| Polycyclic aromatic hydrocarbons (PAHs) are the hydrocarbon compounds, containing two or more benzene rings. They mix more easily with oil than water and can accumulate in organisms. They are ubiquitous in the environment and have been identified as carcinogenic, mutagenic, and teratogenic. In1976, International Agency for Research on Cancer (IARC) listed94kinds of carcinogenic compounds,15of which belonged to the polycyclic aromatic hydrocarbons. One PAH compound, benzo[a]pyrene, is notable for being the first chemical carcinogen to be discovered in the environment. With the acceleration of urbanization in Shanghai, the increasing number of private cars, organic pyrolysis in industrial production and incomplete combustion of fossil fuels, atmospheric concentrations of PAHs are increasing, which is threatening the security of urban environment seriously.City greening plants are a major component of urban landscaping and are urban natural purifiers. Each city has thousands of plant species, which are used to beautify the environment, provide shade, reduce noise, adjust the temperature, lower wind speed and so on. Meanwhile, the plants are highly dependent on their growth environment, especially, green trees’ leaves can accumulate PAHs existing in gaseous and particulate state through dry and wet deposition and gas diffusion. In the urban landscape construction, city greening plants play an important role in improving the urban environment quality.In this study, the contents of PAHs were quantitative detected in the leaves of cinnamomum camphora, viburnum odoratissimum, mgnolia grandiflora and nerium oleander in spring, summer, autumn and winter by GC-MS spectrometer. We compared the adsorption ability of PAHs for different tree species in different seasons. And then we further analysised the spatial and temporal distribution of PAHs in Cinnamomum camphora leaves giving the large adsorption of PAHs in them. We preliminary analysised the sources of PAHs and did a simple ecological risk assessment in the Cinnamomum camphora leaves, in order to provide a theoretical basis for the urban garden department to select strong adsorption species and provide a scientific basis for urban environmental health and management.PAHs contents were81.33-1731.75ng/g (mean value:443.68ng/g),110.03-787.24ng/g (mean value:251.80ng/g),102.52-760. llng/g (mean value:240.15ng/g),85.90-652.51ng/g (mean value:226.76ng/g) in leaves of Cinnamomum camphora, Viburnum odoratissimum, Mgnolia grandiflora and Nerium oleander respectively. Distribution characteristics in different species in four seasons: cinnamomum camphora> viburnum odoratissimum, magnolia grandiflora and nerium oleander. Distribution characteristics in spring, summer and winter: camphor tree> viburnum odoratissimum> magnolia> oleander. PAHs levels of distribution in autumn: camphor> oleander> magnolia grandiflora> viburnum odoratissimum. Seasonal variations of PAHs is the most obvious in camphor leaves: winter> autumn> summer> spring; PAHs in leaves of magnolia grandiflora and viburnum odoratissimum:winter> summer> spring> autumn; PAHs concentrations’ distribution in oleander leaves: fall> winter> summer> spring, and the PAHs concentrations in all samples were quite similar.Distribution characteristics of different rings PAHs had a general trend in four tree species:4-ring>3-ring>5-ring>2-ring>6-rings (representing58.25%,28.49%,5.68%,5.56%,2.02%of∑16PAHs, respectively). The percentages of3-ring and4-ring shared more than80%of∑16PAHs and the percentages of6-ring were minimum. The contents of the4-ring PAHs had a highest level in camphor leaves, the3-ring PAHs has a highest level in Viburnum odoratissimum leaves, while3-ring and4-ring PAHs are both high in magnolia and oleander leaves.3-ring and4-ring PAHs have significant seasonal difference in Camphor and magnolia leaves and3-ring,4-ring,5-ring and6-ring PAHs have significant seasonal differences in oleander leaves. Each ring had no obvious seasonal variations in leaves of Viburnum odoratissimum.The concentrations of Fl, Pyr and Chry were highest in different seasons, and the contents in camphor leaves were significantly higher than that in Viburnum odoratissimum, magnolia and oleander leaves. The levels of Acy, Ace, BaP, InP, B(ghi)P, D(ah)A, An and BaA were lowest in all samples. Phe was the dominant compound in the four plants leaves, and the levels of Phe were highest in winter. In camphor, viburnum odoratissimum, magnolia and oleander leaves, Chry, Phe, Phe and Phe were highest in spring respectively, while in summer the highest monomers were Phe, Phe, Flu and B(b+k)F respectively; in autumn and winter, Fl was highest in camphor leaves, Phe was highest in Viburnum odoratissimum, magnolia and oleander leaves. The highest monomers’ contents in winter were higher than that in other seasons in leaves.The spatial distribution characteristics of concentrations of PAHs in different seasons showed that high value areas generally appeared in the jinshan chemical industry area, baoshan industrial zone, wujing industrial zone and busy traffic areas of downtown in camphor tree leaves in Shanghai. The contents of PAHs influenced by "rain island" and "heat island" were low in city center in summer. PAHs contents affected by large straw burning were relatively high in the rural areas in autumn. The high value areas expanded than any other seasons obviously in winter. Affecting by prevailing wind direction, a massive areas became the high value areas in the west and south of Shanghai, and high concentrations areas shrinked in baoshan district areas in winter. PAHs concentrations were relatively high in the blades of rural areas in winter.Gradient difference of PAHs concentrations in the camphor tree leaves of spring and summer: urban> suburbs>rural areas; in autumn and winter: rural> suburb> urban areas. In the three regions, the contents of PAHs of winter were significantly higher than that of spring, summer and autumn in camphor tree leaves. In urban areas, the concentrations of PAHs in summer were similar to that in autumn and contents were the lowest in spring. In suburban and rural areas, contents’ characteristic: autumn> summer> spring. In spring, Chry had the highest content in the camphor leaves of the three regions. In summer, the content of Phe was the highest in the blades of the urban and rural areas, the content of Pyr was the highest in suburb and the percentage ranges were larger in2+3-rings,4-ring and5+6-rings PAHs. In autumn, urban, suburban and rural areas had the highest content of Fl. In winter, Fl content is the highest in the three regions, the content of An is higher in rural areas and the distribution of PAHs component ratios is the most concentrated. The content of Phe, Fl, Pyr and Chry of the three regions of winter whose concentrations were relatively higher in leaves was significantly higher than that of spring, summer and autumn.The highest concentrations of PAHs in camphor leaves appeared in industrial areas, followed by tracffic and downtown areas. In residential areas, cultural and educational areas and the park green spaces, the concentrations of PAHs were lower. The contents feature of PAHs in camphor tree leaves in spring and summer: industrial zones> traffic areas> commercial areas> residential areas> cultural and educational areas> park and green spaces; in autumn: industrial zones> traffic areas> residential areas> commercial areas> cultural and educational areas> park green spaces; The contents of PAHs in different function had the most significant differences in the camphor tree leaves in winter. The change tendency: industrial zones> traffic areas> commercial areas> cultural and educational areas> the park green spaces> residential areas. Besides residential areas were special in autumn, the concentrations of PAHs in winter significantly higher than that in spring, summer and autumn in all functions and the concentrations of PAHs in industrial or traffic zones were the highest in spring, summer and winter. The contents of Fl, Pyr, BaA, Chry, BbF and BkF in the industrial areas were significantly higher than that in the other functional areas of the four seasons and the contents of Phe, Fl, Pyr and Chry were minimum in the park and green spaces and residential areas. With characteristic ratios and factor analysis conducted PAHs in the camphor leaves from Shanghai, the source apportionment showed that PAHs in leaves mainly came from vehicle exhaust and incomplete combustion of fossil fuels from center city; PAHs of suburban camphor leaves mainly came from fossil fuels such as coke and coal incomplete combustion, traffic pollution and oil volatile sources; PAHs in the rural camphor leaves came from incomplete combustion of grass, wood, coal, coke and other fuels and traffic pollution.Distributions of toxicity equivalent concentrations of seven kinds of carcinogenic PAHs and16priority-controlled PAHs in cinnamomum camphora leaves: winter> summer> fall> spring. TECs of Industrial zones were obviously higher than that of other functional areas in the leaves, total trend:industrial zone> traffic area> residential commercial and cultural and educational areas> park green space. Toxicity equivalent concentrations of BaP were highest in industrial areas. Potential carcinogenicity of PAHs of industrial areas is higher than that of traffic areas. With the domestic and foreign urban contrasting, we found that TECs in the camphor tree leaves was in the medium to low levels in Shanghai. |
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