Iodine deficiency in Belarusian children as a possible factor stimulating the irradiation of the thyroid gland during the Chernobyl catastrophe.

Ten years after the Chernobyl nuclear plant catastrophe more than 500 children in Belarus are suffering from thyroid cancer. The major cause of the high incidence of thyroid cancer in children under 15 years of age appears to be contamination resulting from that catastrophe, mainly with isotopes of radioactive iodine. Another important factor may be iodine deficiency in the environment. A countrywide program for investigation of goiter prevalence and iodine deficiency has been established in the Republic of Belarus with the assistance of the European World Health Organization office. The program will oversee the examination of 11,000 children and adolescents 6 to 18 years of age from 30 schools in urban and rural areas. The results obtained in a group of 824 children and adolescents (the pilot phase) are typical for significant iodine deficiency and moderate goiter endemism. It is clear that the present situation does not completely reflect the situation that existed at the time of the Chernobyl catastrophe. However, data from epidemiologic studies conducted many years before the accident showed high goiter prevalence in the contaminated areas, indicating that the prevalence of iodine deficiency at the time of the catastrophe was similar to the present one or even greater. Such an assumption could lead to a better understanding of the thyroid pathologies that have been observed.


Introduction
The accident at Chernobyl, the most serious in the history of the nuclear power industry, occurred on 26 April 1986. Among different radionuclides emitted into the atmosphere during the most critical 10 days of the catastrophe were large quantities of various isotopes of radioactive iodine with half-lives ranging from hours to days. Also present was 132Te.
Meteorological conditions on those days caused the heaviest contamination in the Republic of Belarus. More than 23% of the country and 20% of the population were contaminated.
Among the most serious possible somatic health consequences of the catastrophe is the thyroid cancer occurring in those who were children at the time of the accident (1)(2)(3)(4)(5)(6).
The relationship between thyroid cancer and external irradiation of the thyroid is well known. However, in Belarusian, Ukrainian, and Russian children the incidence of thyroid cancer began to increase 4 years after irradiation. Moreover, the disease appears to be a very invasive form (5) (Tables 1, 2). This situation has stimulated many efforts to analyze various contributory factors in addition to radioactive isotopes including iodine deficiency in the environment and, as a consequence, in food and drinking water.

