Residents of High Natural Background Radiation Area


     Background radiation in the environment comprises of variety of sources including both natural and artificial radiation. Natural background radiation (NBR) is defined as radiation of the non-artificial sources of apparent origin and sometimes simply referred to as background radiation (BR) for the environmental interest. Its origin is inhalation of air (mainly 222Ra), ingestion of food and water (40K, 14C, etc.), terrestrial radiation from ground (depending on soil materials), and cosmic radiation (solar and galactic origin). The levels of natural background radiation vary with location, time and altitude. The global average effective dose to humans has been estimated to be 2.40 mSv/year (UNSCEAR Report 2000). This level in Japan is 1.50 mSv/year (http://search.kankyo-housyasen.go.jp).
     However, several regions in the world are known as high background radiation area (here we call HBRA), where the natural background radiation is far excess of the world average one. They include Guarapari (Brazil), Kerala (India), Ramsar (Iran) and Yangjiang (China). Since the exposure levels in these areas are several times (some tenths of times in particular area) higher than the recommended limit for exposure to the public from artificial sources (ICRP 2007 Recommendations; 1 mSv that may have a 5.5% chance of developing cancer), the health consequences of the residents has been continued concern in radioprotection and radiobiological sciences.

[1] Yangjiang, China
Scenario:
Yangjiang county, Guangdon province, is located in the southern China. During geologic history, monazite in mountains was washed out by rain and radionuclide containing monazite sands have been accumulated in the basin region resulting in a high background radiation area (HBRA).    Following the pioneer work by High Background Radiation Research Group of China (Science 209:877-880, 1980), China-Japan cooperative research was established in 1991 and comprehensive studies on cancer risk and cytogenetic analysis on the inhabitants have been carried out until 2001 (Wei, L. and Sugahara, T., J. Radiat. Res., 41<suppl>:1-7, 2000).

The high level of background radiation in this area is due to 232Th and 238U and their decay products. Control populations (CA) were taken from neighboring Hampizai village but without high background radioactivity. The ambient dose to the residents was estimated by NaI (T1) scintillation counter for indoor and outdoor dose and by personal monitors of electronic pocket dosimeter and thermoluminescence dosimeter (TLD). The external dose measure by TLD was converted to the personal dose by conversion from mR to mGy and further to personal dose with phantom using conversion factor of 0.87 and 0.96, respectively. (Morishima, H. et al. J. Radiat. Res., 41<suppl>:9-23, 2000; Nakai, S. et al. (1997): In, Wei, L. et al. eds. High Levels of Natural Radiation 1996: Radiation Dose and Health Effects, Elsevier, Amsterdam, pp.307-315.).

  

1.1. Estimation of personal dose: Nakai, S. et al. (1997): In, Wei, L. et al. eds. High Levels of Natural Radiation 1996: Radiation Dose and Health Effects, Elsevier, Amsterdam, pp.307-315.).
Personal dose monitoring by TLD carried by residents for 2 months* (data as of 1996).
High natural background radiation area (HBRA) Control area (CA)
Family Family member Measured Dose rate** Family Family member Measured Dose rate**
1 2 3 4 5 mean±SD (mGy/year) 1 2 3 4 5 6 mean±SD (mGy/year)
A M(64):478 F(59):424 F(30):365 F(9):379 M(36):390 407.2±45.1 3.42 K F(62):75 M(38):77 F(32):76 M(12):81 77.3±2.6 0.65
B M(68):407 F(58):362 M(33):371 F(13):388 382.0±62.6 3.21 L M(63):80 F(55):77 F(26):83 M(8):92 83.0±6.5 0.70
C F(55):406 M(34):369 F(28):421 398.7±26.8 3.35 M M(70):86 F(37):70 F(10):107 87.7±18.6 0.74
D M(66):429 F(53):404 M(35):371 F(32):380 M(10):407 398.2±23.1 3.35 N M(64)93 F(61):84 M(35):97 M(32):95 F(34):93 F(8):84 91.0±5.6 0.77
E M(80):389 M(43):511 F(39):537 F(11):448 471.3±66.4 3.96 P M(64):64 F(56):77 M(26):103 F(30):78 F(9):92 82.8±17.8 0.70
F F(70):489 M(14):480 M(80):454 F(38):485 M(48):473 476.2±13.8 4.00 *) The data should as [sex](age in year):[TLD reading in mR/y]. Contribution of cosmic rays was estimated to be 0.23mGy/y.
G M(77):447 F(66):450 F(10):436 M(28):485 M(31):458 455.2±18.4 3.83 **) TLD dose in mR unit was converted to mGy and further to personal dose by conversion factor of 0.87 and 0.96, respctively.

