Risk of congenital anomalies in children of parents occupationally exposed to low level ionising radiation

A systematic review of human evidence for the intergenerational effects of exposure to ionizing radiation

PURPOSE

To provide a synthesis of the published evidence pertaining to the intergenerational health effects of parental preconceptional exposure to ionizing radiation in humans.

METHODS

The study populations are the descendants of those who were exposed to ionizing radiation prior to conception. A Boolean search identified publications for review in accordance with Office of Health Assessment and Translation guidelines. Initially, a risk of bias assessment was conducted for each published study and relevant data extracted. Information was organized into adverse health outcome groups and exposure situations. To make an assessment from the body of evidence within each group, an initial confidence rating was assigned, before factors including inconsistencies between studies, magnitude of effect, dose response and confounders were considered. From this, 'an effect', 'no effect' or whether the evidence remained 'inadequate' to determine either effect or no effect, was ascertained. This assessment was based primarily upon the author's conclusions within that evidence-base and, by binomial probability testing of the direction of effect reported.

RESULTS

2441 publications were identified for review which after screening was reduced to 127. For the majority of the adverse health groups, we find there to be inadequate evidence from which to determine whether the health effect was, or was not, associated with parental preconceptional radiation exposure. This was largely due to heterogeneity between individual study's findings and conclusions within each group and, the limited number of studies within each group. We did observe one health grouping (congenital abnormalities) in occupationally exposed populations, where an increase in effect relative to their controls or large magnitude of effects, were reported, although it is noted that the authors of these studies interpreted their findings as most likely not to be associated with parental radiation exposure.

CONCLUSIONS

We find there to be a lack of evidence to enable the formal assessment of radiation-related adverse effects in offspring of exposed humans. This is not the same as there being no clear evidence that effects may occur but does infer that if adverse health effects do arise in children of exposed parents, then these effects are small and difficult to reproducibly measure. Inconsistencies in designing studies are unavoidable, however we highlight the need for an element of standardization and, more sharing of primary datasets as part of open access initiatives, in order for future reviews to make reasonable conclusions. Overall, there is a need for future work to ensure comparable measures between studies where possible.

The Likelihood of Adverse Pregnancy Outcomes and Genetic Disease (Transgenerational Effects) from Exposure to Radioactive Fallout from the 1945 Trinity Atomic Bomb Test

The potential health consequences of the Trinity nuclear weapon test of 16 July 1945 at Alamogordo, New Mexico, are challenging to assess. Population data are available for mortality but not for cancer incidence for New Mexico residents for the first 25 y after the test, and the estimates of radiation dose to the nearby population are lower than the cumulative dose received from ubiquitous natural background radiation. Despite the estimates of low population exposures, it is believed by some that cancer rates in counties near the Trinity test site (located in Socorro County) are elevated compared with other locations across the state. Further, there is a concern about adverse pregnancy outcomes and genetic diseases (transgenerational or heritable effects) related to population exposure to fallout radiation. The possibility of an intergenerational effect has long been a concern of exposed populations, e.g., Japanese atomic bomb survivors, survivors of childhood and adolescent cancer, radiation workers, and environmentally exposed groups. In this paper, the likelihood of discernible transgenerational effects is discounted because (1) in all large-scale comprehensive studies of exposed populations, no heritable genetic effects have been demonstrated in children of exposed parents; (2) the distribution of estimated doses from Trinity is much lower than in other studied populations where no transgenerational effects have been observed; and (3) there is no evidence of increased cancer rates among the scientific, military, and professional participants at the Trinity test and at other nuclear weapons tests who received much higher doses than New Mexico residents living downwind of the Trinity site.

Evidence for a teratogenic risk in the offspring of health personnel exposed to ionizing radiation?!

BACKGROUND

The evidence concerning safety of occupational exposure to ionizing radiation on teratogenic effects mainly relies on animal models, disaster epidemiology and experience in cancer etiology. Following an explorative result on maternal exposure in medical occupations we conducted a feasibility study, addressing congenital anomalies (CA) in the offspring of health workers potentially exposed to radiation.

