| Polycyclic aromatic hydrocarbons (PAHs) are trace and widespread persistent organic pollutants in the environment. Because of their high stability, semi-volatility and fat solublility, these pollutants can accumulate in soils and vegetables through atmospheric dry and wet deposition, wastewater irrigation, road dust, pesticides and fertilizers application and other pathways, which causes increasingly serious pollution to soil-vegetable system, even endangers human health through food chain due to its accumulation and amplification effects. Therefore, pollution effects of PAHs in soil-vegetable system have become a hotspot in the environmental science field in recent years.This study is supported by the project of "Pollution effects of heavy mental in urban dry and wet deposition on soil-vegetable system" (NO.41271472). Several seriously polluted suburban areas in Shanghai were selected to study PAHs in atmospheric deposition, vegetable field soil, nearby road dust and different kinds of vegetables. Moreover, the ecological risk and human health risk of soil-vegetable system were evaluated, and a simulated atmospheric dry deposition experiment was designed to explore contribution rates of atmospheric deposition to soils and edible vegetables under field planting conditions. The main conclusions were as follows:(1) The PAHs fluxes of atmospheric depositions in Shanghai suburbs ranged between 154.78 and 1477.44μg·m-2·month-1 and concentrations were from 7.87 to 12.47μg·g-1 PAHs in vegetable field soils ranged between 258.05 and 535.30ng·g-1 with a mean value of 364.56ng·g-1. In nearby road dust, it ranged from 791.61 to 6196.49ng·g-1 with a mean value of 2378.14ng·g-1. Among the various vegetable species detected, the highest PAHs concentration was observed in the leafy vegetables with a mean value of 263.51ng·g-1, followed by the stemmed species with a mean value of 204.60ng·g-1, while the fruity and rhizomatic species accumulated the lowest amount with a mean value of 126.92ng·g-1 and 78.87ng·g-1 respectively. The concentrations of PAHs in different tissues of vegetables showed that the highest was in leaves, followed by stems, while the lowest was in rhizomes. As a whole, total concentrations of sixteen PAHs in atmospheric depositions was the highest, followed by road dusts and vegetable field soils, while vegetables accumulated the lowest.(2) The PAHs concentrations of atmospheric depositions in Shanghai suburbs showed that the highest was observed in busy main highways (FX), followed by sampling sites near a teel plant (BS) and adjacented to a municipal solid waste incineration plant (PD), while atmospheric deposition near a thermal power plant accumulated the lowest amount. Vegetable field soils around a teel plant (BS) showed the highest concentration level, followed by soils in the downwind of a thermal power plant (MH4), while soils in outer suburbs (QP) showed the lowest concentration level. Vegetables growing near a municipal solid waste incineration plant (PD) accumulated the highest PAHs concentrations, followed by growing in the downwind of a thermal power plant (MH1 and MH4), then growing near a teel plant (BS), while the vegetables growing in outer suburbs (QP) accumulated the lowest. Generally speaking, point source discharges of the municipal solid waste incineration plant and the teel plant taking iron ore and coal as raw materials could bring about fearfully contamination to soil-vegetable system, moreover, meteorological parameters such as the prevailing wind direction could also have an important effect on it.(3) The sources of PAHs were similar in atmospheric depositions, vegetable field soils, nearby road dusts and different vegetables in Shanghai suburbs. It mainly derived from pyrolysis source, such as incomplete combustion of grass, wood, coal and petroleum products. However, PAHs in vegetables at a few sampling sites such as Baoshan, Fengxian, Jingdong Road of Minhang showed complicated sources of combustion and leakage of petroleum products. PAHs in soils mainly came from transportation fuels accounting for nearly 51.9%. PAHs in road dusts showed a complex source of transportation fuels, coal combustion and petroleum products leakage, which contributed to about 46.3%. Coal combustion is a major source of PAHs pollution in vegetables accounting highly for 61.8%. PAHs in atmospheric deposition, vegetable field soil and nearby road dust dominated by medium and high molecular weight PAHs (4 rings,5-6 rings), while in vegetables low molecular weight PAHs (3 rings) are the dominators.(4) Vegetable field soil was slightly polluted in Shanghai suburbs, and the possibility of PAHs risk was relatively low. The highest toxicity equivalency quantity in edible vegetables was observed in leafy species, followed by the stemmed ones, while the fruity and rhizomatic species showed the lowest value. Health risk assessment indicated that non-carcinogenic individual PAHs in edible vegetables had little risk on human health, while carcinogenic individuals showed a high cancer risk. The highest cancer risk emerged in a sampling site located in the downwind of a thermal power plant and adjacented to busy main highways as well (MH1), followed by other sampling sites adjacented to a municipal solid waste incineration plant (PD) and near a teel plant (BS), while in less polluted outer suburbs (QP) and near busy main highways (FX) the cancer risk of vegetables was at a relatively low level.(5) The contribution rates of PAHs concentrations from atmospheric deposition to vegetables was much higher than that to soils accounting for 78.04% and 0.18% respectively by a simulated atmospheric dry deposition experiment. The soil growing cabbages accumulated the most PAHs from atmospheric dry deposition, followed by growing pakchois and romaine lettuces, however, the soil growing asparagus lettuces accumulated the lowest amount. Among various vegetables, romaine lettuces accumulated the most PAHs from atmospheric dry deposition, followed by cabbages and pakchois, while asparagus lettuces accumulated the lowest amount. |
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