Chromosome aberrations observed in high levels of natural radiation areas in China

In order to study the health effect of such high radiation levels at extremely low dose rates, we have analyzed chromosome aberrations (dicentric and ring chromosomes and translocations) in the lymphocytes of residents in a high background radiation area (HBRA) in the remote areas in the Southern China (for review see Hayata et al. Cytogenet. Genome Res. 104, 237-239, 2004). In addition, we analyzed translocation in the residents in a large city, Beijing, as a positive control of HBRA (Wang et al., China Occup.Med. 35, 112-114, 2008). The level of radiation is 3 to 5 times higher in HBRA than those in CA and Beijing, because the soil and building materials contain nuclides of Th-232 and U-238 decay products in HBRA. In this presentation we show the results of the analyses of chromosome aberrations in HBRA, CA and Beijing.Prier to the chromosome study, individual radiation dose was measured with a pocket dose meter (Aloka PDM-10) put on the body for 24 hours or estimated from the dose rate measured by a Nal scintillation survey meter (Aloka TCS-166) in their homes. The lymphocytes were cultured for 48 hours with PHA and Colcemid, and harvested according to our improved method for the study of chromosome aberrations induced by low dose radiation (Hayata et al., J. Radiat.Res.33: Suppl. 231-241, 1992). Analysis of chromosome aberrations was performed using a microscope equipped with an automated stage so that all metaphases including normal cells can be re-analyzed by the other examiner.Unstable types of chromosome aberrations (dicentrics and rings) were examined in 22 members of 8 families in HBRA and 17 members of 5 families in CA. From each family 3 generations participated in this study. Totally 101, 395 cells and on average 2,600 cells per subject were analyzed. To compare the diference of the frequencies, two-tail u-test was made. To investigate the cumulative dose effect dependence, linear regression analysis was performed. Frequencies of dicentric + ring in relation to accumulated dose showed positive dose response. The frequencies seem to increase with age in both HBRA and CA. The rate of increase is about 3 times higher in HBRA than that in CA. Difference of the frequencies between HBRA and CA group becomes statistically significant after middle age. Effect of high level of natural radiation to the chromosome aberrations is detected. It is demonstrated that the chromosome aberrations is sensitive enough to show the small effect of the elevated level of natural radiation in HBRA.With respect to stable types, i.e., translocations, 26 elders and 6 children in HBRA, 25 elders and 8 children in CA, 20 elders in Beijing were examined. Total number of metaphases analyzed was 390,566 (4,595 per subject). Translocations were analyzed by the chromosome painting method using whole chromosome painting probes for #1, 2, and #4. Statistical analysis was done by the Mann-Whitney s U test and Spearman rank correlation test.Genomic frequencies of translocation in 1,000 cells per adult were 11.5+/-4.2 and 9.6+/-5.0 in HBRA, CA and Beijing, respectively. The frequencies in child were 3.8+/-1.1 in HBRA and 3.2+/-2.0 in CA. The frequencies of translocations were much higher than that of dicentrics and rings both in HBRA and in CA. Statistically there was no difference in the frequencies of translocations among age matched groups in HBRA, CA and Beijing.A significant increase of chromosome aberrations due to the elevated level of natural background radiation was observed in dicentrics but not in translocations. Dicentrics and translocations are induced by radiation on about equal rate (Zhang and Hayata, J. Hum. Genet.48, 531-534,2003). Frequencies of translocations were much higher than those of dicentrics and varied widely in the present study. Therefore, it is concluded that condition of the elevated level of natural radiation in HBRA in China to the induction of stable type chromosome aberrations does not have a significant effect compared with the contribution of environmental non-radiation-mutagens, i.e., chemical mutagens and/or metabolic factors. The present chromosome study predicts that the risk of malignant and/or congenital diseases caused by the increased amount of radiation in HBRA, where the level of background radiation is 3 to 5 times higher than those in CA and Beijing, is invisibly small. In fact, epidemiological studies performed in this area detected no significant increase in either cancer morbidity (Tao et al., J. Radiat. Res., 41, Suppl. 31-41, 2000).The 3rd Asian Chromosome Colloquiu