Fukushima fallout: Chromosome aberration analysis in field mice in Fukushima contaminated area
   
Accident scenario and Contamination: see ¤Scenario 

[1] Studies insmall Japanese field mice, Apodemus argenteus (Solid Giemsa/C-banding methods) 

     Wild mice (Apodemus argenteus and Mus musculus) (image by Wikipedia 2015) living differently contaminated area by Fukushima TEPCO nuclear power plant accident were captured and chromosome aberrations were studied in cultured splenic lymphocytes. The mice were confirmed to have been born well before the accident and dose due to the internal and exposures were estimated by the activity concentration of 137Cs and 134Cs in mice and measurement of ambient dose at the site of capture.
    For reference, the dose-response relationships of chromosome aberrations in splenic lymphocytes have been obtained by experimentally irradiating laboratory mice with acute doses of X-rays.

Reference 

     Kubota, Y., Tsuji, H., Kawagoshi, T., Shiomi, N., Takahashi, H., Watanabe, Y., Fuma, S., Doi, K., Kawaguchi, I., Aoki, M., Kubota, M., Furuhata, Y., higemura, Y., Mizoguchi, M., Yamada, F., Tomozawa, M., Sakamoto, D. H. and Yoshida, S. (2015): Chromosomal aberrations in wild mice captured a areas differently contaminated by the Fukushima Dai-ichi nuclear power plant. Environ. Sci. Technol., 49:10074-10083.
     Kubota, Y., Takahashi, H., Watanabe, Y., Fuma, S., Kawaguchi, I., Aoki, M., Kubota, M., Furuhata, Y., Shigemura, Y., Yamada, F., Ishikawa, T., Obara, S. and Yoshida, S. (2015): Estimation of absorbed radiation dose rates in wild redents inhaviting a site severely contaminated by the Fukushima Dai-ichi nuclear power plant accident. J. Environ. Radiol., 142:124-131.  
Sampling area Location Sampling Ambient dosea No. of Activity at captureb, Bq/kg(wetmas) Dose ratec (mGy/day) Accumurated No. of Aberrationse
time (ƒĘSv/h) animals 134Cs 137Cs Internal External dosed (mGy) cells cte csb Dic R F Dmin Others
Non-contaminated 93 km WNW to NPS July 2013 0.1}0 6 - - - 0.002 - 11,764 11 4 6(2) 1(0) 22 9 9
Slightly contaminated 28 km S to NPS July 2012 0.5}0.2 9 2,656 (988, 4,540) 4,480 (1,866, 7,041) 0.025(0.01, 0.04) 0.01 8.83 19,952 14 3 9(4) 0 38 18 3
Moderately contaminated 15 km NW to NPS July 2012 30.9}5.4 9 33,450 (4,932, 77,136) 51,052 (7,980, 12,3967) 0.289 (0.078, 0.69) 0.84 188.3 18,730 22 18 23(12) 0 34 33 7
Heavily contaminated area 3.0 km W to NPS July 2012 80.5}7.7 7 60,762 (4,080, 15,2545) 90,652 (5,420, 229,084) 0.481 (0.032, 1.3) 2.2 749.4 14,955 10 18 27(14) 0 50 37 11
a) Measured values at 1m above ground at location of capture. .
b) The activity concentration was measure at saclifice, and the activity was converted to those at the time of capture considering the time spent from capture and saclifice (rearing period) and biological half life of radionuclides.
The activity concentration is shown by an average (lowest, highest) values.
c) The external dose rate (D in mGy/day) was calculated based on the measured ambient dose rate (X in ƒĘSv/h) by D=(X)~1.138~24.
d) Accumurated dose: [Dose rate in mGy/day] multiplied by [estimated age in days]
e) Dic: dicentrics, R: centric rings (numbers in parentheses are those with associated fragments), F: acentric fragments, Dmin: minute dots (S), cte: chromatid exchanges, csb: isochromosome breaks, Others: marker chromosomes, deletions, translocations.
.
The reference dose-response relationships of dicentrics and total aberrations have been obtained for the splenic lymphocytes oflaboratory mice ,C3H/HeJ and Japanese field mice, after acute irradiation with X-rays.
For instance, the dose responses of dicentrics are Y=0.0634+0.003D for C3H mice and Y=0.0512+0.0022D for Japanese field mice (D in mGy).
For total aberrations, they are Y=0.4758+0.0062D and Y=0.5006+0.0081D, respectivly.
.
Commentary to the dose-response relationships
      It is noticeable that there appears relatively large number of chromatid exchange aberrations and dicentrics without fragments. Therefore, at least some or most of the dicentrics without fragments are likely to be derived aberration arisen from chromatid exchanges aberrations. Even if the chromatid-type aberrations (induced in S/G2 of replication cycle) have any relevance to radiation, they may not be simply related to the dose-accumulation. When only dicentrics with associated fragments are considered, their frequencies are well correlated to the dose or dose-rate (right panel).

