Fallout from the Chernobyl nuclear disaster and congenital malformations in Europe

Investigators estimate that the population exposure that resulted from the Chernobyl fallout is in the range of natural background radiation for most European countries. Given current radiobiologic knowledge, health effects-if any-would not be measurable with epidemiologic tools. In several independent reports, however, researchers have described isolated peaks in the prevalence of congenital malformations in the cohort conceived immediately after onset of the fallout. The consistency of the time pattern and the specific types of malformation raise concern about their significance. In this study, the author summarizes findings from Turkey, Belarus, Croatia, Finland, Germany, and other countries, and implications for radiation protection and public health issues are discussed.

[Genetic consequences of ionizing radiation of parents on their offspring (review of the literature)]

The article is a review of the current published literature concerning possible genetic sequelae of exposure of human beings to ionizing irradiation. Data are submitted obtained from studies by leading specialists in radiation medicine and radiation biology.

Risk estimation for multifactorial diseases. A report of the International Commission on Radiological Protection

This report reviews data on naturally-occurring multifactorial diseases and develops a mathematical model to predict the impact of radiation-induced mutations on the frequencies of these diseases in the population. It provides an outline of the aetiological features and examples of multifactorial diseases, interpreted to arise as a result of the joint action of genetic and environmental factors. Examples include common congenital abnormalities (such as neural tube defects, cardiovascular malformations, cleft lip+/-palate etc.) and chronic diseases (such as coronary heart disease, essential hypertension, diabetes mellitus etc.). These diseases are not readily explained on the basis of simple mendelian patterns of inheritance. The report considers the concepts and models used to explain the inheritance patterns of multifactorial diseases with particular emphasis on the multifactorial threshold model (MTM) of disease liability. The MTM is useful for predicting risk to relatives of those affected from information on their population frequencies. In these predictions, the heritability (h(2)) provides a measure of the relative importance of transmissible genetic effects in the overall phenotypic variation. Conceptual differences between mendelian and multifactorial diseases are discussed. The genetic basis of a multifactorial disease is that a genetically susceptible individual may or may not develop the disease depending on the interaction of a number of risk factors, both genetic and environmental. Three chronic multifactorial disease entities are reviewed in depth, viz. diabetes mellitus, essential hypertension, and coronary heart disease. The report considers briefly mechanistic population genetic models developed to explain polygenic variation. The basic conclusion is that the concepts of liability and threshold (underlying the MTM model) and that of mutation-selection balance (from population genetic models) together provide a basis for developing a model for assessing the impact of radiation-induced mutations on the frequencies of multifactorial diseases in the population.The mutation component (MC) of genetic diseases quantifies the responsiveness of the genetic component of a disease to an increase in mutation rate (e.g. after radiation exposure). This report integrates the concepts of liability and threshold (from the MTM model) and of mutation-selection equilibrium (from mechanistic population genetic models) into the 'Finite Locus Threshold Model' (FLTM) for estimating MC for multifactorial diseases and the relationship between MC and h(2) of these diseases. Computer simulation studies illustrate the effects of one-time or a permanent increase in mutation rate on MC for multifactorial diseases.Finally, the report addresses the estimation of the radiation risk of multifactorial diseases. A formal revision of the estimates of risk of multifactorial diseases (and also of mendelian diseases) contained in the 1990 Recommendations of ICRP, Publication 60, must await the results of studies currently underway. While future genetic risk estimates are likely to be lower than those in current use, until the new ones become available, those provided in Publication 60 may be regarded as being adequate for use in radiological protection- they are unlikely to underestimate risk.

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.

[The morphological status of the maxillodental system in children living in an area contaminated by radionuclides as a result of the accident at the Chernobyl Atomic Electric Power Station]

The present study has been done in the framework of federal programme "Children of Chernobyl" with the aim to determine spread and structure of dental jaw abnormalities in children born and living in the radiation polluted regions after Chernobyl accident in 1986. 183 children have been examined in Donskoi town of Tula Province with the polluted soil by Cs-137 up to 5 Ci/km. All the examined children were divided into 2 groups: group 1--born in 1980-1986 and group 2--born in 1987-1994. It was determined that 76.5% of children have dental jaw system abnormalities. The most spread ones were occlusion abnormalities in combination with teeth abnormalities (28.9% cases) while the state of dental jaw system corresponding to the age standard was 2 times rarer in children born after the Chernobyl accident.

