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1.
Migration of 14C derived from 14C-acetic acid was examined by using soils sampled from paddies in four administrative areas in Japan (Aomori, Yamanashi, Ehime and Okinawa) and rice plant in a tracer experiment to understand the fate of 14C in the paddy soil-to-rice plant system. The loss of 14C radioactivity levels derived from 14C-acetic acid was caused by soil microorganism breakdown. A part of the 14C fixation to soil was caused by microbial assimilation into the fatty acid fraction. 14C moved upward via two different types of 14C dynamics in soil: quick movement upward; and constant but slow movement upward. 14C was highly assimilated into the plant panicle and that was caused by the root-uptake and the transfer of 14C. Migration of 14C derived from 14C-acetic acid relied heavily upon changes of chemical forms and characteristics of 14C-compound as caused by microorganisms in soil.  相似文献   

2.
Environemtnal 14C levels around various types of nuclear installations within the UK have been monitored during recent years. Enhanced 14C levels have been detected around both the nuclear fuel reprocessing plant as Sellafield and the thermal nuclear power station complex at Hunterston. From these measurements, the radiological impact of the 14C discharges on the local population is assessed. It is conservatively estimated that the 14CO2 emissions from Sellafield between 1952 and 1985 could have delivered an 8·4 man Sv collective effective dose equivalent commitment to the population living within 40 km of the site. The maximum possible collective dose to the population within 15 km of Hunterston in 1984 was 15 × 10−3 man Sv. Conservative estimates of maximum annual effective dose equivalents to individuals around Sellafield and Hunterston are 0·2 mSv (in 1982) and 12 μSv (in 1984), respectively. These dose levels do not exceed the limits recommended by ICRP but the former value clearly indicates that, for the larger discharges at least, consideration and optimisation of 14C releases are fully justified. The same 14C measurements are also used to test the validity of two atmospheric dispersion models, the Gaussian plume and the so-called ‘hyperbolic’ models. The former is excellent in predicting downwind 14C levels around Hunterston but is unsatisfactory when applied to Sellafield, whereas the latter proves reliable at both sites. Further investigations suggest that the Gaussian plume model's poor performance at Sellafield can be explained by inaccurate input data.  相似文献   

3.
Carbon-14 was added to the epilimnion of a small Canadian Shield lake to investigate primary production and carbon dynamics. The nature of the spike and subsequent monitoring allowed the investigation of both short-term and longer-term processes relevant to evaluating impacts of accidental and routine releases and of solid waste disposal. Data from this experiment were used in the BIOMOVS II program as a validation test for modelling the fate of the 14C added to the lake. Four models were used: (1) a simple probabilistic mass balance model of a lake; (2) a relatively complex deterministic model; (3) a complex deterministic model; and (4) a more complex probabilistic model. Endpoints were 14C concentrations in water, sediment and lake whitefish over a thirteen year period. Each model produced reasonable predictions when compared to the range of the observed data and when uncertainty in model predictions is taken into consideration. The simple lake model did not account for internal recycling of 14C and, in this respect, its predictions were not as realistic as those of the more complex models for concentrations in water. However, the simple model predictions for the 14C inventory remaining in lake sediment were closest to the observed values. Overall, the more complex probabilistic model was the most accurate in simulating 14C concentrations in water and in whitefish but it overestimated 14C retention in the lake sediments, as did the other complex models. Choice of parameter values for transfer rate to sediment and gaseous evasion are important in influencing model predictions. Although predicted concentrations of 14C in fish of dynamic models were more accurate than those using equilibrium bioconcentration factors typically used in assessments, large variability in observed 14C concentrations in whitefish emphasizes the need for a better understanding of the important processes that influence these contaminant concentrations.  相似文献   

4.
A dynamic compartment model was investigated to describe 14C accumulation in rice plants exposed to atmospheric 14C with temporally changing concentrations. In the model, rice plants were regarded to consist of three compartments: the ear and the mobile and immobile carbon pools of the shoot. Photosynthetically fixed carbon moves into the ear and the mobile carbon pool, and these two compartments release a part of this carbon into the atmosphere by respiration. Carbon accumulated in the mobile carbon pool is redistributed to the ear, while carbon transferred into the immobile carbon pool from the mobile one is accumulated there until harvest. The model was examined by cultivation experiments using the stable isotope, 13C, in which the ratios of carbon photosynthetically fixed at nine times during plant growth to the total carbon at the time of harvest were determined. The model estimates of the ratios were in relatively good agreement with the experimental observations, which implies that the newly developed compartment model is applicable to estimate properly the radiation dose to the neighboring population due to an accidental release of 14C from nuclear facilities.  相似文献   