METHODS

In a prospective follow-up study, we enrolled women, identified by mandatory registration at the office of radiation protection as wearing a dosimeter. The participating women answered a questionnaire and if pregnant agreed to an examination of their infant. CA were diagnosed and categorized, and demographic and anamnestic findings (including dosimeter values) were ascertained. Mainz Birth Registry data were used for comparison, and a nonresponder analysis was performed.

RESULTS

Answers were received from 286 of 604 (51%) women exposed and 183 (30.3%) of them participated in the study including 88 nonparticipants who provided exposure data only. Further sources of ionizing radiation and other factors relevant for CA did not differ between the groups. Thirty pregnancies occurred among the participants. Eight of the resulting 27 infants were diagnosed with CA (30%) compared with 6.2% of the comparison group.

CONCLUSION

Previous explorative findings were corroborated by this feasibility study. The increased prevalence for CA could not be explained by any other factor. A preferable prospective active design is achievable, and the participation rate is essential to calculate valid results and answer this important issue. Birth Defects Research (Part A) 106:475-479, 2016. © 2016 Wiley Periodicals, Inc.

Paternal programming of offspring cardiometabolic diseases in later life

Early - intrauterine - environmental factors are linked to the development of cardiovascular disease in later life. Traditionally, these factors are considered to be maternal factors such as maternal under and overnutrition, exposure to toxins, lack of micronutrients, and stress during pregnancy. However, in the recent years, it became obvious that also paternal environmental factors before conception and during sperm development determine the health of the offspring in later life. We will first describe clinical observational studies providing evidence for paternal programming of adulthood diseases in progeny. Next, we describe key animal studies proving this relationship, followed by a detailed analysis of our current understanding of the underlying molecular mechanisms of paternal programming. Alterations of noncoding sperm micro-RNAs, histone acetylation, and targeted as well as global DNA methylation seem to be in particular involved in paternal programming of offspring's diseases in later life.

Radiation Risk to the Fluoroscopy Operator and Staff

OBJECTIVE

Recent articles discussing cases of brain cancer in interventionalists have raised concerns regarding the hazards of occupational exposure to ionizing radiation. We review the basics of radiation dose and the potential radiation effects, particularly as they pertain to the operator. Then we present the data regarding the risk of each type of radiation effect to the fluoroscopy operator and staff, with special attention on cancer induction, radiation-induced cataracts, and the pregnant operator.

CONCLUSION

Although the evidence overwhelmingly shows that exposure to higher doses of radiation carries a risk of cancer and tissue reactions, the risks of chronic exposure to low-level radiation are less clear. Many studies examining occupational exposure to radiation fail to show an increased risk of stochastic effects of radiation, but the positive results raise concern that the studies are underpowered to consistently detect the small risk. The lack of information in these studies about radiation doses and adherence to radiation protection further confound their interpretation. Large prospective studies of populations with occupational exposure to low-level radiation might clarify this issue. More clearly established are the risks of radiation to the fetus and the risk of cataracts in interventional cardiologists and interventional radiologists. Interventionalists can mitigate these risks by following established radiation safety practices.