1.2. Chromosome aberration analysis (Dic+cR)

     Blood samples were taken from 22 members from 8 households in high background radiation area (HBRA) and 17 members from 5 households in control area (CA). Dicentric chromosomes (Dic) and centric rings (cR) were scored in solid Giemsa stained preparations by the aid of metaphase finding system. Cumulative dose was 130.9-358.9 mGy for residents of HBRA and 6.0-59.2 mGy for those of CA. Average dose rate was 3.70 mGy/y for HBRA and 0.70 mGy/y for CA. 

References 

     Jiang, T., Wang, C. –Y., Chen, D. –Q., Yuan, Y., Wei, L. –X., Hayata, I., Morishima, H., Nakai, S. and Sugahara, T. (1997): Preliminary report on quantitative study of chromosome aberrations following life time exposure to high background radiation in China. In: Wei, L. –X., Sugahara, T. and Tao, Z. eds., High Levels of Natural Radiation: Radiation Dose and Health Effects. Elsevier, Amsterdam, pp.301-306.
     Jiang, T., Hayata, I., Wang, C., Nakai, S., Yao, S., Yuan, Y., Dai, L., Liu, Q., Chen, D., Wei, L. and Sugahara, T. (2000): Dose-effect relationship of dicentric and ring chromosomes in lymphocytes of individuals living in the high background radiation area in China. J. Radiat. Res., 41(suppl.):63-68.
     Hayata, I., Wang, C., Zhang, W., Chen, D., Minamihisamatsu, M., Morishima, H., Wei, L. and Sugahara, T. (2004): Effect of high-level natural radiation on chromosomes of residents in southern China. Cytogenet. Genome Res., 104:237-239. 
     Wang, C., Zhang, W., Minamihisamatsu, M., Wei, L., Sugahara, T. and Hayata, I. (2008): Chromosome aberrations observed in high levels of natural radiation areas in China. In; Taniguchi, K. and Zhang, X. eds., “Advances in Chromosome Sciences”, Vol. 3., pp.56-58.
[1] High background radiation area (HBRA) [2] Control area (CA)
Subject Age Dose/y Total dose Cells No. of Subject Age Dose/y Total dose Cells No. of
code (y) (mGy)* (mGy) scored Dic+cR code (y) (mGy)* (mGy) scored Dic+cR
A01 64.1 3.68 235.9 3,092 13 L02 55.8 0.72 40.2 2,006 2
A03 37.1 3.57 132.4 1,781 6 L06 26.7 0.68 18.2 3,081 3
A09 9.4 3.29 30.9 2,037 1 L07 8.2 0.90 7.4 3,056 3
B01 68.9 3.28 226.0 3,034 9 M01 70.5 0.84 59.2 2,016 3
B05 33.3 3.56 118.5 3,011 7 M04 37.8 0.67 25.3 3,021 3
B11 11.6 3.40 39.4 2,044 3 M08 10.3 0.75 7.7 3,032 4
D01 72.8 3.00 218.4 3,020 11 N01 64.9 0.74 48.0 2,010 4
D03 34.1 3.28 111.8 3,060 7 N04 32.9 0.76 25.0 2,823 4
D12 11.2 3.54 39.6 2,047 2 N08 8.2 0.73 6.0 2,009 3
E01 80.8 2.74 221.4 2,569 14 P01 64.4 0.69 44.4 1,908 3
E08 11.5 3.56 40.9 2,004 2 P02 56.3 0.60 33.8 1,889 0
F01 80.7 3.89 313.9 2,970 15 P05 30.8 0.63 19.4 3,104 5
F07 13.2 4.21 55.6 2,030 2 P08 9.8 0.64 6.3 2,125 1
G01 77.2 3.52 271.7 2,966 7 T01 70.6 0.65 45.9 3,145 9
G06 10.9 3.54 38.6 2,256 3 T2a 47.3 0.65 30.7 4,249 6
X01 74.5 4.23 315.1 3,502 11 T2b 37.7 0.66 24.9 3,309 5
X02 34.4 4.31 148.3 2,960 5 T03 10.4 0.66 6.9 3,016 0
X03 11.4 4.44 50.6 2,992 3 *) Estimated personal external dose.
Y01 89.5 4.01 358.9 791 3
Y2a 46.6 4.01 186.9 3,282 13
Y2b 19.9 4.07 81.0 1,743 1
Y03 10.8 4.19 45.3 2,395 2


   

       When the frequencies of Dic+cR were plotted against age (X in year), the regressions were   y=0.5717+0.0444X (R2=0.744) for HBRA and y=0.7227+0.01151X (R2=0.211) for CA.