5.
Nuclear power plants release 14C during routine operation mainly as airborne gaseous effluents. Because of the long half-life (5730 years) and biological importance of this radionuclide (it is incorporated in plant tissue by photosynthesis), several countries have monitoring programs in order to quantify and control these emissions. This paper compares the activity of 14C in soils taken within 1 km from a Brazilian nuclear power plant with soils taken within a reference area located 50 km away from the reactor site. Analyses of total carbon, δ13C and 137Cs were also performed in order to understand the local soil dynamics. Except for one of the profiles, the isotopic composition of soil organic carbon reflected the actual forest vegetation present in both areas. The 137Cs data show that the soils from the base of hills are probably allocthonous.  相似文献   

6.
Atmospheric air samples were taken within 3 km from power plants encompassing five different distances and wind directions. Samples were taken between 2002 and 2005 aiming to evaluate the environmental 14C enrichment due to the operation of Brazilian nuclear power plants. The sampling system consisted of a pump connected to a trapping column filled with a 3 M NaOH solution. The trapped CO2 was analyzed for 14C by using a single stage accelerator mass spectrometry (SSAMS).  相似文献   

7.
Differences in natural 14C content of rings from trees from urban and rural locations have been compared on a year by year basis. The differences as a fraction of the urban tree's radioactivity reflect the local excess 14C-free carbon dioxide from fossil fuel combustion in the urban environment. New York City, Boston, and Washington, D.C., show different degrees of excess carbon dioxide. New York City averages about 6% excess carbon dioxide between 1950 and 1970. From this is infered an average carbon monoxide concentration during this period of 5 ppm.  相似文献   

8.
The Suess Effect is a term which has come to signify the decrease in 14C in atmospheric CO2 owing to admixture of CO2 produced by the combustion of fossil fuels. This term is here extended, as a concept, to the shifts in isotopic ratio of both 13C and 14C in any reservoir of the carbon cycle owing to anthropogenic activities. To explain this generalized Suess Effect a four reservoir global model of the natural carbon cycle is developed in which isotopic fractionation and radioactive decay are fully taken into account. The model includes the cases in which the deep ocean is treated either as a single undifferentiated box model reservoir or is vertically differentiated with eddy diffusion governing the transport of carbon. Also, the governing equations are expressed with sufficient generality to apply simultaneously to both rare isotopes. In so far as possible, the model is expressed without approximation of the isotopic processes even though this leads to non-linear differential equations to describe the rates of change of rare isotopic carbon within carbon reservoirs. Linear approximations also developed and solved using the method of Laplace transforms. The sensitivity of the predicted Suess Effects to uncertainties in the assigned values of the model parameters is investigated in detail, including estimates of some of the effects of linearizing the governing equations.The approximation of Stuiver, in which the atmospheric Suess Effect is assumed to be 0.018 times the corresponding effect for 14C, is examined in detail and shown to arise when both isotopic fractionation and radioactive decay are left out of the model. This approximation, although correct as to order of magnitude, is found to be too imprecise to be recommended in modeling studies.As found in previous work, the predicted atmospheric Suess Effect for 13C for a given airborne fraction of industrial CO2 is of similar magnitude whether the land biosphere has been a net source or sink of carbon during recent times. On the other hand, the corresponding effect for a surface ocean water is considerably smaller than otherwise if the land biosphere has been a source of CO2 instead of a sink. The model is thus useful in indicating the need to consider isotopes in several reservoirs simultaneously.Although the emphasis is on formulating models rather than surveying and interpreting data, observational data are summarized and compared with model predictions. The oceanic data are seen to be too meager as yet to help settle the question of biospheric response to man's activities.  相似文献   

