| Street dust is one part of urban ecological system, and it also plays an important role in the circulation flow of water, gas and solid three-phase medium. It can influence the regional environmental quality and human health due to the attachment of various pollutants, including heavy metals, organic pollutants, N/P nutrients and others. Located at a sensitive region, the county town of Chunan (Qiandaohu Town) was selected as the research objects. The paper analyzed the composition of grain diameters, main pollution matter content and pollution source of street dust in county town of Chunan., and evaluated environmental risks and health risks street dust pollutant was discussed and the environmental risk was assessed in the paper. The main conclusions were as follows:Four sites in commercial district, traffic district and integrated district of Qiandaohu Town was selected as sampling sites to collected dust in spring, summer and winter. The dust size analysis results showed that the distribution of dust size was single peak trend. The main particle size was between 150～360μm, which accounted for 33.86% of the total particles amount. The size of 65～150μm and size larger than 360μm particles was accounted for 26.57% and 25.53% of the total particulate matter, respectively. And the smallest particles with size less than 65μm particles accounted for 14.03% of the total particulate matter. The particle size distribution characteristic of street dust in different sites was not obvious.According to the monitoring results, the contents of total phosphorus, ammonia and nitrogen were 588.29μg/g and 13.67μg/g, respectively. The content of nutrients in street dust was varied in the sample sites. The lowest content of nutrients of street dust was found in Lake North Road located in traffic area while the contents of nitrogen was relatively high in monitoring sites of Xin’an Street and Xin’an road located in the commercial district. The content of total phosphorus in Nanshan Street located in the integrated district was higher than others. The assemble ability of the street dust to nutrient gradually decreased with the increase of particle size. Total phosphorus and ammonia nitrogen was assembled mainly by the medium particle size. Meanwhile, the content of nutrients in street dust was relatively high in summer compared with spring and winter.Heavy metal was another important pollutant in dust. The average contents of Ni, Pb, Cd, Cu, Zn, and Cr in the street dust of Qiandaohu Town were 84.77 mg/kg, 233.55 mg/kg,4.61 mg/kg,142.11 mg/kg,293.19 mg/kg and 815.46mg/kg, respectively. Compared to existing studies results of Zhejiang Province, the average concentrations of Cr, Ni and Pb exceeded the province’s average concentration by 46%,238% and 25.3%, respectively. While the concentrations of Zn and Cu were lower than that of province average concentration by 13.6% and 56%. Meanwhile, the distribution of heavy metals of dust street was varied in different sample sites. The highest concentration of Zn, Ni, Cr and Pb was found in traffic district, followed by the commercial district and integrated district. Cd and Cu were higher in the commercial district, followed by traffic district and integrated district. In addition, The assemble ability of dust for most heavy metals increased gradually with the increase of particle size except Pb. The content peak of most heavy metals except Cd was found in summer according to the seasonal distribution.Compared with the two-level of Soil environmental quality standard, the content of Cr was at a light pollution level,while the other elements were all in no pollution levels. The environmental risk analysis for heavy metals in the street dust was evaluated based on the soil environmental background values of Hangjiahu Plain in Northern Zhejiang province. The results showed that the geological accumulation index of Pb and Cr in street dust were the highest. The geological accumulation index of Pb indicated that Pb in commercial district (Xin’an Street), traffic district and integrated district were at a medium to heavy pollution level. However, the index of Cr showed it was at a heavy pollution level every district. The geological accumulation index of Cu and Ni was at a medium pollution level except traffic districts. The results also showed that Cd and Zn had no accumulation in street dust town. According to the ecological hazard index of heavy metals, the Cd in street dust in the county town was at the ecological hazard level. Most heavy metals in street dust had reached the potential ecological hazard level in the commercial district (Xin’an Street) and traffic district while they were still at the mild ecological hazard level in the commercial district (Xin’an North Road) and the integrated district. |
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