| In this paper, the assessment on the situation of ecogeochemical environment for major pollution elements in Pearl River Delta as the research area is done by application of systems theory and chemical kinetics theory, under the guidance of regional geochemistry theory; On the basis of acid rain eluviation test, forecasting and warning are made for ecoenvironmental quality of Pearl River Delta in the approximately-natural means; Based on the investigation of contents of available substances in main soil types, the quality status of agro-nutrients in the soils of Pearl River Delta is systematically assessed. Detailed research techniques are: On the basis of systemic regional soil geochemical survey with top soils and deep soils, characteristics of spatial distribution, allocation and combination are investigated for regional elements, and point-to-plane method is used to carry out the environmental (including radioactive environmental) and agro-geochemical investigation in key typical zones, and to investigate the features of allocation, distribution, transfer and collection of key elements in various mediums (soil, water and plant), and to further summarize and study the features of regional geological circulation and ecological circulation of key elements, and to conduct quality assessment of regional environment and agricultural soils. Main achievements are described as follows:1. Environmental pollution of Pearl River Delta is serious, and geochemical quality of regional environment is bad.(1) In the plain area (Distributive area of Quaternary transitional sediments) , there is a large regionally distributed Level-3 Cd-polluted soil (according to Environmental quality standard for soils of PRC) and medium F-polluted area (according to the standard specified by the project), and in the city and its surrounding districts and some planting (breeding) area, there is a large Level-3 Hg- and As-polluted soil and an area with high geochemical backgrounds of Cu, Pb and Zn, but there is a large geochemical anomaly district with high contents of U and Th in low-relief terrains and hilly areas. The distribution of contaminated soil (Level 2 minimum) in Pearl River Delta not only is controlled by geological and geochemical background, but also has close relationship with human activities, and the pollution intensity of city and surrounding districts and planting areas is obviously strengthened. Besides reflecting the situation of geological and geochemical environment, contaminated area is also superimposed with pollution caused by human activities, which not only intensify the pollution intensity, but also enlarge the scope of pollution. The main pollution in Pearl River Delta is involved in Cd, F, Hg, U and Th, among them, Cd, F, U and Th pollution is mainly led by geological action, and their pollution depths are in accordance with the thickness of rich geologic body; Hg pollution is caused by economic activities of human, arising from human factors; The pollution depth is mostly 0~80cm, while that will reach below 2m in Huangpu District of Guangzhou City and Nanzhuang of Foshan City.(2) For contaminated areas caused by different genetic types, there is obvious difference in the chemical speciation of different pollution elements. For the pollution caused by geological setting, distribution of pollution elements in various existing forms is homogenous; While for the pollution caused by human, pollution element is mainly combinedto one certain chemical speciation. Cd content is relatively large in sulfides, and its content is secondly large in iron-manganese's oxides, organic compounds, while there is relatively low Cd content in ion exchangeable and water soluble. Hg is mostly combined to sulfides, but hardly exists in other four phases.(3) On the vertical section, the section adjacent to groundwater level is the part where geochemical environment rapidly changes, and there is a large proportion of water soluble.The highest ratio of Cd content in water soluble to its total is found in the middle layer of the groundwater level, and the ratio is secondly larger in the ground surface, and the lowest ratio is achieved in deep seat. Cd content is mostly 7-13ng/g in aqueous phases of ground surface (with a content ratio of 1.2-2.4% ), 10-20 ng / g in the middle (with a content ratio of 2-3%), and 3-10 ng / g on the bottom (with a content ratio of 0.5-1.5%) .The Cd content of water soluble in soils will be increased with the increase of total, however, when it is increased to one certain degree (reaching balanced state), it will be maintained at the level of balance, although the total is still increased, and on the present conditions of water soluble in soils of investigated area, the absorption point is 13ng / g.F content of water soluble and the ratio of it to total do not vary greatly from ground surface to deep seat. F content is mostly 4—6 ng / g in water soluble of ground surface (with a content ratio of 0.4—0.7 % ), 3—5 ng / g in the middle (with a content ratio of 0.3—0.65 % )> and 3—5.5 ng / g on the bottom (with a content ratio of 0.40—0.7% ) . There is a complex relationship between total F content in soils and water soluble, with bad linear relation, and in whole, there is a trend of rise for F content in water soluble when the total is increased, but the amplitude is small.The highest ratio of Hg content in water soluble to its total is found in the middle layer of the groundwater level, and the ratio is secondly larger in the ground surface, and the lowest ratio is achieved in deep seat. Hg content is mostly 1.5—3 ng / g in water soluble of ground surface (with a content ratio of 1.4—2.5 %), 2.5—4.5 ng / g in the middle (with a content ratio of 2—4 % ), and 1.2—2.5 ng / g on the bottom (with a content ratio of 1.2—2.5 %) .