Natural radionuclides in soil-A trial for estimating uptake capacity of pollutants by soils and for evaluating soil heterogeneity

土壤中的天然放射性核素-土壤吸收污染物能力和评价土壤异质性的试验

• 批准号: 13680614
• 负责人: FUJIYOSHI Ryoko
• 金额: $ 2.24万
• 依托单位: Hokkaido University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13680614/
• 关键词: soil; natural radionuclide; vertical profile; environmental change; 収着; 環境変遷

The objective of the study is to elucidate heterogeneity of the soil composition within a pertinent soil horizon by measuring variability of the vertical profiles of environmental radionuclides (^<40>K, ^<226>Ra, ^<137>Cs and ^<210>Pb) in the soil, and to obtain data on partition coefficient of heavy metals (Mn(II) and Zn(II)) using a radiotracer technique. For these purposes, two types of the location were selected : one is a site of alluvial deposits down to a depth of 3.5 m on the campus of Hokkaido University. The samples were collected from November 2000 to March 2001 by the courtesy of Prof. Kasahara (Graduate School of Science, Hokkaido University). And the other is several sites covered with conifer and beech stands of different age at Wetzstein, Tharandt, Hainich and Leinefelde in Germany. The samples were collected in November 2001 (Wetzstein) and in March, 2002 (Tharandt, Hainich and Leinefelde) by the help of Prof. T. Paces (Geological Survey, Czech Republic) and Dr. Reiner … More Zimmermann (Max Plank Institute, Germany).Gamma spectrometry was used to obtain activity concentrations of these nuclides for the alluvial sediment to know their background values. The results also show that there appeared a minimum of ^<40>K activity at certain depth within a deposition layer of the same origin. Such an anomaly was also observed in other properties of the sediment at this depth such as moisture and organic contents. It is likely that depositional and/or post-depositional situation would have been changed probably by water action like heavy rain, percolating groundwater or melting snow.Investigation of the forest soils in Germany gave the results that vertical, profiles of ^<40>K depend on local geology (400-1100 Bqkg^<-1>). Its activity concentration increases with soil depth, and with increasing density. Radium-226 activity is varied with depth ranging from 20 to 55 Bqkg^<-1> for all the soil samples investigated, which suggests that the soil is rather heterogeneous in composition within a horizon of interest. An activity ratio between ^<210>Pb and ^<226>Ra could be a measure of gaseous ^<222>Rn emanation at each depth. The ratio gave values between 0.3 and 0.5 for most of the depths except for the uppermost part (<10 cm in depth) where ^<210>Pb activity is quite high due to dry- and wet deposition from the atmosphere. High values of the ^<137>Cs activity were observed only in the upper portion of some sites. This nuclide was mostly derived from the Chernobyl accident in Russia (April, 1986), and its vertical profile has been used extensively for estimating deposition rate of the surface soil so far. The deposition rate obtained is 1.8 and 2.7 mm/y for the Wetzstein coniferous forest soils of 40 and 120 years old in stand age. The result seems to be related with mean stand age of the forest. However, there was no distinct relationship between deposition rate (1.2 to 2.2 mm/y) and stand age at other forest sites. It must be investigated further in detail that all the sites did not give an exponential decay of ^<137>Cs activity with depth. Concerning the ^<137>Cs profile with depth, there appeared two more types of ^<137>Cs profiles for the forest soils investigated in this study : One is the sites where radiocesium was little present even in the uppermost portion of the soil. Such a profile might be resulted from surface runoff. Canopy effects are also possible to affect the ^<137>Cs distribution on top of the soil. In addition, there were several sites where ^<137>Cs disappeared at certain depth and appeared again at much deeper depth. Such a profile may be due to biological activities like some type of micro- and macro-organisms inhabiting there. It must be added that there remain several facts not to be explained yet in this study.On the partition of divalent metals to the forest soils, Zn(II) is always sorbed to a greater extent than Mn(II). Partition coefficient of Zn(II) (K_d(Zn)) is in the range between 100 and 200 (L/kg) at a depth deeper than 10 cm, and about a half of the K_d(Zn) value appeared on the Mn(II) sorption (K_d(Mn)). Partition coefficients of Mn(II) and Zn(II) were quite high at the surface portion of the soil. These values decreased remarkably after a heat treatment of the samples at 450℃. The results indicate that the soil organic matter is likely to provide sites for the metal(II) sorption, which is supported by a positive correlation between organic content and cation exchange capacity (CEC) of the soil.In summary, change in K_d values with soil depth suggests relative contribution of inorganic and organic components to uptake metal ions.Present study also gave applicability of environmental radionuclides and their variability of vertical profiles for estimating possible changes in soil environment. The line of this work should be continued further to evaluate consequences of bioturbation often observed in various soils. Less

