Characteristics Of Lead Pollution In Atmospheric Particulate Matters And Its Migration And Accumulation In Plant Leaves

Atmospheric particulate matter(PM)is the primary pollutant that affects the ambient air quality in China,while discussing the treatment of atmospheric particulate matter in various circles of society,the research of toxic components in particulate matter has important theoretical guiding significance for effectively improving the quality of ecological environment and safeguarding human health.In this study,the central city in the southern of the Yangtze River Delta(Hangzhou)was taken as the research area to study the concentration,chemical speciation,source identification and regional transport of lead(Pb)in different size particulate matters during winter and spring,which are the high incidence seasons of air pollution.Pot and hydroponic experiments were carried out to further explore the bioaccumulation characteristics of Pb in forage grass(ryegrass)and vegetables(green cabbage)which were exposed to the PM of different seasons,size ranges and emission sources.Finally,Pb content in edible parts of green cabbage and broccoli from multiple counties(districts)of Zhejiang province was investigated.The correlation between Pb in atmosphere and soil and Pb enrichment in vegetables was analyzed,and the level of atmospheric contribution of Pb in vegetables from each sampling area was discussed.Main conclusions are as follows:(1)In winter and spring,Airborne lead was mainly concentrated in fine particulate matter,and the volume concentration of Pb in PMTotal,PM3.3 and PM1.1(65.28±38.43,49.05±31.49 and 28.34±16.29 ?g/m3)in winter were higher than that in spring 51.85±9.39,39.70±6.94 and 20.49±2.96 ?gg/m3).The proportion of bioavailable Pb in fine particulate matter was higher than that in coarse particulate matter,and the proportion in spring was higher than that in winter.Combined with the Pb stable isotope technique and the backward trajectory model,it was found that industrial sources,coal combustion and exhaust emissions were the main sources of airborne Pb in Hangzhou.The influence of exogenous sources input was obvious in winter,while in spring,exogenous sources were less affected.(2)By the pot and hydroponic experiments,the lead accumulation characteristics of ryegrass and green cabbage,which were exposed to the PM of different seasons,size ranges and emission sources,were explored.It was found that accumulation ability of the spring plants to the airborne Pb was stronger than that in the winter.Seasonal variations of temperature and precipitation may be the important factors affecting the foliar uptake of Pb in atmospheric particulate matter by plants.The surface dust retention ability of ryegrass leaf was strong,which can effectively enrich the Pb in coarse particulate matters,and green cabbage was less affected by the change of atmospheric particle size.According to the results of lead distribution in leaf subcellular and tissue,the main way of foliar uptake airborne Pb by ryegrass was deposition-infiltration-permeation,and green vegetables can directly absorb the Pb in fine particulate matters by the stomata of lower epidermis.Pb in the fly ash from coal combustion had the highest concentration ratio in cell wall.Pb in waste incineration fly ash had the most obvious migration trend from plant leaf epidermal tissue to sponge tissue and Pb in coal burning fly ash was mainly concentrated in the upper and lower epidermal tissue.The different accumulation characteristics of Pb on leaf surface were mainly related to the size of particulate matters,dissolution characteristics of Pb,and the structure of leaf surface,including dust retention ability and stomatal density.(3)The investigation results of Pb content in green cabbage and broccoli from multiple counties and districts of Zhejiang province showed that the Pb content of two kinds of vegetables were both lower than the national food safety standard limit value of China.The average concentration of lead in green cabbage and broccoli were 0.0179±0.0085 and 0.0192±0.0164 mg/kg,respectively.Correlation analysis and Pb stable isotope source analysis showed that the average contribution rate of airborne Pb to green cabbage was more than 70%,and as high as 91.53%to broccoli.