Although background ionizing radiation is a known mutagen, few studies have examined transgenerational effects in human beings.
Chernobyl, in the former USSR, was the site in 1986 of probably the worst accident ever to have occurred at a nuclear plant. Considerable quantities of radioactivity were released into the atmosphere, much of which was dispersed over the former Soviet Union and Western and Northern Europe. The radioactivity from the accident was washed from the skies and entered the food chain, notably in areas of high rainfall. Subsequent to the accident, people in the area around Chernobyl were evacuated. They have not been allowed to return.
Although not apparent for the first 3 years after the accident, by the end of 1994 a clear increase in childhood thyroid cancers was being seen in children from the surrounding areas. As the data available so far cover only approximately 10 years since the incident. it is too early for there to be significant information concerning other cancers. No relevant data were found regarding whether there was any change in the incidence of reproductive toxicity or in the incidence of congenital anomalies in the surrounding areas.
A study was performed using the workforce at the Sellafield nuclear reprocessing plant in Cumbria in the UK, which is considered to be the most highly exposed workforce in Western Europe and North America (Parker 1999). The aims of this study, which is part of a larger program investigating the health of the children of the Sellafield workforce, were to determine whether there was evidence of an association between stillbirth risk and paternal exposure to ionizing radiation.
Data from birth registration documents for all singleton live births (248 097) and stillbirths (3715) in Cumbria between 1950 and 1989 were analyzed. Within this cohort, the 9078 live births and 130 stillbirths to partners of male radiation workers employed at Sellafield were identified, A significant positive association was found between the risk of a baby being stillborn and the father's total exposure to external ionizing radiation before conception. There was a higher risk for stillbirths with congenital anomalies; (nine stillbirths with neural tube defects). Although the possibility of an unmeasured risk factor for stillbirth being confounded with paternal preconception irradiation cannot be excluded, extensive checks confirmed that the statistical models were a good fit to the data and there was not statistical evidence of unmeasured factors (Parker 1999).
UK Atomic Energy Authority, Atomic Weapons Establishment and British Nuclear Fuels Study
In contrast, another study of a similarly exposed workforce to that at Sellafield showed no increase in fetal death and congenital malformations in babies born to nuclear industry employees (Doyle 2000). This study analyzed pregnancies reported by an occupational cohort of nuclear industry workers in the UK. Employment and radiation monitoring data supplied by the employers was linked to each pregnancy conceived after the first employment within the nuclear industry. The men reported a total of 23 676 singleton pregnancies and the women reported 3585 pregnancies.
Among the pregnancies in female workers, the risk of early miscarriage before 13 weeks' gestation was higher if the mother had been monitored before conception, but this was not dose-related. The risk of stillbirth was also higher if the mother had been monitored before conception, but this finding was based on a small number of cases, of which 13 of 29 were exposed. The risk of any major malformation or of specific groups of malformations was not associated with maternal monitoring, the dose received during pregnancy, or the dose received before conception.
Overall, no evidence of a link between exposure to low-level ionizing radiation before conception and an increased risk of adverse reproductive outcome in men working in the nuclear industry was found. Similarly, there was no evidence of an association for women between monitoring before conception and malformations in the babies. The findings relating maternal preconceptual monitoring to increased risk of fetal death remain equivocal, and require ongoing investigation (Doyle 2000). In a second study, the hypothesis linking exposure to low-level ionizing radiation among men with primary infertility was not supported (Doyle 2001).
In a critique of the first study, it was pointed out that 12% of the pregnancies reported by male radiation workers and 15% reported by female workers ended in fetal death. However, the female workers were on average 10 years younger than the male workers at the time of the survey. Moreover, pregnancies reported by female workers were more recent than those reported by the men. Both of these factors contribute to a much lower expected fetal death rate in female workers than in male workers, especially for late events such as stillbirths (Parker 2001). However, Doyle and co-workers did not accept the statement that men arc less likely than women to report stillbirths (fetal deaths after 24 weeks' gestation).