这项研究的目的是通过测量土壤中环境放射性核素(Ra、137&gt；Cs和^&lt；210&gt；Pb)垂直剖面的变异性，并利用放射性示踪技术获得重金属(Mn(II)和Zn(II))的分配系数数据，以阐明土壤中特定土层内土壤组成的异质性。为此，选择了两种类型的地点：一种是北海道大学校园内3.5米深的冲积物遗址。这些样本是由北海道大学科学研究生院Kasahara教授于2000年11月至2001年3月收集的。另一个是德国韦茨斯坦、萨兰特、海尼奇和莱因费尔德的几个地点，覆盖着不同年龄的针叶树和山毛榉。样本是在2001年11月(韦茨坦)和2002年3月(塔兰特、海尼奇和莱因费尔德)在T.Pace教授(捷克共和国地质调查局)和Reiner…博士的帮助下收集的More Zimmermann(Max Plank Institute，德国)。伽玛能谱被用来获得这些核素的活度浓度，以供冲积沉积物了解它们的背景值。结果还表明，在同一来源的沉积层中，在一定深度处出现了最低的~(40)&K活度。在这个深度的沉积物的其他性质中也观察到了这样的异常，如水分和有机含量。沉积和/或沉积后的情况很可能已经被暴雨、地下水渗透或融化的水作用所改变。对德国森林土壤的调查结果表明，垂直的剖面取决于当地的地质(400-1100Bqkgk；-1)。其活性浓度随着土壤深度的增加和密度的增加而增加。在所调查的所有土壤样品中，~(226)Re的活度随着深度的变化而变化，范围从20到55Bqkgkg^-1；这表明在感兴趣的土层内土壤的组成是相当不均匀的。^&lt；210&gt；铅和^&lt；226&gt；Ra之间的活度比可以用来衡量气体^&lt；222&Rn在每个深度的释放。大多数深度的比值在0.3到0.5之间，除了最上面的部分(&lt；10厘米深)，由于大气的干湿沉积，^&lt；210&gt；铅的活度相当高。~(137)Cs和~(137)Cs的高值仅在某些地点的上部观察到。这种核素主要来源于俄罗斯切尔诺贝利事故(1986年4月)，到目前为止，它的垂直剖面被广泛用于估算表层土壤的沉积速率。40年生和120年生的Wetzstein针叶林土壤在林龄时的沉积速率分别为1.8和2.7 mm/年。这一结果似乎与森林的平均林分年龄有关。然而，其他林地的沉积速率(1.2~2.2 mm/年)与林龄之间没有明显的关系。必须进一步详细调查，所有的地点都没有给出~(137)Cs活度随深度的指数衰减。关于~(137)Cs剖面随深度的变化，本研究调查的森林土壤~(137)Cs剖面还出现了两种类型：一种是土壤最上部也很少有放射性铯存在的地点；这种剖面可能是由地表径流引起的。树冠效应也可能影响土壤表层的~(137)Cs分布。此外，有几个地点的^&lt；137&gt；Cs在一定深度消失，并在更深的深度再次出现。这种情况可能是由于生物活动所致，比如栖息在那里的某种类型的微型和宏观有机体。必须补充的是，本研究中仍有几个事实没有得到解释。在二价金属对森林土壤的分配上，锌(II)的吸附总是大于锰(II)。在10 cm以下，锌的分配系数(K_d(锌))在100~200(L/公斤)之间，K_d(锌)值约有一半出现在对Mn(II)的吸附(K_d(Mn))上。Mn(II)和Zn(II)在土壤表层的分配系数较高。样品经450℃热处理后，这些值显著降低。结果表明，土壤有机质可能为金属离子的吸附提供了场所，土壤有机质含量与阳离子交换量(CEC)呈正相关，K_d值随土壤深度的变化表明无机组分和有机组分对金属离子的吸附作用相对较大。这项工作应该继续下去，以评估在各种土壤中经常观察到的生物扰动的后果。较少

项目成果

Fujiyoshi R., Suzuki Y., Sawamura S.: "Vertical profiles of ^<40>K and ^<226>Ra in subsoil in Sapporo, Japan"Relation between their activity concentration and soil properties. (in prep.).

Fujiyoshi R.、Suzuki Y.、Sawamura S.：“日本札幌下土中 ^<40>K 和 ^<226>Ra 的垂直剖面”它们的活性浓度与土壤性质之间的关系。

Ryoko Fujiyoshi: "Investigation of the soil radon variation during the winter months in Sapporo, Japan"Chemosphere. (2001)

Ryoko Fujiyoshi：“日本札幌冬季土壤氡气变化的调查”Chemosphere。

Nakayama M., Mitsutaka D., Fujiyoshi R., Sawamura S.: "Sorption of manganese(II) and zinc(II) to soils alluvial in origin using a radiotracer technique"J. Radioanal. Nucl. Chem.. 254(2). 331-334 (2002)

Nakayama M.，Mitsutaka D.，Fujiyoshi R.，Sawamura S.：“使用放射性示踪剂技术对冲积土中的锰（II）和锌（II）进行吸附”J。

Fujiyoshi R., Morimoto H., Sawamura S.: "Investigation of the soil radon variation during the winter months in Sapporo, Japan"Chemosphere. 47. 369-373 (2002)

Fujiyoshi R.、Morimoto H.、Sawamura S.：“日本札幌冬季土壤氡气变化的调查”Chemosphere。

Fujiyoshi R., Sawamura S.: "Mesoscale variability of vertical profiles of environmental radionuclides (^<40>K, ^<226>Ra, ^<210>Pb and ^<137>Cs) in temperate forest soils in Germany"(in prep.).

Fujiyoshi R.、Sawamura S.：“德国温带森林土壤中环境放射性核素（^<40>K、^<226>Ra、^<210>Pb 和 ^<137>Cs）垂直剖面的中尺度变异性”（