① 川本妙子さん。原爆投下当時3歳。23歳の時に甲状腺機能低下症。その後、糖尿病、骨髄異形成症候群(白血病の前段階と言われる)、68歳、72歳で脳梗塞。
② 斉藤徹磨さん。原爆投下当時13歳。30歳過ぎてから体調を崩しがちになり、高血圧、白内障、糖尿病、心臓弁膜症、高脂血症。
③ 高東征二さん。原爆投下当時3歳。投下当時自宅の中にいた。見上げた空の色が、赤、黄、青、緑と色を変えた。チリや灰が降ってきたことを記憶している。しかし、その後の記憶がない。比較的健康で、雨に濡れた記憶もない。しかし、運動の過程で知り合った研究者からは、「チリや灰など、放射性微粒子が浮遊する空間にいたのだから被ばくしています」と言われている。高血圧を発症し、2019年、74歳の時に脳梗塞で入院。その後、不整脈、心房細動のカテーテルアブレーション治療を受けた。
Cummingら(128)はマウスにおける3H誘発特異的遺伝子突然変異に関する最初の一連の実験を完了し、あらゆる哺乳動物におけるそのような遺伝子突然変異に関する利用可能な唯一のデータを提供した。既存の原子力施設だけでなく、計画中の制御熱核反応炉からもトリチウムが放出される可能性があることを考慮すると、これらのデータは非常に重要である。合計 14 群の雄を使用した。その結果、トリチウムの崩壊によるベータ線は、精原細胞および減数分裂後の段階で特定の遺伝子座の突然変異を誘発することが示された。精原細胞に照射した生殖細胞から生まれた合計20 626個に16個の突然変異が、また、減数分裂後のステージに照射した7943個に11個の突然変異が確認された。精原細胞の平均吸収線量は700rad、後生物細胞のそれは430radと推定された。これらのデータから推定される突然変異率は、精原細胞では1遺伝子座当たり1.58 10-7 rad-1、その他の段階では1遺伝子座当たり4.60 10-7 rad-1である。これらの突然変異率は、X線またはガンマ線による同等の外部被曝線量から予想される統計的限界の範囲内である。精子形成後段階のRBEの点推定値は1に近く、信頼区間はかなり広い。精原細胞のRBEは2をやや上回り、信頼区間には1も含まれている。7つの遺伝子座における突然変異体の分布は、ガンマ線によって生じた分布とは異なる可能性があることを示すいくつかの兆候がある:注目すべきは、突然変異のうち1つだけがs遺伝子座にあったという観察である(予想では約5、6個となる)。最近の研究では、Cumming と W. L. Russell (129) が精原細胞における突然変異の誘発に注目し、トリチウム照射に関するより広範なデータの収集に従事している。
(c) トリチウム水によるヒトリンパ球の染色体異常の誘発 ( HTO )
Hori and Nakai (233) と Bocian ら (39) は、in vitro でトリチウム水に暴露されたヒトリンパ球に染色体異常が誘発されることを報告している。HoriとNakaiの研究では、トリチウムの濃度は1 10-6 μCi/mlから1 10-2 μCi/mlで、細胞は培養中の全期間(48時間)被曝させられた。Bocianらは2つの方法を用いた。1つは(著者らの用語で「急性被曝」)、リンパ球をPHA刺激前に2時間被曝させ(濃度範囲、1.71-14.36 mCi/ml)、その後洗浄、培養したもの(53時間培養)、もう一つは(「長期的な系列」)は細胞を53時間にわたって被曝させた(濃度範囲、0.063-0.51 mCi/ml)。
SOURCES AND EFFECTS OF IONIZING RADIATION United Nations Scientific Committee on the Effects of Atomic Radiation 1977 report to the General Assembly, with annexes
Tritium (3 H)
(a) Induction of dominant lethals in mice
Carsten and Commerford (81) and Carsten and Cronkite (80) have published the results of their studies on the induction of dominant lethals in mice (random-bred, Hale-Stoner-Brookhaven strain) fed with tritiated water (HTO). The HTO test animals were first-litter mice resulting from breeding of eight-week-old animals that had been maintained on HTO (3 μCi/ml) since weaning at four weeks of age. The control animals were first-litter mice taken from the colony and maintained on tap water. From the second generation animals. four experimental groups were established for dominant lethal tests. Group l consisted of animals where both the male and female were on HTO. Group 2 females received HTO. males, tap water. In group 3, the situation was the reverse of that in group 2. and group 4 received only tap water (both males and females). At eight weeks of age, in each group. each male was mated to five females for a 5-day period, and 15 days after the mid-point of this breeding period, the females were killed and their uterine contents examined for assessing dominant lethality.