(4) In the area polluted by Hg, there are many sulfide minerals of Hg—cinnabar. The cinnabar is well-crystallized, mostly looking like scarlet edge angle, and results of electron probe analysis and Raman spectrum analysis further confirm the presence of cinnabar. There is a good corresponding relationship between the occurring positions in plains or sections and Hg pollution intensity or pollution layers, indicating that there is necessary relationship between them in the aspect of genesis. These cinnabars occur in the areas of alluvial plain, and it is hard to create genetic relation between these cinnabars and those hydrothermal cinnabars, therefore, its genesis and the relationship between the genesis and Hg pollution of soils are deeply discussed, which will have a vital impact on environmental geochemical research thoughts and methods, especially, the information of agro-geological investigation conducted in plain areas at present will have direct significance when it is utilized in environmental quality assessment, and significant progress may be achieved in the above mentioned field when systematical research is carried out on the basis of the discovery.(5) There is a more obvious relation between elements content in active phases and the content of plants in the soil. Compared with requirements of limits in food hygienic standard, F is higher than the limit of food hygienic standard for crops, Cd is approximate to the limit of food hygienic standard for crops; Hg is less than the limit of food hygienic standard for crops.It has the possibility for contents of F and Cd in crops to exceed the limits of food hygienic standard. In the ground soil of Pearl River Delta, Cd content in active phases is highest, and F content is secondly larger, and Hg content is lowest.(6) In the Distributive area of Quaternary transitiomal sediments of Pearl River Delta (plain area) where crops cannot satisfy the requirements of limits in food hygienic standard, the highest abnormal index ratios are obtained from F (54 samples, abnormal index ratio=61.36%)and Cd (39 samples, abnormal index ratio=44.32%) , and then Pb ranks secondly (16 samples, abnormal index ratio=18.18%).I preliminarily think that there is no obvious linear relation between soil element content or bioavailability and the content in crops, but with statistical significance, in the districts with high-content elements in soil, the abnormal index ratio is relatively high. Ecological effects caused by element pollution arising from geological factors should be paid more attention.(7) Ecological effects of pollution caused by toxic and hazardous elements in soils of Pearl River Delta are remarkable, and besides the impacts on quality of agricultural products, they also influence the health of humans. Results of investigation show that Cd content of soils is remarkably pertinent to its content in hairs of humans, so toxic and hazardous elements in soils directly influence the human body.(8) Through the research of the relationship between the total in soils,the portion in water soluble, and their contents in vegetables, and according to the requirements of limits in food hygienic standard, on the current environmental conditions of soils, critical Cd content in water soluble should be 12 ng / g, and its critical total content in soils should be 270ng / g; critical F content in water soluble should be 4.5 μ g / g, and its critical total content in soils should be 400 μ g / g.(9) Direct influence of Hg pollution on eco-environment is the formation of mercury gas in soils. There is a close relation between the concentration of mercury gas and Hg content in soils, soil temperature, and it will rise with the increment of both Hg content in soils and soil temperature. The thermal release temperature of Hg in soils is primarily 200℃—300℃.(10) In the investigated area of Pearl River Delta, radioactive anomaly belt often occurs in the geochemical anomaly zone with high contents of U and Th in soils, and specific activity of radioactive species in the zone remarkably violates the requirements of radioactive hygienic control standard for construction materials. The information of radioactive anomaly of U and Th in the zone may be used to assess the quality of radioactive environment.2. On the basis of acid rain eluviation test, forecasting and warning are made for the pollution and harm of Pearl River Delta in the approximately-natural means. There is the remarkable difference with equivalent tests at home and abroad in the treatment of soil column, more approximate to the natural status. Test results show that acid rains have a remarkable impact on ecogeochemical environment quality of Pearl River Delta. On the one hand, acid rain may lead to great loss of cation in solis, and reduce the buffer capacity of soils for acid rain and self-cleaning ability for toxic and hazardous elements; on the other hand, it destroys various balances of chemical speciation of toxic and hazardous elements in soils, leading to the transformation of elements existing in a stable chemical speciation into the unstable phase to be absorbed by plants, which can do more serious harm to the production of plants.3. On the basis of investigating results of effective phases in main soil types, the qualityassessment of nutrients and beneficial elements in plants of Pearl River Delta is systematically conducted. Pearl River Delta is rich in agricultural nutrients and beneficial elements. The effective quantities of N, P and K are primarily moderate~abundant, and effective quantities of beneficial elements such as Fe, Mn, Cu, Zn and Mo are mainly "very abundant", while B content is primarily "moderate", however, Ca is widely "relatively absent". Cu and Zn are not only beneficial elements in soils, but also heavy metal elements mainly monitored for environmental quality of soils, and due to their excessive contents, they have become pollution elements.
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