Application of an enzyme-linked immunosorbent assay for the detection of clenbuterol residues in swine urine and feeds

The present study outlines applications of an enzyme-linked immunosorbent assay (ELISA) for the analysis of clenbuterol residues. Antisera were raised from rabbits immunized with diazotized clenbuterol-bovine serum albumin (BSA) conjugate. The assay was specific to clenbuterol with a half-maximum inhibition concentration (IC₅₀) of 1.8 ng/mL and 2.5 ng/mL in blank swine urine and phosphate buffer solution, respectively. The assay had high cross-reactivity (86%) with mabuterol, but low with other adrenergic agonists and antagonists. The average recovery of clenbuterol, as measured with the ELISA, ranged from 90% to 112% in swine urine samples and from 86% to 95% in feeds, respectively. This new assay was compared with commercial ELISA test kits. An excellent correlation (r ² = 0.98) between the two methods and satisfactory recoveries suggest that the new assay can be suitable for the determination of clenbuterol residues in real samples. The assay was used to analyze clenbuterol residues in 103 swine urine samples and 68 feed samples collected from northern China. Approximately 50% of the urine samples and 25% of the feed samples analyzed were found positive (concentration of clenbuterol ≥ 1 ppb). The results indicate that clenbuterol was misused in some of the areas surveyed.     

Production of the monoclonal antibody against tylosin for immunoassay of macrolide antibiotics in milk

The objective of the present study was to develop an immunoassay for multi-determination of the residues of four macrolide antibiotics in milk. Tylosin was derivatized with 6-aminohexanoic acid to synthesize a hapten that was used to produce the monoclonal antibody. The obtained monoclonal antibody simultaneously recognized tylosin, acetylisovaleryltylosin, tilmicosin and desmycosin with crossreactivities of 100%, 91%, 49% and 76%, respectively. Then an indirect competitive immunoassay was developed to determine the four analytes in milk simultaneously. The limits of detection for the four analytes were in the range of 5.5–11.7 ng/mL depending on the compound. The recoveries of the four analytes from fortified blank milk were in the range of 78%–96% with coefficients of variation lower than 11.4%. The developed immunoassay could be used as a practical tool for rapid screening the residues of the four anlytes in milk.     

Investigation of the positive artifact formation during sampling semi-volatile aerosol using wet denuders

Wet denuders are used in several steam-based semi-continuous aerosol monitors to avoid gaseous absorption artifacts and pre-humidify the air stream, while simultaneously allowing measurements of water-soluble gaseous species. Unlike dry denuders, wet denuders saturate the sample air stream with water vapor, which can lead to re-partitioning of water-soluble volatile species to the aerosol phase, thereby causing a positive artifact in aerosol measurements. This paper investigates the magnitude of the positive artifact formation occurring in wet denuders using modeling techniques. Gaseous nitric acid was used as an example of volatile water-soluble gas in both flat and annular wet denuders. We have also verified the occurrence of the positive artifact in a flat wet denuder through a laboratory experiment. The model results indicate that the magnitude of the artifact is rather limited under typical conditions being less than 2.5% of ambient nitric acid concentration for the flat denuder and less than 0.6% for the annular denuder. The magnitude of the artifact increases with condensational sink of the aerosol (i.e. with the mean aerosol size and number concentration) and aerosol water solubility. While the artifact is relatively small in the absolute sense, it could be substantial for aerosol nitrate measurements, especially in ammonia limited conditions, when the concentration of the nitric acid is high and the concentration of nitrate is low. Therefore, we recommend that the artifact is assessed regularly by replacing the wet denuder with a dry denuder.     

我国矿山生态环境保护法律制度完善问题研究

在资源主导型的经济发展模式下,矿产资源无疑是我国经济社会发展的重要支柱.但矿业是高污染行业,特别是近年来我国矿产资源持续大规模的勘探开采,引起了一系列严重的矿山环境问题,矿山生态环境急剧恶化,其影响已涉及经济社会发展的方方面面,因此加强和完善我国矿山生态环境制度建设至关重要.文章首先介绍了我国矿山环境恢复机制的现行制度框架,在此框架的基础上,对我国矿山环境状况恶化的现实进行了深层次的原因分析,剖析了目前我国针对矿山环境问题的意识、立法执法、资金技术的现实状况.接下来,对我国矿山生态环境恢复治理机制进行了宏观构建.笔者认为,要从三个方面对我国的矿山生态环境恢复机制进行构建.首先是调整矿山生态环境保护法律制度;第二,完善矿山环境保护机制;第三,建立矿山企业自身环保机制.     

