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排序方式: 共有91条查询结果,搜索用时 31 毫秒
41.
日本于2001年4月1日生效的一项新法规规定,从国外进口不在所列名单中的转基因产品被视为非法。日本政府开始对进口货物进行检测,以确保其中不含不在名单中的转基因产品,如果含有且在目前阶段可以被检测出来,则必须对其进行标识。日本政府已批准了37种通过生物技术生产出来的产品。  相似文献   
42.
Potent estrogenic hormones are consistently detected in the environment at low concentration, yet these chemicals are strongly sorbed to soil and are labile. The objective of this research was to improve the understanding of the processes of sorption, mobility, and transformation for estrogens in natural soils, and their interaction. Equilibrium and kinetic batch sorption experiments, and a long-term column study were used to study the fate and transport of 17beta-estradiol and its primary metabolite, estrone, in natural soil. Kinetic and equilibrium batch experiments were done using radiolabeled 17beta-estradiol and estrone. At the concentrations used, it appeared that equilibrium sorption for both estrogens was achieved between 5 and 24 h, and that the equilibrium sorption isotherms were linear. The log K(oc) values for 17beta-estradiol (2.94) and estrone (2.99) were consistent with previously reported values. Additionally, it was found that there was rate-limited sorption for both 17beta-estradiol (0.178 h(-1)) and estrone (0.210 h(-1)). An approximately 42 h long, steady-flow, saturated column experiment was used to study the transport of radiolabeled 17beta-estradiol, which was applied in a 5.00 mg L(-1) solution pulse for 44 pore volumes. 17beta-estradiol and estrone were the predominant compounds detected in the effluent. The effluent breakthrough curves were asymmetric and the transport modeling indicated that sorption was rate-limited. Sorption rates and distributions of the estrogens were in agreement between column and batch experiments. This research can provide a better link between the laboratory results and observations in the natural environment.  相似文献   
43.
Autoignition temperature tests using the ASTM E659 test method have been conducted for N,N-dimethylacetamide (DMAC) and N,N-dimethylformamide (DMF) in test vessels with volumes of 0.5 l, 5 l, and 12 l. Tests were conducted at three different laboratories yielded good agreement (standard deviation with 5 °C) in all cases except for DMAC in the 0.5 l test vessel (standard deviation of 23 °C). Scaling correlations have been developed for the decrease of autoignition temperature with increasing volume and for increasing values of the vessel volume to surface area ratio. The variations for DMAC are steeper than the literature values for almost all other combustible liquids. Cool flames were observed for DMAC at temperatures as much as 44 °C below the autoignition temperature and for DMF at temperatures as much as 171 °C below its autoignition temperature. The DMF cool flame temperatures in the 5-l and 12-l test vessels are approximately equal to the DMF autoignition temperature in a closed 12-l test vessel. Gas samples taken after the cool flame and hot flame tests reveal the presence of high concentrations of diamines and dimethylamino acetonitrile, and small concentrations of many other partial decomposition/oxidation components.  相似文献   
44.
Moore JW  Schindler DE  Ruff CP 《Ecology》2008,89(2):306-312
Understanding how abundance regulates the effects of organisms on their ecosystems remains a critical goal of ecology, especially for understanding inter-ecosystem transfers of energy and nutrients. Here we examined how territoriality and nest-digging by anadromous salmon mediate trophic subsidies to stream fishes. Salmon eggs become available for consumption primarily by the digging of salmon that superimpose their nests on previous nests. An individual-based model of spawning salmon predicted that territoriality and habitat saturation produce a nonlinear effect of salmon density on numbers of available eggs to resident predators. Field studies in Alaskan streams found that higher densities of salmon produce disproportionately more eggs in stream drift and in diets of resident fishes (Arctic grayling and rainbow trout). Bioenergetics model simulations indicated that these subsidies produce substantially enhanced growth rates of trout. These results demonstrate that small changes in salmon abundance can drive large changes in subsidies to stream food webs. Thus, the ecological consequences of population declines of keystone species, such as salmon, will be exacerbated when behavior generates nonlinear impacts.  相似文献   
45.