Maternal occupational exposure to ionizing radiation and birth defects

So far, only a few studies investigated occupational exposure to ionizing radiation in pregnancy to cause birth defects (BDs). No association between BDs and ionizing radiation, although described for high-dose exposure, could ever be confirmed for employees, or specific job titles. Here, an explorative analysis of a prospective population-based birth cohort used to quantify the prevalence of BDs in infants between 1/2007 and 2/2008 is presented. An active examination of all livebirths by specially trained paediatricians in two defined areas was performed. Additionally, a study-specific questionnaire distributed among all becoming mothers in the surveyed regions included questions on maternal occupational exposure to ionizing radiation within the first trimester of pregnancy. In 3,816 births (including 165 infants with BDs; 4.3%), maternal answers concerning possible exposures to medical and occupational ionizing radiation were available. Relative risk (RR) estimates in mothers surveyed for occupational exposure to ionizing radiation (wearing a radiation dosimeter) and BDs in the offspring were calculated exploratively. A higher prevalence of infants with BDs (n = 4; 13.8%) was documented in newborns of the 29 surveyed mothers compared to that in 3,787 births from unexposed mothers (n = 161; 4.3%), corresponding to a RR of 3.2 (1.2-8.7). Excluding deformations, the RR increased to 4.0 (1.5-10.7). Adjustment for possible confounders did not change the results substantially.

Birth defects in the vicinity of nuclear power plants in Germany

Living in the vicinity of nuclear power plants (NPP) is discussed here in terms of adverse health effects. A prospective population-based cohort study was conducted to evaluate whether the prevalence of birth defects in the vicinity of NPPs is elevated and scrutinize a possible distance correlation. A birth cohort born to mothers living within 10 km of two selected NPPs (study region) was compared to a region without NPP (comparison region), and an active surveillance of all live births, stillbirths, and induced abortions in the defined regions was performed. Between 01/2007 and 02/2008, all newborns were examined by specially trained study paediatricians according to the protocols of the Birth Registry Mainz Model. The cohort consisted of 5,273 infants (90% completeness). The outcome measure was an infant with birth defect(s). The prevalence of infants with birth defects was 4.5% in the study region and 4.7% in the comparison region, which corresponds to a relative risk (RR) of 0.94 (lower 95% confidence level (CL): 0.76). Thus, the prevalence of birth defects in the regions surrounding NPPs was not increased compared to those of the comparison region. Adjustment for potential confounders did not substantially change the result (RR 0.90, lower 95% CL 0.73). The adjusted and unadjusted distance approach (1/distance in km) did not show any correlation to vicinity to a NPP (p = 0.38). Specifically, within the study region, the prevalence of birth defects showed no upward trend with decreasing distance. Birth defect prevalence and most descriptive parameters in the comparison region were identical to those in the Birth Registry Mainz Model.

Male-mediated developmental toxicity in mice after 8 weeks'exposure to low doses of X-rays

PURPOSE

The aim of the study was to investigate the effects of subchronic irradiation of male mice on reproduction ability and induction of male-mediated teratogenesis.

MATERIALS AND METHODS

Male mice were irradiated to 0.05 Gy, 0.10 Gy and 0.20 Gy daily for 8 weeks, 5 days per week. The total doses were 2.00 Gy, 4.00 Gy and 8.00 Gy, respectively. After the end of exposure each male was caged with two untreated females. The females were sacrificed on day 17 based on the finding of a vaginal plug. Females were examined for the number of live and dead implantations and the incidence of congenital malformations of survival foetuses.

RESULTS

The fertilization ability of males was not diminished. The exposure to 0.20 Gy daily significantly decreased the percent of pregnant females and the number of total implantations. Exposure to 0.10 Gy and 0.20 Gy daily caused decreases in the number of live foetuses and induced dominant lethal mutations (over 50% at the highest dose). Exposure to each dose significantly enhanced the number of deaths (especially early) implants. The incidence of gross and skeletal malformations was not statistically significant, except for skeletal malformations at the highest dose.

CONCLUSIONS

Results confirmed that irradiation of male germ cells cause genetic effects which could be transmitted to the offspring. After subchronic exposure to low doses the majority of mutations caused premature death. Subchronic exposure to low doses of X-rays did not induce external and skeletal malformations of surviving foetuses.

Are the risks from tritium exposures being underestimated?

