Transport of engineered antibiotic resistance plasmids in porous media has been reported to potentially cause significant spreading of antibiotic resistance in the environment. In this work, transport of an indigenous resistance plasmid pK5 in porous media was investigated through packed column experiments. At identical ionic strengths in CaCl2 solutions, the breakthroughs of pK5 from soil columns were very close to those from quartz sand columns, indicating that transport of pK5 in quartz sand and soil was similar. A similarity in transport behavior was also found between pK5 and an engineered plasmid pBR322 that has approximately the same number of base pairs as pK5. The influence of surfactants, a major group of constituents in soil solutions, was examined using an engineered plasmid pcDNA3.1(+)/myc-His A. The impact of an anionic surfactant, sodium dodecyl sulfate (SDS), was negligible at concentrations up to 200 mg·L–1. Cetyltrimethyl ammonium bromide (CTAB), a cationic surfactant, was found to significantly enhance plasmid adsorption at high concentrations. However, at environmentally relevant concentrations (<1 mg·L–1), the effect of this surfactant was also minimal. The negligible impact of surfactants and the similarity between the transport of engineered and indigenous plasmids indicate that under environmentally relevant conditions, indigenous plasmids in soil also have the potential to transport over long distances and lead to the spreading of antibiotic resistance.
A disaster referred to by the press as the ‘UK flooding crisis’ occurred between December 2015 and January 2016. This study employed three different levels of analysis to identify a multidimensional perspective adopted in the disaster reporting of the British Broadcasting Corporation (BBC). These levels revealed details about the social actors and their interactions. The set of news exposed diverse viewpoints on the crisis, from loss and damage to distinct affected subgroups to the various social engagement actions of aid and the multiplicity of technical response measures. The conclusions highlight considerable social amplitude in the BBC's coverage; however, owing to the reductionist approach of this media communicator, the field of action involving different social actors was not very clear in the content of the news, particularly with regard to cohesion, conflict/obstruction, and concernthe concept of crisis in its essence. In addition, the paper suggests new questions for future reports. 1 相似文献
South Asia is one of the regions of the world most vulnerable to natural disasters. Although news media analyses of disasters have been conducted frequently in various settings globally, there is little research on populous South Asia. This paper begins to fill this gap by evaluating local and foreign news media coverage of the earthquake in Nepal on 25 April 2015. It broadens the examination of news media coverage of disaster response beyond traditional framing theory, utilising community capitals (built, cultural, financial, human, natural, political, and social) lens to perform a thematic content analysis of 405 news items. Overall, financial and natural capital received the most and the least emphasis respectively. Statistically significant differences between local and foreign news media were detected vis‐à‐vis built, financial, and political capital. The paper concludes with a discussion of the social utility of news media analysis using the community capitals framework to inform disaster resilience. 相似文献
The estimation of humidity in the unsaturated zone of soils and NAPL saturation in contaminated aquifers may be based on the interpretation of electrical resistivity index logs. In the present work, concepts of the theory of the two-phase flow in pore networks are employed to interpret the form of the equilibrium and dynamic resistivity index curves of large porous samples. A resistivity cell is constructed to measure the capillary and electrical properties of large samples of unconsolidated porous media. The drainage capillary pressure and resistivity index curves of a sand column are measured by using the micropore membrane (porous plate) method, where a 0.5% wt/vol NaCl aqueous solution is displaced by n-dodecane. The dynamic resistivity index curves are measured by using the continuous injection technique for various orientations of the sand column. Based on concepts of the two-phase flow theory, concerning the dominant displacement growth pattern in a pore network and arising from the cooperative effects of capillary, buoyancy, and viscous forces, approximate relationships are developed for the resistivity index and saturation exponent as functions of the water saturation. The saturation exponent decreases as the displacement advances and the fluid distribution across the sand column tends to be homogenized after oil breakthrough. Both the resistivity index and saturation exponent increase as the displacement pattern tends to become compact and stable. In the destabilized flow pattern, as the Bond number decreases, the resistivity index may increase respectably within a narrow range of values of the Bond number. This happens when the thickness of the unstable capillary finger exceeds the lateral dimension of the porous sample and becomes a fractal percolation cluster. The saturation exponent becomes almost constant and independent of water saturation only over the destabilized displacement pattern at high values of the Bond number. 相似文献
The background of this work is the international decision process with regard to the selection of chemicals to be assessed with priority. In order to stress the precautionary principle, mass flows were analysed rather than concentrations, threshold values, etc., as preferred by the chemical legislation (which still excludes the marine area). Lindane, hexachlorobenzene (HCB), trichloroacetic acid and its sodium salt, medium-chained chlorinated paraffins and tributyltin (TBT) were selected due to their great relevance for the marine area. Trichloroacetic acid is an interesting model compound on account of its accidental formation by degradation of volatile chlorinated hydrocarbons and during chlorination processes. In addition, a hypothetical compound was modelled, representing a highly water-soluble substance with low vapour pressure. The balancing area is the Baltic Sea and its catchment area. In order to model the substance flows, the 'Input/Output-load model' has been developed. The model quantifies the shift and the distribution of a yearly load of the substance investigated from the terrestrial-limnic into the marine compartment (Baltic Sea). Water-soluble substances, which are usually considered to be of no concern, may enter the sea in great amounts and, if not degradable, remain there. It turned out to be necessary to take into account remobilisation, unintended formation and point as well as line-sources. 相似文献
Biologically active carbon (BAC) system was set up in a water plant of South China during January to December 2007,to study the invertebrate community characteristics of BAC filter.Thirty-seven invertebrate species were found,of which 28 belonging to rotifers.Filter operation could lead to an output of invertebrates in high abundances with the filtrate,and the maximum density could reach 5608 individuals/m 3.Average abundances in the effluent water increased in 27-33 folds in comparison to the influent water during the sampling period.Invertebrate community succession had the following trend:filter-feeding animals → small benthic invertebrates → large benthic and resistant invertebrates.Abundances of large-sized invertebrates (copepod adult and oligochaete) at bigger-media column were significantly higher than that at small-media column.The results implied the abundant species diversity of invertebrate in BAC filter.The relationship between invertebrate and biofilm still remain to be studied in detail. 相似文献