Seasonal Variation Of Contents And Health Risks Of Heavy Metals In Surface Dust In Zhengzhou City

Zhengzhou City was selected as the research object. Based on the field survey, sampling and laboratory analysis, comparative study was done on the content level, spatial distribution, enrichment characteristics, pollution and health risk assessment of Cr, Ni, Zn, Pb and Cu in surface dust in different seasons in Zhengzhou City. The main conclusions drawn are as follows:(1) Concentrations of Cr, Cu, Ni, Pb and Zn in surface dust in different seasons in Zhengzhou City exceeded the background value, suggesting there are different degrees of pollution. In addition to Cr in the medium variation, the rest heavy metals are in the strong variation in spring. except Cr and Cu in the medium variation, the rest heavy metals are in the strong variation in summer. There is a large external disturbance of the source of heavy metals in strong spatial variation in surface dust, and the variation is largely attributable to uneven spatial distribution of human activities such as transportation, industrial activities, building construction and so on.(2) On the whole, concentrations of heavy metals in spring surface dust were slightly higher than summer in Zhengzhou City, whereas spring and summer were both lower than winter. As the winter is heating period, burning of various fuels has been frequent, making the concentrations of heavy metals in atmospheric particulates increase, causing that the concentrations in the surface dust increase. Therefore the winter was slightly higher than the other seasons. During the spring month in arid climates, sand and dust weather occurred quite, resulting in higher levels of heavy metals. As the summer is non-heating period and rainy, surface run-off often occurred, so the concentrations of heavy metals is lower.(3) The results of analysis of correlation and cluster show that traffic and industrial emissions are the main sources of heavy metals in surface dust in Zhengzhou City.(4) There was a significant difference in pollution levels of dust metals in different area. The pollution by Cr, Cu and Pb mainly concentrated in the western industrial zone, whereas Ni in the northwest corner of Zhengzhou and Zn in the downtown area.(5) There was a significant difference in the concentrations of different heavy metals on different particle sizes, and the concentrations varies considerably with the seasons. It can be seen that from the seasonal comparison in the same particle size, the concentrations of heavy metals on three particle sizes (coarse particles (> 0.25 mm), medium particles (0.15 ~ 0.25 mm), fine particles (<0.15 mm)) reached the maximum in winter. The concentrations of heavy metals in fine particles were higher than that of coarse particles and particles. The content of Ni in coarse particles in summer was higher than that in spring. The other 4 elements, on the contrary, were spring> summer; The content of Cr and Pb in medium particles (0.15 ~ 0.25 mm ) in spring was higher than that in summer, whereas the order of the contents of the other 3 heavy metals was summer> spring; The content of Cu in fine particles (<0.15 mm) in summer was higher than that in spring, whereas the order of the contents of the other 4 heavy metals was spring > summer. Although particle size distribution had a significant influence on pollutant concentrations, fine particles makes a large proportion of dust, the order of percentage of particle sizes was fine particles> coarse particles > medium particles in spring, whereas the order of percentage of particle sizes was fine particles > medium particles> coarse particles in summer and winter.(6) The values of HQ of the five heavy metals in 90 collected samples via different exposure routes were less than 1. Hand-to-mouth ingestion poses the highest non-cancer risk, followed by dermal exposure, whereas risks of exposure by inhalation are lowest. the values of HI of metals in the order of Pb> Cr> Ni> Zn> Cu were less than 1, indicating posing no health hazard to people. Cr caused higher cancer risk than Ni, but their risks are both lower than the threshold values, indicating a lower risk of cancer and without health hazards.