Genetic monitoring of the human population from high-level natural radiation areas of Kerala on the southwest coast of India. I. Prevalence of congenital malformations in newborns

In the densely populated monazite-bearing sands of Kerala, on the southwest coast of India, natural radiation dose rates range from 1. 0 to over 35.0 mGy per year in certain well-defined high-level natural radiation areas. As a part of the program to assess the health effects of this naturally occurring high-level natural radiation on human populations, monitoring of newborns is being undertaken to determine the incidence of congenital malformations. From August 1995 to December 1998, a total of 36,805 newborns were screened, including 212 (0.58%) stillbirths. There were 36,263 singletons, 536 (1.45%) twins, and 6 born as triplets. The overall incidence of malformations was 1.46% and was dependent on maternal age. The stillborns exhibited a very high malformation rate of 20.75% compared to 1.35% among the live births. Likewise, twins also had a higher malformation rate (2.99%) compared to singletons (1.44%). About 3.5% of the newborns originated from consanguineous marriages. Consanguinity also led to a relatively higher rate of malformations (1.97%) as well as of stillbirths (1.18%). About 92% of the deliveries took place by the maternal age of 29 years and only 1.2% among women above 34 years old. The stratification of newborns with malformations, stillbirths or twinning showed no correlation with the natural radiation levels in the different areas. Thus no significant differences were observed in any of the reproductive parameters between the two population groups based on the monitoring of 26,151 newborns from high-level natural radiation and 10,654 from normal-level natural radiation (dose rate </=1.5 mGy/year) areas of the Kerala coast.

Evaluation of the impact of Chernobyl on the prevalence of congenital anomalies in 16 regions of Europe. EUROCAT Working Group

BACKGROUND

Surveillance data from population-based congenital anomaly registers in 16 regions of Europe (mainly Western Europe) were analysed to assess the impact of the Chernobyl accident on the prevalence of selected congenital anomalies.

METHODS

Three cohorts of pregnancies were defined: those exposed during the first month following Chernobyl (External Exposure Cohort), the first year (Total Exposure Cohort) and the two subsequent years (Control Cohort). Expected numbers of congenital anomalies in these cohorts were calculated from 1980-1985 baseline rates. Registries were grouped into three exposure categories according to first-year exposure estimates.

RESULTS

There was no overall or dose-related increase in prevalence in the two exposed cohorts for Down's Syndrome, neural tube defects, other central nervous system defects or eye defects. There was a statistically significant overall 22% (95% CI: 13-31%) excess of Down's Syndrome in the Control Cohort, with no dose-response relationship.

CONCLUSIONS

Chernobyl had no detectable impact on the prevalence of congenital anomalies in Western Europe, suggesting that in retrospect the widespread fear in the population about the possible effects of exposure on the unborn fetus was not justified. An increasing prevalence of Down's Syndrome in the 1980s, probably unrelated to Chernobyl, merits further investigation.

[Facial cleft birth rate in former East Germany before and after the reactor accident in Chernobyl]

Cleft lip palates (CLP) are caused by a variety of factors. Ionizing radiation is only one of these factors. The meltdown of the nuclear reactor at Chernobyl on April 26, 1986, and the subsequent radioactive fallout did not cause any acute radiation sickness in Germany. Nevertheless, in West Berlin a significant increase of trisomy-21 cases was reported in births 9 months after the Chernobyl reactor accident. In our study we analyzed the influence of the radioactive fallout after the Chernobyl disaster on the rate and regional distribution of CLP newborns in the former German Democratic Republic (GDR). In contrast to the Federal Republic of Germany an ongoing malformation register for CLP newborns had existed in the former GDR since 4 July 1967. Environmental data were collected from national and international environmental authorities and atomic energy agencies. Population statistics were taken from the statistical year-book of the former GDR. During a 10-year period from 1980 to 1989, the average number of CLP newborns in the GDR was 1.88 per 1,000 live births. A significant prevalence increase was recorded in 1983, 1987 und 1988. In comparison to the mean rate in the period from 1980 until 1986, 1987 demonstrated an increase of 9.4%. Regional prevalence increases were seen in the three northern districts of Schwerin, Rostock and Neubrandenburg, where the radioactivity measurements in general showed higher levels of the radionuclides caesium-137 und strontium-90 than in other districts. Owing to the comprehensive malformation register for CLP patients in the GDR, this is the first study for Germany, analyzing the CLP rate before and after the fallout in Chernobyl. The results support the allegation of the influence of radiation-induced increase of CLP newborns after the Chernobyl reactor accident.

