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621.
622.
Selenium geochemistry of paddy soils in Yangtze River Delta 总被引:12,自引:0,他引:12
Selenium (Se) content both in total and bioavailable forms were very low (25-35 and 9.5 micrograms/kg, respectively) in waterlogged paddy soils in the central Yangtze River Delta. This was due to changes in geochemistry and the inherent properties of the parent materials of these lowland paddy soils. The very low Se content (23 micrograms/kg) in the parent material resulted in low total Se content in the soil. The main chemical changes under long-term waterlogged conditions are depletion of molecular oxygen, decrease of redox potential, and reduction of Fe (III) to Fe (II) and SeO3(2-) to Se0. This led to low availability of Se in soils, and subsequently low Se content (29 micrograms/kg) in brown rice grain produced in this region. It has been suspected that low Se content in staple food might be one of the major reasons for a high infection rate of the intestine and stomach cancers and the higher death rate caused by these diseases in the region. Foliage spray of Na2SeO3 at early heading stage of rice plant growth improved the Se content of brown rice grain, hull, and straw, and would improve human and animal health. 相似文献
623.
Accumulation features of organochlorine pesticides and heavy metals in fish from high mountain lakes and Lhasa River in the Tibetan Plateau 总被引:4,自引:0,他引:4
Organochlorine pesticides and heavy metals were analyzed in fish from remote mountain lakes and Lhasa River in Tibetan Plateau. Concentrations of summation operatorHCH, summation operatorDDT and HCB in fish muscles were in the range of 0.13-2.6 ng/g, 0.78-23 ng/g, 0.31-3.2 ng/g based on wet weight, respectively. Heavy metals were routinely found with different levels in fish. The Cu and Zn levels were relatively high with the maximum concentrations reaching 2.0 and 6.9 microg/g, respectively. Accumulation of OCPs and heavy metals are quite different in tissues and organs. Gill seems to accumulate more OCPs due to absorption by its larger surface per tissue. Heavy metal levels were generally high in liver, eggs and gill, and low in brain and muscle. Results from this study demonstrate that the Tibetan Plateau functions as a regional contaminant convergence zone by long-range atmospheric transport and orographic cold trapping. 相似文献
624.
云阳县生态危机的现状及其对策 总被引:5,自引:0,他引:5
为了改善生态环境,发展贫困地区经济,树立人与延期共同,协调发展观念,建立合理的农业结构和作物布局,详述了四川云阳县生态危机的现状和存在问题,提出了保护环境,发展立体农业的合理布局的建议。 相似文献
625.
Investigation of head injuries by reconstructions of real-world vehicle-versus-adult-pedestrian accidents 总被引:2,自引:0,他引:2
A sizeable proportion of adult pedestrians involved in vehicle-versus-pedestrian accidents suffer head injuries, some of which can lead to lifelong disability or even death. To understand head injury mechanisms, in-depth accident analyses and accident reconstructions were conducted. A total of 120 adult pedestrian accident cases from the GIDAS (German in-depth accident study) database were analyzed, from which 10 were selected for reconstruction. Accident reconstructions initially were performed using multi-body system (MBS) pedestrian and car models, so as to calculate head impact conditions, like head impact velocity, head position and head orientation. These impact conditions then were used to set the initial conditions in a simulation of a head striking a windshield, using finite element (FE) head and windshield models. The intracranial pressure and stress distributions of the FE head model were calculated and correlated with injury outcomes. Accident analysis revealed that the windshield and its surrounding frames were the main sources of head injury for adult pedestrians. Reconstruction results indicated that coup/contrecoup pressure, Von Mises and shear stress were important physical parameters to estimate brain injury risks. 相似文献
626.
627.
Waste incineration is a politically sensitive issue in the UK. The major current technology is based on direct combustion of wastes in a moving-grate furnace. However, general public opinion prefers non-direct burning technologies. Waste gasification is one of those nearest technologies available. By reducing the primary air-flow rate through the grate of a packed-bed system, operation of the existing solid-waste incineration equipment can be easily converted from combustion mode to gasification mode without major modification of the hardware. The potential advantages of this are lower dust carry-over in the flue gases, lower bed temperature (and therefore lower NO(x) formation in the bed), simplified gas-treatment procedures and lower running cost, among other benefits. The major disadvantages are, however, reduced throughput of the wastes and possibly higher carbon in the ash at exit. In this study, numerical simulation of both combustion and gasification of municipal solid wastes in a full-scale moving grate furnace is carried out employing advanced mathematical models. Burning characteristics, including burning rate, gas composition, temperature and burning efficiency as a function of operating parameters are investigated. Detailed comparisons between the combustion mode and gasification mode are made. The study helps to explore new incineration technology and optimise furnace operating conditions. 相似文献
628.
629.
研究Pb-Cd复合污染对5种树木叶片的生理伤害和La-Gly-VB6对Pb-Cd污染胁迫的缓解作用。实验结果表明,La-Gly-VB6能明显减轻Pb-Cd污染造成的植物叶片叶绿素含量下降、质膜透性增加,过氧化氢酶活性改变和Pb富集量上升。说明La-Gly-VB6对Pb-Cd污染胁迫具有一定的防护作用。 相似文献
630.
Wenjun Z 《Environmental monitoring and assessment》2007,125(1-3):301-312
Our world is largely dependent upon the forestry productions. Through the exploitation of forest reserves, we manufacture
various industrial products, furniture, and obtain fuel and energy. Forestry productions should be conducted without large-scale
deforestation and environmental degradation. In present study we perform a review and forecast analysis on forestry productions
worldwide, with the objectives of providing an insight into the trend for several types of forestry productions in the future,
and providing referential data for sustainable forestry productions and environmental management. Polynomial functions are
used to fit trajectories of forestry productions since 1961 and forecasts during the coming 20 years are given in detail.
If the past pattern continues, world fibreboard production would dramatically grow and reach 224,300,000 ± 44,400,000 m3 by the year 2020, an increase up to 240.7 to 408.9% as compared to the present level. Roundwood production of the world would
change by −55.5 to 70.4% and reach 3,526,600,000 ± 2,066,800,000 m3 by 2020. In 2020 world production of sawlogs and veneer logs would change by −100 to 164.6% and reach 1,212,900,000 ± 1,242,600,000 m3. Global wood fuel production would change by −68.9 to 1.4% and reach 1,130,900,000 ± 600,800,000 m3 by 2020. Forestry productions in developed countries would largely surpass productions in developing countries in the near
future. World forestry production grew since 1961 excluding wood fuel. Roundwood and wood fuel account for the critical proportions
in the forestry productions. Wood fuel production has being declined and rapid growing of roundwood production has slowed
in recent years. Widespread use of regenerative wood substitutes and worldwide afforestation against deforestation will be
among the most effective ways to reduce deforestation and environment degradation associated with forestry productions. 相似文献