       When plotted against the accumulated dose (X in mGy), the regression was best fitted by   y=0.6812+0.01151X (R2=0.657) for residents of HBRA and CA combined.




  [Commentary] for alternative formalism of dose-response relationship.



1.3. FISH translocation assay 
     Blood samples were taken from 6 children and 32 elderly persons in high natural background radiation area (HBRA) 8 children and 25 elderly persons in control area (CA). (One elderly person, HW14, in HBRA is not included because he has medical exposure.)
     The blood samples were transferred to the cytogenetic laboratory and processed for chromosome aberration analysis within 7 hours after venipuncture. Chromosome painting (FISH) was performed using whole chromosome painting probes for chromosome 1, 2 and 4. The genome equivalent frequency of translocations, FG-Tr, was calculated according to the formula of Lucas et al., Int. J. Radiat. Biol., 62:53-63, 1992.
     In the earlier reports (Hayata et al. 2000, Zhang et al. 2003), the translocation frequencies have been compared between children and elderly persons, and in the second report (Zhang et al. 2004) the authors discussed on the effects of smoking in elderly persons. Since two data sets have some duplication, the data are combined here. 
References  

     Hayata, I., Wang, C., Zhang, W., Chen, D., Minamihisamatsu, M., Morishima, H., Yuan, Y., Wei, L. and Sugahara, T. (2000): Chromosome translocation in residents of the high background radiation areas in southern China. J. Radiat. Res., 41 (suppl.):69-74.
     Zhang, W., Wang, C., Chen, D., Minamihisamatsu, M., Morishima, H., Yuang, Y., Wei, L., Sugahara, T. and Hayata, I. (2003): Imperceptible effect of radiation based on stable type chromosome aberrations accumulated in the lymphocytes of residents in the high background radiation area in China. J. Radiat. Res., 44:69-74.
    Zhang, W., Wang, C., Chen, D., Minamihisamatsu, M., Morishima, H., Yuan, Y., Wei, L., Sugahara, T. and Hayata, I. (2004): Effect of smoking on chromosomes compared with that of radiation in the residents of a high-background radiation area in China. J. Radiat. Res., 45:441-446. 
    Wang, C., Zhang, W., Minamihisamatsu, M., Wei, L., Sugahara, T. and Hayata, I. (2008): Chromosome aberrations observed in high levels of natural radiation areas in China. In; Taniguchi, K. and Zhang, X. eds., “Advances in Chromosome Sciences”, Vol. 3., pp.56-58.
Cytogenetic data 
[1] High background radiation area (HBRA) [2] Control area (CA)
Subject Sex Age Smoking Dose/y Total dose* Cells Translocations Subject Sex Age Smoking Dose/y Total dose* Cells Translocations
code (M, F) (year) (y/n) (mGy) (mGy) scored No FG/1000 code (M, F) (year) (y/n) (mGy) (mGy) scored No FG/1000
YO01 M 89.5 n 2.92 261.3 2,233 11 13.7 TO01 M 70.6 y 0.53 37.4 1,424 5 9.8
XO01 M 74.5 - 3.08 229.5 2,093 13 17.3 SO01 M 58.7 - 0.56 32.5 653 1 7.3
HO01 M 59 y 2.39 141.1 4,454 15 9.4 CO01 M 61.2 y 0.80 49.1 3,023 19 17.5
HO02 M 53.3 y 2.78 148.2 5,669 18 8.8 CO02 M 57.5 y 0.65 37.2 2,208 9 11.3
HO03 M 58.1 y 3.18 184.5 8,375 30 10.0 CO03 M 57.1 y 0.67 38.4 3,275 21 17.8
HO04 M 53.2 y 2.76 146.6 4,514 17 10.5 CO04 M 65.3 y 0.63 41.0 1,186 6 14.1
HO05 M 66.2 y 2.62 173.7 2,333 6 7.1 CO11 M 55.6 y 0.65 36.1 3,345 17 14.1
