The “Short Cut” Approach for the Reality of Enhanced Groundwater Contamination

Based on the reality of (a) soil heterogeneity in the vadose zone, (b) enhanced desorption from soil and solubility in water of water insoluble contaminants in the presence of surfactants, and (c) wetting/drying cycles of groundwater recharge (a major cause of fractures formation), a coherent “short-cut” conceptual approach is advanced to account for enhanced groundwater contamination. This is an attempt to close the gap between theory, lab simulations and conventional modelling-based predictions, and observed higher concentrations and more rapid arrival times of contaminants reaching groundwater. Recent data concerning chloride ion and non-ionic surfactants concentrations in aquifers and groundwater wells, combined with previous results concerning the concentrations of tritium, chlorides, metals, organic hydrocarbons and surfactants in the unsaturated and saturated zones of Israel's aquifers, are accounted for in terms of the “short-cut” approach. The contradiction between predictions of groundwater contamination made with conventional, deterministic, homogeneous models and the actual observed behavior of contaminants in soils and aquifers is thus explaind. The “short cut” approach should not be perceived as a better type of model to guide modelling. Rather, it is a proposal for a conceptual change from the realistically invalid, but commonly accepted, conventional “buffer-protective soil/long-term groundwater contamination” to the “short cut” conceptual model to explain the enhanced groundwater contamination actually observed. Although the validity of the proposed approach is strongly supported by the data here presented for the case of Israel (serving as an illustrative case study), selected results and conclusions drawn from studies conducted worldwide suggest its general applicability and usefulness. A major conclusion evolved from the “short-cut” conceptual model is that contemporary groundwater management policies, based on the current perception of groundwater contamination processes and their modelling, may result in an irreversible detrimental effect on the environmental situation in the long run. In any case, prevention, rather than correction/remediation, is strongly recommended as the strategy of choice for rational long-term management of groundwater resources.     

Relationship between electrogenic performance and physiological change of four wetland plants in constructed wetland-microbial fuel cells during non-growing seasons

To find suitable wetland plants for constructed wetland-microbial fuel cells(CW-MFCs),four commonly used wetland plants, including Canna indica, Cyperus alternifolius L., Acorus calamus, and Arundo donax, were investigated for their electrogenic performance and physiological changes during non-growing seasons. The maximum power output of12.82 mW/m~2 was achieved in the A. donax CW-MFC only when root exudates were being released. The results also showed that use of an additional carbon source could remarkably improve the performance of electricity generation in the C. indica and A. donax CW-MFCs at relatively low temperatures(2–15°C). However, A. calamus withered before the end of the experiment, whereas the other three plants survived the winter safely, although their relative growth rate values and the maximum quantum yield of PSII(Fv/Fm) significantly declined, and free proline and malondialdehyde significantly accumulated in their leaves.On the basis of correlation analysis, temperature had a greater effect on plant physiology than voltage. The results offer a valuable reference for plant selection for CW-MFCs.     

MODELED IMPACTS OF DEVELOPMENT TYPE ON RUNOFF VOLUME AND INFILTRATION PERFORMANCE1

ABSTRACT: Development type has emerged as an important focal point for addressing a wide range of social, cultural, and environmental concerns related to urban growth. Low impact development techniques that rely heavily on infiltration practices are increasingly being used to manage storm water. In this study, four development types (conventional curvilinear, urban cluster, coving, and new urbanism) were modeled both with and without infiltration practices to determine their relative effects on urban runoff. Modeling was performed with a modified version of the Natural Resources Conservation Service (NRCS) runoff method that enables evaluation of infiltration practices. Model results indicate that urban cluster developments produce the smallest volume of runoff due to the large portion of land kept in a natural condition. Infiltration practices are most effective for small storms and in developments with Hydrologic Group A soils. Significant reductions in runoff can be achieved in all four development types if infiltration practices treat many impervious surfaces. As more infiltration practices are implemented, the differences in runoff among development types diminish. With a strategic combination of site layout and infiltration design, any development type can reduce hydrologic impacts, allowing developers to consider other factors, such as convenience, marketability, community needs, and aesthetics.     

PCM thermal conductivity effect on mechanism of PV/PCM thermal control characteristics

ABSTRACT

According to the structure of photovoltaic/phase change material (PV/PCM), the mechanism of internal heat transfer, transmission, storage, and temperature control is analyzed, and a two-dimensional finite element analysis model of PV/PCM structure is established. This study is carried out on the effect of PCM thermal conductivity on internal temperature distribution characteristics of PV/PCM and temperature control characteristics of solar cells. The results show that the increase in thermal conductivity of PCM can prolong the temperature control time of solar cell in PV/PCM system, for example, when the thermal conductivity is increased from 0.2 W/(m·K) to1.5 W/(m·K) under a thickness of 4 cm, the duration when PV/PCM solar cell temperature is controlled below 40°C and extended from 52 min to 184 min. In addition, PV/PCM experimental prototypes are designed with the LA-SA-EG composite PCM peak melting point of 46°C and thermal conductivity of 0.8 W/(m·K) and 1.1 W/(m·K), respectively. The results indicate that compared with PCM-free solar cells, the maximum temperature of PV/PCM prototype solar cells with thermal conductivity of 0.8 W/(m·K) and 1.1 W/(m·K) is reduced by 10.8°C and 4.6°C, respectively, with average output power increased by 4.1% and 2.2%, respectively, under simulated light sources. Under natural light conditions, the average output power is increased by 6.9% and 4.3%, respectively. The results provide theoretical and experimental basis for the optimization of PV/PCM design by changing the thermal conductivity of PCM.     

镉引起肾脏毒性的细胞凋亡通路

肾近端小管是镉主要的作用靶器官,但人们对镉引起肾脏毒性的作用机制仍不清楚。在体内外的研究中,镉能够诱导肾近端小管上皮细胞的凋亡,这表明通过细胞凋亡通路引起上皮细胞的凋亡可能是镉引起肾脏毒性的关键环节之一。部分研究表明镉在不同细胞可通过多个途径来引起细胞凋亡,包括线粒体介导的及死亡受体介导的凋亡通路。本篇综述将在以往镉相关及细胞凋亡的文献报道及其重大发现的基础上,特别是在肾脏及肾脏近端小管上皮细胞的研究基础上,来阐述镉通过细胞凋亡来诱导肾脏毒性的作用机制。     

5种卤代乙酰胺类消毒副产物对小鼠淋巴瘤细胞Tk基因致突变性研究

卤代乙酰胺类(HAc Am)消毒副产物(DBPs)是饮用水中新兴含氮类DBPs之一。为探究HAc Ams的致突变性,选择小鼠淋巴瘤细胞作为受试细胞,分别考察了一氯代乙酰胺、二氯代乙酰胺、三氯代乙酰胺、一碘代乙酰胺、二碘代乙酰胺(DIAc Ams)共5种HAc Ams对小鼠淋巴瘤细胞Tk基因突变的影响。结果表明,在0.05~20μmol·L~(-1)暴露浓度下,5种HacAms类DBPs对小鼠淋巴瘤细胞呈现出一定的细胞毒性,随着暴露浓度的升高,细胞毒性增强。暴露4 h后,5种HacAms中只有DIAc-Ams呈现出显著的致突变性(暴露剂量高于5μmol·L~(-1)),且以小集落为主。上述研究结果为研究HacAms对哺乳动物细胞的致突变作用提供了基础数据。