The Health Status of Children Exposed to Radiation as a Result of the Chernobyl Nuclear Power Plant Disaster

The dissertation is devoted to a comprehensive clinical-epidemiological investigation of the health status of children exposed to radiation as a result of the Chernobyl nuclear power plant disaster, with a focus on the Bryansk Region as the most affected region. The combined negative influence of low doses of ionizing radiation and natural iodine deficiency on the health of the pediatric population is examined, including the dynamics of thyroid pathology, demographic indicators, and medical-social consequences. In the work, remonitoring of iodine sufficiency of the population was conducted, the radiation situation in the territory of the region was assessed, morbidity among children, including thyroid cancer, was analyzed, and a system for accounting and monitoring the principal health indicators of children, compatible with the Russian State Medical-Dosimetric Register, was developed.

Relevance of the Research

At the United Nations Conference (1992, Rio de Janeiro), the Russian region and the countries of the CIS were identified among the most contaminated areas on the continent [218].

According to V.I. Chiburev [243], "the anthropogenic load on the natural environment is increasing, the quality of the air, water basin, and soil is deteriorating, and a situation of ecological disaster is forming in many regions and cities." In 230 cities with a population of 64 million people (43% of Russia's residents), annual average levels of pollution exceed hygienic norms [181].

One of the most complex ecological problems is the radiation situation in Russia, which is determined by the consequences of major radiation accidents (at the Chernobyl Nuclear Power Plant (ChNPP) in 1986 and the Mayak Production Association in 1957).

The Chernobyl disaster was the most severe in the history of nuclear energy development. According to the UN Chernobyl Forum [471], the activity of material released into the environment from the destroyed reactor active zone amounted to approximately 50 MCi.

It is obvious that the assessment of adverse effects on the human body caused by environmental pollution represents a most important task of medicine at the present stage and has enormous, not only medical, but also social significance. The health status of children is one of the most sensitive indicators reflecting changes in environmental quality [57]. The high vulnerability and sensitivity of the child's organism, which is in the process of development, not only determines the state of children's health at the present time but also exerts an influence on their further development and condition [210].

More than 17 regions of Russia were subjected to radioactive contamination as a result of the Chernobyl disaster, the most affected of which is the Bryansk Region [156, 157, 236]. As of January 1, 2001, more than 400,000 people resided in the contaminated territories of the region. Of these, 240,000 people, including more than 47,000 children, resided in the territories of the southwestern districts of the region (SWT), where the contamination density exceeded 5 Ci/km².

The objective assessment of the medical consequences of the Chernobyl disaster remains one of the most relevant and complex problems to this day [104]. This is explained by the contradictory scientific data on the influence of low doses of radiation on the human body [42, 112, 205].

In large-scale epidemiological studies of the effects of radiation on population health conducted prior to the Chernobyl disaster, where radiation accidents had occurred, no increase in the number of diseases was identified, with the exception of neoplasms associated with exposure to ionizing radiation [470].

In the first months after the Chernobyl disaster, short-lived radioactive iodine nuclei, which concentrated in the human thyroid gland and selectively irradiated it, made a significant contribution to the external radiation dose [24, 193]. However, as experts of the IAEA acknowledge [152], as a result of the Chernobyl disaster, there was a pronounced unevenness of thyroid irradiation (up to 100 times) even within a single age group and one limited administrative district.

The situation was further complicated by the fact that the majority of territories contaminated by radionuclides had long before the accident been classified as endemic zones for iodine deficiency [82]. Iodine deficiency contributed to enhanced absorption of radioactive iodine nuclei by the thyroid gland, which was clearly manifested in children — the contingent most sensitive to iodine deficiency [127].

From July 1986, the doses of radiation received by the population of contaminated territories began to be determined primarily by incorporated radionuclides of cesium-137 and strontium-90. The average accumulated effective doses of radiation for the population residing in territories radioactively contaminated after the Chernobyl disaster are estimated for the period 1986-2001 [24]. They include doses of external irradiation, internal irradiation of the whole body by cesium and strontium radionuclides, as well as doses of thyroid irradiation by radioactive iodine nuclei in 1986. However, the methodology proposed in this document does not allow for the estimation of individual annual effective doses for children of various ages [45].

Thus, the absence of data on the actual individual doses of radiation received by children diminishes the value of the conducted clinical-epidemiological studies among the pediatric population.

In the first years after the Chernobyl disaster, the efforts of practicing physicians and research were directed toward assessing the condition of the thyroid gland and identifying possible clinical consequences of its damage, such as autoimmune thyroiditis, thyroid neoplasms, acquired and congenital hypothyroidism [193, 325, 342, 385, 418, 441, 442]. However, in children residing in territories with contamination density exceeding 5 Ci/km² in 1986-1987, only changes in the functional activity of the pituitary-thyroid system were detected [1, 6, 237, 258].

Assessments of the morpho-functional state of the thyroid gland in children in subsequent years after the Chernobyl disaster are contradictory, which is primarily associated with the heterogeneity of the studied contingents and the diversity of methodological approaches [479].

