| Polycyclic aromatic hydrocarbons?PAHs?are a group of persistent organic pollutants that are prevalent in the urban environment,and are known to have carcinogenic,genotoxic,and mutagenic effects on living organisms,which is ubiquitous in atmospheric particulate matter.The United States Environmental Protection Agency?USEPA?has listed 16 PAHs as priority pollutants.At present,high-speed urban life and human activities lead to air pollution in urban became serious.PAHs in the urban environment has been greatly affects human beings health and ecosystems functions,which gradually become one of hot issue in pollution ecology.Massive urban vegetation coverage is the interacting interface between environmental pollutants and plants.On the one hand,Plant leaf surface has a cetain ability to capture atmospheric particulates and carried PAHs.On the other hand,plant could degraded partly PAHs from environment through their leaves.Hence,plant leaf surface provides an effective and convenient way for regional environmental monitoring,and plays a key role in the migration and transformation of environment pollutants.In our thesis,Nanjing was selected as a research area,with PAHs in the foliar dust on urban plants being the object of study.This study investigated the spatial and temporal distributions of PAHs in foliar dust.Focused on analyzing the difference of particulate matter absorbed on leaf surface and PAHs accumulation,and analyzed the relationship between leaf area and the accumulation of different sizes of PM and PAH concentrations,considered the adsorption capability of PAHs in the plant cuticle and finally potential sources of PAHs,evaluated the ecological and human risks.The main results are as follows:1.The concentration of?16PAHs in foliar dust ranged from 756.19?g/kg19018.14?g/kg,with a mean value of 6912.04?g/kg.There were significant seasonal variations of?16PAHs concentration in foliar dust were observed,which followed in this order:winter>autumn>spring>summer,the spatial distribution of?16PAHs concentration in foliar dust presented a changing trend of traffic hub area>commercial area>educational area>scenic area>park area.The constitution of the PAHs in sampling sites and seasons were most predominantly by 4-,5-rings,followed by 3-,6-ring,and 2-ring with the lowest percentage of?16PAHs.Indeno?123,cd?pyrene?IcdP?,Fluoranthene?Flu?and chrysene?Chr?were the major compounds.There was a spatial trend for the concentration of?166 PAHs to follow the distribution of north-south=high concentration and east-west=low concentration.The highest concentration of PAHs was found in Xuanwu district,while the lowest concentration of PAHs was found in Qixia district.The concentration of?16PAHs in foliar dust varied greatly with areas in four seasons.The area with a low concentration of PAHs in spring.In summer,the area mainly was a low concentration of PAHs.Compared with summer,the area with a high concentration of PAHs showed the tendency to expand in autumn.Compared with the other three seasons,the most areas with a relative higher concentration of PAHs in winter.2.Plants have remarkable species difference in absorbing different-sizes particulate matters?PM?mass and accumulation of?166 PAHs concentration,which followed in this order Platanus orientalis>Pinus sylvestris?Pittosporum tobira>Osmanthus fragrans in different areas.In terms of different sizes PM mass,most 67.54%of the PM on the leaf surfaces of the four tree species was larger than 10?m in diameter.The PM2.510.510 and PM2.5.5 size fractions accounted for21.63%and 10.83%,respectively.In terms of different sizes PM number,PM10 accounted for93.15%of the total particulate on leaves,while PM2.5.5 accounted for 63.94%.From a scanning electron microscopy?SEM?observation of plant leaf surfaces,the ability of the upper surface of the plant leaves to retain PM was significantly higher than of the lower surface.We found that fine or small PM was mainly absorbed in the villi and irregularity grooves,but there was no obvious coarse or fine PM in the shallow grooves near the stoma.The result of multivariate regression analysis showed that the relationship between percentage of PM2.5.5 of unit area were presented highly significant positive correlation with PAHs concentration in foliar dust?p<0.001?.The results indicated that the particle size smaller than 2.5?m played an important role on influencing the?166 PAHs concentration in foliar dust.3.The result of PAHs absorption of plant cuticle showed that the distribution of PAHs was mainly controlled by an adsorption mechanism.According to the value of Kd,which was the calculation by the rate of linear isothermal adsorption curve and showed that the P.massoniana,P.tobira,and O.fragrans had a strong sorption capacity of Naphthalene?Nap?,P.tobira had a stronger sorption capacity than O.fragrans and P.tobira.P.massoniana had an adsorption capacity of Phenanthrene?Phe?that was equivalent to that of O.fragrans,but stronger than that of P.tobira.P.massoniana had a stronger sorption capacity of Fluoranthene?Fl?than O.fragrans and P.tobira.O.fragrans had a stronger sorption capacity of Pyr than P.massoniana and P.tobira.An SEM observation revealed that the P.sylvestris cuticle has a rich microstructure,with stoma distributeddensely on both sides.The surface of O.fragrans cuticle had rough folds,whereas P.tobira cuticle was smooth.However,we did not observe an obvious stoma in both P.tobira and O.fragrans cuticle.The differences in the leaf microstructure of plant cuticle were major causes for the interspecies difference of PAHs adsorption.A Fourier transform infrared?FTIR?analysis revealed that P.massoniana contained fatty components,with the highest lipid content of the three trees.We also observed signals of three plant cuticle in C=O(1734 cm-1),indicating an obvious ester bond absorption peak.Moreover,C-O-C peak(1057cm-1)is most prominent,which related with sugar content.4.According to diagnostic ratio and principal component analysis method conducted PAHs in foliar dust in Nanjing,diesel and gasoline vehicle emissions,coal combustion,the combustion of petroleum and fossil fuels,low temperature combustion,petroleum leakage,and biomass burning were the most important sources of PAHs in the Nanjing urban area.Motor vehicle emissions and the incomplete combustion of coal and biomass were the main PAH sources in the Nanjing suburban area,but petroleum leakage and industrial combustion were important supplements of these sources.Vehicle emissions,and the combustion of coal and fossil fuels were the main PAH sources in suburban Nanjing,with incomplete biomass combustion being an important supplement of the main sources.5.Comparing with Canadian agriculture soil PAHs control standards,the results indicated that Pyr and Phe were the most serious pollution of foliar dust.According to the C-level control standard of PAHs in Netherlands soil,Flu,Chrysene?Chr?and Benzo?a?pyrene?BaP?were the major pollutant.There were seven carcinogenic PAHs that contributed to the potential carcinogenicity risk,accounting for 97.09%,98.61%and 99.12%of all 16 priority PAHs in urban,surban and rural areas,respectively.BaP contribution rate was the greatest,and Dibenzo?a,h?anthracene?DBA?and IcdP was the second and the third one.The lifetime cancer risk model results indicated that the inhalation pathway presented no carcinogenic risk to humans.The incremental lifetime cancer risk?ILCR?values among 10-1310-1010 via inhalation,which indicated no potential risk.However,the ILCR values for ingestion and dermal contact were above 1×10-55 in foliar dust for different gender and age groups,which indicated potential risk.Generally,dermal contact made the largest contribution to the ILCRs.The total value of the ILCRs decreased in the following order:adult>child>adolescent in all areas,with females believed to be more sensitive than males.The value of the ILCRs for dermal contact for all gender and age groups decreased in the following order:adult>adolescent>child,and the value of the ILCRs for ingestion decreased in the following order:child>adult>adolescent. |
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