The results, based on 366 pregnant females in the controls, 764 in group 1, 315 in group 2. and 316 in group 3, clearly demonstrated that dominant lethals are induced by HTO in both sexes. Significantly fewer viable embryos were found when either both mating partners or only the female was maintained on the tritium regimen. Similarly. when both the partners were on tritium, the incidence of early death (dark mole) is significantly higher than in the control group. Treatment of the males only gave similar effects, but these were not significant. When post-implantation mortality (early plus late deaths in the authors’ terminology) is used as the basis for comparison, the increased mortality due to HTO in groups 2 and 3 is of the same magnitude in both sexes, and in group 1 (both sexes on HTO) the effect is nearly twice that in groups 2 or 3. Current experiments are directed at repeating these studies with a lower concentration of 1.0 μCi/ml.
(b) Induction of specific-locus mutations in male mice
Cumming et al. (128) have completed the first series of experiments on 3 H-induced specific-locus mutations in mice, providing the only data available on such gene mutations in any mammal. In view of possible levels of tritium release,. not only from existing nuclear installations but also from contemplated controlled thermonuclear reactors. these data are of great relevance. A total of 14 groups of males was used. Two groups were injected with 0.75 mCi, and the 12 others with 0.50 mCi, of tritiated water per gram of body weight.The results demonstrate that beta radiation from the decay of tritium can induce specific-locus mutations in spermatogonia as well as in post-meiotic stages: 16 mutations have been recovered among a total of 20 626 offspring derived from germ cells irradiated as spermatogonia and 11 in 7943 offspring from irradiated post-meiotic stages. The mean absorbed dose to the spermatogonial cells has been estimated to be 700 rad and that to post-meiotic cells, 430 rad. These data thus permit mutation-rate estimates of 1.58 10-7 rad-1 per locus for spermatogonia and 4.60 10-7 rad-1 per locus for the other stages. These rates are within the statistical limits of what would have been expected from a comparable external dose of x or eamma irradiation. The point estimate of the RBE for post-spermatogonial stages is close to 1, with fairly wide confidence intervals; that for spermatogonia is slightly above 2, with confidence intervals that include 1. There are some indications that the distribution of mutants among the seven loci may differ from that produced by gamma rays: noteworthy is the observation that only one of the mutations was at the s locus (the expectation would be about 5 or 6). In more recent studies, currently in progress at Oak Ridge.,Cumming and W. L. Russell (129) are engaged in collecting more extensive data on tritium irradiation, focusing attention on the induction of mutations in spermatogonia.
(c) Induction of chromosome aberrations in human lymphocytes by tritiated water ( HTO)
Hori and Nakai (233) and Bocian et al. (39) have reported on the induction of chromosome aberrations in human lymphocytes exposed to tritiated water in vitro.Exposures were carried out by the addition of whole blood to the culture medium containing tritiated water. In the work of Hori and Nakai, the concentration of tritium ranged from 1 10-6 μCi/ml to 1 10-2 μCi/ml, and the cells were exposed during their entire period in culture ( 48 h). Bocian et al., used two regimens: in one (“acute exposures” in the authors· terminology), the lymphocytes were exposed for a 2-h period prior to PHA stimulation (range of concentrations, 1.71-14.36 mCi/ml), after which they were washed and cultured (53-h cultures); in the other (“protracted series”) the cells were exposed during 53 h (concentration range, 0.063-0.51 mCi/ml).
The results indicate that with protracted exposures (48 or 53 h) the aberrations produced were mos~ly of the chromatid type. such as gaps. deletions and fragments, and there were relatively few chromatid exchanges. In the concentration range used by Hori and Nakai, the dose-effect curve for the number of breaks induced was quite complex at low concentrations. In the work of Bocian et al. and with the range of concentrations they used, the frequency of chromatid aberrations increased linearly with dose. A quantitative comparison of the frequencies between the two groups of authors is, however, not possible because each group used only one (but different) fixation time, and in addition. the ranges of concentration were different.
In the 2-hour exposure experiments of Bocian et al., chromosome-type aberrations were found to be induced (dicentrics, centric rings, terminal and interstitial deletions). The data for dicentrics plus rings, as well as those on deletions, gave a good fit to a linear plus quadratic model. Using the data obtained in x irradiation experiments (acute doses of 50-300 rad). Bocian et al. have estimated that the RBE for the induction of dicentrics plus centric rings is about 1.2.