HO06 M 55.5 y 2.97 165.0 1,145 5 12.1 CO12 M 63.3 n 0.64 40.7 3,369 14 11.5
HO07 M 61.7 y 3.15 194.1 5,100 21 11.4 CO13 M 55.3 - 0.78 43.3 4,864 20 11.4
HO08 M 66.3 n 2.50 166.0 5,678 38 18.6 CO14 M 61.1 y 0.68 41.3 6,282 21 9.3
HO12 M 58.5 y 2.65 154.9 10,079 28 7.7 CO16 M 59.1 n 0.66 39.1 5,749 22 10.6
HO13 M 55.4 n 2.96 164.3 4,829 18 10.4 CW01 F 61.2 n 0.62 38.2 2,306 9 11.0
HO14 M 54.6 y 2.53 137.9 1,101 8 20.2 CW04 F 67.0 n 1.10 73.6 3,519 7 5.6
HO15 M 54.0 y*** 2.54 137.4 1,629 7 11.9 CW05 F 70.8 n 0.75 52.9 4,666 18 10.8
HW08 F 61.5 - 2.82 173.2 9,736 31 9.0 CW06 F 68.1 n 0.68 46.0 2,409 6 7.0
HW14 F 69.2 - 1.91 132.3** 5,007 42 23.6 CW07 F 53.0 n 0.69 36.7 2,860 9 8.8
HW01 F 64.3 n 2.38 153.4 2,411 7 8.2 CW09 F 70.3 n 0.71 49.7 4,138 9 6.1
HW03 F 56.7 n 3.29 186.5 1,598 6 10.6 CW10 F 61.5 n 0.65 40.2 2,657 4 4.2
HW04 F 58.1 n 2.75 159.7 2,436 8 9.2 CW11 F 55.5 n 0.85 47.2 5,932 10 4.7
HW05 F 67.8 n 2.67 181.2 1,195 2 4.7 CW12 F 63.1 n 0.70 44.0 6,157 14 6.4
HW06 F 70.4 n 2.79 196.4 2,552 13 14.3 CW13 F 65.8 n 0.68 44.7 1,777 7 11.1
HW07 F 55.4 n 2.76 153.1 8,731 23 7.4 CW14 F 67.3 n 0.96 64.8 2,924 14 13.5
HW08 F 61.5 n 2.82 173.2 9,736 31 9.0 CW16 F 70.3 n 0.77 53.9 9,633 43 12.6
HW09 F 64.7 n 2.6 168.4 3,290 17 14.5 CW17 F 65.2 n 0.66 43.1 5,950 13 6.1
HW10 F 69.4 n 2.07 143.6 2,670 10 10.5 CW18 F 69.3 n 0.82 56.6 3,464 6 4.9
HW11 F 69.3 n 2.74 189.5 2,595 27 29.3 TO03 M 10.4 - 0.54 5.6 1,742 3 4.8
HW12 F 65.1 n 2.84 184.6 4,047 13 9.0 SO03 M 10.3 - 0.56 5.8 1,056 1 2.6
HW13 F 68.2 n 2.39 163.0 4,737 19 11.3 CC01 F 13.8 - 0.81 11.1 8,185 17 5.8
HW15 F 65.3 n 2.89 188.9 6,573 33 14.1 CC02 F 12.3 - 0.69 8.5 6,886 13 5.3
HO08 M 66.3 n 2.5 166.0 5,678 38 18.6 CC03 M 12.9 - 0.71 9.2 6,564 8 3.4
XO13 M 74.5 y 3.08 229.5 2,093 13 17.3 CC04 M 12.9 - 0.82 10.7 3,004 0 0
YO03 F 10.8 - 3.02 32.6 1,015 1 2.8 CC05 M 12.8 - 0.78 10.1 21,710 19 2.4
HC01 M 12.8 - 2.48 31.6 7,543 11 4.1 CC11 M 13.0 - 0.81 10.5 7,051 4 1.6
HC02 M 12.1 - 2.15 25.9 10,443 16 4.3 *) External dose in FIA kerma. Internal exposure was not considered.
HC03 M 13.5 - 2.84 38.4 3,826 3 2.2 **) Suspected medical dose is not included.
HC04 F 12.8 - 3.24 41.4 9,469 18 5.3 ***) Former smoker.
HC05 F 12.8 - 2.74 35.1 13,239 19 4.0


 

Results of analysis

     The authors concluded that, unlike unstable aberrations, no significant difference was found in the frequencies between HBRA and CA while they increased with age.

[Commentary]
     For reference, two types of age dependency of translocations may be quoted here from literature. Curve [A] represents the age dependent increase of translocation frequencies in the unselected populations, in which lifestyle factors, such as smoking, alcohol consumption, chemical or radiation exposure, exposure to coal products are not excluded (Ramsey et al., Mutation Res., 338:95-106, 1995). Curve [B] represents the age dependent increase of in populations in which exposure to such possible genotoxic lifestyle factors are excluded (Tucker et al., Mutation Res., 313:193-202, 1994).
     [A]: Y=C+8.06×10-6×age3. [B]: Y=C+3.04×10-4×age2. C was adjusted to pass through the mean frequencies in children. The transloction frequencies have been determined by FISH painting using the chromosome specific probes for chromosome 1, 2 and 4.


