散落核素^7Be和^137Cs在洱海和红枫湖沉积物中蓄积对比

沉积物柱芯分别采自滇西地区的洱海和黔中地区的红枫（及百花）湖，散落核素^7Be和^137Cs在沉积物中的蓄积特征对比分析表明，^7Be在洱海及红枫湖沉积物中的累计值分别为（237±73）Bq/m^2和（783±44）Bq/m^2；按校正到沉降年代的数值，1986年以前^137Cs的累计值分别为（519±26）Bq/m^2及（3704±56）Bq/m^2。由模式计算获知，（1）^7Be和^137Cs在红枫湖沉积物中的蓄积以侵蚀影响为主；在洱海的蓄积受直接散落控制。（2）在洱海和红枫湖地区^7Be大气散落累计值分别为（0．07±0．02）Bq/cm^2及（0．08±0.01)Bq/cm^2；1986年以前^137Cs大气散落累计值分别为（0.11±0.01)Bq/cm^2及（0.37±0.01)Bq/cm^2，显示出滇西与黔中地区之间^137Cs散落的地区差异。这一现象可能反映出青藏高原对滇西地区存在着全球性大气扩散污染物散落的屏蔽效应。

^137Cs在滇西与黔中地区散落的差异—青藏隆起对滇西地区全球性扩散大气污染物散落屏蔽效应的推断

云贵高原是青藏隆起在南亚大陆形成的一个海拔梯度大、地势格局复杂的特异环境单元。该地域兼受东南季风与西南季风的交汇影响，是全球变化的敏感区之一。青藏隆起对云贵高原现代环境影响主要表现在：1）全球性大气扩散污染物的屏蔽效应和局地性大气扩散污染物的滞留效应；2）区域化学风化的增强效应和物理侵蚀的梯级效应；3）地表环境地球化学过程的低纬度－高海拔效应。核素示踪模式分析表明：滇西与黔中地区之间^137Cs自大气散落差异明显[1986年以前，洱海和红枫湖沉积物中^137Cs散落的累计值分别为（0．11±0．01）Bq/cm^2及（0．37±0．01）Bq/cm^2],而^7Be的散落相近。这说明青藏隆起对滇西地区存在全球性扩散大气污染物散落的屏敝效应。

北太平洋西部和印度洋东部及其邻近海域表层水体中^137Cs的分布

对北太平洋西部海域、苏禄海及印尼海、中国南海、印度洋东部海域、孟加拉湾及安达曼海等表层水体中放射性核素 137Cs 的活度进行了测定。结果表明，上述海域表层水体中 137Cs 活度显示了较大的变化范围，最低值出现在南极附近的南大洋 ( 1.1 Bq m-3)，较高的活度值则出现在北太平洋西部海域及中国南海 ( 3 Bq m-3)。在所研究水域范围内，137Cs 活度的纬度分布特征并没有完全有效地反映出 137Cs 的全球理论大气沉降趋势及其纬度效应。综合本研究及 Miyake 等人 ( 1988 ) 的测定结果，我们计算出 137Cs 自表层海水中的析出速率在苏禄海及印尼海约为 0.016 /a，在孟加拉湾及安达曼海约为 0.033 /a，在国南海约为0.029 /a，这一结果明显低于西北太平洋日本沿海表层水体中 137Cs 的析出速率。这可能是因为在这些海域，横向及纵向的水体混合过程相对都较慢，而且颗粒物对 137Cs 的吸附析出过程也比较弱所致。

Inventories and concentration profiles of 137Cs in undisturbed soils in the northeast of Buenos Aires Province, Argentina

Inventories and vertical distribution of (137)Cs were determined in La Plata region undisturbed soils, Argentina. A mean inventory value of 891 ± 220 Bq/m(2) was established, which is compatible with the values expected from atmospheric weapon tests fallout. The study was complemented with pH, organic carbon fraction, texture and mineralogical soil analyses. Putting together Southern Hemisphere (137)Cs inventory data, it is possible to correlate these data with the mean annual precipitations. The large differences in (137)Cs concentration profiles were attributed to soil properties, especially the clay content and the pH values. A convection-dispersion model with irreversible retention was used to fit the activity concentration profiles. The obtained effective diffusion coefficient and effective convection velocity parameters values were in the range from 0.2 cm(2)/y to 0.4 cm(2)/y and from 0.23 cm/y to 0.43 cm/y, respectively. These data are in agreement with values reported in literature. In general, with the growth of clay content in the soil, there was an increase in the transfer rate from free to bound state. Finally, the highest transfer rate from free to bound state was obtained for soil pH value equal to 8.