[The incidence of congenital developmental defects among the newborn infants of Rivne Province]

A study was made of frequency of developmental defects among newborn babies in Rivne Province and two its regions (the northern territories relatively free from contamination and those affected by radioactive contamination) that are under control because of the Chernobyl accident. Variations in the frequency of developmental defects (DD) over the studied period (1985-1997) in the province averaged 153 to 372.8 per 10,000 newborns, i.e., the parameter increased more than 2.4-fold. In the controlled regions it averaged 163 to 401.1 per 10,000 neonates (an increase 2.5 as much). A linear increase in DD prevalence might be related both to effects of adverse environmental factors and improvement in diagnosis and registration of pathological states. Retrospectively, 17 DD forms were registered, which, according to the European Register, were grouped under the heading "old defects", and 16 forms placed in the category "new defects". Comparison of DD prevalence with data of the European Register showed that, on the whole, prevalence of some DD among neonates in Rivne Province over the stated period (1985-1997) corresponds to analogous indices in other regions of Europe.

Radiation-related brain damage and growth retardation among the prenatally exposed atomic bomb survivors

Many studies of prenatally exposed survivors of the atomic bombings of Hiroshima and Nagasaki have shown that exposure to ionizing radiation during gestation has harmful effects on the developing human brain. Data on the occurrence of severe mental retardation as well as variation in intelligence quotient (IQ) and school performance show significant effects on those survivors exposed 8-15 and 16-25 weeks after ovulation. Studies of seizures, especially those without a known precipitating cause, also exhibit a radiation effect in survivors exposed 8-15 weeks after ovulation. The biologic events that subtend these abnormalities are still unclear. However, magnetic resonance imaging of the brains of some mentally retarded survivors has revealed a large region of abnormally situated gray matter, suggesting an abnormality in neuronal migration. Radiation can induce small head size as well as mental retardation, and a review of the relationship between small head size and anthropometric measurements, such as height, weight, sitting height and chest circumference, shows that individuals with small head size have smaller anthropometric measurements than normocephalics. This suggests that radiation-related small head size is related to a generalized growth retardation. Finally, the issue of a threshold in the occurrence of one or more of these effects, both heuristically and from a regulatory perspective, remains uncertain. Simple inspection of the data often suggests that a threshold may exist, but little statistical support for this impression can be advanced, except in the instance of mental retardation.

Congenital anomalies of the central nervous system at autopsy in Croatia in the period before and after the Chernobyl accident

In this study, we analyzed the frequency, type and sex distribution of congenital anomalies of the central nervous system (CNS) at autopsy in the period prior to and after the Chernobyl accident in northwest Croatia, one of the areas with the highest exposure to nuclear contamination from Chernobyl. All autopsies in both periods were performed by the same technique, i.e. dissection of the trunk and head, and inspection of the extremities. There were 53 infants with congenital anomalies of the CNS in the period prior to, and 99 in the period after the Chernobyl accident. Our results showed a statistically significant increase in the incidence of CNS anomalies in general (chi 2 = 4,719, p < 0.05, D. F. = 1) and of neural tube defects (chi 2 = 5.380, p < 0.05, D. F. = 1) in the period after the Chernobyl accident. Differences in the incidence of various CNS anomalies, in all types of anomalies, and in sex distribution were not statistically significant. Studies of the association between the Chernobyl accident and congenital anomalies showed no clear changes in the prevalence of anomalies at birth which might have been associated with the accident. This study provided some additional data on the frequency of CNS anomalies in the period after the Chernobyl accident in one of the areas with the highest exposure to the nuclear contamination from Chernobyl. We suggest that the frequency of all anomalies, including CNS, in the period after the Chernobyl accident should be carefully monitored.

Morbidity in a large cohort study of children born to mothers exposed to radiation from Chernobyl

