| 其他摘要 | Mercury(Hg) is the only heavy metal elements that mainlyexist in the atmosphere as gaseous elemental forms. Gaseouselemental mercury is the main component of atmospheric mercury, about 90% of the total, having low water solubility and strong chemical inertness, and therefore it has a longer residence time in the atmosphere (1-2 years).Therefore，only gaseous elemental mercury is a global pollutant. A correct understanding for the atmospheric Hg sources is the key toCorrectlypreventing and controlling environmental pollution and formulating corresponding measures of reducing emissions. Atmospheric Hg sources mainly have two ways: one is the anthropogenic emissions of mercury to the atmosphere, the other is a natural process to the atmospheric Hg. In recent years, Chinese scientists have strengthened the human activities on the study of mercury pollution prevention and control, and government departments have introduced more environmental protection measures, and have taken more responsibility for the global mercury pollution. However, with the deep study on mercury pollution in the world constantly, scientists began to realize that we should pay high attention to mercury contribution of natural sources to atmospheric Hg emission while strengthening on the control of man-made activitiesemissionto the atmosphere. Compared with the artificial source, natural sources of atmospheric mercury is relatively more abundant, more complex influence factors, and therefore difficult to estimate its emission fluxes. The majority of the world's land surface is covered by vegetation. some scientists believe that the mercury emission fluxes of vegetation is an important source of atmospheric mercury, and also the other thinks, the vegetation may be atmospheric mercury sink. However, it is not clear now about the exchangeprocess and mechanismbetween vegetation and the atmosphere of mercury. Therefore, only by understanding the exchange mechanism and fluxbetween vegetation and the atmospheric mercury, can we correctly estimate the natural Hg flux of the surface to atmosphere. This study selected four typical crops, the largestplanting area in China, such as rice(Oryza.sativa L.), wheat (Triticum L.), maize (Zea mays L.) and rape (Brassica campestris L.) as the research objects, used the single and stable mercuryisotopetracertechnology, and X ray fluorescence technology (SR-XRF) and X - ray absorption technology (XANES), to researchtheexchange process and mechanism between atmospheric mercury and four kinds of crops.The main results of the thesis are as follows: 1、Abovegroundparts especially leaves of fourcrops that Maize, rice, rape and wheathas strong accumulation abilityon atmospheric mercury. But because of the different species of them, the abilities of accumulating atmospheric mercury were also distinct. All the same,four crops was the sink of atmospheric mercury . 2、Aftermercuryabsorptionfrom the atmosphere of four crops leaves, 73-95% of the mercury stays in the leaves, 3-22% transfer to the stemthrough internal transport, but only less than 5% of the mercury can be transferred to the root. This may be related to the mechanism of resistanceof crops. When the plants feel heavy metal stress, Hg may be binding with PCs to alleviate the harm of mercury on plants. 3、The mercury absorbed by corn, rice, wheat and rape can not release into the atmosphere.Therefore, the four crops are net sinks of atmospheric mercury. 4、TheXANES analysis shows that mercury existed in leave mainly as γ-(Glu-Cys)2-Ser complexesand black HgSforms after absorbed by leaves of rice, corn and wheat, so as to reduce the toxicity of mercury on the plant and enhance the resistance of plants to heavy metal stress . 5、TheSR-XRF analysis results show that in rice leaves, mercury is leaves after absorption, small part of the distribution in mesophyll tissue, and most of the mercury cloth in the vascular bundles, mainly concentrated in the xylem of vascular bund |
修改评论