Mercury in sport fish from the Sacramento-San Joaquin Delta region, California, USA

Total mercury (Hg) concentrations were determined in fillet tissue of sport fish captured in the Sacramento-San Joaquin River Delta and surrounding tributaries, a region particularly impacted by historic gold and mercury mining activity. In 1999 and 2000, mercury concentrations were measured in 767 samples from ten fish species. Largemouth bass (Micropterus salmoides), the primary target species, exhibited a median Hg concentration of 0.53 mug g(-1) (N=406). Only 23 largemouth bass (6%) were below a 0.12 mug g(-1) threshold corresponding to a 4 meals per month safe consumption limit. Most of the largemouth bass (222 fish, or 55% of the sample) were above a 0.47 mug g(-1) threshold corresponding to a 1 meal per month consumption limit. Striped bass (Morone saxatilis), channel catfish (Ictalurus punctatus), white catfish (Ameirus catus), and Sacramento pikeminnow (Ptychocheilus grandis) also had relatively high concentrations, with 31% or more of samples above 0.47 mug g(-1). Concentrations were lowest in redear (Lepomis microlophus) and bluegill (Lepomis macrochirus) sunfish, with most samples below 0.12 mug g(-1), suggesting that targeting these species for sport and subsistence fishing may reduce human dietary exposure to Hg in the region. An improved method of analysis of covariance was performed to evaluate spatial variation in Hg in largemouth bass captured in 2000, while accounting for variability in fish length. Using this approach, Hg concentrations were significantly elevated in the Feather River, northern Delta, lower Cosumnes River, and San Joaquin River regions. In spite of elevated Hg concentrations on all of its tributaries, the central Delta had concentrations that were low both in comparison to safe consumption guidelines and to other locations.     

Revisiting neighbourhood change from a Canadian perspective: Some supporting evidence from Vancouver

This paper argues that the several models of neighbourhood change developed in the United States are generally not applicable to Canadian cities due to differences in urban form, socioeconomic characteristics, and a host of institutional factors. A simple model is presented which extends the arbitrage model of neighbourhood dynamics. Several hypotheses are advanced and then tested on a data base covering three Vancouver, B.C. neighbourhoods from 1955 to 1981 by estimating several hedonic price equations. The hypotheses receive partial support. Implications for policymakers are then discussed.We wish to thank Jim Fitzsimmons and Judy Fountain for their computer assistance and the British Columbia Assessment Authority for providing us with data. Helpful comments on an earlier version of this paper were provided by Lawrence Jones and Douglas Diamond. We also like to acknowledge the financial support of the Canada Mortgage and Housing Corporation, the Real Estate Council of British Columbia, the University of British Columbia and the British Columbia Youth Employment Program.     

Mercury vapor in residential building common areas in communities where mercury is used for cultural purposes versus a reference community

BACKGROUND: Exposure to elemental mercury (Hg0) in residential buildings can occur from accidental spills, broken objects (thermometers, fluorescent fixtures, thermostats), and deliberate introduction, one mode of which involves cultural practices by individuals who believe dispersal of mercury in a residence will bring luck, enhance health or ward off harm. OBJECTIVES: To determine whether mercury vapor levels in common areas of residential buildings is higher in a community where cultural uses are likely (study areas S1, S2) than in a reference community (C1) where cultural use is unlikely, and whether levels can serve as a signal of significant cultural mercury use. METHODS: We monitored Hg0 vapor with a portable spectrophotometer in the three communities. We randomly selected sites in S1 and C1 community, and also include sites in S2 specified by local health officials who suspected cultural mercury use. We evaluated 122 multifamily buildings and 116 outdoor locations. FINDINGS: We found >25 ng/m3 Hg0 in 14% of buildings in study areas compared to only one reference building. In the latter we identified an accidental mercury spill from a bottle that had been brought into the building. Both the mean and maximum indoor mercury vapor levels were greater in the study communities than in the reference community. In all communities, we observed mean indoor Hg0 vapor concentration greater than outdoors, although in two-thirds of buildings, indoor levels did not exceed the area-specific outdoor upper-limit concentration. CONCLUSION: After controlling for factors that might influence Hg0 vapor levels, the most plausible explanation for greater Hg0 levels in the study area is a relationship to cultural use of mercury. None of the measured levels exceeded the ATSDR minimum risk level for residences of 200 ng/m3 Hg0 although levels in living quarters might be greater than those in the common areas.     

The tyranny of distance prevails: HTTP protocol latency and returns to fast fibre internet access network deployment in remote economies

Public policies to deploy enhanced local broadband access infrastructure in locations physically very far removed from the firms and customers with whom they transact are frequently justified by claims of increased competitiveness arising from the elimination of the ‘tyrannies of distance’. Yet relative distance-based disadvantages remain in respect of time-dependent applications and those hosted on distant infrastructures or requiring data sourced from distant locations. Trading off the effects of faster local access and latency on the time taken to load a Web page based on the HTTP Web protocol, we demonstrate that the increasing returns to distance rapidly overcome the effect of faster local access bandwidth as the distance the data must travel increases. We conclude that claims that investment in ultra-fast local broadband access will unconditionally facilitate a step-change in national economic performance are without foundation. In the absence of some compelling underlying competitive advantages, the ‘transformational’ economic benefits will be local rather than international in nature. At best, government investment in nationwide fast fibre networks is a defensive strategy that enables ongoing participation in the international economy, but at relatively higher costs than those faced by larger economies in closer proximity to end markets.     