Recommendation. Environmental ionizing radiation will have an effect; however, no realistic primary prevention method is realistic. This is also evident with the higher levels of ionizing radiation linked with travel flights, radon, and other background radiation. If a new nuclear power accident happens, exposing a population to low-level radiation in a way similar to that after Chernobyl, data from UNSCEAR, the United Nations study group evaluating the measures and decisions taken after Chernobyl, may help to make the right decisions - including, for example, restricting food intake from an exposed area.
2.23.11 Video display terminals (VDTs)
The potential reproductive hazards of being exposed to electromagnetic radiation emitted from VDTs has been the subject of debate for many years (Paul 1993, Scialli 1990). The major concern started in Canada in 1980, where a cluster of four infants with severe malformations was described. The mothers worked at the same place -a newspaper department in Toronto. The cluster was linked to the fact that the women had worked with VDTs during pregnancy. The publication of this cluster in the lay press (TGM 1980) soon brought forward reports on other clusters of reproductive failure from different parts of Canada and the US (Bergquist 1984). Many of these reports concluded that significant levels of ionizing radia tion were not emitted by VDTs. Furthermore, the non-ionizing radiation and magnetic Fields associated with these units are not produced in biologically significant amounts (see, for example, Blackwell 1988). There have been reports of a number of adverse pregnancy outcomes allegedly associated with exposure to VDTs. Four case-control studies report no association between congenital anomalies and maternal exposure to VDTs (Tikkanen 1990, McDonald 1986, Ericson 1986A, 1986B, Kurppa 1985).
At the General Telephone Company of Michigan, a cluster of miscarriages was investigated when 6 of 29 pregnancies in VDT-exposed women spontaneously miscarried, compared with 8 of 97 pregnancies in those not exposed to VDTs (Lichty 1985). Although this difference was statistically significant, the author commented that it may not be biologically significant. There was a possibility that other work-related factors might be involved, because the jobs of women working with VDTs and non-exposed women were considerably different. Mathematical models of clusters have been published showing that a number of random groups of pregnant women should have higher than "normal" rates of adverse outcome, regardless of exposure status (Abenhaim 1991, Bergqvist 1984).
The results of a large case-control study have suggested a small but significantly increased incidence of miscarriage for women who work on VDTs for more than 20 hours per week during the first trimester of pregnancy (Goldhaber 1988). A degree of recall bias cannot be excluded in this retrospective investigation, because the women were questioned about their VDT use more than 2 years after the pregnancies in question (Robinson 1989). A causal relationship with other unmeasured parameters, such as job-related stress, long working hours, and poor ergonomic conditions, may have been a contributory factor (see, for example, McDiarmid 1994).
The U.S. National Institute for Occupational Safety and Health (NIOSH) monitored the incidence of spontaneous abortion in 882 pregnancies that included occupational use of VDTs during gestation (Schnorr 1991). The data from this very comprehensive investigation do not indicate any association between the use of VDTs, exposure to the accompanying electromagnetic fields, and an increased risk of spontaneous abortion. These findings were consistent with the results of two other studies in Finland (Lindbohm 1992) and in Italy (Grasso 1997). The Finnish study did find an increased risk of spontaneous abortion for women who worked with VDTs that emitted a high level of extremely low-frequency magnetic field, but the numbers involved were low (<20 per group), so the clinical significance of this observation is questionable.
Similar negative results were reported in a case-control study that was designed to minimize a possible role of non-occupational factors relating to the incidence of spontaneous abortions (Roman 1992). Another study also reported no significant increased risk of reduced birth weight or premature deliveries among women working with VDTs (Grajewski 1997). Overall, from the investigations to date, the risks (if any) associated with VDT exposure are low (Parazzini 1993). The VDT events have at least been useful as a warning of how society can come to conclusions despite scientific facts. Kalian (1988) quotes the pertinent remark from Foster (1986) about the VDT debate: "Controversy about possible hazards from video display terminals is unavoidable when the data are ambiguous and the stakes arc high."
Recommendation. There is, to date, no evidence to indicate that pregnant women working with VDTs have an increased risk of spontaneous abortion, congenital anomalies, reduced birth weight, or premature deliveries. Pregnant women may continue working with VDTs. However, ergonomic conditions, working hours, and job-related stress should be carefully considered.
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