in surface dust,exposure characteristics,influencing factors,and environmental effect etc.Heavy metals in surface dust have natural and anthropogenic sources,and the anthropogenic source accounts for a large proportion.The main anthropogenic sources are traffic pollution,industrial pollution and urban construction.Metals sources are different.Now,heavy metals content in urban dust are increasing gradually,particularly for the anthropogenic element of Zn,Cu,Pb and Cd.Meanwhile,platinum family element(PGEs) such as Pt,Rh and Pd have also enrichment gradually.Heavy metals in urban surface dust have three exposure characteristics:(a) Spatial distribution difference.Generally,heavy metals in urban dust in industrial zone have higher concentration than those in residential area,cultural and educational area and commercial district.And heavy metals in urban dust in high traffic flow area have higher concentration than those in medium traffic flow and low traffic flow area.(b) Size distribution difference.Overall,heavy metal content in urban surface dust decreases with the increasing of the dust particle size.Different heavy metals,due to theirs different source,have different enrichment regularity in different particle size dust.Zn,Pb and Cr anthropogenic source elements mainly distributed in particle size dust,and natural source elements such as Fe and Mn frequently uniform enriched in different particle size.(c) Existence speciation difference.Heavy metal element in surface dust mainly exists in the residue form.Exposure of heavy metals in surface dust mainly affected by urban traffic activities(including traffic flow,speed and variable frequency and vehicles features),street location and terrain,and meteorological factors(such as rainfall,wind etc).Atmospheric particles,ground surface soil,surface rainoff have obvious influence mechanism with the urban dust,which the migration processes of dust between these media often directly caused atmosphere,soil,water pollution with heavy metals.It is suggested that we should increase our emphasis on the time-series and small-scale research,and the affect of geographical factor to the exposure characteristics and migration mechanism of heavy metals in surface dust.