State of the practice review of heap leach pad design issues

The authors present a summary of the state of the practice of containment design in copper and gold heap leaching, focusing on recent advancements and how these applications differ from the more conventional landfill design practices. Advancements both within the Americas and worldwide are presented, including consideration of increasing heap depths, which are now approaching 150 m (with ore densities generally in the range of 1500–1800 kg/m³). Liner system performance under these pressures will be reviewed, including the latest developments in drainage pipe performance testing. The authors will also explore the recently emerging technology of using concentrated sulfuric acid pre-curing for copper ores and the related compatibility issues with conventional geomembrane materials.     

Home,the culture of nature and meanings of gardens in late modernity

The growth in the provision of gardens has been an important feature of housing in the UK during the 20th century, and yet the significance of the humble domestic garden has been neglected in studies of housing and home. This paper examines the role of the garden in the meaning of home, and draws on theoretical discussions of nature, environmental risk and social uncertainty in late modernity. Secondary empirical data is used to investigate the changing uses of gardens and practices of gardening. A survey of garden owners provides primary empirical data to examine meanings of gardens and personal experiences of nature. The paper concludes that the garden is an important site for privacy, sociability and sensual connections to nature, and these activities can be understood as negotiations and practices to address the social and environmental paradoxes of late modern life.     

R410A与R22在家用空调中的应用比较(2)

本文部分（2）利用Bin参数分析法对R410A与R22空调的全年运行耗电进行计算,采用寿命期气候性能（LCCP）指标对R410A与R22的温室效应总体影响进行考查,同时对R410A与R22空调的生产成本进行比较。结果表明R410A空调由于运行效率高,在使用过程中可以显著节约耗电和运行费用,而且随着原材料价格的上涨和R410A压缩机生产能力的扩大,R410A与R22空调具有相近的生产成本;同时,通过减小温室间接效应以及空调的制冷剂充灌量或泄露量,与R22相比,R410A反而还会有利于降低对气候变暖的影响。     

A multi-scale analysis of urban form and commuting change in a small metropolitan area (1990–2000)

Issues of growth, especially the spatial nature of recent urban development and its implications for travel patterns, have received a great deal of attention. In particular, questions persist as to how the spatial distribution of workers and jobs influences commute patterns. This paper investigates changes in commuting and land use patterns using measures of jobs–housing balance, commuting efficiency and other statistics. A smaller urban area is chosen for study (Tallahassee, FL, USA)and data on its workers, jobs, and commute patterns are obtained from the Census Transportation Planning Package for 1990 and 2000. The key research questions investigated probe whether there were substantial changes in urban form and commuting over the period. A two-tiered approach is taken where change is explored at the regional and local scales using GIS, optimization procedures, and inferential statistical techniques. The results reveal the extent of the spatial changes in the study area between 1990 and 2000. Major findings included stability in urban structure over the time period, as well as a persistent strong relationship between land use and commute patterns. These results are discussed in light of their implications for other cities and for future work.     

Locating Chinese urban housing policy in an international context

China’s economic development has often been contrasted with that of other transition economies in Europe, but academics have fought shy of making direct comparisons of urban housing reform in the two systems. This paper fills this gap by making such direct comparisons. Adopting the market - housing model advocated by the World Bank as an analytical framework it finds that extensive housing privatisation in China is supported by a system of urban housing property rights and a growing residential mortgage market. Although China has a distinctive institutional framework, there is also much variety among the European transition countries, and a distinctive Chinese model was not identified; so this micro-level analysis did not support the contention that China represents a form of "contested modernity." Nonetheless, a crucial point arises from China's hybrid status as a developing as well as a transition country. The bulk of the urban migrant population remains excluded from formal housing policy and enabling strategies that form an element of the market - housing model especially in developing countries are not so much replaced by a distinctive Chinese model as by a yawning gap.     

Can carbon offsetting pay for upland ecological restoration?

Upland peat soils represent a large terrestrial carbon store and as such have the potential to be either an ongoing net sink of carbon or a significant net source of carbon. In the UK many upland peats are managed for a range of purposes but these purposes have rarely included carbon stewardship. However, there is now an opportunity to consider whether management practices could be altered to enhance storage of carbon in upland peats. Further, there are now voluntary and regulated carbon trading schemes operational throughout Europe that mean stored carbon, if verified, could have an economic and tradeable value. This means that new income streams could become available for upland management. The ‘Sustainable Uplands’ RELU project has developed a model for calculating carbon fluxes from peat soils that covers all carbon uptake and release pathways (e.g. fluvial and gaseous pathways). The model has been developed so that the impact of common management options within UK upland peats can be considered. The model was run for a decade from 1997-2006 and applied to an area of 550 km² of upland peat soils in the Peak District. The study estimates that the region is presently a net sink of − 62 ktonnes CO₂ equivalent at an average export of − 136 tonnes CO₂ equivalent/km²/yr. If management interventions were targeted across the area the total sink could increase to − 160 ktonnes CO₂/yr at an average export of − 219 tonnes CO₂ equivalent/km²/yr. However, not all interventions resulted in a benefit; some resulted in increased losses of CO₂ equivalents. Given present costs of peatland restoration and value of carbon offsets, the study suggests that 51% of those areas, where a carbon benefit was estimated by modelling for targeted action of management interventions, would show a profit from carbon offsetting within 30 years. However, this percentage is very dependent upon the price of carbon used.