9.
Many long-lived radionuclides are present in groundwater at the Nevada Test Site (NTS) as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. In conjunction with a comprehensive geochemical review of radionuclides (3H, 14C, 36Cl, 99Tc and 129I) that are presumably mobile in the subsurface, we synthesized a body of radionuclide activity data measured from groundwater samples collected at 18 monitoring wells, to qualitatively assess their migration at the NTS over distances of hundreds of meters and over timescales of decades. Tritium and 36Cl showed little evidence of retardation, while the transport of 14C may have been retarded by its isotopic exchange with carbonate minerals in the aquifer. Observed local reducing conditions (either natural or test-induced) will impact the mobility of certain redox-sensitive radionuclides (especially 99Tc) that were otherwise soluble and readily transported under oxidizing conditions. Conversely, strongly oxidizing conditions may impact the mobility of 129I which is mobile under reducing conditions. The effect of iodine speciation on its transport deserves further attention. Indication of delayed transport of some “mobile” radionuclides (especially 99Tc) in the groundwater at the NTS suggested the importance of redox conditions of the natural system in controlling the fate and transport of radionuclides, which has implications in the enhanced performance of the potential Yucca Mountain repository, located adjacent to the NTS, to store high-level nuclear wastes as well as management of radionuclide contamination in legacy nuclear operations facilities.  相似文献   

10.
The level and identity of [14C] residues in bluegills (Lepomis macrochirus)_exposed to 2.5 mg/L [14C] triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid) have been determined. The highest level of radioactivity observed in the flesh of a fish at any time point (0.13 mg/kg, calculated as equivalent mg triclopyr/kg fish) was less than 5% of the fish exposure level of 2.5 mg/L, while the maximum level in the remainder (head, skin, and viscera) was about 95% (2.33 mg/kg) of the fish exposure level, indicating no concentrating effect. The principal components observed in the fish tissues were triclopyr, 3,5,6-trichloro-2-pyridinol, 2-methoxy-3,5,6-trichloropyridine and a conjugate. These components accounted for greater than 75% of all the residues observed.  相似文献   

11.
This paper summarized the study carried out in Krakow, Poland in 1975-76 on the estimated local air pollution as measured by carbon isotopes and total sulphur measurement in plants. Good correlation was found between δ14C value and the total sulphur (measured by radionuclide excited X-ray fluorescence) in beech leaves collected in the late summer, indicating the common source of both pollutants. Sampling and measurement of σ13C in atmospheric CO2 has shown that σ3C can be used as a pollution indicator only in the winter period when no fluctuations exist ddue to plant respiration. A method of CO2 sampling using molecular sieve proved to be feasible for instantaneous sampling with no isotope fractionation. The highest pollution by fossil CO2 was measured in winter (12.8% excess. During spring and summer the average contribution of fossil CO2 was 4.5 to 5.6%.  相似文献   

12.
Few analytical techniques are sensitive enough to detect environmental concentrations of uranium in waters where humic acids are present. One objective of this study was to devise a technique for measuring humic-complexed and uncomplexed uranium at these concentrations. Three techniques were combined to determine the binding capacity and conditional stability constant of uranium with Aldrich® humic acid. Free UO22+ was separated from bound by chelating resin; the CC bonds were destroyed by photo-oxidation and UO22+ was quantified by laser fluorometry. The binding capacity (BC) of 3·5 mg C liter−1 Aldrich humic acid solution was estimated to be 1·14 × 10−6MUO22+ with an asymptotic standard error of 5·0 × 10−8MUO22+. UO22+ was bound to humic acid by a continuum of sites with different strengths. The frequency distribution of these sites was log-normal. A Gaussian-Scatchard model was used to estimate the overall conditional stability constant for uranium concentrations of 5·25 × 10−8Mto 2·1 × 10−7M in the presence of 3·5 mg liter−1 humate (1·14 × 10−6M = φ). The estimates of the mean and standard deviation for the log of the stability constants were 6·5 and 0·8, respectively. When these mean and standard deviations were used to determine the mole-average number of binding sites at three points on the Gaussian distribution, the estimators of log-stability constants were found to be: K1 = 5·2, K2 = 6·5 andK3 = 7·7 with mole fractions of the total number of binding sites associated with each region of 0·21, 0·55 and 0·21, respectively. The thermodynamic, geochemical simulation model GEOCHEM and the three-component Gaussian-Scatchard estimates allowed accurate prediction of the relative proportion of UO22+ bound to humates for a soft water pond across the entire range of metal-ligand ratios studied. Approximately 22% of the UO22+ was predicted to be associated with dissolved organic carbon.  相似文献   

