Tracer diffusion from a horizontal fracture into the surrounding matrix: measurement by computed tomography

The vertical diffusion of NaI solution from a horizontal fracture into and within the surrounding matrix was tracked and quantified over time using an artificially fractured chalk core (30x5 cm) and a second-generation X-ray computed tomography (CT) scanner. The different tracer-penetration distances imaged in the matrix above and below the horizontal fracture are indicative of a greater tracer mass penetrating into the lower matrix. The enhanced transport in the matrix below the fracture was related to the Rayleigh-Darcy instability induced by the density differences between the heavier tracer solution in the fracture (1.038) and the distilled water that had initially resided in the matrix. Our observations suggest that below the fracture, the tracer is propagated by an advection-diffusion process that is characterized by both higher rates and higher concentrations relative to its propagation by diffusion above the fracture. The experimental results suggest that the prediction of contaminant migration in a rock intersected by both vertical and horizontal (e.g. along bedding planes) fractures is difficult because of density effects that result in different solute-penetration rates.     

Dissolution-induced preferential flow in a limestone fracture

Flow in a rock fracture is surprisingly sensitive to the evolution of flow paths that develop as a result of dissolution. Net dissolution may either increase or decrease permeability uniformly within the fracture, or may form a preferential flow path through which most of the injected fluid flows, depending on the prevailing ambient mechanical and chemical conditions. A flow-through test was completed on an artificial fracture in limestone at room temperature under ambient confining stress of 3.5 MPa. The sample was sequentially circulated by water of two different compositions through the 1500 h duration of the experiment; the first 935 h by tap groundwater, followed by 555 h of distilled water. Measurements of differential pressures between the inlet and the outlet, fluid and dissolved mass fluxes, and concurrent X-ray CT imaging and sectioning were used to characterize the evolution of flow paths within the limestone fracture. During the initial circulation of groundwater, the differential pressure increased almost threefold, and was interpreted as a net reduction in permeability as the contacting asperities across the fracture are removed, and the fracture closes. With the circulation of distilled water, permeability initially reduces threefold, and ultimately increases by two orders of magnitude. This spontaneous switch from net decrease in permeability, to net increase occurred with no change in flow rate or applied effective stress, and is attributed to the evolving localization of flow path as evidenced by CT images. Based on the X-ray CT characterizations, a flow path-dependent flow model was developed to simulate the evolution of flow paths within the fracture and its influence on the overall flow behaviors of the injected fluid in the fracture.     

Peroxidase activity,lignification and promotion of cell death in tobacco cells exposed to static magnetic field

Bio-effects of static magnetic fields on cell growth and cell death have been investigated in suspension-cultured tobacco cells as undifferentiated, embryonic plant cell model. The cells in their logarithmic growth phase were exposed to static magnetic field with the magnitudes of 10 mT and 30 mT for 5 h/day. Exposure to static magnetic field ceased the growth and caused an increase in cell death of exposed tobacco cells compared to those cells which were not treated with the field. Promotion of cell death was accompanied by a harmonized increase in the activity of peroxidase and increase of lignifcation of cell walls.     

Designing an integrated model for strawberry growers’ behavior toward implementation of good agricultural practices in Iran

Environment, Development and Sustainability - Good agricultural practices (GAPs) include conscious agricultural techniques that are not harmful to human health and the environment, with the goal of...     

活性氮和人类健康:眼前和长远的意义

活性氮对人类健康的影响表现在许多有益和不利的方面.有益方面,最为重要的是活性氮不断增加全球和区域性的食物供给,并提高了可利用食物的营养质量.在贫困、干旱、洪涝、战争以及难民涌入等因素造成食物紧缺时,膳食中氨基酸和蛋白质的摄入量不足是引起营养不良的主要原因.已掌握的大量数据即便还是有限的,也足以表明环境中活性氮流通量的增加通过其他一些作用途径对人类健康产生了显著的影响.职业原因和广大人群室内和户外生活所接触到的空气污染中的活性氮对人类的健康产生了不良影响.活性氮还可通过水污染和全球变暖影响人类健康,其产生的水污染包括地下水污染产生的高铁血红蛋白血症以及使鱼类死亡和对人体有毒的赤潮富营养化.环境中活性氮类的污染物普遍存在,因此,很难界定活性氮对人们健康产生特定影响的程度.鉴于活性氮影响到全人类,为了确定氮相关污染物及其衍生物对人类健康产生的有利和不良影响的程度和性质,需要多学科合作,进行长期的研究.     

