Disposition and metabolism of 2,3,7,8-tetrachlorodibenzofuran (TCDF) in rainbow trout     

A. Robert Maslanka  Ruth Steward  Jyotsna Pangrekar  Subodh Kumar  Harish C. Sikka   《Marine environmental research》1992,34(1-4)

In order to elucidate the metabolic fate of 2,3,7,8-tetrachlorodibenzofuran (TCDF) in fish and to thereby facilitate the assessment of the risks posed by this environmental toxin, we determined the whole body half-life, tissue distribution and metabolism of [³H TCDF in rainbow trout (Onchorynchus mykiss), treated orally. A whole body biphasic elimination pattern resulted in the excretion of 60% of the administered chemical during the first 3 days, after which a much slower elimination-rate (half-life = 14 days) was observed. Significant amounts of water-soluble metabolites were found in both bile and liver. Of the TCDF-derived radioactivity in bile, approximately 50% represented glucuronide conjugates, predominantly 4-hydroxy-2,3,7,8-TCDF: substantial amounts of the sulfate conjugate of this same metabolite were also present. Except at early time points, muscle contained the predominant fraction of TCDF-derived radioactivity, amounting to 25–65% of the total radioactivity present in the fish. More than 95% of the radioactivity present in muscle represented unmetabolized TCDF.  相似文献   

Laboratory effects of microcosm size and the pesticide chlorpyrifos on benthic macroinvertebrate colonization of soft estuarine sediments     

David A. Flemer  Barbara F. Ruth  Charles M. Bundrick  James C. Moore 《Marine environmental research》1997,43(4):243-263

A 42-d flow-through experiment was conducted to evaluate the effects of the organo-phosphate pesticide, chlorpyrifos, and microcosm size (small: 144 cm²; large: 400 cm²) on benthic estuarine macroinvertebrate colonization. Nested central and perimeter (outside margin) cores were used to assess animal distribution within microcosms. Fine-grained, organically-rich (approximately 4.0% organic carbon and 20% dry wt) sediments were nominally fortified with chlorpyrifos controls, low (1.0) and high treatments (10.0 μg⁻¹ wet sediment). Large microcosms contained a significantly (p < 0.05) higher average taxa richness (10.9) than small microcosms (8.6) but small microcosms contained a significantly greater average animal density (295.8; numerical abundance adjusted to unit area) than large microcosms (120.5). Density of the polychaete, Neanthes succinea, the amphipod, Corophium acherusicum, and the barnacle, Balanus sp., was significantly greater in small microcosms but density of Ensis minor was significantly greater in large microcosms. In small and large microcosms, respectively, densities averaged significantly greater numbers in perimeter cores (e.g. 203.1 and 75.1) vs central cores (71.9 and 45.4). Average density decreased significantly with increasing chlorpyrifos concentration from controls (326.8), to low (123.8) and high (78.8) treatments. The density decrease was significantly related only to C. acherusicum whose densities decreased from controls (285.8) to low (88.5) and high (43.9) dosed microcosms. Application of an equilibrium partitioning model indicated that density of C. acherusicum was sensitive to an estimated interstitial water concentration of approximately 0.48 μg liter⁻¹. Non-metric multidimensional scaling ordination analyses provided important insights into response patterns not available through ANOVA procedures. A permutation procedure (ANOSIM) detected a significant size effect (p < 0.0001) and a significant effect between controls and low (p < 0.042) and high doses (p < 0.013) but not between low and high chlorpyrifos treatments (p < 0.465). A single species, C. ascherusicum, as in the ANOVA analyses, dominated contributions to community average percent dissimilarity in most combinations of microcosm size and chlorpyrifos treatment effects (range: 8.4–21.9%). Community structure differed significantly in several combinations of microcosm size, core position and chlorpyrifos treatment. Results confirm earlier work that intrinsic design factors influence benthic macroinvertebrate community structure and determine taxa available to pesticide exposure in microcosms.  相似文献   

Tracing sources and cycling of phosphorus in Peru Margin sediments using oxygen isotopes in authigenic and detrital phosphates   总被引：4，自引：0，他引：4  

Deb P. Jaisi  Ruth E. Blake 《Geochimica et cosmochimica acta》2010,74(11):3199-6261

