Simulation of wind-driven dispersion of fire pollutants in a street canyon using FDS

Air quality in urban areas attracts great attention due to increasing pollutant emissions and their negative effects on human health and environment. Numerous studies, such as those by Mouilleau and Champassith (J Loss Prevent Proc 22(3): 316–323, 2009), Xie et al. (J Hydrodyn 21(1): 108–117, 2009), and Yassin (Environ Sci Pollut Res 20(6): 3975–3988, 2013) focus on the air pollutant dispersion with no buoyancy effect or weak buoyancy effect. A few studies, such as those by Hu et al. (J Hazard Mater 166(1): 394–406, 2009; J Hazard Mater 192(3): 940–948, 2011; J Civ Eng Manag (2013)) focus on the fire-induced dispersion of pollutants with heat buoyancy release rate in the range from 0.5 to 20 MW. However, the air pollution source might very often be concentrated and intensive, as a consequence of the hazardous materials fire. Namely, transportation of fuel through urban areas occurs regularly, because it is often impossible to find alternative supply routes. It is accompanied with the risk of fire accident occurrences. Accident prevention strategies require analysis of the worst scenarios in which fire products jeopardize the exposed population and environment. The aim of this article is to analyze the impact of wind flow on air pollution and human vulnerability to fire products in a street canyon. For simulation of the gasoline tanker truck fire as a result of a multivehicle accident, computational fluid dynamics large eddy simulation method has been used. Numerical results show that the fire products flow vertically upward, without touching the walls of the buildings in the absence of wind. However, when the wind velocity reaches the critical value, the products touch the walls of the buildings on both sides of the street canyon. The concentrations of carbon monoxide and soot decrease, whereas carbon dioxide concentration increases with the rise of height above the street canyon ground level. The longitudinal concentration of the pollutants inside the street increases with the rise of the wind velocity at the roof level of the street canyon.     

Age dependent acute oral toxicity of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and two anaerobic N-nitroso metabolites in deer mice (Peromyscus maniculatus)

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) transforms anaerobically into N-nitroso compounds: hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX). Exposure to these N-nitroso metabolites may occur in areas contaminated with explosives, as anaerobic degradation occurs via some bacteria and is one remediation strategy used for RDX. Few papers report acute oral toxicity and none have evaluated age dependent toxicity of RDX or its N-nitroso metabolites. Median lethal dose (LD₅₀) was determined in deer mice (Peromyscus maniculatus) of three age classifications 21 d, 50 d, and 200 d for RDX, MNX, and TNX using the US EPA up-and-down procedure (UDP). Hexahydro-1,3,5-trinitro-1,3,5-triazine and N-nitroso metabolites caused similar overt signs of toxicity. Median lethal dose for 21 d deer mice were 136, 181, and 338 mg/kg for RDX, MNX, and TNX, respectively. Median lethal dose for 50 d deer mice were 319, 575, and 338 mg/kg for RDX, MNX, and TNX, respectively. Median lethal dose for 200 d deer mice were 158, 542, and 999 mg/kg for RDX, MNX, and TNX, respectively. These data suggest that RDX is the most potent compound tested, and age dependent toxicity may exist for all compounds and could play a role in RDX and RDX N-nitroso metabolite ecological risk evaluation of terrestrial wildlife at RDX contaminated sites.     

Effects of HMX exposure upon metabolic rate of northern bobwhite quail (Colinus virginianus) in ovo

We evaluated the use of the gas exchange rate as an ecologically relevant indicator of chemical stress in avian embryos/eggs. Northern bobwhite quail (Colinus virginianus) were exposed to octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) via feed containing nominal concentrations of 0, 12.5, 50.0, and 125.0 mg kg(-1). Metabolic rates (oxygen consumption) of developing quail eggs were then measured via respirometry to examine potential effects of HMX exposure. Metabolic rates were examined on 5, 9, and 21 d of incubation. Next, concentrations of HMX in embryos/eggs were determined by liquid chromatography-mass spectrometry. Mean (+/-SE) concentrations of HMX in eggs were 21.0+/-5.9, 1113+/-79.0, 3864+/-154.0, and 7426+/-301.1 ng g(-1) in control, low, medium and high dose groups, respectively. There were significant differences in oxygen consumption among the three embryo ages, however differences among the ages were not consistent among dose groups (age x dose group interaction p<0.0001). Oxygen consumption rates did not vary as a function of HMX in embryos (p=0.18). No evidence was observed for alterations of in ovo metabolic rates associated with HMX exposure.     