Markovian–Octant analysis based stable turbulent shear stresses in near-bed bursting phenomena of vortex settling chamber

The coherent structure in near-bed turbulent boundary layer of vortex chamber, particularly the bursting events and their associated shear stresses play the main role in sediment flushing process and consequently the trap efficiency of the vortex settling chamber. Hence, three-dimensional velocity measurements were made at 48 points near the bed of physical model of vortex chamber by using Micro-ADV. The pattern of sediment deposition at the bed of vortex settling chamber reveals three separate regions formed by three predominant currents of inlet flow, flushing flow and outlet over flow. Additionally, due to the instability and three-dimensional nature of the bursting events near the bed of chamber, the new method of Markovian–Octant analysis was applied to study the different classes of near-bed stable shear stresses of vortex chamber in three dimensions. Moreover, the role of each class of stable shear stresses on Sediment transport mechanism at the bed of vortex chamber is investigated.     

Pesticide residues in cow milk consumed in São Paulo City (Brazil)

Residues of pesticides were surveyed in 132 samples of cow milk collected from bulk transports (38 samples of raw milk) and market (94 samples of pasteurised milk). These samples were analysed by the multiresidue analytical method DFG S19 for pesticide contamination. More than 70 active substances were studied and the identification and quantification were made by gas chromatographic technique. The results showed that 0.76% of samples were contaminated with HCH (alpha isomer) and 10.60% with endosulfan (alpha and beta isomers). Both pesticides, endosulfan and HCH, found in milk samples, indicated their use in agriculture practices, although legislation in Brazil does not permit the use of HCH since 1985 and endosulfan can be used only in a few crops. These compounds should not be present in milk because there are implications on human health. Organophosphorus, carbamates, pyrethroids, herbicides, and fungicides were not detected in cow's milk samples.     

Fate of polycyclic aromatic hydrocarbons during composting of lagooning sewage sludge

The fate of 16 polycyclic aromatic hydrocarbons (PAHs), targeted by the USEPA agency, has been investigated during composting of lagooning sludge. Composting shows efficient decrease of the content and the bioavailability of each PAH. Biodegradation and sorption are suggested as the main mechanisms contributing to this decrease. During the stabilization phase of composting, extensive microbial degradation of PAHs, mainly those with a low number of aromatic rings, was achieved following development of intense thermophilic communities. However, partial sorption of PAH to non-accessible sites temporarily limits the mobility mainly of PAHs with a high number of aromatic rings plus acenaphthene and acenaphthylene, and allows them to escape microbial attack. During the maturation phase, the development of a mesophilic population could play an important role in the degradation of the remaining PAH. During this phase of composting, PAH sequestration and binding of their oxidative metabolites within new-formed humic substances might also explain PAH decrease at the end of composting. The tendency of change of content or bioavailability of various PAH compounds during composting is found to be strongly related to the number of their aromatic rings, their molecular weight and structure.     

Reactive nitrogen and human health: acute and long-term implications

Reactive-nitrogen (Nr) has a wide variety of beneficial and detrimental effects on human health. The most important of the beneficial effects are increasing global and regional food supplies and increased nutritional quality of available foods. However, lack of adequate dietary intake of amino acids and proteins is a serious cause of malnutrition when food supplies are inadequate because of poverty, drought, floods, wars, and displacements of people as refugees. There is sufficient, though limited, quantitative data indicating that increased circulation of Nr in the environment is responsible for significant human health effects via other exposure pathways. Nr can lead to harmful health effects from airborne occupational exposures and population-wide indoor and outdoor air pollution exposures to nitrogen dioxide and ozone. Nr can also affect health via water pollution problems, including methemoglobinemia from contaminated ground water, eutrophication causing fish kills and algal blooms that can be toxic to humans, and via global warming. The environmental pollutants stemming from reactive nitrogen are ubiquitous, making it difficult to identify the extent to which Nr exerts a specific health effect. As all populations are susceptible, continued interdisciplinary investigations are needed to determine the extent and nature of the beneficial and harmful effects on human health of nitrogen-related pollutants and their derivatives.