Twinning in the offspring of parents with chronic radiation exposure from nuclear testing in Kazakhstan.

The population of the Semipalatinsk region of Kazakhstan was chronically exposed to radioactive fallout from above-ground nuclear tests conducted during 1949-1956 by the Soviet Union. We investigated the effect of radiation exposure and other factors on risks of twinning overall and of same- and different-sex twinning and hence estimated dizygotic and monozygotic twinning rates in 11,605 deliveries around Semipalatinsk, 141 of which were twin, to 3992 mothers exposed to fallout during 1949-1956. Overall, the same-sex twinning rate was 7.85 [95% confidence interval (CI): 6.24, 9.47] per 1000 and the opposite-sex twinning rate was 4.45 (95% CI: 3.23, 5.67). Twinning rates did not differ significantly between radiation exposure categories, parental age at main radiation exposure, or year of birth. Different-sex, but not same-sex, twinning increased with maternal age (P(trend) = 0.04) but not with other demographic factors and was increased soon after radiation exposure [OR = 4.08 (95% CI: 1.11, 15.07)] for births occurring within 5 years compared with more than 20 years after exposure; this effect was similar in villages with low and high radiation exposure, however, so interpretation is uncertain.

Sex ratio in the offspring of parents with chronic radiation exposure from nuclear testing in Kazakhstan.

The former Soviet Union conducted a nuclear test program in the Semipalatinsk region of northeastern Kazakhstan in 1949-1989. The population in the vicinity of the test site was chronically exposed to radiation fallout, especially from above-ground tests during 1949-1956. Male:female sex ratio has been proposed as a measure of reproductive health, with some reports suggesting an alteration in the sex ratio of offspring of parents exposed to radiation. We investigated the impact of radiation exposure and other factors on the sex ratio in the population inhabiting the exposed region. A total of 11,464 singleton births of 3,992 mothers exposed to radiation during 1949-1956 were analyzed. The overall sex ratio was 1.07, similar to the current sex ratio in Kazakhstan (1.06). The sex ratio increased from 1.04 where mothers received <20.0 cSv to 1.12 where mothers received > or =60.0 cSv. However, the linear trend across exposures was not significant (P = 0.42). No consistent association was found between the sex ratio and the time since parental radiation exposure, parental age at exposure, or year of birth. Sex ratio was significantly associated with maternal age, birth order and possibly ethnicity but not with paternal age, parental educational level or season. In conclusion, no significant association was found between radiation exposure level and sex ratio, but some previously suggested demographic factors were positively associated with sex ratio.

Radiation exposure due to local fallout from Soviet atmospheric nuclear weapons testing in Kazakhstan: solid cancer mortality in the Semipalatinsk historical cohort, 1960-1999.

Little information is available on the health effects of exposures to fallout from Soviet nuclear weapons testing and on the combined external and internal environmental exposures that have resulted from these tests. This paper reports the first analysis of the Semipalatinsk historical cohort exposed in the vicinity of the Semipalatinsk nuclear test site, Kazakhstan. The cohort study, which includes 19,545 inhabitants of exposed and comparison villages of the Semipalatinsk region, was set up in the 1960s and comprises 582,750 person-years of follow-up between 1960 and 1999. Cumulative effective radiation dose estimates in this cohort range from 20 mSv to approximately 4 Sv. Rates of mortality and cancer mortality in the exposed group substantially exceeded those of the comparison group. Dose-response analyses within the exposed group confirmed a significant trend with dose for all solid cancers (P < 0.0001) and for digestive and respiratory cancers (P = 0.0255 and P < 0.0001), whereas no consistent dose-response trend was found for all causes of death (P = 0.4296). Regarding specific cancer sites, a significant trend with dose was observed for lung cancer (P = 0.0001), stomach cancer (P = 0.0050), and female breast cancer (P = 0.0040) as well as for esophagus cancer in women (P = 0.0030). The excess relative risk per sievert for all solid cancers combined was 1.77 (1.35; 2.27) based on the total cohort data, yet a selection bias regarding the comparison group could not be entirely ruled out. The excess relative risk per sievert based on the cohort's exposed group was 0.81 (0.46; 1.33) for all solid cancers combined and thus still exceeds current risk estimates from the Life Span Study. Future epidemiological assessments based on this cohort will benefit from extension of follow-up and ongoing validation of dosimetric data.