Review of Existing Data
Iodine Deficiency in Belarus The first information on the study of urinary iodine concentration in Belarus comes from several groups of investigators. Before analyzing these data, however, it is worth noting that according to Delange and colleagues (7), median urinary iodine excretion in a normal population of school-age children (6-16 years of age) is more than 100 pg/liter, with a range of 85 to 163 pg/liter. Mityukova et al. (8) conducted investigations from 1990 to 1994 on 1680 children from 14 settlements in nine regions of Gomel, Vitebsk, and Minsk Oblasts (8). They found a wide range of urinary iodine levels; 163 children had iodine urinary excretion below 20 pg/liter, which is considered severe iodine deficiency according to the World Health Organization (WHO) classification (9).
A second source of information is the data obtained by the International Council for Control of Iodine Deficiency Disorders (ICCIDD) team (Gutekunst and Gerasimov), who performed studies from 21 to 24 June 1991 (10). They investigated 321 adults and 270 children from the rehabilitation camp in the Gomel region. The children came from the city of This paper is based on a presentation at the International Conference on Radiation and Health held 3-7 November 1996 in Beer Sheva, Israel. Abstracts of these papers were previously published in Public Health Reviews 24 (3)(4): 205-431 (1996). Manuscript received at EHP 10 April 1997; accepted 30 June 1997. Gomel and surrounding regions affected by the Chernobyl accident.
The goiter prevalence in this group was 8.5% in children who had a median urinary iodine excretion of 10.7 pg/liter and 46% in children excreting iodine at levels lower than 10 pg/liter.
Another source of information is the investigation sponsored by the Sasakawa Health Foundation and conducted in Mogilev and Gomel Oblasts (11).
In Mogilev Oblast 12,356 children were investigated from 15 May 1991 through 31 December 1993. Goiter prevalence in this oblast ranged from 4 to 35%. The data on urine iodine excretion showed that among 1729 children, urinary iodine concentration was over 100 pg/liter in only about 30 cases; in more then 30% of the children it was less than 10 pg/liter. In Gomel Oblast 12,791 children were investigated and goiter prevalence was 5 to 45%. Urine iodine concentration was measured in 235 children. Only a few of them excreted more than 100 pg/liter; 44 cases, (about 20%) excreted less than 10 pg/liter.
As the data on urinary iodine excretion in Belarus are limited it was decided to begin the investigations using the protocol applied in similar studies performed in Poland.
Studies done in Poland from March 1992 to February 1993 showed that two eastern regions of Poland bordering Belarus had low urinary iodine excretion and high prevalence of goiter (12).
For example, in Bialystok region goiter prevalence in 1431 children investigated was 41% in rural and 36% in urban populations. The mean urinary iodine excretion was 52.07 pg/liter in children without goiter and 42.3 pg/liter in children with goiter. In Lublin region goiter was found in 21.8% of 1686 children investigated. Average urinary iodine excretion was 52.6 pg/liter in children with goiter and 56.76 pg/liter in children without goiter (13).
The results observed in Polish regions so close to Belarus suggested the possibility of a similar situation in Belarus, stimulating countrywide epidemiologic studies.
The results of the investigation of goiter prevalence and urinary iodine excretion completed to date are important. However, they come mainly from two oblasts, Mogilev and Gomel, and differ significantly. Some of these results indicate that goiter prevalence is rather low and urinary iodine excretion rather high. One of the explanations may be the iodine supplementation given to these children after the Chernobyl accident, probably in large and uncontrolled quantities, and which may continue today. Therefore, WHO and the Belarusian authorities determined there is an urgent need to extend the study on goiter prevalence across the whole country to produce a statistically significant survey in school-age children and adolescents that includes estimations of thyroid volume and structure by ultrasonography and urinary iodine concentration. Program Goals The goals of the WHO International Iodine Deficiency Program are a) to determine the extent and severity of iodine deficiency in various geographical areas of the country; b) to study thyroid size and structure in relation to iodine deficiency in children and adolescents of Belarus 6 to 18 years of age, born before and after the Chernobyl accident, and to consider those elements with respect to radioactive iodine; and c) to create a map of iodine status of all the regions involved, forming the basis for an effective and safe strategy for iodine prophylaxis in Belarus.
To realize these goals, approximately 11,000 children and adolescents from 30 schools. selected at random and located in 15 urban and 15 rural regions will be examined. The following age groups will be investigated: 6 to 8, 11 to 12, 13 to 14, Approximately 360 children will be examined from each school. Figure 1 shows the six oblasts of Belarus.

Preliminary Results from Two Schools
Results from studies of a group of 824 children and adolescents are presented in Gembicki et al. (14) and Perez et al. (15). Four hundred thirty children from urban Minsk and 394 children from rural Stankovo were examined. The presence of goiter investigated by palpation was observed in 64.7% of the children in Minsk and 71.8% in Stankovo (Table 3).
In Minsk grade IB goiter was observed in 44.2% of the group and grade II in 20.5%; in Stankovo observed percentages were 48.2 and 23.6%, respectively. In Minsk thyroid volume in the children as determined by ultrasonography ranged from 4.66 to 13.71 ml in boys, depending on age, and 4.38 to 11.38 in girls. In Stankovo, thyroid volumes were 4.5 to 16.48 ml in boys and 4.52 to 12.83 in girls (Table 4).
Urinary concentration of iodine in casual samples was greater than than 100  concentrations below 20 pg/liter were seen in 6.4% of the children from Minsk and 8.1% from Stankovo (Table 5).

Discussion
The most recent ICCIDD recommendations (7) concerning the upper limit of normal thyroid volume in school children, as determined by ultrasonography, are presented in Table 6.
The ICCIDD also suggests that when 5% of a population has thyroid volumes over the recommended limits, the region must be recognized as an endemic goiter area. In the pilot studies we found that in comparable age groups 6.3 to 13% of the children exceeded these recommended values (Table 7) (14,15).  Therefore, after analysis of the results of the pilot study (14,15), we concluded that the results were typical for at least moderate goiter endemism and significant iodine deficiency.
Low iodine uptake causes compensatory thyroid hyperplasia and higher uptake of iodine. Radioiodine fallout during nuclear accidents may also accumulate more radioactive iodine, increasing the possibility of unexpected pathologies in iodine-deficient thyroid glands. In an irradiated thyroid where a malignant transformation may have been initiated, iodine deficiency may act to accelerate the appearance of cancer at a clinical level.

Conclusions
These preliminary results indicate at least moderate goiter endemism and significant iodine deficiency, and will be essential in developing a safe strategy for goiter prophylaxis, as well as a better understanding of the pathogenesis of thyroid disorders observed in this study.