細胞あたりの染色分体切断の割合を計算したものが、実験対象と方法(Materials and methods)表1の最後の欄に記載されています。トリチウム(μCi/mL)の被ばく線量と細胞あたりの染色分体切断数(対照群の同切断数を差し引いています)との関係は図2に示されています。線量に対する切断数は対数目盛で示されています。[3H]チミジンは、トリチウム化水よりおよそ100倍染色体異常を生じる効果的があるように見えます。被ばく線量は細胞培養の際のトリチウム濃度を意味するので、[3H]チミジンの一見の高い線量効果はトリチウムが染色体DNAに取り込まれることによる非常に局所的なベータ線照射によって引き起こされた、と解釈することができます。
その線量―応答関係は両方のケースで変わった曲線を描きました。これは注目に値します。染色体異常が生まれる率はトリチウム水の場合は5μCi/mL以下で、[3H]チミジンの場合は5×10-2μCi/mL以下でそれぞれより少なくなっています。我々はこの2つの曲線について、べき乗数則(the power low model)Y = k D nに基づいて、最小二乗法回帰分析を行いました。Yが細胞あたりの染色分体切断数であり、DはμCi/mLで表された被ばく線量、kとnは定数です。
対数変換すると、この関係は直線、log Y =log k+ n log D となります。表2で示すように、べき乗数則は、データに極めて良く適合しています。統計分析のこれらの結果から、我々は、48時間のトリチウムへの慢性暴露によって誘発される染色体異常の線量―応答関係は、2つの要素を持っているととりあえず結論しました。高い線量での線量―応答関係では、線量D のべき指数nは、トリチウム水では0.953と[3H]チミジンでは0.790と1.0から大きく外れず、線量に対する細胞あたりの切断数が線量に直線的に依存することを示しています。P値については、トリチウム水では0.1>P> 0.05、[3H]チミジンでは0.3>P> 0.2でした。しかし、低い線量の範囲では、線量D のべき指数nがトリチウム水では0.380、[3H]チミジン0.338であり1.0からかなり逸脱して、明らかに線形動力学に当てはまりません。このときP値はP < 0.001でした。したがって、部分的ヒットまたは部分的ターゲットによって引き起こされることが明らかになりました。トリチウム水と[3H]チミジンにいずれにおいても、細胞の染色分体切断の数は、いずれの線量においてもポアソン分布を示しました。ただし[3H]チミジンの50μCi/mLおよび10μCi/mLの2つのケースは例外です。ここでは選択的な細胞死が恐らく起こるかもしれません。したがって、極めて低い線量の範囲で示された変わった線量依存関係は、染色体異常の偏った記録とする根拠にはならないかもしれません。
Genetic risk assessment for potential hazard from environmental tritium to man becomes important with increasing nuclear-power industry. The purpose of this short review is to discuss the possible genetic effects of tritium from a view of genetic risk estimation.
The discussion is based mainly on our experimental results on the chromosome aberrations induced in human lymphocytes by tritium at the very low-level. The types of chromosome aberrations induced by radiation from tritium incorporated into the cells are mostly chromatid types. The most interesting finding is that the dose-response relationship observed in both tritiated-water and tritiated-thymidine is composed of two phases. The examination on the nature of two-phase dose-response relationship is very important not only for the mechanisms of chromosome aberrations, but also for the evaluation of genetic risk from low-level radiation.
Hori, T. and S. Nakai. Chromosome aberrations induced by low level tritiated water. Paper submitted to UNSCEAR. にも、また、1977年に発表された UNUSUAL DOSE–RESPONSE OF CHROMOSOME ABERRATIONS INDUCED IN HUMAN LYMPHOCYTES BY VERY LOW DOSE EXPOSURES TO TRITIUM TADA-AKI HORI and SAYAKA NAKAI 1978年 にも、トリチウム水 37ベクレル/Lの実験結果の記述はない。削除されている。
1) J. J. COHEN and G. H. HIGGINS; The socioeconomic impact of low-level tritium releases to the environment, “Tritium, ” ed. A. A.MOGHISSI and MW. CARTER, 14 (1973).
2) “Tritium, ” ed. A. A. MOGHISSI and M.W.CARTER (1973).
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of chromosome aberrations in the liver of the Chinese hamster, Radiat. Res.,59, 693 (1974).
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Environmental Behavior of Tritium Masanobu Sakanoue (ReceivedSeptember30,1985) Abstract Various studies about the behavior of tritium in the environment are reviewed with comments on several origins of their occurrences. For atmospheric tritium,different chemical species and their seasonal variation have been studied. The average tritium concentration in river waters was found to be1.5~2times higher than that of precipitations at various sites of Japan. The vertical distribution of tritium in ground water has raised an interest for the samples collected from different wells in depth. The effect of the accidental release of tritium and the tritium level around nuclear facilities are also mentioned.
(2)トリチウムについて、① 自然界でも宇宙線によってトリチウムが作られていること ② トリチウムの出す放射線はベータ線であり、そのエネルギーが非常に弱いこと ③ トリチウム水の海洋放出に関する国際基準は60,000ベクレル/Lであり、東京電力が今回計画しているトリチウム水の放射能濃度はその40分の1の1,500ベクレル/Lであること をもってして、「科学的に安全である」とか「他の韓国、カナダ(原発からのトリチウム水やトリチウム水蒸気放出)、イギリス、フランス(核燃料の再処理工場からのトリチウム水やトリチウム水蒸気放出)もしているのだから」と経済産業省は主張している。