Tritium is a radionuclide that will be used and produced in fusion reactors. Tritium toxicity is well known, but its health consequences are more difficult to assess, due to difficulties in assessing doses and to the very few cases of contamination that have occurred since it started being used. The assessment of risks resulting from tritium exposure is based on ICRP models that enable the calculation of doses in tissues, by means of a weighting factor WR, based on the relative biological effectiveness of the various radioactive emissions. Some authors are currently asking for a revision of the weighting factor used for tritium beta-ray emissions, arguing that tritium could be incorporated into DNA. A review of the extensive research conducted on this subject shows that the relative biological effectiveness of tritium is not so different from that of gamma emissions, which are taken as reference radiations. This supports the drive to keep the current weighting factor of 1 for tritium beta emissions, initially proposed and then reaffirmed by the ICRP.

Systematic review of epidemiological studies of exposure to tritium

Tritium (3H) is a radioactive isotope of hydrogen. A number of factors combine to create a good deal of interest in the risks arising from exposure to tritium of both workers and members of the public. Tritium is ubiquitous in environmental and biological systems and is very mobile due to its occurrence as tritiated water. In this paper we systematically review epidemiological data relating to tritium exposure with a view to assessing the risk of such exposure using those studies that are potentially informative. The usefulness of the available studies of cancer and other adverse health effects in workforces and members of the general public is often impaired by a lack of tritium-specific dose data, low doses and small numbers of cases. A number of workforce studies have been identified in which tritium-specific individual doses have been estimated, although none of them, as presently reported, enable reliable inferences to be made on risks associated with exposure to tritium. In general, the available epidemiological studies on the offspring of radiation workers or on pregnancy outcome in areas subject to releases of tritium do not contain enough detail to estimate risks from tritium exposure. Although the studies presently reported are uninformative on risks from tritium, a number of the occupationally exposed cohorts would be potentially informative, particularly if data were suitably combined.

Paternal Laboratory Work and Congenital Malformations

Animal studies indicate male-mediated teratogenicity for certain carcinogens/mutagens. Nevertheless, paternal occupational determinants of malformations in humans have been sparsely investigated. Data on male employees at Swedish universities from 1970 to 1989 were linked to the Medical Birth Register. The relationship between major malformations and exposure to laboratory work and to specific laboratory agents/techniques before the third trimester were analyzed using logistic regression. For major malformations, "laboratory work in general" (n = 3237) gave an adjusted odds ratio (OR) of 1.3 (95% CI = 0.8-2.1) and carcinogenic solvent use (n = 2489) of 2.0 (95% CI = 0.8-4.9) around the time of conception. For carcinogenic solvents and neural crest malformations, OR was 4.9 (95% CI =1.5-15.8). In conclusion, the prevalence of congenital malformations was not increased in offspring of males with laboratory work in general (1970-1989). Paternal work with agents such as carcinogens could, however, be of concern.

Genetic effects of radiotherapy for childhood cancer

Radiation-induced heritable diseases have not been demonstrated in humans and estimates of genetic risks for protection purposes are based on mouse experiments. The most comprehensive epidemiologic study is of the Japanese atomic bomb survivors and their children, which found little evidence for inherited defects attributable to parental radiation. Studies of workers exposed to occupational radiation or of populations exposed to environmental radiation appear too small and exposures too low to convincingly detect inherited genetic damage. In contrast, survivors of childhood cancer form the largest group of people exposed to high doses of ionizing radiation before reproduction and offer unique advantages for studying trans-generation effects. A wide range of gonadal doses are possible, several comparison groups are readily available (including siblings), and there is a strong willingness among cancer survivors to participate in health studies. Cancer patients also have detailed medical records that facilitate both the accurate estimation of gonadal doses and the assessment of potentially confounding factors, such as intercurrent illness, personal and family medical histories, lifestyle characteristics such as tobacco use, and circumstances at delivery. An international study is nearing completion of over 25,000 survivors of childhood cancer in the United States and Denmark who gave birth to or fathered over 6,000 children. Doses to gonads are being reconstructed from radiotherapy records with 46% over 100 mSv and 16% over 1,000 mSv. Adverse pregnancy outcomes being evaluated include major congenital malformations, cytogenetic abnormalities, stillbirths, miscarriages, neonatal deaths, total deaths, leukemia and childhood cancers, altered sex ratio, and birth weight. The main analyses are based on dose-response evaluations. Blood studies of trios (cancer survivor, spouse or partner and offspring) have been initiated to evaluate mechanistic evidence for the transmission of any radiation-induced genetic damage such as minisatellite mutations. Markers of cancer susceptibility such as chromosomal radiosensitivity and genotype profile will also be examined. In the United States series to date, 4,214 children were born to cancer survivors among whom 157 (3.7%) genetic diseases were reported in contrast to 95 (4.1%) reported conditions among 2,339 children born to sibling controls. In the Denmark series the comparable figures were 82 (6.1%) birth defects among 1,345 children of cancer survivors and 211 (5.0%) among 4,225 children of sibling controls. Coupled with prior studies, these preliminary findings, if sustained by ongoing dose-response analyses, provide reassurance that cancer treatments including radiotherapy do not carry much if any risk for inherited genetic disease in offspring conceived after exposure.