Many (bio)geochemical processes that bring about changes in sediment chemistry normally begin at the sediment-water interface, continue at depth within the sediment column and may persist throughout the lifetime of sediments. Because of the differential reactivity of sedimentary phosphate phases in response to diagenesis, dissolution/precipitation and biological cycling, the oxygen isotope ratios of phosphate (δ¹⁸O_P) can carry a distinct signature of these processes, as well as inform on the origin of specific P phases. Here, we present results of sequential sediment extraction (SEDEX) analyses combined with δ¹⁸O_P measurements, aimed at characterizing authigenic and detrital phosphate phases in continental margin sediments from three sites (Sites 1227, 1228 and 1229) along the Peru Margin collected during ODP Leg 201. Our results show that the amount of P in different reservoirs varies significantly in the upper 50 m of the sediment column, but with a consistent pattern, for example, detrital P is highest in siliciclastic-rich layers. The δ¹⁸O_P values of authigenic phosphate vary between 20.2‰ and 24.8‰ and can be classified into at least two major groups: authigenic phosphate precipitated at/near the sediment-water interface in equilibrium with paleo-water oxygen isotope ratios (δ¹⁸O_w) and temperature, and phosphate derived from hydrolysis of organic matter (P_org) with subsequent incomplete to complete re-equlibration and precipitated deeper in the sediments column. The δ¹⁸O_P values of detrital phosphate, which vary from 7.7-15.4‰, suggest two possible terrigenous sources and their mixtures in different proportions: phosphate from igneous/metamorphic rocks and phosphate precipitated in source regions in equilibrium with δ¹⁸O_w of meteoric water. More importantly, original isotopic compositions of at least one phase of authigenic phosphates and all detrital phosphates are not altered by diagenesis and other biogeochemical changes within the sediment column. These findings help to understand the origin and provenance of P phases and paleoenvironmental conditions at/near the sediment-water interface, and to infer post-depositional activities within the sediment column.  相似文献   

Identification and definition of primary and reworked tephra in Late Glacial and Holocene marine shelf sediments off North Iceland     

Esther Ruth Gudmundsdóttir  Jón Eiríksson  Gudrún Larsen 《第四纪科学杂志》2011,26(6):589-602

Nine tephra layers in marine sediment cores (MD99‐2271 and MD99‐2275) from the North Icelandic shelf, spanning the Late Glacial and the Holocene, have been investigated to evaluate the effectiveness of methods to detect tephra layers in marine environments, to pinpoint the stratigraphic level of the time signal the tephra layers provide, and to discriminate between primary and reworked tephra layers in a marine environment. These nine tephra layers are the Borrobol‐like tephra, Vedde Ash, Askja S tephra, Saksunarvatn ash, and Hekla 5, Hekla 4, Hekla 3, Hekla 1104 and V1477 tephras. The methods used were visual inspection, magnetic susceptibility, X‐ray photography, mineralogical counts, grain size and morphological measurements, and microprobe analysis. The results demonstrate that grain size measurements and mineralogical counts are the most effective methods to detect tephra layers in this environment, revealing all nine tephra layers in question. Definition of the tephra layers revealed a 2–3 cm diffuse upper boundary in eight of the nine tephra layers and 2–3 cm diffuse lower boundary in two tephra layers. Using a multi‐parameter approach the stratigraphic position of a tephra layer was determined where the rate of change of the parameters tested was the greatest compared with background values below the tephra. The first attempt to use grain morphology to distinguish between primary and reworked tephra in a marine environment suggests that this method can be effective in verifying whether a tephra layer is primary or reworked. Morphological measurements and microprobe analyses in combination with other methods can be used to identify primary tephra layers securely. The study shows that there is a need to apply a combination of methods to detect, define (the time signal) and discriminate between primary and reworked tephra in marine environments. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Farmers and perverse outcomes: The quest for food and energy security,emissions reduction and climate adaptation     

Ruth Beilin  Tamara Sysak  Serenity Hill 《Global Environmental Change》2012,22(2):463-471

Victorian farmers have experienced significant impact from climate change associated with drought and more recently flooding. These factors form a convergence with a complex of other factors to change production systems physically; and farmers’ decision making is variously described as adaptive or maladaptive to these drivers of change. Recently updated State Government policies on farming, climate and water have immediate and long term implications for food production systems but are not readily interpreted at a local scale. Further, peak oil and energy security are only partially integrated into either climate or water policy discourse. In effect, despite some far-sighted words about the meaning of climate change, uncertainty is largely met with a ‘business as usual’ mantra. Farmer narratives are used to demonstrate their systemic and increasing vulnerability and likelihood of perverse outcomes. The Future Farming strategy and Our Water Our Future are briefly analyzed, as are potential implications of the rhetoric of newly elected conservative government. Using ideas from Bourdieu and Bhabha we suggest that the reliance on farmers being able to innovate and take up opportunities associated with the uncertainty of large scale changes in climate and energy availability are misguided. It is more likely that current policy directions entrench the values of the global market and its elite, leaving farmers locked-in to historical structural responses that will not be successful in the long-term and will diminish their ability to imagine radical and diverse ways of avoiding the maladaptive structures currently surrounding their production systems.  相似文献   

