1 CHS National Cancer Control Center and Department of Community Medicine and Epidemiology, Carmel Medical Center and Technion S. Neaman Institute, Haifa, Israel.
2 The Hannah Khoushy Child Development Center, Bnai Zion Medical Center, Haifa, Israel.
3 Technion Faculty of Medicine, Haifa, Israel.
Received for publication May 7, 2003; accepted for publication March 19, 2004.
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ABSTRACT |
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accidents, radiation; child; cognition; health; neurobehavioral manifestations; radiation
Abbreviations: Abbreviation: ADHD, attention-deficit/hyperactivity disorder.
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INTRODUCTION |
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Although a lot of attention was first paid to the physical health consequences of the radiation-exposed groups, concern was also raised regarding the neurodevelopmental sequelae in those who were exposed to radiation in utero or at a young age. It could be hypothesized that prenatal and early childhood irradiation of the brain could lead to neurobehavioral dysfunction (2).
Studies of the survivors of the atomic bombs in Hiroshima and Nagasaki, Japan, indicated that the fetal brain is most susceptible to high doses of ionizing irradiation for 815 weeks after conception. Fetal exposure to high doses of radiation increased the risk of mental retardation, small head size, subsequent seizures, and poor performance on conventional tests of intelligence (3, 4).
After the Chernobyl accident, an excess of thyroid cancers among exposed children was reported and, more recently, some genetic changes of unclear importance have also been described in children possibly influenced by the Chernobyl radiation exposure (5, 6). Psychological stress, anxiety, and fear, especially in adults, were reported in several studies after the Chernobyl accident (712). Studies of the impact of the Three Mile Island accident showed in one study greater psychological distress among women who were pregnant or had young children (13) but showed in another study no such effect (14). Further, young children living near the Three Mile Island reactor did not differ from children living next to another reactor in their prevalence of behavioral problems (15).
In addition to several hundred thousand individuals who were relocated within the former Soviet Union after the disaster, hundreds of thousands more left the country. Many of them emigrated to Israel. Israeli immigrants from the Chernobyl region manifested high levels of anxiety and concern about radiation. Additionally, they showed inaccurate preconceptions about the health risk of chronic radiation exposure and sought extensive health care for what they feared would be long-term illnesses caused by the Chernobyl Nuclear Power Plant disaster (16, 17). No differences were found in the cognitive and neuropsychological functioning of evacuated children who were in utero or up to 15 months of age at the time of the accident when they were compared with their classmates in Kiev (18).
The present study, among others, was designed to evaluate possible influences of the exposure to ionizing radiation after the Chernobyl accident on the neurobehavioral and cognitive performances of Israeli immigrants who were young children at the time of the accident.
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MATERIALS AND METHODS |
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The area of origin in the former Soviet Union was defined as the settlement of origin in their home countries recorded by the Ministry of Immigrant Absorption in Israel upon registration of their families for immigration. This indicator was validated by information collected during the participants interview. Final assignment to area of exposure was based on the true origin of the child and not on the information appearing in the official documents.
All the children were invited, with their mothers, to the CHS National Cancer Control Center at the Carmel Medical Center in Haifa, Israel. The Israeli Chernobyl Health Effects Study took place during the years 19982001. Participating children were thus aged 1218 years at the time of the study.
Data collection
After signing an informed consent form, the childs mother was interviewed by trained Russian-speaking interviewers who used a standardized questionnaire. The questionnaire sought demographic data, residential and personal radiation exposure (for dose estimation) data, and information on exposure to various risk factors during the relevant pregnancy, disease status, and health behavior patterns of the relevant child. All children undertook a cognitive test and a questionnaire evaluating their behavior. A complete physical examination, self-reported puberty staging according to the Tanner scale, and venous blood tests including hematology and thyroid panels were also conducted but are not discussed in this report. Assessment of attention-deficit/hyperactivity disorder (ADHD) was carried out using the short Conners Rating Scales-Revised for children and their mothers (19). Nonverbal intelligence was examined by the Raven Standard Progressive Matrices Test (20). This test is not language dependent and, therefore, functions well in a new immigrant population.
Measurement of cognitive ability
Cognitive ability of the children was measured by using the Raven Standard Progressive Matrices Test (1996 edition) (20). This nonverbal intelligence test was selected because the study population of immigrant children had diverse levels of knowledge of Hebrew. The test consists of 60 diagrammatic puzzles. Each puzzle has one part missing, which the child has to fill in with one of the options provided after proper explanation by the test administrator. No time limit was set for completion of the test.
The childs score was calculated as the total number of problems solved correctly. A table of percentile norms (20, table SPM 14) was used to interpret the scores. These norms enabled us to compare the performances of children in the various exposure groups.
Assessment of attention
The assessment of ADHD was carried out by using Conners Rating Scales-Revised. These scales are a comprehensive assessment of psychopathology and problem behaviors of children and adolescents.
The Adolescent Self-report Scales and the Parent Rating Scales (which relate to the childs behavior) (19) were chosen for this study. The short forms (27-item questionnaire) yielded scores on four parameters (appearing in both the adolescent and parent questionnaires): oppositional problems, cognitive problems, hyperactivity, and risk of ADHD. Children were provided with a Hebrew version of the questionnaire, and their mothers were provided with a Russian version. Conners Rating Scales-Revised are available in only English, Spanish, and French. Because we needed a Hebrew version for the children and a Russian version for their mothers, the questionnaires were translated into Hebrew and Russian and then translated back into English to validate the translation. The crude scores of the Conners test were translated into T scores, which are age and gender specific. T scores of 65 or more usually indicate a significant clinical problem, while T scores between 56 and 64 warn of a possible problem.