17β-estradiol (E2) is a natural estrogenic hormone found in animal manure and urine, which may cause endocrine disruption in sensitive organisms. 17β-Estradiol has been widely detected in the environment, and animal agriculture may be an important source. The objectives of this study were to investigate the potential sources and/or spatial and temporal characteristics contributing to detections of E2 at the farm-scale. Soil cores, segmented into 0.15 m increments, were taken down to the water table from four locations (three potential E2 sources and one control) at or around a swine (Sus scrofa domesticus) farm on five different dates between 2006 and 2007. Estradiol was quantified in the soil-water extracts using liquid chromatography-with tandem mass spectrometry (LC/MS/MS) analysis. Estradiol detections were widespread and found in 128 out of 345 extractions (37%). Concentrations ranged from 0 to 1910 ng L−1 (porewater equivalents). A location that received field application of manure had significantly lower E2 concentrations compared to other locations. Also, the spring 2007 E2 concentrations were significantly higher than all other sample dates, perhaps related to climatic and hydrological events. Results suggested E2 was not directly related to manure sources, but was widespread in this environment. Where E2 was detected, highest concentrations favored the upper profile, while the greatest frequency of detections was in the lower profile and near the water table. Detections of E2 were associated with high organic mater contents in the upper profile and high sand contents in the lower profile. The study suggests that E2 is widespread in some soil environments, raising questions as to the source and mechanisms that facilitate its transport and mobility.  相似文献   
46.
Bhadha, Jehangir H., Casey Schmidt, Robert Rooney, Paul Indeglia, Ruben Kertesz, Elizabeth Bevc, and John Sansalone, 2009. Granulometric and Metal Distributions for Post‐Katrina Surficial Particulate Matter Recovered From New Orleans. Journal of the American Water Resources Association (JAWRA) 45(6):1434‐1447. Abstract: Hurricane Katrina and the resulting failure of the levees that surrounded and protected New Orleans generated a significant detained volume of stormwater within the urban area of New Orleans. Between the inundation resulting from levee failure and eventual pumped evacuation of stormwater from the urban area of New Orleans, a large mass of storm‐entrained particulate matter (PM) was deposited in the inundated areas. This study examined the granulometry and granulometric distribution of metals for post‐Katrina surficial PM deposits recovered from 15 sites (10 inundated and 5 non‐inundated) in New Orleans. Results of this examination were compared to pre‐Katrina data from New Orleans. While post‐Katrina analysis of PM indicates that Pb, Zn, and Cu concentrations for PM are reduced for all sites, inundated sites had higher Cu, Pb, and Zn concentrations for the settleable (~25‐75 μm) and sediment (>75 μm) size fractions. A comparison between total metal concentration and the bioavailable (leachable) fraction for PM reveals that inundated sites had up to 19% higher leachable metal concentration compared to non‐inundated sites. The reduction in PM‐bound total metal concentrations for recovered PM can be explained through a combination of scouring (and therefore change in granulometry from pre‐Katrina) that resulted from transport of suspended PM by storm flows and pumped evacuation; as well as leaching and PM‐based redistribution from extended contact with rainfall and during stormwater detention. New Orleans has been exposed to elevated levels of metals through decades of activities that include vehicular transportation, chemical, industrial, and oil production facilities resulting in higher metal concentrations for urban soil‐residual complexes. As a result, the influent storm flows associated with Katrina as an episodic event cannot solely explain the distribution and fate of PM‐associated metal concentrations.  相似文献   
47.
A study was conducted to evaluate the effects of dietary nitrocompounds on bird performance, ammonia volatilization, and changes in manure nitrogen (N). A total of 200 one-day-old male chicks (Cobb 500) were used for this study. The chicks were raised in electrically heated battery brooders for 18 days. On day 1, birds were allocated into five treatment groups with four replicated pens: (T1) control, a corn and soybean meal diet (3,100 kcal kg?1 metabolizable energy (ME) and 21% Crude Protein (CP)); (T2) 16.7 mg kg?1 nitroethanol (NEL); (T3) 33.3 mg kg?1 NEL; (T4) 16.7 mg kg?1 nitropropanol (NPL); and (T5) 33.3 mg kg?1 NPL. The body weight gain, feed intake and feed efficiency were measured on days 7, 14 and 18. Volatized ammonia (VA) and other N forms were measured at collection and following 2 weeks of incubation at 30°C. Broiler growth was not adversely affected by the nitrocompounds at concentrations up to 33.3 mg kg?1. The results show that initial manure pH was reduced by adding nitroethanol (NEL) and nitropropanol (NPL) to the diet by 0.2 and 0.5 pH units, respectively. Total VA after 2 weeks was unaffected by dietary treatment. The amounts of uric acid decomposed and ammonia produced were closely balanced in the control sample. However, this balance was significantly different among the manures produced by birds receiving nitrocompound treatments. The inclusion of NEL and NPL resulted in the presence of measurable amounts of Xanthine not found in the control group. This study indicates that supplementation of nitroethanol or nitropropanol into broiler diets up to 33.3 mg kg?1 influences uric acid degradation and ammonia production in broiler manure while maintaining optimal growth performance.  相似文献   
48.