Noble-gas-rich separates from the Allende meteorite     

Ulrich Ott  Ruth Mack 《Geochimica et cosmochimica acta》1981,45(10):1751-1788

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Review of archaeointensity methods     

Ruth Thomas 《Surveys in Geophysics》1983,5(4):381-393

Most of the traditional methods of determining the intensity of the ancient geomagnetic field from archaeological materials utilized thermal demagnetization of the natural remanent magnetization (NRM) and of the laboratory induced thermoremanent magnetization (TRM). When applied rigorously these methods are foolproof. They are, however, very time consuming and the number of samples with which they can be used is limited. Attempts to speed up these traditional methods have generally led to the use of subjective criteria in assessing the reliability of the results and archaeomagnetic research has recently been concentrated on extending the range of samples to which the method can be applied. Through the use of alternating field, rather than thermal, demagnetization of NRM and TRM it has become possible to apply corrections for alteration occurring during laboratory firing of the archaeological samples and develop objective criteria of reliability. Recent research has shown that it may be possible to determine archaeointensities the laboratory redeposition of lake sediments.  相似文献   

A contribution to Pleistocene chronology in southeast Essex,England     

Ruth Gruhn  Alan Lyle Bryan  A.J. Moss 《Quaternary Research》1974,4(1):53-71

Parallel to the Essex coast north of the mouth of the Thames, a series of gravel spreads ranging in altitude from near sea level westward to more than 200 ft O.D. (mean sea level) proved to be the remnants of an abandoned Thames/Medway terrace system, rather than a series of “raised” beaches, as their location had suggested. The seaward side of the ancient river valley has subsequently been “captured” by subsidence.Evidence is given for five terraces, with surface levels between 5 and 75 ft O.D. Because of subsidence of the Essex coast, the terrace levels are not easily correlatable with either the Thames or Medway terrace levels. Temporal placement is attempted on the basis of one site in the 25 ft Barling terrace, which yielded a Middle Acheulian archaeological assemblage associated with a cool temperate fauna including an early form of mammoth. An ice wedge cast in the Barling terrace was filled with floodloam which weathered to a parabraunerde soil during an interglacial climate warmer than now. For these reasons man is thought to have lived on the floodplain of the Barling terrace either at the onset of the Wolstonian (Riss) glacial or during an interstadial of that stage. The question of possible linkages between Swanscombe and Clacton terraces is discussed.  相似文献   

Irrigated agriculture and place‐making in the East Kimberley     

Ruth Lane 《The Australian geographer》2004,35(1):77-94

This paper explores the way in which lived experiences of farmers in the Ord Valley have intersected with representations of the Ord Valley over time. I contrast the development of Stage 1 of the Ord River Irrigation Scheme in the 1960s with a proposal put forward in the late 1990s for greatly expanding the area of irrigated agriculture as Stage 2 of the scheme. I examine the rhetoric employed in planning documents and public media coverage of the first and proposed second stages of the Ord Irrigation Scheme and explore its connections with social identifications of farmers in the Ord Valley since the 1960s. I then argue the value of this approach for understanding the dynamic relationship between the spatial practices and social identifications of farmers and representations of place and land use in public media and planning processes.  相似文献   

Claiming space and community: rural women’s strategies for living with, and beyond, fear     

Ruth Panelli  Anna Kraack 《Geoforum》2005,36(4):495-508

Following the well-established literature on women’s fear in urban contexts, a small but important literature has also begun to document accounts of boldness, fearlessness and empowerment. We extend this work by considering ways in which women live with, and beyond, experiences of fear. We argue that fear and fearlessness are not discrete and separate states, but rather they are often simultaneous conditions that women negotiate in complex ways. Moving away from a sense of victims and passivity, we suggest that women have spatial and social strategies that can be adopted when they face fear or take up forms of action that might be termed ‘bold’ or ‘courageous’. Consequently, this work draws on Koskela’s [Gender, Place and Culture 4 (1997) 301] previous discussion of ‘bold women’ in Finland to develop a notion of agency and highlight strategies that some rural women adopt in New Zealand.  相似文献