13.
Global atmospheric CO2 concentration has increased since the beginning of reliable monitoring in 1958 at a mean rate of about 0.9 ppm CO2/yr. Now, atmospheric CO2 concentration is at 330 ppm. From about 1860 up to 1974, man's intervention in the global carbon cycle caused a likely increase of 76.6 × 1015 gC, corresponding to 36 ppm CO2 in the atmosphere, if a preindustrial content of 294 ppm CO2 or 625.3 × 1015 g C is adopted to be valid. A further rise of atmospheric CO2 seems to be inevitable and probably will be responsible for a climatic warming in the next several decades; therefore, a global examination of carbon reservoirs and carbon fluxes has been undertaken to determine their storage capacity for excess carbon which orginated mainly from burning fossil fuels and from land clearing. During 1860–1974 about 136 × 1015 g C have ben emitted into the atmosphere by fossil fuel combustion and cement production. At present, the emission rate is about 5 × 1015 g C/yr. The worldwide examination of carbon release, primarily by deforestation and soil cultivation since 1860, is estimated to be about 120 × 1015 g C. The net transfer of carbon to the atmosphere owing to man's interference with the biosphere is now believed to be about 2.4 × 1015 g C/yr. An oceanic uptake of roughly 179 × 1015 g C since 1860 is open to discussion. According to the chemical buffering of sea surface water only about 35.5 × 1015 g C could have been absorbed. It is argued, however, that oceanic circulations might have been more effective in removing atmospheric excess carbon of anthropogenic origin.  相似文献   

14.
The levels of Chernobyl-derived 103Ru, 106Ru, 134Cs and 137Cs were measured in Algoma, Ontario rain samples collected as weekly composites until September 30, 1986. The radionuclides were consistently measurable until about mid-June. The data, when analyzed in conjunction with 7Be measurements, yield a mean tropospheric residence time of about 14 days for the four radionuclides. This value is significantly lower than the previous estimates based on nuclear explosion-derived radionuclides but is within the range of values reported using radon daughters.  相似文献   

15.
A specimen of Araucaria angustifolia from the south of Brazil was analyzed for 13C/12C variations in the cellulose of the tree rings. Those data, when compared with the growth pattern of the tree, showed a good correlation (r = ? 0.72) over a period of 200 years. A collection of six European trees was analyzed for the same effect and, although the expected inverse relation is evident from the graphical representation, the correlation coefficients are small. This is certainly due to the large scatter of δ13C data from those trees.  相似文献   

16.
A shallow-land radioactive waste repository operated in boggy forest environment from 1963 to 1989. During the operation period, a considerable amount of technogenic radionuclides, in solidified state, was disposed into the vault established in the geological structure at the depth of up to 3 m. Environmental monitoring activities started after the closure of the repository in 1989. Recent investigations revealed transfer of radiocarbon and plutonium to the groundwater in the prevailing flow direction. Activity concentration of 239,240Pu in non-filtered fraction of the groundwater from observation well no. 4 determined by alpha-spectrometry was 6.4 × 10−5 Bq l−1 in 2005, and 3.2 × 10−4 Bq l−1 in 2006. Further analysis of colloid-facilitated transport of plutonium is planned. Variation of 14C activity concentration in the same well was monitored in 2006. It varied from 0.2 ± 0.1 Bq l−1 in October to 2.8 ± 0.6 Bq l−1 in June and July. Results imply further research into radiocarbon transfer to atmosphere and selected plant species.  相似文献   

17.
The Proserpina dam was built in Roman times to provide drinking water to Emerita Augusta (today's Mérida in SW Spain). During maintenance work, a sediment core was extracted, offering an excellent opportunity to analyze the historical environmental impacts of the dam and its reservoir over the 2000 years since Roman times. In order to establish an accurate chronology, 14C ages were determined by accelerator mass spectrometry (AMS). Core samples were assayed for their content in uranium and thorium series isotopes, 40K, and the anthropogenic radionuclides 137Cs, 90Sr, and 239+240Pu. Potassium-40 presented the highest activity level and was not constant with depth. The uranium and thorium series were generally in equilibrium, suggesting there had been no additional input of natural radionuclides. The presence of 137Cs was only found in relation with the global fallout in the early 1960s. Multi-element assays were performed using the PIXE and PIGE techniques. Some variations in the multi-element concentrations were observed with depth, but the sediment core could be considered as clean, and no presumptive anthropogenic pollutants were found. Nevertheless, an unusually high Zn content was detected at depths corresponding to pre-Roman times, due to geological anomalies in the area.  相似文献   

