90Sr and 137Cs contamination of polished rice in Japan: Survey and analysis during the years 1959-1995
90Sr and 137Cs contamination of polished rice in Japan: Survey and analysis during the years 1959-1995
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DOI：
10.3769/radioisotopes.50.80
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发表时间：
2001-03-01
期刊：
影响因子：
--
通讯作者：
Kodaira, Kiyoshi
中科院分区：
文献类型：
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作者：
Komamura, Misako;Tsumura, Akito;Kodaira, Kiyoshi
本文讨论了全球范围的放射性沉降物对日本精米的影响。为此目的，一组水稻表土和糙米样品，每年从实验稻田在1959年至1995年在日本各地的17个站。根据展示精米样品中90 Sr和137 Cs含量（mBq/kg）全国平均值逐年变化的图表，1963年是第一个也是最高峰，90 Sr为269，137 Cs为4179。这两种核素的平均沉降水平也是当年最高的。此后，样品的~（90）Sr和~（137）Cs含量继续急剧下降，第二个峰值出现在1975年，为29 cntdot 192，第三个峰值出现在1995年，为5cntdot 46。可以认为，~（90）Sr和~（137）Cs是通过暴露在大气中的茎、叶和谷壳直接进入水稻籽粒的，也可以认为是通过水稻根从表层土壤中吸收后间接进入籽粒的。通过对污染途径的分析，最终确定了90 Sr和137 Cs在1963年降尘水平最高时的直接污染占70-95%，在1985年降尘核素停止检测后的几年中，主要是通过间接途径造成的。讨论了精米中~（90）Sr和~（137）Cs含量的地区差异，特别是日本海沿岸和太平洋沿岸地区的差异，精米和糙米中~（90）Sr和~（137）Cs分配率的差异，以及~（90）Sr和~（137）Cs在整株植物中转移的相对困难性。
This paper discusses the influences of global-scale radioactive fallout on polished rice in Japan. For this purpose, a set of paddy topsoil and unpolished rice samples was collected annually from experimental paddy fields at seventeen stations across Japan during the years from 1959 to 1995. According to the graph presenting year-to-year variations in the nationwide averages of 90Sr and 137Cs contents (mBq/kg) of the polished rice samples, the year 1963 marked the first and highest peaks with 269 for 90Sr and 4179 for 137Cs. The average fallout levels of the two nuclides were the highest in that year, too. Thereafter, 90Sr and 137Cs contents of the samples continued to decline drastically, the second peaks being in 1975 with 29cntdot192 and the third peaks in 1995 with 5cntdot46, respectively. It can be conceived that 90Sr and 137Cs nuclides are directly taken into rice grains from stems, leaves and husks which are exposed to the atmosphere, or they are indirectly taken into the grains after they are absorbed from paddy topsoil by the roots. Through the analysis of contamination pathways, it was finally confirmed that for both 90Sr and 137Cs, the direct contamination comprised 70-95% in 1963 when the fallout levels were the highest, and that in the years following 1985 when the fallout nuclides ceased to be detected, the rice contamination was produced mainly through the indirect pathway. Discussions also include the regional differences in the contents of polished rice, especially those between the Japan Sea coast and Pacific coast areas, differences in distribution rate of 90Sr and 137Cs between polished and unpolished rice, and relative difficulties of 90Sr and 137Cs being translocated in thoughout plants.