| With the rapid development of industrialization and urbanization in China, the industry-resident-agriculture mixed zone has beem formed outside the urban built-up area. The heavy metal pollutants, produced by industrial production and vehicle exhaust, can access into the soil-vegetable system by atmospheric depositon and wastewater irrigation, which will not only affect the growth of crops but also threaten people’s health. Therefore, the environment and food safety problems caused by heavy metals can not be ignored. At present, the researches, focusing on the contamination feature and risk evaluation of heavy metals in urban atmospheric deposition, soil, road dust and vegetables, are comprehensive, thus it is significant to further discuss the pollution source and contribution of urban atmospheric deposition and the soil-vegetable system.This study was sponsored by Natural Science Foundation of China, Pollution effects of heavy metals in urban dry and wet deposition on soil-vegetable system (41271472). Several typical industrial zone, such as Baosteel, Wujing Chemical Area, Yuqiao Waste Incineration Plant, and exurb Qingpu, were selected as study areas, and heavy metals (Zn, Cr, Cu, Pb, Cd, Hg) and metalloid (As) were regarded as research objects. The pollution effects, source and contribution of heavy metals in the soil-vegetable system from urban atmospheric deposition were discussed through three parts: the spatial and temporal flux variation feature of particle heavy metals in atmospheric deposition, the pollution characteristics and sources of heavy metals in soil and vegetables at the suburban area of Shanghai, and the lead isotope simulation experiments. The main conclusions are as follows:(1) The monthly average flux of particle heavy metals (Zn, Cr, Cu, Pb, Cd, Hg and As) in atmospheric deposition were 3271.76,2264.60,504.43,1340.60,57.37,7.58, and 30.42μg/m2. Generally, the highest flux appears in November, January or June (or July) in the whole year. Meanwhile, the fluxes at Baosteel and Wujing are higher than other sampling sites. According to the back trajectory results, during every November to March, the high frequency of haze days and the rise of heavy metal flux are properbly related to the pollutant air mass coming from north China; and from June to October, influenced by SE monsoon and typhoon, the air quality and deposition flux is mainly controlled by the local pollution discharge.(2) The average concentrations of Zn, Cr, Cu, Pb, Cd, Hg, and As in soils were 122.51,79.75,24.54,28.14,0.15,0.82,6.49 mg/kg, lower than those nearby road dusts. Nemerow and Igeo assessment showed that the pollution level of road dust is more serious than that of agricultural soil in suburban Shanghai. The contamination of Hg in soil is ubiquitous, and there is a close relation between location and pollution near Yuqiao area, at west of Baosteel and south of Wujing area. In winter, the average concentrations of Zn, Cr, Cu, Pb, Cd, Hg, and As in edible parts of leafy vegetables (Cabbage and Greens) were 37.0,1.94,4.81,0.73,0.44,0.02,0.52 mg/kg, which were widely lower than those in root parts. Also, the enrichment capacity of roots is much stronger than leaves. Health risk evaluation indicates that the Target Hazard Quotient (THQ) of edible parts are all less than 1, which means no health risk to people. Compared with different age groups, children may have the highest health risk when eating the same vegetables.(3) The correlation analyses reveal that Pb, Cr, Cu, As and Zn in soil and dust may have the same source, for instance, the industrial emissions, vehicle exhaust, fertilizer, etc. The factor analyses find that Pb and As may belong to industry source, Cr and Hg may belong to both industry and agriculture source, Zn and Cu may belong to industry-traffic-agriculture mixed source, and Cd belongs to agriculture sourc. The Pb isotope ratios suggest that Pb in soil is mainly derived from the Yangtze estuarine sediments, while Pb in vegetables and dusts is polluted by human activities, such as vehicle exhaust, burning coal, industrial emissions, etc.(4) Combined with the Pb isotope ratios, the results calculated by modified Voutsa pollution contribution model suggest that during the growth cycle of leafy vegetables, there is a little influence on both edible and root parts from atmospheric dry and wet deposition. The contributions of Pb from soil in vegetables can reach to more than 80%, and is more obvious from root absorption.In conclusion, the industrial emission from steel and chemical enterprises at suburban area of Shanghai has a certain influence on near atmospheric deposition particles, soil, road dust and outdoor vegetables. And the source and contribution of soil-vegetable system is complicated, which is related to both soil and atmospheric deposition. |
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