      Since doses within the exposed group vary condiderably among individuals, the response to dose and dose rate are smoothed by moving window averaging, MWA=5w1s, (right panels). (responses of dicentrics without fragments). Although the data are those of nonhuman biota, they are included here because they are very informative in considering the effects of radioactive fall-out on the residents. Please note that the commentary added during data compiling does not necessarily reflect the conclusion of authors. 

  


[2] Studies in large Japanese field mice, Apodemus speciosus (FISH-painting method)  

     Further to confirm the observations in small Japanese field mice (Apodemus argenteus) and Mus musculus (Kubota et al. 2015), the studies were extended to another field mice, large Japanese field mice (Apodemus speciosus) (image by Wikipedia 2015). In this species, C-banding method for identification of centromeres was inefficient because the centromere region was stained only poorly and hampered the identifications of precise location of centromere in the rearranged chromosomes. Then, the authors made efforts newly develop chromosome painting probes for FISH analysis. The probes obtained for chromosomes 1, 2 and 5 were applied to the A. speciosus chromosomes.
     The sampling areas were the same as those described for small field mice described previously (Kubota et al. 2015). The splenic lymphocyte cultures were established as described (Kubota et al. 2015). Cheomosome rearrangements were readily identified by FISH painting, but,  with uncertainty of the centromere position even with DAPI counter stain, the exchanges could not distinguish between reciprocal translocation and dicentric formation. Therefore, translocations and dicentrics were lumped together to see the effect. The exchanges increased with the increase of dose rate and accumulated dose.
     FISH painting also revealed that chromosome 2 was more frequently involved than expected from its physical target size, more interestingly, possibly at a fragile site known in leukemic cells.  

Reference:
     Kawagoshi, T., Shiomi, N., Takahashi, H., Watanabe, Y., Fuma, S., Doi, K., Kawaguchi, I., Aoki, M., Kubota, M., Furuhata, Y., Shigemura, Y., Mizoguchi, M., Yamada, F., Tomozawa, M., Sakamoto, S. H., Yoshida, S. and Kubota, Y. (2017): Chromosomal aberrations in large Japanese field mice (Apodemus speciosus) captured rear Fukushima Dai-ichi nuclear power plant. Environ. Sci. Technol., 51(8): 4632-4641. 

Radiological data at the site of capture and accumulated dose to the mice.
Sampling area Date of sampling Ambient dose at the site No. of mice Dose rate Accumulated dose
(ƒĘSv/h)* captured Internal (mGy/day) External (mGy/day) assigned to the mice (mGy)
(1) Non-contaminated area Jul-2013 (0.1}0) 7 - - -
(2) Slightly contaminated area Jul-2012-Oct-2014 (0.3}0.1)-(0.4}0.2) 9 0-0.036 0.008-0.011 1.26-13.49
(3) Moderately contaminated area Jul-2012-Oct-2014 (7.5}30.-(30.7}7.4) 10 0.01-0.245 0.205-0.838 26.73-439.89
(4) Heavily contaminated area Jul-2012 (80.0}13.6) 11 0.066-1.486 2.185 245.385-1386.63
*) Dose rate at 1m above ground.


Commentary:
     Exchange aberration frequencies (translocations+dicentrics) in relation to the accumulated dose assigned to the mice. A: Scattered plots in three contaminated areas as reproduced from Figure 3 of Kawagoshi et al. 2017. B: The same data smoothed by moving window averaging, MWA=w5s1.