贫困地区可持续发展指标体系及其综合评估--以湖南湘西贫困地区为例

本文依据贫困地区可持续发展固有的制约因素，特殊的内涵与目标，首次利用压力（Pressure)——状态（State)——响应（Respons)模型，构建了贫困地区可持续发展指标体系，并采用专家咨询与定量模型相结合的方法，对湖南湘西贫困地区可持续发展水平作了实证评估与分析。     

Different mechanisms of extinction of conditioned taste aversion are dependent on time intervals of extinction following conditioning

After extinction, the reappearance of a conditioned response induced by an unconditioned stimulus which is weaker than that used during the conditioning training indicates that the extinction procedure does not eliminate the original conditioned memory. Recent studies on fear conditioning have shown that rats exhibited little or no recovery of conditioned responding if the time interval between fear acquisition and extinction was short, suggesting that the extinction process may erase the original conditioning trace in this situation. In the present study, a saving experiment was conducted in rats to investigate whether an aversive response could be recovered following extinction training with different time intervals after acquisition of conditioned taste aversion (CTA). Male Long–Evans rats developed CTA by associating a 0.2% sucrose solution with malaise induced by intraperitoneal injection of 4 ml/kg 0.15 M LiCl and were subjected to extinction training with an interval of 5 h (5H group) or 24 h (24H group) after acquisition of CTA. Rats in the 5H group, but not in the 24H group, exhibited no aversive responding to the sucrose solution followed by the injection of a lower dose of LiCl (1 ml/kg). These findings indicate that the extinction procedure administered at different time points following the acquisition of CTA affects recovery of extinguished aversive memory and suggest that an unlearning process may be involved in the mechanisms of CTA extinction with short intervals between acquisition and extinction.     

Communities of different plant diversity respond similarly to drought stress: experimental evidence from field non-weeded and greenhouse conditions

Accelerating rate of species loss has prompted researchers to study the role of species diversity in processes that control ecosystem functioning. Although negative impact of species loss has been documented, the evidence concerning its impact on ecosystem stability is still limited. Here, we studied the effects of declining species and functional diversity on plant community responses to drought in the field (open to weed colonization) and greenhouse conditions. Both species and functional diversity positively affected the average yields of field communities. However, this pattern was similar in both drought-stressed and control plots. No effect of diversity on community resistance, biomass recovery after drought and resilience was found because drought reduced biomass production similarly at each level of diversity by approximately 30?%. The use of dissimilarity (characterized by Euclidean distance) revealed higher variation under changing environments (drought-stressed vs. control) in more diverse communities compared to less species-rich assemblages. In the greenhouse experiment, the effect of species diversity affected community resistance, indicating that more diverse communities suffered more from drought than species-poor ones. We conclude that our study did not support the insurance hypothesis (stability properties of a community should increase with species richness) because species diversity had an equivocal effect on ecosystem resistance and resilience in an environment held under non-weeded practice, regardless of the positive relationship between sown species diversity and community biomass production. More species-rich communities were less resistant against drought-stressed conditions than species-poor ones grown in greenhouse conditions.     

长江三角洲城市旅游与城市发展协调性及影响因素

城市旅游业作为城市服务业的重要部门,是推动城市发展的后续动力。运用信息熵赋权法和TOPSIS法相结合,从经济水平、社会发展、公共交通、城市绿化、环境保护、旅游发展6个方面对长江三角洲2003年和2008年的城市旅游与城市发展的协调性进行分析,借助ArcGIS软件的空间聚类法分析了城市旅游与城市发展协调水平的空间格局及演变,最后探讨影响因素。结果表明:长江三角洲16城市的城市旅游协调水平在研究期间相对稳定,具体可被划分为4个等级,第一、二等级城市数量较少,得分显著高于第三、四等级城市。城市旅游协调水平空间上存在较大差异,北部城市得分高于南部城市,基本格局保持稳定,呈现以上海、南京、杭州三个城市为核心向外围边缘城市的空间衰减。产业发展、城市旅游发展模式、城市旅游重大项目投资、区位条件是长江三角洲城市旅游协调水平产生空间分化的主要影响因素,可制定以城市旅游发展为手段的方式推动城市发展,促进区域均衡发展。