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排序方式: 共有555条查询结果,搜索用时 15 毫秒
71.
Abstract Metabolic fate of two dichloromethyl diaryl phosphonates (32P labelled) in/on rice plants was investigated. The test compounds were found to be less persistent on the surface of rice leaves with half lives 7.4 and 6.7 days respectively. Main degradation product from both the phosphonates were dichloromethyl phosphonic acid with trace of dichloromethyl‐O‐aryl phosphonate as a transitory intermediate product. 相似文献
72.
Roy S. Whitson L. A. Crowder 《Journal of environmental science and health. Part. B》2013,48(5):545-562
Abstract The effect of toxaphene upon ion fluxes of the central nervous system (CNS) of the cockroach, Periplaneta americana (L.), was studied in vitro. The CNS, divided into three sections (brain, thoracic, and abdominal), was exposed to 10 M toxaphene in saline containing 24Na+, 42K+, 36Cl‐, or 45Ca++. Uptake and efflux of these ions were evaluated. Toxaphene was responsible for significant increases in the internal levels of 42K+ and 45Ca++, but had little affect upon Na or 36Cl‐ movements. The resulting concentration changes of the ions may be involved in the neural activity observed with toxaphene poisoning. Of the three CNS sections, significant changes were more numerous and occurred earlier in abdominal sections. 相似文献
73.
Christopher J. Yahnke Warren E. Johnson Eli Geffen Deborah Smith Fritz Hertel Michael S. Roy Cristian F. Bonacic Todd K. Fuller Blaire Van Valkenburgh Robert K. Wayne 《Conservation biology》1996,10(2):366-375
The temperate rain forest of Chiloé Island, Chile, is inhabited by an endemic fox ( Dusicyon fulvipes ) first described by Charles Darwin and now designated Darwin's fox. Despite morphological differences, Darwin's fox has been considered only an insular subspecies of the mainland chilla fox ( D. griseus ). This follows the assumption that the island population, with an estimated population of less than 500, has been separated from the mainland chilla fox for only about 15,000 years and may have received occasional immigrants from the mainland. Consequently, this island population has not been protected as endangered or bred in captivity. Recently, a population of Darwin's fox was discovered on the Chilean mainland 600 km north of Chiloé Island. This population exists in sympatry with chilla and possibly culpeo ( D. culpaeus ) foxes, which suggests that Darwin's fox may be reproductively isolated. To clarify the phylogenetic position of Darwin's fox, we analyzed 344 bp of mitochondrial DNA control-region sequence of the three species of Chilean foxes. Darwin's foxes from the island and mainland populations compose a monophyletic group distinct from the two other Chilean fox species. This indicates that Darwin's fox was probably an early inhabitant of central Chile, and that its present distribution on the mainland may be a relict of a once much wider distribution. Our results highlight the ability of molecular genetic techniques to uncover historical relationships masked by recent events, such as local extinctions. The "rediscovery" of Darwin's fox as a distinct species implies that greater significance should be given to the protection of this species and its unique habitat and to documenting the extent of its mainland distribution. 相似文献
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75.
The temporal pattern and dose-rate dependence of liver cancer in rats fed 2-fluorenylacetamide (2-FAA) was compared to analytical formulas derived from a specific model. The model was based on the idea that carcinogens have two distinct actions on cells: (1) transformation and (2) acceleration of progression. Transformed cells are by definition progressing toward cancer, but their rate of progression may depend on several factors, specifically, the amount of carcinogen. In the experiments the carcinogen was removed from the diet after various times and the rate of tumor progression was estimated from the time of tumor occurrence. The results were consistent with the idea that 2-FAA accelerated the progression of the cancers. The model provides a simple explanation of Druckrey's law in that the temporal occurrence of tumors induced by a carcinogen represents the acceleration of a naturally occurring disease progression. 相似文献
76.
77.
This paper identifies newer areas of arsenic contamination in the District Kanker, which adjoins the District Rajnandgaon where high contamination has been reported earlier. A correlation with the mobile phase episodes of arsenic contamination has been identified, which further hinges on the complex geology of the area. Arsenic concentrations in both surface and groundwater, aquatic organisms (snail and water weeds) soil and vegetation of Kanker district and its adjoining area have been reported here. The region has been found to contain an elevated level of arsenic. All segments of the ecoysystem are contaminated with arsenic at varying degrees. The levels of arsenic vary constantly depending on the season and location. An analysis of groundwater from 89 locations in the Kanker district has shown high values of arsenic, iron and manganese (mean: 144, 914 and 371 μg L−1, respectively). The surface water of the region shows elevated levels of arsenic, which is influenced by the geological mineralised zonation. The most prevalent species in the groundwater is As(III), whereas the surface water of the rivers shows a significant contamination with the As(V) species. The analysis shows a bio-concentration of the toxic metals arsenic, nickel, copper and chromium. Higher arsenic concentrations (groundwater concentrations greater than 50 μg L−1) are associated with sedimentary deposits derived from volcanic rocks, hence mineral leaching appears to be the source of arsenic contamination. Higher levels of arsenic and manganese in the Kanker district have been found to cause impacts on the flora and fauna. A case study of episodic arsenical diarrhoea is presented. 相似文献
78.
79.
Maitra Asmita Keesari Tirumalesh Roy Annadasankar Gupta Saibal 《Environmental science and pollution research international》2021,28(15):18553-18566
Environmental Science and Pollution Research - Fluoride contamination in groundwater is a major problem throughout the world as well as in India. High-fluoride content was reported in the hot... 相似文献
80.