Cancer and non-cancer epidemiological study in the high background radiation area of Yangjiang, China

The major objective of this study is to examine cancer mortality risk associated with low-level radiation exposure occurring in the high background radiation area (HBRA) in Yangjiang of Guangdong Province, China. The average annual effective doses received by the inhabitants from natural sources of external and internal exposures in HBRA are estimated to be 2.10 and 4.27 mSv, respectively, and the corresponding doses in the control area (CA) to be 0.77 and 1.65 mSv. We analyzed the mortality of non-cancer diseases as well in order to shed light on the comparability of the HBRA and the CA. We examined mortality for cancer and non-cancer diseases during the period 1979-1998. The prospective mortality study followed 125,079 subjects during the period 1979-1998, accumulated 1,992,940 person-years (PYs) at risk, and ascertained 12,444 deaths, including 1202 cancer deaths. The mortality of all cancer showed no difference between the HBRA and the CA [relative risk (RR)=1.00; 95% confidence interval (CI), 0.89 to 1.14]. When cancer deaths were limited to persons with pathological diagnosis, the RR changed only slightly (RR=0.99; 95% CI, 0.78 to1.26). The RR was not evidently modified by sex or age or follow-up period (1979-1986, 1987-1998). In site-specific cancer mortality analysis, only cancer of the esophagus showed a statistically significant excess in the HBRA (RR=2.61; 95% CI, 1.11 to 7.66). However, the observed excess mortality of esophageal cancer did not show a monotonic increase with external radiation dose or cumulative lifetime dose. The RR comparing non-cancer mortality in the HBRA with that in the CA was 1.06 (95% CI, 1.01 to 1.10), which was a statistically significant increase. However, the excess was limited to those aged under 50 and the latter half of the observation period (the period 1987-1998), suggesting that the excess mortality may be due to recent changes in lifestyles of the younger generations. In the cause-specific analysis of non-cancer deaths, disease of the digestive organs showed a statistically significant increase. This appears to be mainly due to liver diseases. In conclusion, the present study showed no increase of cancer mortality in the HBRA. However, it is difficult for the present study to support or deny the possibility that the radiation-related cancer risk associated with chronic exposure to low-dose radiation may be different from the risk associated with high dose ranges or high dose-rate exposure. The observed increase of non-cancer mortality in the present study is unlikely to be attributable to radiation exposure.