Low level inhalation experiments with four different cadmium compounds in rats†

This long‐term inhalation study was designed to describe the toxicity and the carcinogenic risk from Cd compounds because it had been shown from former long‐term inhalation studies that cadmium choloride induced primary lung tumors in Wistar rats. It was therefore logical to examine whether other cadmium compounds to which human beings are more frequently exposed have also carcinogenic potency. In a long‐term inhalation study cadmium aerosols consisting of cadmium chloride (CdCl₂), cadmium oxide (CdO) as dusts and fumes, cadmium sulfate (CdSO₄), cadmium sulfide (CdS) and a combination of cadmium oxide/zinc oxide were used. Wistar rats were continuously exposed in inhalation chambers for 18 months 22 hrs a day or for 40 hrs a week. The studies will be terminated at the mean survival life time of the species. The aerosols were generated by several different systems. The particles of the cadmium aerosols have the average mass medium diameters in the range from 0.2 to 0.5 μm.     

Morphological and chemical characteristics of atmospheric particles in the Metropolitan Zone of Toluca Valley (Mexico)

Scanning electron microscopy with energy-dispersive spectroscopy has been used for both morphological and elemental chemistry analyses of atmospheric particles. This technique allows the in situ observation of individual aerosol particles in the sample chamber. Aerotransported particles were analysed from seven monitoring stations located in the Metropolitan Zone of Toluca Valley (MZTV). Several different morphologies were identified: aggregates, porous spheres, rough and smooth compact material. The elemental composition included C, Na, Mg, Al, Si, S, Cl, K, Mn, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn and Ce. These are semiquantitative analyses considering the bulk sample or individual particles. It was possible to correlate or confirm some chemical associations such as C–S, Ca–S–O and Si–Al–O, probably due to the presence of compounds derived from incomplete combustion, building tailing materials and aluminosilicates of cortical origin. Bioaerosols such as pollen, spores, brochosomes and diatoms were identified in the zone; all these types of particles have a natural origin too. Several types of suspended particles were identified in the MZTV, they were from different sources (natural and anthropogenic) to which the population can be potentially exposed, and may cause harm in the short- and long-term, according to their chemical element composition and size.     

云南地区中国种子植物特有属的研究

物种特有现象的研究具有重要的区系地理学和保护生物学意义。利用大尺度的植物物种分布信息,探讨了云南地区中国种子植物特有属的科、属组成,区系性质及其地理分布格局。结果表明,云南地区拥有中国种子植物特有属125属,分属于59科,共含种子植物246种,是中国种子植物特有属的重要分布地区之一。含特有属较多的科主要为菊科Compositae、苦苣苔科Gesnefiaceae、伞形科Umbelliferae、禾本科Gramineae和唇形科Labiatae。从各属所包含的物种数来看,单型属占主体地位。根据科的分布区类型构成,云南地区中国种子植物特有属主要起源于热带地区。从属的生活型构成来看,主要以草本植物属为主,而木本植物属所占比重相对较小,暗示着研究区域内特有属的区系兼有年轻成分和古老成分,但以年轻成分为主。从空间分布格局来看,特有属主要分布在“田中线”以东地区。与过去的研究结果不同,我们发现云南地区拥有3个重要的特有属分布中心和3个次级分布中心。     

长期施肥对旱地土壤杂草种子库生物多样性影响的研究

为探讨长期施肥对旱地土壤杂草种子库生物多样性的影响,我们在安徽蒙城地区的一个长期肥料试验定位监测点开展了相关研究。采用镜检法对旱地土壤表层（0～15 cm）中土壤杂草种子的种类进行鉴定并计数,记录杂草种子22种,隶属15科。不同施肥处理区杂草种子丰富度以NP1/2K区最高（14.7种）,PK区最低（10.7种）;其中陌上菜（Lindernia procumbens）、栗米草（Mollugo pentaphylla）、醴肠（Eclipta prostrata）、泽星宿菜（Lysimachia candida lindl）四种杂草的种子密度较大,分别在不同的处理区占据优势;从整个试验区来看,烟台飘拂草（Fimbristylis stauntoni）在所有处理中的密度都比较大,处于优势地位。长期不同施肥方式下,农田土壤杂草种子库的物种多样性有显著差异：PK区Shanon-Wiener指数大于其他处理区,但是Simpson优势度指数最低;NPK区Simpson优势度指数最高;PK、CK区Pielou均匀度指数大于其他处理区。田间杂草种子库的群落结构及其物种组成也发生了一定的变化,Whittaker指数表明,与不施肥处理相比较,半量的P和缺N的影响最显著,缺P次之,缺K和平衡施肥则没有显著影响。Sorenson群落相似性指数和Bray Curtis指数聚类分析结果表明,与不施肥相比较,长期施用N、P、K肥能显著改变旱地土壤杂草种子库的组成。本研究表明长期平衡施肥处理更有利于维持和保护旱地土壤杂草种子库的生物多样性。     

