The stability of trophic mass-balance models of marine ecosystems: a comparative analysis

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mass-balance marine trophic models are used to explore the stability of systems when briefly impacted by a fishery on the key ‘wasp–waist' populations occurring at intermediate trophic levels. The results are related to different ecosystem goal functions previously identified as representative of three attributes of ecosystems development: community complexity, homeostasis and energetics. System recovery time, the time required for all functional groups to returns to baseline level, and here used as a measure of model stability, was inversely correlated to Finn's Cycling Index, i.e. to the fraction of ecosystem throughput that is recycled, and to the mean length of trophic pathways in the systems. Systems with higher capacity to recycle detritus are systems with a higher ability to recover from perturbations. The results are in agreement with the E.P. Odum's theory of ecosystem development, where recycling is interpreted as a chief positive feedback mechanism that contributes to stability in the mature systems by preventing overshoots and destructive oscillations due to external impacts.     

异味混合物中组分浓度与其强度贡献关系研究

由挥发性有机污染物(VOCs)等引起的恶臭污染已经成为一个严重的环境问题,而污染物种类繁多,浓度差异大和物质间相互作用规律复杂等因素,对异味强度等感官评价研究造成极大困难.本研究针对室内环境,选取典型挥发性有机污染物组成多种异味混合物,6名专业嗅辨员组成嗅觉评价小组,分别评价异味混合物和相应各组分物质单独存在时的异味强度,分析混合物中各组分含量与混合物整体异味强度之间的联系.结果表明,当混合物中某物质异味活度(odor activity value,OAV)的自然对数值占混合物总量的比例小于20%时,其对混合物的异味强度贡献基本为零.利用该方法预先忽略多组分异味混合物中的部分物质,可以在异味物质相互作用规律和异味感官评价等研究中起到重要简化作用.     

Nerve conduction studies in sprayers occupationally exposed to mixture of pesticides in a mango plantation at Lucknow,North India

In this study, nerve conduction, organochlorine (OC) pesticide residues in blood and cholinesterase activity levels of pesticide sprayers employed in mango plantations at Lucknow, North India, were determined. Fifty-two sprayers from mango plantations who regularly spray mixture of pesticides like organophosphates (OP), OCs, and carbamates were considered as exposed group. Eighteen subjects with similar socio-economic status of exposed group, who do not handle pesticides, were selected as controls. Questionnaire-based interviews related to personal and occupational histories of the study subjects were carried out. Sprayers did not use any personal protective equipment during pesticide handling. The blood-pesticide analyses of sprayers show higher mean values of hexachlorohexane (HCH), γ-HCH, δ-HCH, total HCH, op-DDT compared with the controls. Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activites were significantly reduced among sprayers. Risk of motor nerve conduction deficits was observed in sprayers with low AChE activity. Negative correlation of motor and sensory nerve conduction deficits was observed with the duration of exposure and age among sprayers. The study demonstrated that the prolonged exposure to mixture of pesticides, ergonomic factors, decline in cholinesterase activity may lead to nerve conduction dysfunction. The findings suggest the need for controlled use of pesticides in the plantation and indicated the need for training and implementation of hygiene practices like proper usage of personal protective equipments.     

Pathways for the oxidation of sarin in urban atmospheres

The nerve agent sarin has recently been deployed by terrorists in a major city. The molecule is volatile and made its way to many victims by passing as vapor through a highly reactive medium. Here we estimate rates and pathways for the removal of gas phase sarin from a generalized urban atmosphere. Only information from the open scientific literature is used. By structure reactivity comparisons with the organophosphorus pesticides, hydroxyl radical hydrogen abstraction may occur in as little as one hour. Decomposition of side chains after hydroxyl attack leads to organic oxygenates which preserve the phosphonofluoridate and so toxicity. The aqueous aerosol surface is contacted in minutes and offers access to a range of dissolved nucleophiles. Substitution displaces the fluoride leaving group, giving safe phosphoric acid analogs. Because of uncertainties in the electron distribution and in aqueous decay mechanisms, the time constants must be viewed as lower limits.     

嗅觉标准液的人群测试

嗅觉标准液是可使人的嗅觉阈值测试标准化,科学化,数量化,应用嗅觉标准液对人群的嗅觉阈值测试,可以了解我国人群嗅觉状及特点,以便应用标准液筛选嗅觉试验员和鼻科临床无创伤检验等方面。     

城市污水处理厂恶臭挥发性有机物的感官定量评价研究

采用自制低温吸附装置和臭气袋采集了广州典型城市污水厂6个处理车间的空气样品.应用热解析/气相色谱-质谱联用仪分析恶臭挥发性有机物的组成和含量,参照国标的三点比较式臭袋法测量样品的恶臭浓度,并针对恶臭挥发性有机物进行感官定量评价.结果表明,①城市污水处理厂检测出烷烃、烯烃、芳香烃等7大类共70种挥发性有机物,其中30种属于恶臭挥发性有机物,它们的浓度范围为0.37～1 872.24μg.m-3,在污泥脱水、污泥浓缩和曝气池最高;②主成分分析可以将主要恶臭挥发性有机物分为苯系物、卤代烃、醛类、碳氢化合物和含氮、硫的挥发性有机物5类;③多元线性回归分析能建立化学浓度与恶臭感官浓度的定量表达式,计算出恶臭挥发性有机物对该厂恶臭气味的贡献率占25%,感官浓度的预测值和实测值拟合良好,建立的预测方程对污水处理车间低浓度恶臭挥发性有机物的敏感度高于人鼻嗅辨的敏感度.     

基于人工神经网络的地面水环境质量评价模型

针对确定水体类别比较困难这一问题 ,引入人工神经元网络理论和思想 ,通过建立基于 BP人工神经网络模型 ,对地面水体环境质量进行评价。     

Selective accumulation of chlorinated paraffins (C12 and C16) in the olfactory organ of rainbow trout

Three ¹⁴C-labelled polychloroalkanes (C₁₂ and C₁₆), representing low (23% Cl by weight), medium (51%), and highly (68%) chlorinated paraffin (CP) mixtures, were presented to rainbow trout via the water. The uptake in fat-rich tissues was positively correlated to the degree of chlorination of the preparations. Notably, all preparations gave rise to a high and selective uptake of radioactivity in the olfactory organ and gills. This selective radiolabelling may reflect a general ability of these organs to enrich xenobiotics from the surrounding water. The olfactory organ may be a hitherto unforseen target for toxic environmental pollutants in fish.     

Receptor neurones in three heliothine moths responding to floral nd inducible plant volatiles

Summary. Some plant volatiles are produced in response to herbivory of several insect species, including heliothine larvae. In the present study of female heliothine moths, four co-located receptor neurone types were identified, of which three types responded strongest to the inducible compounds E--ocimene, E,E--farnesene and E,E-TMTT, respectively. The fourth type responded strongest to geraniol, which is a common floral volatile. The narrow tuning of each receptor neurone type was demonstrated by responses to a few structurally-related monoterpenes, sesquiterpenes, homo-terpenes and monoterpene alcohols, respectively, out of hundreds of plant constituents tested. The four neurone types showed the same relation of spike amplitudes and ranking of effective compounds in the three heliothine species; the polyphagous Heliothis virescens and Helicoverpa armigera and the oligophagous Helicoverpa assulta. The results indicate the presence of functionally similar types of plant odour-receptor neurones in the three related species, and suggest conservation or reappearance of functionally similar olfactory receptors in related species, independent of the evolution of polyphagy and oligophagy.