1.4. Interaction with smoking 
References 
     Zhang, W., Wang, C., Chen, D., Minamihisamatsu, M., Morishima, H., Yuan, Y., Wei, L., Sugahara, T. and Hayata, I. (2004): Effect of smoking on chromosomes compared with that of radiation in the residents of a high-background radiation area in China. J. Radiat. Res., 45:441-446. 
     Zhang, W., Wang, C., Minamihisamatsu, M., Wei, L., Sugahara, T. and Hayata, I. (2008): Effects of smoking on the chromosome aberrations induced by environmental mutagens. In; Taniguchi, K. and Zhang, X. eds., “Advances in Chromosome Sciences”, Vol. 3., pp.59-61. 
 

Results of analysis

     The interaction between background radiation and smoking was assayed by translocations revealed by HISH painting technology in elderly residents (Table in section 1.3). The effect of smoking was evident in CA, but non-significant in HBRA. The authors concluded that the elevated level of natural radiation in HBRA played a less significant part than smoking in bringing about the induction rate of stable-type aberrations (translocations) in those area.

[Commentary]
     This observation may offer important proposition that the low doses of low LET radiation may interfere with generation of misrejoining when the DNA damage (by smoking) pass through DNA replication of hematopoietic stem cells. Pathway choice in the repair of DNA DSB and its relevance to low doses of low LET radiation. 



1.5. Radioadaptive response? 

     Elevated natural background radiation renders the lymphocytes radioresistant? This question was experimentally tested in the peripheral blood lypmphocytes of children.

    Peripheral blood was taken from children (12-13 years) living in HBRA (Hele and Shaxin villeges) and CA (Shengzhuli and Xingang villages). The background radiation level was 2.63 mGy/year, 2.45 mGy/year, 0.64 mGy/year and 0.64 mGy/year in Hele, Shaxin, Shengzhuli and Xingang, respectively. The experiments to see radioadaptive response were carried out for 10 children selected from residents of HBRA and 10 from CA. For each child, 2 ml peripheral blood was drown and immediately mixed with 2 ml RPMI 1640 culture medium containing heparin. The blood samples were then irradiated with acute dose of 1.5 Gy gamma-rays, incubated for 2 hours, and then cultured for chromosome preparation.

References 

     Comprehensive Report of China-Japan Joint Research Project “Epidemiological Study in High Background Radiation Area”, Phase II (from October 1995 through January 1998) to the Radiation Health Research Foundation, Japan.
(Data compiled by Dr. L. Wei and courtesy of Dr. T. Sugahara) 

High background radiation area (HBRA): Irradiation with 1.5 Gy gamma-rays in vitro Control area (CA): Irradiation with 1.5 Gy gamma-rays in vitro Summary of data
Subject Cells No. of Cells with indicated number of dicentrics Subject Cells No. of Cells with indicated number of dicentrics In vitro Area Cells Dicentric aberrations
code scored dics 0 1 2 3 4 code scored dics 0 1 2 3 4 dose scored No. dics/100 cells
H21 400 92 308 70 11 0 0 H1 400 136 264 103 15 1 0 0 CA 19,800 4 0.0202
H22 400 96 304 66 15 0 0 H2 400 98 302 78 10 0 0 HBRA 24,400 5 0.0205
H23 400 73 327 55 9 0 0 H3 400 99 301 78 9 1 0 1.5 Gy CA 4,000 1,022 25.55*
H24 400 101 299 74 12 1 0 H4 400 101 299 80 9 1 0 HBRA 4,000 872 21.80*
H26 400 73 327 69 2 0 0 L5 400 87 313 69 9 0 0 *) p<0.001
H27 400 69 331 60 3 1 0 L7 400 84 316 69 6 1 0
H29 400 83 317 73 5 0 0 L8 400 96 304 78 9 0 0
H30 400 119 281 96 10 1 0 L9 400 115 285 87 11 2 0
H31 400 97 303 67 12 2 0 L10 400 96 304 87 3 1 0
H32 400 69 331 59 5 0 0 L11 400 110 290 94 8 0 0
.


Commentary

     The expression of radioadaptive response may be tested by comparing the magnitude of chromosomal response (see, sammary results in the Table above).

     Alternatively, the changes in the chromosomal susceptibilty may be visualized by the changes in the effective dose profiles (Figures on left). The effective dose is about 10 % reduction in HBRA. But, the profile shows broadening being spreading towards lower doses. This suggests that the lymphocytes are expressing radioadaptive response, but their activity could be heterogeneous.