Review of recent epidemiological studies on paternal occupations and birth defects

The main findings reported by recent epidemiological studies on paternal occupations and birth defects are reviewed, and the main limitations associated with these studies discussed. Epidemiological studies on paternal occupations and birth defects were reviewed for the period 1989 to 1999 inclusive. Systematic searches were made with search engines with related keywords. There were several common paternal occupations that were repeatedly reported to be associated with birth defects. These paternal occupations were janitors, painters, printers, and occupations exposed to solvents; fire fighters or firemen; and occupations related to agriculture. The common weaknesses in most of these studies include inaccurate assessment of exposures, different classification systems, different inclusion criteria of birth defects, and low statistical power. It is concluded that epidemiological studies, reported in the past decade, suggest that several common paternal occupations are associated with birth defects. Future studies could be focused on these specific, rather than general, occupational groups so that causative agents may be confirmed and thus enable appropriate preventive measures to be taken.

Fetal death and congenital malformation in babies born to nuclear industry employees: report from the nuclear industry family study

BACKGROUND

There is some concern about the genetic effects of exposure to low-level ionising radiation, but the evidence is sparse and conflicting. Most work has concentrated on cancer in offspring and little has been done on adverse reproductive outcome. We aimed to assess whether the offspring of men and women who are occupationally exposed to ionising radiation are at increased risk of fetal death and congenital malformation.

METHODS

We analysed pregnancies reported by an occupational cohort of nuclear industry workers in the UK, employed at establishments operated by the Atomic Energy Authority, Atomic Weapons Establishment, and British Nuclear Fuels. Employment and radiation monitoring data supplied by employers was linked to each pregnancy.

FINDINGS

11,697 men and 1903 women reported one or more singleton pregnancy conceived after first employment within the nuclear industry, the men reporting a total of 23,676 singleton pregnancies and the women 3585. The risks of fetal death and congenital malformation were not related to whether the father had been monitored before conception or to the dose of radiation received. Among pregnancies reported by women, the risk of early (<13 weeks of gestation) miscarriage was higher if the mother had been monitored before conception (odds ratio [OR] 1.3, 95% CI 1.0-1.6), but there was no trend with dose. The risk of stillbirth was also higher if the mother had been monitored before conception (OR 2.2, 95% CI 1.0-4.6), but the finding was based on only 29 cases (13 exposed). The risk of any major malformation, or of specific groups of malformations, was not associated with maternal monitoring, or dose received, before conception.

INTERPRETATION

We found no evidence of a link between exposure to low-level ionising radiation before conception and increased risk of adverse reproductive outcome in men working in the nuclear industry. Similarly for women there was no evidence of an association between monitoring before conception and malformation in offspring. The findings relating maternal preconceptual monitoring to increased risk of fetal death are equivocal and require further investigation.