Statistical analyses
Statistical analyses using SPSS/PC, version 10.07 (SPSS, Inc., Chicago, Illinois), software included comparison of different exposure groups (all groups, or highest exposure group vs. others) by means of analysis of variance. After studying individual scores, we used models that adjusted the test scores for the following potential effect modifiers, identified in the univariate analysis: childs gender, birth order, number of siblings, family status (two parents or single parent), timing of exposure (in utero vs. not in utero), and parents level of education.
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RESULTS |
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The age of the participating children at the time of the study ranged from 12 to 18 years. About a fourth of the children were aged 1213 years at the time of the test, 45 percent were aged 1415 years, and 31 percent were aged 1618 years.
The exposure groups differed significantly in the level of education of their parents. Higher levels of education for both parents were noted in residents of the Moscow-St. Petersburg group, followed by residents of Kiev and Minsk (low- or no-exposure group), and were lowest in members of the high-exposure groups (table 2).
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Mothers scores were significantly higher (p 0.001 for each of the subscales) than their childrens scores. This was true for each of the five residence groups. The subjective assessment of the childrens health status by their mothers was found to correlate negatively with the mothers score on the Conners test. In all radiation exposure groups, mothers who rated their children highest (good to excellent health status) scored lowest on the Conners test (p < 0.001).
Mothers from all radiation exposure groups who were pregnant at the time of the accident rated their children with significantly higher Conners test scores in three of four categories than did those who were not pregnant. The scores, however, were mostly in the normal range (table 5).
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DISCUSSION |
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Other findings in the study may indirectly validate the study results. The educational level of the parents was found, as expected, to be a strong positive predictor of performance. Good correlations between cognitive parameters in both tests and higher Conners test scores of mothers versus their children correspond to the current knowledge in this field.
Interestingly, the neurobehavioral assessment of ADHD showed that mothers who were pregnant at the time of the accident scored their children with significantly higher scores than did nonpregnant women for their children. This was shown without any relation to exposure. Childrens assessment scores, in the hyperactivity and the ADHD index, were significantly higher among those who were in utero at the time of the accident. This too was unrelated to exposure level.
Our results may suggest that mothers who were pregnant or had very young children at the time of the accident, regardless of their location in the former Soviet Union, had higher levels of anxiety and fear of the radiation. This might stem from lack of information and inaccurate preconceptions about the exact magnitude and spatial distribution of radiation. Such a sense of fear might either distort their perception or, alternatively, have been transmitted to their children who showed higher hyperactivity and ADHD index scores among the younger ages.
Similar results were found by Ginzburg (7), who reported high levels of anxiety and stress among adults from contaminated and noncontaminated villages. Nearly half of this study population, regardless of the true level of exposure, were unsure if they had a radiation-related illness. Two other studies from the Chernobyl area reported a high risk of psychiatric disorders among women with children under the age of 18 years residing in the exposed areas (21, 22). A study on the psychological effects of the Three Mile Island accident showed that women who were pregnant or had young children experienced the greatest psychological distress after the accident (13). The trauma brought on by the Chernobyl accident, experienced by mothers, was reflected in another study in their perceptions of their childrens well being, particularly somatic symptoms. This anxiety, however, was not transmitted to the children themselves (8).
Two previous studies of the Chernobyl accident suggested lower cognitive performance among children exposed prenatally when compared with nonexposed children (2, 23). One of these studies (2) included evacuated children who were described as having been significantly more exposed than our study population. The second study (23) related to prenatally exposed children only, and it was based on very small numbers of children. Furthermore, these studies did not control for possible confounders (mainly, level of parents education) as did our study, which did not demonstrate a similar lower performance. It is possible that emigration to a new place, remote from the irradiated area, played a role in lowering the anxiety level in the family.
We could not evaluate what, if any, influence the site of residence in Israel had. Moreover, we could also not determine if the level of education received by these children in Israel had an effect. However, because of Israels mandatory-education law, it highly likely that all these young children received formal education in Israeli schools. Given the small size of Israel and given that most of our participants came from one of nine cities in the country, it is unlikely that residence in Israel biased our results.
In a comparison of the cognitive and neuropsychological functioning of children who were between in utero and up to 15 months of age at the time of the Chernobyl disaster and who were evacuated to Kiev and their Kiev school classmates, no difference in performance was found (18).
Self-assessment of the childs health by the mothers was, as expected, negatively correlated with the attention assessment scores of the child. Health self-assessment has been found in many studies to correlate positively with physical health status (24).
In conclusion, the results of our large, population-based study of children who had been exposed to low-dose ionizing radiation do not show differences in neurobehavioral or cognitive performance compared with results of nonexposed children. Thus, low-radiation events probably do not result in deviations in neurobehavioral and cognitive performance. Lower neurobehavioral performance of children who were in utero or young at the time of the accident, in all exposure groups, may possibly hint at a broader, country-wide, Chernobyl-related effect resulting in increased levels of anxiety in the pregnant mothers or mothers of very young children in the former Soviet Union.
Attention should be paid by agencies caring for relevant former Soviet Union populations to the possible effects of the anxiety of their subjects on the behavioral and cognitive functioning of the children. Providing validated information with regard to the true health effects of the Chernobyl accident may help to lower the level of anxiety.
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ACKNOWLEDGMENTS |
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The authors would like to thank the pediatricians Drs. Irena Chistyakov, Marina Umansky, and Leonid Ganelis and interviewers Tanya Agranovsky and Yael Aerov for their help in carrying out the study.
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NOTES |
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REFERENCES |
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