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Rate of Double Strand Breaks of Genome-sized DNA by β-rays from Tritium–Dependence on Tritium Concentration, Water Temperature andDNA Concentration–
下谷内 宏統1, 波多野 雄治2, 剣持 貴弘3, 和田 拓郎4, 大矢 恭久5, 中村 浩章5	 
Hiroto Shimoyachi, Yuji Hatano, Takahiro Kenmotsu, Takuro Wada, Yasuhisa Oya, Hiroaki Nakamura
1

富山大学理工学教育部, 2富山大学水素同位体科学研究センター, 3同志社大学生命医科学部,
4静岡大学総合科学技術,5静岡大学理学部 6核融合科学研究所
Graduate School of Science and Engineering, Univ. of Toyama, Hydrogen Isotope Research Center,
Univ. of Toyama, Faculty of Life and Medical Sciences, Doshisha Univ.,
Graduation School of Integrated Science and Technology, Shizuoka Univ.,
Faculty of Science, Shizuoka Univ., National Institute for Fusion Science 	 

Quantitative evaluation of the rates of DNA
damages by low energy β-rays is important for better
understanding of biological effects of tritium. In theprevious study [1], we measured the rate of double
strand breaks (DSBs) in high concentration tritiatedwater (5.2 MBq/cm3) using a single molecule
observation method. Clear irradiation effects wereobserved after 7 days immersion under sterilized
conditions though the influence of microorganisms(e.g. bacteria) was far stronger under non-sterilizedconditions. In this study, the dependence of the rateof DSBs on tritium concentration, DNAconcentration and water temperature were examined.
Giant genome DNA molecules of bacteriophage
T4 GT7 (166 kilo base pairs) were used as samples in
the present work. DNA molecules were immersedand suspended in sterilized tritiated water andnon-radioactive sterilized water at 3 °C and 10 °C for
1–35 days. For comparison, 60Co γ-ray irradiation
was also performed. The tritium concentration wasadjusted to be 1300 Bq/cm3 and 4 –5.2 MBq/cm3.
The concentration of DNA was set to be 0.1–105nmol base pairs/cm3. After mixing with a fluorescentdye, a drop of DNA solution was put on a glass
substrate coated with poly-L-lysine. The DNA
molecules were extended and fixed on the surface ofglass substrate. Then, the length of DNA molecules

was measured using a fluorescence microscope.
The effects of β-rays from tritium for the DNA
molecules were not observable at 1300 Bq/cm3 after
the immersion for 35 days. Meanwhile it was foundthat the rate of DSBs clearly increased at
5.2MBq/cm3 even after the immersion for 7 days. Basedon experimental results, the effects of β-ray
irradiation were far smaller than those of oxidationand thermal effect at low dose rate (0.1 mGy/day at
1300 Bq/cm3). No significant difference wasobserved in the rate of DSBs at 10 °C and 3 °C intritiated water of 4 MBq/cm3. The DSB rates under
the irradiation of tritium β-rays and 60Co γ-rays
decreased with increasing DNA concentration inwater. This is because a DNA molecule acts as ashield for other DNA molecules against reactive
species at high DNA concentrations. There was novisible difference in the DSB rate between tritium
β-rays and 60Co γ-rays in a low DNA concentration
region (< 10 nmol base pairs/cm3). At higher DNA
concentrations, the rate of DSBs under the β-rayirradiation was slightly higher than that under theγ-ray irradiation probably due to a larger linear
energy transfer (LET) value of the former. Detailed
discussion will be given in the presentation.

[1] Y. Hatano et al., Fusion Eng. Design, 146 (2019) 100-102.