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91.
Bioaccumulation by Hyalella of all metals studied so far in our laboratory was re-evaluated to determine if the data could be explained satisfactorily using saturation models. Saturation kinetics are predicted by the biotic ligand model (BLM), now widely used in modelling acute toxicity, and are a pre-requisite if the BLM is to be applied to chronic toxicity. Saturation models provided a good fit to all the data. Since these are mechanistically based, they provide additional insights into metal accumulation mechanisms not immediately apparent when using allometric models. For example, maximum Cd accumulation is dependent on the hardness of the water to which Hyalella are acclimated. The BLM may need to be modified when applied to chronic toxicity. Use of saturation models for bioaccumulation, however, also necessitates the need for using saturation models for dose-response relationships in order to produce unambiguous estimates of LC50 values based on water and body concentrations. This affects predictions of toxicity at very low metal concentrations and results in lower predicted toxicity of mixtures when many metals are present at low concentrations. 相似文献
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M.A. Pereira P.S. Sabharwal P. Kaur C.B. Ross A. Choi T. Dixon 《Environment international》1981,5(4-6)
Male Chinese hamsters were exposed to diesel exhaust and clean air for six months at the Center Hill Facility of the U.S. Environmental Protection Agency in Cincinnati, Ohio. The animals were kept in specially constructed inhalation chambers and exposed to clean air or diesel exhaust for eight hours daily. The animals were sacrificed and slides prepared to study the mutagenic effects of diesel exhaust by four in vivo short term mammalian bioassays. Sperm morphology bioassay revealed a 2.67-fold increase in sperm abnormalities in the animals exposed to diesel exhaust as compared to those exposed to fresh air. Micronucleus bioassay revealed a 50% increase in the number of micronuclei in polychromatic erythrocytes obtained from animals exposed to diesel exhuast. However, no increase in sister chromatid exchange or chromosomal abnormalities was observed in bone marrow cells of animals treated with diesel exhaust. During these studies a decrease in mitotic index was observed in animals treated with diesel exhaust. 相似文献
95.
L. J. Lane M. H. Diskin D. E. Wallace R. M. Dixon 《Journal of the American Water Resources Association》1978,14(5):1143-1158
ABSTRACT: Significant errors in estimating surface runoff and erosion rates are possible if a watershed is assumed to contribute runoff uniformly over the entire area, when actually only a portion of the entire area may be contributing. Generation of overland flow on portions of small semiarid watersheds was analyzed by three methods: an average loss rate procedure, a lumped-linear model, and a distributed-nonlinear model. These methods suggested that, on the average, 45, 60, and 50% of the drainage area was contributing runoff at the watershed outlet. Infiltrometer data support the partial area concept and indicate that the low infiltration zones are the runoff source areas as simulated with the distributed-nonlinear model. 相似文献
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Burger J Campbell KR Campbell TS Shukla T Dixon C Gochfeld M 《Environmental monitoring and assessment》2005,110(1-3):171-184
We compared the levels of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in a small species of fish (Central
stonerollers, Campostoma anomalum) collected from East Fork Poplar Creek (EFPC) and a reference site in eastern Tennessee. Stonerollers are minnows in the
Cyprinidae family that serve as prey for many carnivores in aquatic systems. Fish were collected from East Fork Poplar Creek
within the U.S. Department of Energy's Y-12 National Security Complex, part of the Oak Ridge Reservation, and from a reference
stretch of the Little River in East Tennessee. Whole fish were homogenized for analysis. Concentrations of all metals (except
arsenic) were significantly higher in stonerollers from EFPC compared to the reference site. Mercury levels in minnows from
EFPC averaged 0.4 ppm (μg/g), four times higher than the average for fish in the U.S. in general. This was higher than levels
in fish from the nearby Clinch River and higher than fillets of white bass (Morone chrysops) from the same creek. Most metal levels were inversely related to size and weight of the stonerollers, perhaps due to growth
dilution. 相似文献
98.
Preface 总被引:1,自引:0,他引:1
Robert K. Dixon 《Mitigation and Adaptation Strategies for Global Change》2007,12(3):323-324
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Wetlands are critical natural resources in developing countries where they perform a range of environmental functions and provide numerous socio-economic benefits to local communities and a wider population. In recent years, however, many wetlands throughout eastern Africa have come under extreme pressure as government policies, socio-economic change and population pressure have stimulated a need for more agriculturally productive land. Although wetland drainage and cultivation can make a key contribution to food and livelihood security in the short term, in the long term there are concerns over the sustainability of this utilization and the maintenance of wetland benefits. This article draws upon recent research carried out in western Ethiopia, which addressed the sustainability of wetland agriculture in an area of increasing food insecurity and population pressure. It discusses the impacts of drainage and cultivation on wetland hydrology and draws attention to local wetland management strategies, particularly those characterized by multiple use of wetlands, where agriculture exists alongside other wetland uses. The article suggests that where multiple wetland uses exist, a range of benefits can be sustained with little evidence of environmental degradation. Ways of promoting and empowering such sustainable wetland management systems are discussed in the context of the wider need for water security throughout the region. 相似文献