3种硝化抑制剂对小麦幼苗生长毒性的比较

在土壤(山西土)中加入不同种类、不同浓度的硝化抑制剂(氢醌、硫脲、双氰胺),研究了其对小麦发芽势、发芽率和幼苗生长的影响.结果表明:双氰胺对小麦发芽势和发芽率的抑制作用不明显,硫脲对小麦发芽势和发芽率有一定的抑制作用,而氢醌对小麦发芽势和发芽率抑制明显;双氰胺和氢醌对小麦幼苗生长的影响不大,而硫脲能显著降低小麦幼苗的根长、茎长、根重和茎重;双氰胺对小麦种子和幼苗毒性相对较小,硫脲毒性相对较大,小麦的根重、茎重和根伸长可以作为硫脲对小麦危害的敏感指标.     

The need to look beyond the production and provision of relief seed: experiences from southern Sudan

Free distribution of seeds in selected areas of southern Sudan has been widespread as a way of increasing food security. Field research in areas targeted for seed relief found that farmer seed systems continue to meet the crop and varietal needs of farmers even following the 1998 famine. Donor investments in seed multiplication of improved sorghum have not been sustained due to a lack of effective demand for the improved seed beyond that created by the relief agencies. The article argues that rather than imposing outside solutions, whether through seed provisioning or seed production enterprises, greater attention needs to be given to building on the strengths of existing farmer systems and designing interventions to alleviate the weaknesses. The case is made to support dynamically the process of farmer experimentation through the informed introduction of new crops and varieties that can potentially reinforce the strength and diversity of local cropping systems.     

The role of research institutions in seed-related disaster relief: Seeds of Hope experiences in Rwanda

The article describes the efforts of a coalition of agricultural research centres, Seeds of Hope (SOH) in the rebuilding, of Rwanda, after the genocide and war of 1994. Research involvement in emergency relief and rehabilitation was unusual at the time and SOH had to forge its unique complementary role. Focusing on crop and variety development and conservation it: provided technical advice to relief agencies on seed procurement; used its baseline ken to assess the effects of war on seed diversity and seed security; made preparations to restore specific germplasm (which, fortunately, proved unnecessary) and spent substantial effort on rebuilding human resource capacity in research as well as basic scientific facilities. The involvement of SOH highlighted the critical, yet very different, roles for research during emergency versus rehabilitation periods and demonstrated the cost effectiveness of building in a diagnostic component--before massive seed or germplasm distributions are programmed.     

Disasters and development in agricultural input markets: bean seed markets in Honduras after Hurricane Mitch

The bulk of developing countries' populations and poor depend on agriculture for food and income. While rural economies and people are generally the most severely affected by natural disasters, little is known about how disasters and subsequent relief activities affect agricultural markets with differing levels of development. The article addresses this gap, drawing evidence from bean seed markets in Honduras after Hurricane Mitch. Case studies are used to address hypotheses about a disaster's effects on supply and demand in seed markets, farmers' responses and the performance of relief interventions in markets showing differing levels of development. The results show the importance of tailoring relief interventions to the markets that they will affect and to the specific effects of a disaster; the potential to use local and emerging seed distribution channels in a relief intervention; and opportunities for relief activities to strengthen community seed systems.     

Modelling of Air Quality with CAMx: A Case Study in Switzerland

The three-dimensional Eulerian model CAMx (Comprehensive Air QualityModel with Extensions) was applied for the first time to simulate bothgaseous and particulate photochemical air pollution in Switzerland during July 28–30, 1993. The meteorological input data were prepared using the Systems Applications International Mesoscale Model (SAIMM). The CAMx model results were compared with the measurements carried out at ground level andfrom airborne measuring platforms within the frame of the Swiss POLLUMET research programme. In general, the CAMx performance for gaseous species wasfound to be better than that of the previously used Urban Airshed Model (UAM)and the Variable Grid Urban Airshed Model (UAM-V). The most significant improvement for the gaseous species is in the prediction of HNO₃ concentrations, due to the inclusion of aerosol chemistry. Aerosol species such as NO₃ ^-, NH₄ ⁺, SO₄ ^2-, and secondary organic aerosols were calculated in one particle size range (0.04–2.5 m) and compared with a few measurements available. Although July 29 was reasonably well simulated, overestimated wind speeds by SAIMM for July 30 caused a too fast transport of pollutants. Similarly to measurements, significant spatial correlation of the secondarily formed aerosols with ozone and formaldehyde is found in the afternoon.     

On the Size Dependence of Particle Deposition

Measurements of dry deposition ofparticles 0.1 to 1.0 m diameter to forest bythroughfall and eddy correlation methods giveresults of 1.0 cm s^-1 or more, whilemechanistic models do not explain values greaterthan about 1 mm s^-1. Results of othermethods involving radioactive tracers arerecalled. These data indicate values of about 5 mm s^-1. The possibility of additionalmechanisms, omitted from the models, is difficultto exclude, but much of the remaining discrepancymay be due to the wide size distribution of theadventitious radioactive tracers in the atmosphere.