The results of recent observations conducted in CIS countries indicate an increase in thyroid cancer (TC) among persons who received irradiation in childhood and adolescence [174, 225, 226, 249, 328, 364, 419, 439, 440]. The first publications appeared in which dose dependencies of thyroid cancer development were analyzed [440].

The contradictory nature of the data on the frequency of thyroid pathology among persons who received thyroid irradiation as a result of the Chernobyl disaster, in our opinion, is associated with the underestimation of the possible combined negative influence of radiation and iodine deficiency on the thyroid gland.

Its assessment is considerably complicated by the fact that the majority of territories contaminated by radionuclides, including the Bryansk Region, had long before the disaster been classified as endemic zones for iodine deficiency [82]. Until recently, there was no system of monitoring for iodine-deficiency diseases (IDD) in the territory of the region, which was important after the Chernobyl disaster.

The influence of iodine deficiency on the development of the entire spectrum of thyroid pathology, including thyroid cancer, is universally recognized [131, 255, 256, 280, 455, 473].

In addition, the consequences of iodine deficiency, depending on the period of life in which the organism experienced iodine deficiency, may manifest as congenital anomalies, increased perinatal mortality indicators, violations of mental and physical development, and reproductive system disorders [358].

In recent years, publications have appeared dedicated to the combined influence of iodine deficiency and irradiation on the development of thyroid pathology only. These are mainly experimental data obtained on animals [349, 362].

Far less studied is the demographic situation in radioactively contaminated territories [151]. The question of the association of morbidity with the consequences of radiation exposure remains a matter of discussion [14-23, 26, 37, 38, 116, 137, 141, 142, 164, 230, 255].

This is primarily due to the absence of unified methodological approaches to the collection of information on health status, its assessment [57], and the contradictory scientific data on the influence of low doses of radiation on the human body [42, 112, 205].

Thus, the analysis of the existing literature indicates that at the present time, the assessment of demographic indicators, morbidity among children, including IDD, and the development of a system for accounting and monitoring their health status 15 years after the Chernobyl disaster, remains a relevant scientific and practical task.

Goal of the Research

On the basis of a comprehensive clinical-epidemiological investigation of the medical-social consequences of the long-term combined influence of low doses of radiation and iodine deficiency on children, to develop a system of unified accounting for the principal health indicators, compatible with the Russian State Medical-Dosimetric Register (on the example of the Bryansk Region).

Tasks of the Research

1. To analyze the ecological situation in the Bryansk Region (radiation situation, severity of iodine deficiency).

2. To create a base of informational-statistical data for monitoring the prevalence of iodine-deficiency diseases among the population of the Bryansk Region and for assessing the effectiveness of programs for their prevention and treatment.

3. To conduct an analysis of the medical-social consequences of the long-term combined influence of low doses of radiation and iodine deficiency on the population of the Bryansk Region.

4. To analyze clinical-statistical indicators of the health of children residing in radioactively contaminated territories of the Bryansk Region, taking into account iodine sufficiency.

5. To assess the effectiveness of conducted preventive measures for the health improvement of children in the examined territories of the Bryansk Region.

6. To develop principles of clinical-statistical assessment, analysis, and electronic accounting of the principal health indicators of children in the Bryansk Region.

Scientific Novelty of the Research

Remonitoring of iodine sufficiency of the population in the Bryansk Region territory after the Chernobyl disaster was conducted for the first time. It was established that in the SWT, children reside under conditions of mild iodine deficiency and are subjected to radiation exposure, primarily through incorporated cesium radionuclides entering with food products.

For the first time, 15 years after the Chernobyl disaster, a comprehensive assessment of demographic indicators was conducted. Higher rates, compared with data for the Russian Federation (RF), of annual decline in natural population growth coefficients were established in the SWT (-10.8‰ in 2001) and in the Bryansk Region as a whole (-9.9‰) in the same year. Over the investigated period, a decline in birth rate coefficients was noted simultaneously with a decline in infant mortality coefficients in the SWT from 19.9‰ in 1986 to 15.4‰ in 2001, in the Bryansk Region from 17.5‰ to 15.4‰. A corresponding decline was also noted for the RF from 19.3‰ to 14.7‰.

It was established that the increase in morbidity among children and its more elevated indicators in radioactively contaminated territories of the Bryansk Region are associated primarily with the improvement of diagnostic quality due to the wide use of modern medical equipment and in-depth medical examinations within the structure of specialized dispensary surveillance.

For the first time, an epidemiological cross-section of morbidity of children in the Bryansk Region with malignant neoplasms was conducted, and the rates of increase and relative risk of this pathology by nosological groups over a 15-year observation period were established. From 1992 to 2000, after a long latent period, the morbidity of thyroid cancer (TC) became higher (p<0.05) than data for the RF (by 10 or more times), mainly due to a sharp increase in this pathology among children residing in the SWT, which coincides with projected data and is confirmed by relative risk indicators.