Reproductive health was reviewed in four oblasts of the Republic of Belarus that were either heavily exposed (Mogilev and Gomel) or lightly exposed (Brest and Vitebsk) to ionizing radiation after the meltdown of a nuclear reactor in Chernobyl. A retrospective analysis was conducted on pregnancies occurring between January 1, 1982, and December 31, 1990, and a comparison of results was made between pregnancy outcomes prior to and after the meltdown for individuals residing in heavily exposed and lightly exposed oblasts. Pregnant women who resided in heavily exposed oblasts appeared to be at risk for development of toxemia, renal insufficiency and anemia. Neonates born in heavily contaminated areas were apparently at risk for development of anemia and congenital malformations and perinatal death. In addition, a cohort of 757 neonates, 0-18 months old, with a normal physical examination, was identified for laboratory analysis of hematological, immunological, endocrinological and nutritional status. Decreased levels of copper and zinc were documented in erythrocytes from neonates from heavily contaminated oblasts, findings that may be related more to inadequate nutrition than to radiation exposure. Increased absolute "null" lymphocyte number and diminished absolute T lymphocyte number with a reduction in the "helper" (i.e., T4) subclass of T cells were evident in neonates born-in heavily exposed oblasts. Geographic differences in reproductive health and immune status are apparent in Belarus that may be related to radiation exposure. Additional studies are required to exclude confounding variables and possible selection bias.

Overview of 1993 research activities in Belarus related to the Chernobyl accident

This overview describes the medical and biological consequences of the Chernobyl nuclear power plant accident that had been assessed by Belarus scientists as of 1993. In particular, childhood thyroid cancer has increased in both frequency and severity. Other malignant tumors may have also increased, as may have childhood diseases that result from impaired immune function. It is unknown whether these increases in human disease (other than thyroid cancer) are due to improved methods of reporting or to exposure to ionizing radiation. In addition to the medical consequences of radiation damage, there are also significant psychological problems endured by the population living in contaminated areas. The Republic of Belarus has participated in several international programs for the study and management of widespread radiation exposure, and will continue to do so. Programs to address issues of radiation protection and population safety are being implemented wherever possible.

Changes in registered congenital anomalies in the Republic of Belarus after the Chernobyl accident

A descriptive analysis of birth defects and malformations was performed to assess whether the rates of these defects correlate with the geographic areas of Belarus that received different levels of 137Cs contamination resulting from the Chernobyl catastrophe. Since this accident in 1986, the frequency of both congenital and fetal abnormalities in the Republic of Belarus has apparently increased. This increase is most prominent in areas with at least 555 9Bq/m2 radioactive contamination, although it has not been possible to correlate the individual dose received by a pregnant woman with the incidence of congenital malformations. The types of anomalies that were most increased in frequency were multiple congenital malformations, polydactyly, and reduction limb defects. These malformations are commonly associated with dominant new mutations. Chromosomal disorders such as occur in Down syndrome were not increased in frequency, nor could teratogenic effects be attributed to exposure to ionizing radiation. Preventive measures have apparently reduced the number of births with congenital abnormalities but have had no apparent effect on the frequency of fetal defects. Results of our analysis are consistent with the hypothesis that ionizing radiation released during the Chernobyl accident may have placed fetuses and neonates at risk for congenital malformations. Epidemiological studies are now required to determine whether a mother's radiation dose correlates with congenital malformations in her children.

[The status of the progeny of male rats subjected to low-dose external gamma irradiation exposure]

In studies on 120 mature males of Wistar rats and 252 female rats of the same line, 20-day-old fetuses and 974 young rats of the first generation, anomalies of antenatal and postnatal development were found after exposure of spermatids and spermatozoa to gamma-radiation in doses 0.25-1.0 Gy. After exposure of male rats to radiation in dose 0.25 Gy, reliable delay of pelvic bone ossification was observed as compared to the control.

[Genetic or ecogenetic consequences of the Chernobyl accident? (facts and hypotheses)]

The results of investigations indicated the necessity of genetic monitoring in population using the data of family examination in medical genetic centres. Indices of the frequency of developmental abnormalities in newborns are not suitable for monitoring because they do not permit to differentiate between new mutations and inherited ones. The dissemination of these abnormalities among newborns in Kiev mostly coincides with the same index in other European regions and is lower than in Canada and West Australia. According to the data of Kiev regional medical genetics centre, about 80% of developmental abnormalities occur as a result of inherited mutations but not new ones. Under the conditions of environmental pollution, ecogenetic consequences assume a new importance.

Exposure to radioactive iodine-131 for scintigraphy or therapy does not preclude pregnancy in thyroid cancer patients

Radiation is known to be mutagenic. The aim of the present study was to ascertain whether exposure to 131I induces genetic damage, as assessed by pregnancy outcomes and the health status of offspring of women previously exposed to 131I during thyroid carcinoma treatment.

METHODS

Data on 2113 pregnancies were obtained by interviewing female patients treated for thyroid carcinoma who had not received any significant external radiation to the ovaries.