137Cs Inventory in sedimentary columns from continental shelf of São Paulo State

137Cs is an artificial radioactive isotope produced by 235U fission. This radionuclide has a high fission yield and a half-life of 30 years. It has been detected in the environment since 1945 and its principal contamination source has been nuclear tests in the atmosphere. There are other sources of 137Cs contamination in the environment, such as: release from nuclear and reprocessing plants, radioactive dumping and nuclear accidents (Chernobyl, for example). This paper presents an inventory of 137Cs on the Continental Shelf of São Paulo State, a region located between Cabo de Santa Marta Grande (Santa Catarina state) and Cabo Frio (Rio de Janeiro state). In this area, 9 cores were collected by the Instituto Oceanográfico da Universidade de São Paulo (São Paulo University Institute of Oceanography). The cores were sliced at every 2 cm; sub-samples were lyophilized, grinded and stored in plastic containers. 137Cs was determined by 661 keV photopeak using a gamma spectrometry detector (Ge hyperpure). The analysis was performed by efficiency and background in different counting times. 137Cs concentration activities varied from 0.3 to 3.6 Bq kg-1 with a mean value of 1.2±0.6 Bq kg-1. The inventory of 137Cs in this area was 13±7 Bq m-2. Values obtained are in agreement with the Southern Hemisphere, a region contaminated by atmospheric fallout due to past nuclear explosions.

Application of 137Cs and 210Pb radionuclides to determine sedimentation rates of recent sediments from admiraty Bay, Antarctica Peninsula

Studies about natural and artificial radionuclides in areas such as the Antarctic are key to understand natural and dynamic processes in marine environments. These studies are important to determine levels of radioactive elements and local sedimentation rates. Five marine sediment cores were collected in different points of Admiralty Bay, in the Antarctic Peninsula. The purpose of this study was to determine 137Cs, 226Ra and 210Pb and sedimentation rates at each site. 137Cs, 210Pb and 226Ra were assayed by gamma-counting through direct measurement of the peak at 661 keV, 47 keV and 609 keV, respectively. Sedimentation rates were obtained by 137Cs and 210Pb (CIC and CRS). The activities for 137Cs ranged from 0.84 to 7.09 Bq kg-1; to 226Ra from 6.77 to 31.07 Bq kg-1 and for 210Pb ranged from 1.10 to 36.90 Bq kg-1. The sedimentation rates obtained by the three models ranged from 0.11±0.01 cm y-1 to 0.46±0.05 cm y-1. The levels of 137Cs registered in this study, as well as in other studies in the Antarctic region indicate that global fallout is the main cause of artificial radionuclides present in this environment, since the Antarctic has not suffered a direct action of human activities that released radioactive elements. The possible grain size variations that occur in the studied points of Admiralty Bay may explain the differences found in the vertical distribution of radionuclides, because of the different values of sedimentation rates and respective dating determined in their profiles

137Cs concentrations in the southeastern Baltic Sea in 1997-2000

Variations of 137Cs concentration in the southeastern Baltic Sea were investigated over the period 1997-2000, i.e. in 11-14 years after the Chernobyl Nuclear Power Plant accident. Rate of "self-cleaning" proved to be very slow. Some results obtained in 1999 were almost the same as those measured after the accident, in 1986. Calculated results showed that "Chernobyl" caesium-137 would be "cleaned" in the Baltic Sea by 2020-2022. In 2000 average concentration had to be about 50-60 Bq/m**3. Sometimes mentioned concentrations were observed. In some cases higher concentrations averaging from 67 to 80 Bq/m**3 were registered in the southeastern Baltic Sea in 1999; and in some samples 137Cs concentrations were very high. They varied from 110 to 212 Bq/m**3. No steady correlation was observed between 137Cs concentration, salinity and temperature in surface water of the area. Distribution of radionuclide concentration sometimes depends on direction of water mass transport. Abnormally high concentrations of 137Cs in the southeastern Baltic Sea may result from additional radioactive waste discharge.