For the first time, it was demonstrated that iodine deficiency and the effect of radioactive iodine nuclei in doses (on average exceeding 400 mGy) on the thyroid gland exert a unidirectional negative influence on the health status of children whose age at the time of the Chernobyl disaster ranged from the neonatal period to 2 years, and make a substantial contribution to the formation of diffuse nontoxic goiter.

For the first time, on the basis of an analysis of neonatal screening data for congenital hypothyroidism (CH), the ineffectiveness of dietary iodized salt (iodine content of 40±15 mg per kg of salt) for the mass prevention of iodine deficiency among the population of the Bryansk Region was proven.

It was established that in the SWT, the problem of iodine deficiency was exacerbated over the investigated period. According to ultrasonography (US) of the thyroid gland, an increase in the prevalence of diffuse nontoxic goiter among children aged 7-12 years was noted from 12.2% in 1998 to 19.8% in 2001 (p<0.05), against the background of persisting mild iodine deficiency. Corresponding median urinary iodine values by year were 62 µg/L and 69 µg/L.

For the first time, a unified system for accounting for the principal health indicators of children in the Bryansk Region residing in territories with radiation contamination density exceeding 5 Ci/km² was developed, compatible with the Russian State Medical-Dosimetric Register (RGMDD).

Practical Significance of the Research

As a result of remonitoring, data on the degree of iodine deficiency and the prevalence of IDD among children in the Bryansk Region were obtained for the first time.

An assessment of the radiation situation in the territory of the region was conducted. A system of individual dosimetry was developed and implemented for establishing the fact and levels of exposure to the organism from Cs-137 and other isotopes.

A computer program for monitoring IDD and iodine sufficiency of the population of the Bryansk Region was developed for the annual assessment of the effectiveness of preventive measures conducted in the territory of the region.

Among children residing in radioactively contaminated territories, whose age at the time of the Chernobyl disaster ranged from the neonatal period to 2 years, the highest prevalence of diffuse nontoxic goiter was noted, and the principles of their dynamic dispensary surveillance were substantiated.

An algorithm for the stepwise assessment of the health status of children exposed to radiation as a result of the Chernobyl disaster, using statistical and epidemiological data, was developed. A simplified methodology for the collection of clinical-statistical information on the principal health indicators of children residing in territories with radiation contamination density exceeding 5 Ci/km², using a unified statistical card, was substantiated.

At the basis of Klintsy Central District Hospital (CDH) and Bryansk Diagnostic Center No. 1 (BDC No. 1), with the aim of obtaining objective information on morbidity, disability, and mortality among residents subject to inclusion in the RGMDD, an electronic system for the collection and processing of all medical information in healthcare and preventive institutions (HPI) of the southwestern territories was developed. The created system has been implemented and allows for the automatic transfer of necessary information into the RGMDD.

- The effectiveness of the developed computer program, which allows for the prompt and reliable analysis of medical-dosimetric information and the health status of children residing in radioactively contaminated territories, was demonstrated.

The data obtained on the health status of children made it possible to substantiate the principles and stages of medical surveillance of children under conditions of the combined influence of radiation and iodine insufficiency in the Bryansk Region.

Presentation of the Work and Publications

The materials of the dissertation were presented at a conference of the Smolensk State Medical Academy, at meetings of the Bryansk Regional Society of Pediatricians and Endocrinologists (1997-2001).

The results of the work and the main provisions of the dissertation were reported at: the Regional Scientific and Practical Conference "Science and Practice" (Bryansk, 1995), the All-Russian Scientific and Practical Conference "Chernobyl: 10 Years Later. Results and Prospects" (Bryansk, 1996), the International Scientific and Practical Conference "Environmental Pollution and Human Health" (Smolensk, 1999), the International Scientific Forum "Oncology at the Turn of the XXI Century. Opportunities and Prospects" (Moscow, 1999), the International Symposium "Diagnostic Medicine" (Yerevan, 1999), the International Scientific and Practical Conference "Problems of Sustainable Development of Radioactively Contaminated Territories of the CIS Countries" (Bryansk, 2000), the Scientific and Practical Conference "Medical-Biological and Extreme Pediatrics" (Moscow, 2000), the Second Russian Congress of Medical Geneticists (Kursk, 2000), the Second International Conference "The Influence of Low Doses of Radiation on Human Health" (Dublin, 2001), the Fifth Russian Oncological Conference (Moscow, 2001), the International Scientific and Practical Conference "Ecology, Safety and Sustainable Development - XXI Century" (Bryansk, 2002), the Sixth European Congress of Endocrinology (Lyon, 2003).

The materials obtained on the health status and principles of dispensaryization formed the basis of methodological recommendations for physicians "Methodological Foundations of Health Status Assessment in Technogenically Contaminated Regions" (Bryansk, 2002); a methodological guide "Biological Effects of Ionizing Radiation" (Bryansk, 2000); a methodological guide "Types and Sources of Ionizing Radiation and Their Principal Characteristics" (Bryansk, 2000). A monograph "Health of Children: Health Status Assessment, Pre-diagnostic Diagnosis, Rehabilitation" (Smolensk, 2000) was prepared and published.

Based on the results of the work, 57 printed publications were produced, including 11 in foreign editions.