A radiative transfer model and photochemical box model are used to examine the effects of clouds and aerosols on actinic flux and photolysis rates, and the impacts of changes in photolysis rates on ozone production and destruction rates in a polluted urban environment like Houston, Texas. During the TexAQS-II Radical and Aerosol Measurement Project the combined cloud and aerosol effects reduced j(NO2) photolysis frequencies by nominally 17%, while aerosols reduced j(NO2) by 3% on six clear sky days. Reductions in actinic flux due to attenuation by clouds and aerosols correspond to reduced net ozone formation rates with a nearly one-to-one relationship. The overall reduction in the net ozone production rate due to reductions in photolysis rates by clouds and aerosols was approximately 8 ppbv h?1.  相似文献   
49.
Nitrous acid (HONO), nitric acid (HNO3), and organic aerosol were measured simultaneously atop an 18-story tower in Houston, TX during August and September of 2006. HONO and HNO3 were measured using a mist chamber/ion chromatographic technique, and aerosol size and chemical composition were determined using an Aerodyne quadrupole aerosol mass spectrometer. Observations indicate the potential for a new HONO formation pathway: heterogeneous conversion of HNO3 on the surface of primary organic aerosol (POA). Significant HONO production was observed, with an average of 0.97 ppbv event?1 and a maximum increase of 2.2 ppb in 4 h. Nine identified events showed clear HNO3 depletion and well-correlated increases in both HONO concentration and POA-dominated aerosol surface area (SA). Linear regression analysis results in correlation coefficients (r2) of 0.82 for HONO/SA and 0.92 for HONO/HNO3. After correction for established HONO formation pathways, molar increases in excess HONO (HONOexcess) and decreases in HNO3 were nearly balanced, with an average HONOexcess/HNO3 value of 0.97. Deviations from this mole balance indicate that the residual HNO3 formed aerosol-phase nitrate. Aerosol mass spectral analysis suggests that the composition of POA could influence HONO production. Several previously identified aerosol-phase PAH compounds were enriched during events, suggesting their potential importance for heterogeneous HONO formation.  相似文献   
50.
This study investigates hydrological controls on E. coli concentration and loading in two artificially drained agricultural watersheds (58 and 23 km(2)) of the U.S. Midwest. Stream E. coli concentrations are significantly (p < 0.02) lower at base flow than high flow; however, E. coli load is significantly higher at high flow than at low flow (p < 0.001). Although E. coli concentrations are not significantly higher (p = 0.253) in summer/fall (3269 MPN/100 mL) than in the winter/spring (2411 MPN/100 mL), E. coli load is significantly higher (p < 0.05) in winter/spring (346 MPN/day) than in summer/fall season (75 MPN/day). Correlation analysis indicates that discharge and precipitation are the best indicators of E. coli concentration and 7-d antecedent precipitation (7dP), the best indicator of E. coli loading in the watersheds studied regardless of flow conditions and location. However, E. coli concentration and loading best correlate to 7dP and turbidity at base flow. A spatial dependency is also observed at base flow with E. coli concentration and load correlating better to 7dP in the headwaters and to turbidity in the lower reaches of the watersheds studied. For high flow conditions, E. coli concentration and loading are poorly correlated to most variables, except stream water temperature and 7-d antecedent discharge. These results are consistent with those reported in the literature and suggest that, at least during base flow conditions, turbidity and 7dP may be usable in artificially drained landscapes of the Midwest to identify potential hot spots of E. coli contamination.  相似文献   
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