18.
To better understand how Batrachupems tibetanus responds to different temperature regimes in the blood parameters and to estimate the change in plasma cortisol level in this species exposed to different temperatures, the animals were stochastically divided into three groups and exposed respectively to 4.6°C, 14.6°C and 19.6°C for 12 days. The concentrations of glucose, total protein, albumin, triacylglycerol, Ca2+, K+, Na+, Cl, and plasma cortisol level were measured respectively. There was no significant difference between the plasma cortisol level of the control group and the experiment groups. Glucose level at 4.6°C and 19.6°C was significantly lower than glucose level at 14.6°C. The plasma triacylglycerol level was significantly influenced by acclimation temperature. The concentration of total protein, albumin, globulin and the ratio between albumin and globulin were not significantly influenced by temperature when compared with control group. There was no significant change in concentration of Ca2+ at different temperatures. The concentration of K+ was significantly influenced by temperature. Plasma K+ level significantly increased at 19.6°C. The plasma Na+ level and Cl were significantly influenced by temperature. Na+: Cl ratio was significantly influenced by temperature. Therefore, glucose, triacylglycerol, Na+ and Cl levels could be considered as indicators of thermal stress in B. tibetanus; plasma cortisol, albumin, globulin levels, and albumin/globulin ratio are not influenced by temperature.  相似文献   

19.
Characteristics of carbon storage and density in different layers of forest ecosystems should be studied comprehensively and in more detail. Using forest inventory data in combination with field survey data, we explored the characteristics of carbon storage and density in different layers of forest ecosystems in Liaoning Province of China. Results showed that total carbon storage was 813.034 Tg C. The carbon storage of soil layer accounted for 81.0% of the total storage with 658.783 Tg C, followed by those of arbor, litter and shrub layers with 128.403 Tg C (15.8%), 22.723 Tg C (2.8%) and 3.125 Tg C (0.4%), respectively. The average carbon density for the forest ecosystems were 183.571 Mg C ha–1, with soil layer (148.744 Mg C ha–1) being the highest one, followed by arbor layer (28.992 Mg C ha–1), litter layer (5.131 Mg C ha–1) and shrub-grass layer (0.706 Mg C ha–1). Carbon storage in different forest ecosystems varied from 1.595 to 319.161 Tg C, while C density ranged from 165.067 to 235.947Mg C ha–1, with the highest and lowest values being observed in soil layer and shrub-grass layers, respectively, implying that soil is the main body of forest carbon storage. Young-aged forests accounted for a greater proportion of forests in the Province than forests in other age classes; and proper management of forests could increase the carbon sequestration in the forest ecosystems. The comparison with previous estimations of carbon storage for forest ecosystem implied that methods and data used for forest carbon storage estimation affected the results of estimates obviously.  相似文献   

20.
The limnological record of human impact on catchment land cover and on lake sedimentation during the historical period has been established for Pinto Lake in Central Coastal California. In addition, the sedimentary record of the ‘pre-impact’ condition preserves evidence of a climatic control on the nature of lake sedimentation. Chronological marker horizons have been determined using pollen data in combination with the documented land-use history and introductions of exotic species. Further chronological data have been determined using 14C and 137Cs. The impact of Mexican and Euro-American immigrants and their ‘imported’ land-use practices is clearly reflected in an order of magnitude increase in the rate of lake sedimentation to c. 9 kg m−2 year−1 (c. 2 cm year−1) between 1770 and 1850. Here, the occurrence of exotic plant species indicates disturbance as early as c. 1769–1797, whilst redwood deforestation between 1844 and 1860 represents the most significant human impact. Changes in the nature of sedimentation prior to this reveal a high degree of sensitivity to changes in precipitation where subtle decreases in lake level and the supply of runoff-derived mineral matter have resulted in two periods of organic lake sedimentation c. 650–900 and 1275–1750. Set against this background condition of high sensitivity, the dramatic impacts of Euro-American settlement are unsurprising. An erratum to this article can be found at  相似文献   

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