| In order to control the pollution of road sediments in Xi’an, it is necessary to study the pollution characteristics of heavy metals. Four typical functional areas 12 main streets(commercial district,industrial district, residential and tourist district) with traffic volume of <10000pcu/d、10000-30000 pcu/d and >30000pcu/d were select as research objects. In four months(October 2013, January 2014, May 2014, August 2014),selecting sampling points of different sampling places and keep sampling six days continuously, to study the road sediment pollution of Xi’an. From the end of August 2014 to early September, between three rain, three sampling places in the tourist district, collecting 27 samples in 9 days to study the law of road sediment accumulation, the impact of the traffic flow and runoff erosion to sediment accumulation on the road. Measuring several pollution indicators of each sample, such as COD、dissolved COD、NH4+-N、NO3--N、NO2--N、Pb、Zn、Cu、Ni、Cr、Cd、V、Ba, to study the road sediment pollution of Xi’an and the impact of the traffic flow and runoff erosion to sediment accumulation on the road. using the potential ecological risk index to evaluate the ecological risk, using Health Risk Assessment Methods of EPA(US) assess their health risks to residents of Xi’an. The results show that:The concentrations of COD、NH4+-N and NO2--N under different traffic flow have significant difference, and the concentration of dissolved COD and NO3--N have no significant difference. The concentration of NH4+-N、NO3--N and NO2--N has the same change(winter>spring>summer>autumn).The concentration of Ba、V、Cr、Cu、Ni、Zn in different functional areas have significant differences, the concentration of Cd, Pb had no significant difference. Ba, Pb, Zn and Cd follow the same rule: industrial area > business district > residents district > tourist area, Cu and Cr keep a high value in residential district. V and Ni are close to or slightly higher than the soil background values of Shaanxi Province. The heavy metal elements in road sediments show the distribution characteristics of lower in summer and autumn and higher in spring and winter.The impact of road deposited sediments on human health in Xi’an can not be ignored. The total non-carcinogenic risks of each heavy metal(HI) is 1.19, higher than the critical value, indicating the presence of significant non-carcinogenic health risks. Impact on children is higher than adults, whose non-carcinogenic risk is 0.196. In three kinds of exposure pathways, non-cancer risk indexs are hand- mouth contact > skin absorption> inhalation,The order of non-carcinogenic risk is Pb> Ba> V> Cd> Ni> Cr> Cu> Zn, showing a great hazard. The non-carcinogenic health risks for children of Pb, Ba, V were 0.231,0.481 and 0.148, which may have bad influences on the health of children; As main contaminations for non-carcinogenic health risks, Non-carcinogenic risks of heavy metals for Pb, Ba, V are higher than the others for 1-2 orders of magnitude. The total cancer risk value of Cr、Cd、Ni is 4.25×10-7 The cancer risk of single heavy metal or all inclusive were lower than the cancer risk threshold of 10-6-10-4.The potential ecological risk of heavy metals in road sediments of Xian has reached 1359,which is in the middle level.The potential ecological risk index for the eight heavy metals has reached the level of high ecological risk IV, it should be taken seriously enough; The individual potential ecological risk and pollution indexs for different heavy metals are: Cd> Pb> Cu> Cr> Ni = Ba> Zn> V, Cd> Pb> Zn> Cu> Ba> Cr> Ni> V.When the traffic flow is below 10000pcu/d, the road sediment accumulation is from 4.36 g to 16.88 g. When the traffic flow is between 10000pcu/d to 30000pcu/d, the road sediment accumulation is from 4.86 g to 20.58 g. When the traffic flow is over 30000pcu/d, the road sediment accumulation is from 7.84 g to 32.31 g. In general terms, with the increase in traffic volume, the road sediment accumulation keep an upward trend. In the rain erosion, the road sediment accumulation has an significant reduction. The accumulation of three sampling places’ reduction is 60%, 53%, 48%. |
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