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31.
If no data are available for a specific radionuclide its analogue could be used in radioecological models. They might be used not only in the frame of screening modelling. Relevant processes and features have to be known, such as time scales of these processes, physical, chemical and biological properties of the environment and relevant media. An analogue could only be proven to be valid by comparing its behaviour in the conditions of interest, while confidence in the validity of an analogue will increase as the quality of the justification increases, there will always be some residual uncertainty. Several main types of analogy can be used when measured or recommended values are not available: the same parameter obtained for another isotope of the same element; the same parameter obtained for another element; a different parameter obtained for the same element. There are several cases, when analogues might be applied as indicators of the determining processes in the radioecological studies. 相似文献
32.
Radioxenon isotopes play a major role in confirming whether or not an underground explosion was nuclear in nature. It is then of key importance to understand the sources of environmental radioxenon to be able to distinguish them from those of a nuclear explosion. 相似文献
33.
David W. Ostendorf Baoshan Xing Niki Kallergis 《Journal of contaminant hydrology》2009,106(3-4):118-130
At a former wood preservation plant severely contaminated with coal tar oil, in situ bulk attenuation and biodegradation rate constants for several monoaromatic (BTEX) and polyaromatic hydrocarbons (PAH) were determined using (1) classical first order decay models, (2) Michaelis–Menten degradation kinetics (MM), and (3) stable carbon isotopes, for o-xylene and naphthalene. The first order bulk attenuation rate constant for o-xylene was calculated to be 0.0025 d− 1 and a novel stable isotope-based first order model, which also accounted for the respective redox conditions, resulted in a slightly smaller biodegradation rate constant of 0.0019 d− 1. Based on MM-kinetics, the o-xylene concentration decreased with a maximum rate of kmax = 0.1 µg/L/d. The bulk attenuation rate constant of naphthalene retrieved from the classical first order decay model was 0.0038 d− 1. The stable isotope-based biodegradation rate constant of 0.0027 d− 1 was smaller in the reduced zone, while residual naphthalene in the oxic part of the plume further downgradient was degraded at a higher rate of 0.0038 d− 1. With MM-kinetics a maximum degradation rate of kmax = 12 µg/L/d was determined. Although best fits were obtained by MM-kinetics, we consider the carbon stable isotope-based approach more appropriate as it is specific for biodegradation (not overall attenuation) and at the same time accounts for the dominant electron-accepting process. For o-xylene a field based isotope enrichment factor εfield of − 1.4 could be determined using the Rayleigh model, which closely matched values from laboratory studies of o-xylene degradation under sulfate-reducing conditions. 相似文献
34.
Sivaji Patra Manish Tiwari VishnuVardhan Kanuri Pradipta R. Muduli R. S. Robin 《Chemistry and Ecology》2017,33(8):708-724
The spatial distribution of the C/N ratios and variations in δ13C and δ15N of suspended particulate matter were used to characterise their source in Asia’s largest brackish water lagoon, Chilika, India. In addition, the significance of re-mineralised nutrients in the primary productivity of the shallow lagoon was also determined through quantification of the subsurface nitrogen uptake conditions at two relatively stable locations in the lagoon. The results indicated that the influence of terrestrial organic matter was the maximum in the northern sector and was relatively limited at the central and southern part of the lagoon. In situ 15N uptake experiments (daytime) under biogeochemically stable conditions revealed that the N uptake by phytoplankton ranged between 0.24 and 1.01?mM?m?3?h?1 during pre-monsoon and post-monsoon seasons. New production and regenerated production in the shallow lagoon was also estimated by calculating f-ratios (ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation, have been estimated), which varied from 0.52 in the post-monsoon to 0.38 in the pre-monsoon. Lowering of the f-ratio from post- to pre-monsoon indicated a dominance of mineralisation over the new production. 相似文献
35.
Zheng J Wu F Yamada M Liao H Liu C Wan G 《Environmental pollution (Barking, Essex : 1987)》2008,152(2):314-321
Studies on the distribution and isotope compositions of fallout Pu are important for source characterization of possible future non-fallout Pu contamination in aquatic environments, and useful for dating of recent sediments to understand the pollution history of environmental contaminants. We present the historical record of atmospheric Pu fallout reconstructed from a sediment core from Lake Hongfeng, China. The Pu activity profile was in agreement with the 137Cs profile. Inventories were 50.7 Bq m(-2) for 239+240Pu and 1586 Bq m(-2) for 137Cs. The average 240Pu/239Pu atom ratio was 0.185+/-0.009, indicating that Pu originated from global stratospheric fallout rather than from direct tropospheric or close-in fallout from the Chinese nuclear testing conducted in the 1970s. Our data suggested that Lake Hongfeng would be an ideal setting for monitoring atmospheric fallout and environmental changes in this region. 相似文献
36.
铅锌冶炼厂周边土壤铅源的铅同位素示踪 总被引:1,自引:0,他引:1
以某铅锌冶炼厂周边土壤为研究对象,通过对其原料及周边土壤中铅含量的检测,结果显示:该冶炼厂周边土壤铅质量比在22.73mg/kg~126.51mg/kg之间,平均值为42.68mg/kg,是当地土壤铅背景值的1.85倍.采用铅质量比空间分布分析和同位素混合模型计算分析了冶炼厂周边土壤中铅的可能来源,分析表明:土壤铅质量比的空间分布及铅同位素比值与冶炼厂的焦化原料煤相近,焦化原料煤对周边土壤铅污染贡献最大. 相似文献
37.
江苏洋口港地区地下水的环境同位素组成及其形成演化研究 总被引:4,自引:0,他引:4
江苏洋口港地区是江苏沿海开发重点建设的深水港区,水质优良的地下水是港区经济社会发展的重要基础.本研究利用近期获得的钻孔剖面地层对比数据资料,沿水文径流剖面分层采集水样,通过识别地表水、各含水层地下水的环境同位素(δD、δ~(18)O、~3H、~(14)C)组成指纹特征,以揭示研究区地下水的形成演化规律.结果表明,研究区浅层地下水主要来源于现代大气降水的入渗补给,大气降水在补给地下水过程中经历了明显的蒸发过程;研究区深层地下水的放射性~(14)C年龄主要为15000~26000 a,其稳定同位素δ~(18)O、δD值比现代降水低,是晚更新世末次冰期(大理冰期)的盛冰期降水入渗补给.地下水含水层的氘、氧、碳同位素分布具有明显的呈层性,随着地下水埋藏深度增加,地下水中的δD、δ~(18)O值呈下降趋势.浅层地下水与地表水水力联系紧密,可更新能力较强;深层地下水径流缓慢,总体上处于封闭-半封闭状态,可更新能力弱.江苏沿海平原天然地下水流动是自晚更新世末期以来,伴随着冰退、海平面上升而调整到目前的模式.末次盛冰期以来的自然地理及地质发展史,决定着研究区第四系地下水流系统的演变格局,现代人类活动加强了浅层与深层地下水之间的水力联系.研究在高强度开发地下水条件下的区域水文循环特征,可为沿海地区地下水演变机理和调控研究提供技术支持. 相似文献
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