Distribution And Ecological Risk Assessment Of Heavy Metals In Urban Street Dust From Typical Coal Energy Dominant Huainan City, China

The processes of coal mining, transportation, and coal-burning power plants are the primary anthropogenic sources of dusts, the heavy metals inside dusts seriously harmed to the urban environment. Normally, residential exposures of heavy metals occured via three main paths:(a) direct ingestion of substrate particles; (b) inhalation of resuspended particles through mouth and nose; and (c) dermal absorption of trace elements in particles. Combined with the domestic and foreign literatures and related to scientific fields, the distribution and the ecological risk assessment of heavy metals in urban dusts, were investigated between the coal energy dominant city Huainan and the contrary city Hefei, with using instrumental analysis, chemical experiments, and sequential extractions. The results indicated as follows.(1) In the Huainan city, the average concentrations of Zn, Pb, Cu, Cr, Cd, Ni, Co, V and Hg were 202.59,74.63,62.74,110.69,0.57,35.82,12.18,50.95 and 0.105mg·kg-1, and the highest was Cd. In the Hefei city, the average concentrations of As, Cd, Co, Cr, Cu, Ni, Pb, V and Zn were 7.31,0.26,8.15,92.73,112.82,19.08, 83.32,50.50 and 214.31 mg ·kg-1, and the higher were Cu, Pb and Zn. Compared with the average concentrations of the two cities, it manifested that Co, Cr, Ni, V and Zn in the Huainan city were higher than that in the Hefei city. However, Hefei city had more Cu and Pb.(2) In the Huainan city, among the nine heavy metals, the concentrations of Zn and V were rather evenly distributed in different functional zones, whereas the rest elements were distributed with spatial heterogeneity. Zn, Pb, Cu, Ni, Co, V and Hg were ranked as the top toxic elements in industrial area, and Cr and Cd were ranked as the top toxic elements in traffic area.(3) Generally, in the Huainan city, the concentration of Hg in urban dusts increased with the decrease of particle sizes, which indicated that fine particles had a higher ability to carry Hg. The descending order of the concentration of Hg was: Industrial area> Traffic area> Commercial area> Educational area> Residential area> Scenic area.(4) In the Huainan city, Pb in urban dusts was mainly in the residual fraction and the Fe and Mn oxidizable fraction, the means of each sampling point in summer were: the residual fraction accounted for 74.69%, the Fe and Mn oxidizable fraction accounted for 16.08%, and in winter were:the residual fraction accounted for 53.49%, the Fe and Mn oxidizable fraction accounted for 32.18%, which indicated that Pb was mainly in mineral forms both in summer and winter. In the Hefei city, Pb mainly existed as residual and oxidizable.(5) The assessment of geo-accumulation index demonstrated that the ecological risk reached the slight pollution in the Huainan city. In summer, Zn, Pb and Hg reached the slight or moderate pollution, whereas the other five heavy metals which reached no pollution at all. And in winter, except that Cu, Zn, Pb and Hg reached slight or moderate pollution, the other four metals had no pollution. In the six functional areas, Cu, Pb, Cr, Ni, V, Co and Hg had all reached the highest pollution in industrial area, and Zn reached the highest pollution in educational area. The assessment of geo-accumulation index also showed that the ecological risk reached the slight pollution in the Hefei city. Except that Cd, Cr, Cu, Pb and Zn reached the slight or moderate pollution, the other heavy metals of As, Co, Ni and V had no pollution.(6) The assessment of potential ecological risk index demonstrated that the ecological risk reached the slight level in the Huainan city. In summer, all heavy metals reached slight ecological risk except Hg, which reached the strong ecological risk. In winter, Hg and Cd, reached the serious strong and the strong ecological risk, respectively; but the other heavy metals reached the slight ecological risk. The assessment of potential ecological risk index also demonstrated that the ecological risk reached slight level in the Hefei city. All heavy metals reached the slight ecological risk except Cd, which reached the strong ecological risk.