环境经济学与可持续发展

30年前,自然资源和污染问题还不是经济模式的一部分。但是,在20世纪70年代左右,大量的问题便出现在大众媒体中,这也暹．使经济学家开始考虑：世界的汽油用完了吗？世界上的农民可以生产足够的粮食来应付日益增长的人口吗？我们如何控制污染？将来还会有自然的风光可供我们的孩子去欣赏吗？这些问题使环境经济学逐步流行起来。     

Organochlorine contaminant assessment in great blue herons using traditional and nonlethal monitoring techniques

A nonlethal method is discussed for the evaluation of contaminant concentrations in whole eggs. Concentrations of pentachlorobenzene, hexachlorobenzene, DDE, and the PCB congeners, BZ-60, BZ-118, BZ-138, BZ-180, and BZ-170 were quantified in tissue samples from great blue herons (Ardea herodias). All tissues within whole eggs from two colonies were homogenized together and analysed for these chlorinated contaminants. Contents and chorio-allantoic membranes (CAMs) of additional whole eggs were separated and analysed. Contaminant distributions were determined for the CAM and contents of whole eggs from the same colonies. CAM tissues remaining in hatched eggs were also analysed for comparative purposes. Utilizing the distributions derived for contaminants between CAM and egg contents and the chemical concentrations determined in CAMs from hatched eggs, contaminant burdens in whole eggs were calculated. This process produced concentration estimates that described actual, whole egg burdens of chlorinated contaminants within a factor of 2 (1.03-3.7). Contaminant burdens in eggs from the two colonies were also statistically different for DDE and total PCB concentrations.     

Spatial distribution of lead concentrations in urban surface soils of New Orleans, Louisiana USA

Immediately following hurricane Katrina concern was raised over the environmental impact of floodwaters on the city of New Orleans, especially in regard to human health. Several studies were conducted to determine the actual contaminant distribution throughout the city and surrounding wetlands by analyzing soil, sediment, and water for a variety of contaminants including organics, inorganics, and biologics. Preliminary investigations by The Institute of Environmental and Human Health at Texas Tech University concluded that soils and sediments contained pesticides, semi-volatiles, and metals, specifically arsenic, iron, and lead, at concentrations that could pose a significant risk to human health. Additional studies on New Orleans floodwaters revealed similar constituents as well as compounds commonly found in gasoline. More recently, it has been revealed that lead (Pb), arsenic, and vanadium are found intermittently throughout the city at concentrations greater than the human health soil screening levels (HHSSLs) of 400, 22 (non-cancer endpoint) and 390 μg/g, respectively. Of these, Pb appears to present the greatest exposure hazard to humans as a result of its extensive distribution in city soils. In this study, we spatially evaluated Pb concentrations across greater New Orleans surface soils. We established 128 sampling sites throughout New Orleans at approximately half-mile intervals. A soil sample was collected at each site and analyzed for Pb by ICP-AES. Soils from 19 (15%) of the sites had Pb concentrations exceeding the HHSSL threshold of 400 μg/g. It was determined that the highest concentrations of Pb were found in the south and west portions of the city. Pb concentrations found throughout New Orleans in this study were then incorporated into a geographic information system to create a spatial distribution model that can be further used to predict Pb exposure to humans in the city.     