RESULTS

The incidence of miscarriages was 11% before any treatment for thyroid cancer; this number increased slightly after surgery for thyroid cancer, both before (20%) and after (20%) 131I, but did not vary with the cumulative 131I dose. Miscarriages were more frequent (40%) in the ten women who were treated with 131I [mean dose: 3.8 GBq (108 mCi)] during the year preceding conception. Incidences of stillbirth, preterm birth, low birth weight, congenital malformation and death during the first year of life were not significantly different before or after 131I therapy. The incidence of thyroid disease and nonthyroidal malignancy was similar in children born either before or after their mothers were exposed to 131I.

CONCLUSION

With the exception of miscarriages, there is no evidence that exposure to radioiodine affects the outcome of subsequent pregnancies and offspring. The question of whether an increased incidence of miscarriages within 1 yr of 131I administration relates to gonadal irradiation or to insufficient control of hormonal thyroid status remains to be established.

Ten years after Chernobyl

This review focuses on current findings on the health consequences of the accident at the Chernobyl nuclear power plant in 1986. Acute radiation damage caused by exposure to high doses of ionizing radiation involved a few hundred people, apparently with fewer than 100 deaths within the first few months. Epidemiologically detectable increases in congenital abnormalities have not been reported thus far, with the possible exception of Down's syndrome. Owing to the long latency period of radiation-induced cancer, discernible increases in cancer incidence and mortality are not yet expected for most tumour types, especially among adults. However, dramatic increases in the number of childhood thyroid cancers have already been observed in Belarus and Ukraine and the Bryansk regions of Russia. The increase has been over 100-fold in some areas with heavy contamination. From the viewpoint of overall public health, the outlook of direct health effects of the Chernobyl accident are likely to be severe only among some limited subgroups, such as young children exposed to high levels of fallout nuclides. In absolute terms, the global number of Chernobyl-associated cancer cases can be estimated to be tens of thousands, but only a small fraction of these is likely to be discernible epidemiologically.

Health of children born to medical radiographers

OBJECTIVES

To develop a reliable method for collecting information on reproductive outcome in an occupational setting; and to investigate the health of children born to medical radiographers.

METHODS

The study population comprised 6730 members of the College of Radiographers who were, at the time of survey; aged between 30 and 64 years, on the current membership file of the College, and were resident in Britain.

RESULTS

The postal method developed proved to be reliable, with around 87% of questionnaires being returned. The observed frequencies of reproductive events were broadly in line with findings from other studies: of the 9208 pregnancies reported, 83% were livebirths, 12% were miscarriages (gestational age < 20 weeks), 1% were stillbirths (gestational age > or = 20 weeks), and 1% were other rarer spontaneous adverse events (ectopic pregnancy, blighted ovum, and hydatidiform mole). There was little difference between men and women in the frequency of adverse reproductive events reported, with the exception that male radiographers reported fewer medical terminations, the proportions being 3.1% and 1.4% for women and men respectively. Among children, the overall risks of major congenital malformation (RR 1.0, 95%CI 0.9-1.2), chromosomal anomaly (RR 1.4, 95%CI 0.8-2.3), and cancer (RR 1.2 95%CI 0.7-2.0) were as expected based on general population rates. Borderline excesses of chromosomal anomalies other than Down's syndrome in the children of female radiographers (RR 3.9, 95%CI 1.3-9.0, based on five observations), and cancer in the children of male radiographers (RR 2.7, 95%CI 0.9-6.5, based on five observations) were noted. The numbers on which these risks are based are small and the findings should be interpreted cautiously.

CONCLUSIONS

The postal methods developed for obtaining information about reproductive events and child health proved to be reliable in men, as well as in women. Overall, the findings for medical radiographers are reassuring. Dose-response relations could not, however, be examined as long term dose records of radiographers are not routinely kept in an accessible form.

Hazards of ionising radiation: 100 years of observations on man

In November 1895, when Conrad Röntgen serendipitously discovered X-rays, epidemiology was effectively limited to the study of infectious disease. What little epidemiological work was done in other fields was done as part of clinical medicine or under the heading of geographical pathology. The risks from exposure to X-rays and subsequently from other types of ionising radiation were consequently discovered by qualitative association or animal experiment. They did not begin to be quantified in humans until half a century later, when epidemiology emerged as a scientific discipline capable of quantifying risks of non-infectious disease and the scientific world was alerted to the need for assessing the effects of the radiation to which large populations might be exposed by the use of nuclear energy in peace and war.