Inorganic and organic contaminants in sediments from an urban playa and associated toxicity among Hyalella azteca

Playa wetlands are important components of the Southern High Plains (USA) landscape as they are the major aquatic surface feature. Chemical contaminants associated with playas have been documented, particularly for grassland and agricultural watersheds, but not for playas in urban settings. The objectives of this study were to determine concentrations of inorganic and organic contaminants in sediments from an urban playa within the I-20 Wildlife Preserve and Jenna Welch Nature Study Center in Midland, TX, and evaluate toxicity of these sediments to Hyalella azteca. Concentrations of most trace elements were below sediment quality guidelines with exceptions of lead, cadmium, and arsenic. Concentrations of organic contaminants, particularly PAHs, DDT, DDE, and malathion, were above sediment quality guidelines at various locations within the playa. Decreased survival was observed among H. azteca exposed to sediment from a single location when compared those exposed to reference sediments. This location also produced maximum observed concentrations for five of seven trace elements, potentially due to its location at the lowest elevation within the playa. This study documented concentrations of contaminants in sediments of an urban playa associated with past and present land uses in its urban setting, including those from automotive emissions and historical pesticide use.     

Comparison of photocatalytic degradation of dyes in relation to their structure

The photocatalytic degradation of a series of six acid dyes (Direct Red 80, Direct Red 81, Direct Red 23, Direct Violet 51, Direct Yellow 27, and Direct Yellow 50) has been tested compared in terms of color removal, mineralization, and toxicity (Lactuca sativa L. test) after photocatalysis on immobilized titanium dioxide. The dyes were examined at their natural pH and after hydrolysis at pH 12. Results show that hydrolysis decreases strongly the efficiency of color removal, that full mineralization takes much longer reaction time than color removal, and that toxicity is only very partially reduced. Some structural parameters, related to the structure and the topology of the dye molecules, could be correlated with the apparent color removal rates at natural pH.     

Behavior of juvenile American lobsters, Homarus americanus, under predation risk

The influence of predation risk and food deprivation on the behavior and activity of juvenile American lobsters, Homarus americanus Milne Edwards, was examined in single and paired individuals in laboratory experiments performed during 1988 and in the winter of 1991/92. In the presence of a predator (the tautog Tautoga onitis Linnaeus) restrained behind a barrier, single lobsters significantly reduced the time spent feeding at night, consumed fewer mussels, and quickly brought them back to shelter. Single lobsters did not forage during the day in any treatment. If deprived of food for 60 h, they consumed more mussels and spent more time walking than recently fed (12-h food-deprived) lobsters. Paired lobsters did forage during the day in the presence of a predator. The smaller lobsters (subdominant) in the pairs foraged for a longer time in the presence than in the absence of a predator and significantly longer than single individuals. Shelter occupancy was significantly shorter in single, recently fed lobsters in the presence of a predator compared to time spent sheltering in its absence. Among food-deprived lobsters, paired individuals spent a significantly shorter time within the shelter than single lobsters in the absence of a predator. Larger (dominant) lobsters, however, spent more time than subdominant lobsters within the shelter during all periods of the day. Without a predator, paired lobsters spent significantly more time than single ones in shelter-related activities. Under predation risk, subdominant lobsters concentrated shelter-building time during the day and built a higher percent of alternative shelters than either single or dominant lobsters. In the absence of a predator, paired lobsters walked in the open area for a significantly longer time than single ones in the absence of a predator. This apparently was associated with fighting between dominant and subdominant lobsters and the attempts of the larger lobster to drive the smaller one from its shelter. During the day, lobsters fought for a significantly longer time in the presence than in the absence of a predator. When the tautog was not constrained, mortality rate was similar in both single and paired lobsters. Mortality rate among subdominant lobsters, however, was seven times higher than among dominant lobsters. We suggest that the risk of predation interferes with the ability of single juvenile lobsters to acquire and consume food. They appear to trade off energetic consideration against risk of predation when foraging away from the shelter. The introduction of a conspecific competitor to the system may further increase risk (of the subdominant) to the predator. Intraspecific interactions tend to increase the risk of predation to smaller lobsters but increase the survival rate among larger lobsters. Received: 6 February 1995 / Accepted: 2 September 1997