The Chernobyl accident in 1986 was the result of a nuclear power plant that exploded caused by a flawed reactor design and inadequately trained personnel. The explosion sent tons of radioactive nuclides into the atmosphere and to surrounding countries. Iodine-131 and Cesium-137 are of the most importance in regard to the health effects of the public. Two workers died the night of the accident and 28 died later as a result of acute radiation syndrome. Thousands of cases of thyroid cancer were diagnosed in patients that were children at the time of the accident.
Chernobyl
On April 26, 1986 a nuclear power plant in Chernobyl had an explosion as a result of improperly trained personnel and a flawed reactor design (World Nuclear Association, 1986). Two explosions destroyed unit 4 of the power plant and resulted in massive releases of radioactive materials into the atmosphere. The numerous fires from the explosion caused the main release of the radionuclides (World Nuclear Association, 1986). It was the only accident in the history of commercial nuclear power that resulted in deaths related to radiation. The power plant is located about 20 km south of the border of Belarus and 130 km north of Kiev, Ukraine. The most affected areas from the explosion were in Belarus, Russia, and Ukraine. At the time of the accident there was 115,000-135,000 people living within a 30 km radius of the power plant (World Nuclear Association, 1986).
The World Nuclear Association, states that “the accident caused the largest uncontrolled radioactive release into the environment ever recorded for any civilian operation.” Massive amounts of radionuclides were released for 10 days after the explosion equaling a total of about 14 EBq (World Nuclear Association, 1986). Iodine-131 and cesium-137 are the most important radionuclides to consider from the Chernobyl accident. It is estimated that all of the xenon gas and half of the iodine and cesium were released. Fauber states “46 megacuries of iodine-131, 136 megacuries of xenon radioisotopes, and 2.3 megacuries of cesium-137” were released. Iodine-131 is a short-lived radionuclide with a half-life of 8 days. Cesium-137 has a half-life of 30 years (World Nuclear Association, 1986). The wind and rain caused the radionuclides to spread to areas surrounding the reactor and contamination was found in the ground in every country of the Northern Hemisphere.
The workers and first responders received doses from 1-16 Gy. The 200,000 “liquidators”, which were the workers involved in the clean-up during 1986-1987 received an average of about 100 mSv. Some liquidators received up to 500 mSv. The liquidators that worked after 1987 received lower doses. A few weeks after the accident, 116,000 residents within a 30 km radius were evacuated and most received under 50 mSv, although some received 100mSv or more. The 216,00 people living in the ‘strict radiation control’ areas between 1986 to 2005 received doses averaging 31 mSv. In the ‘contaminated areas’ the 6.4 million people received an average of 9 mSv in the same time period.
Acute radiation syndrome was confirmed in 134 cases out of the initial 237 people diagnosed. The explosion killed two operators on the night of the accident and 28 more were killed within three months as a result of acute radiation syndrome. Between 1987 and 2004, nineteen more workers died but their deaths cannot be attributed to radiation exposure. Diarrhea, vomiting, fever and erythema were the first initial symptoms of the workers diagnosed with radiation sickness. “The differential white blood cell count showed reduced circulation lymphocytes (lymphocytopenia) which was the initial indictor of the severity of the exposure and became evident in the first 24-36 hours for those most severely irradiated.” In those who received 6-16 Gy, vomiting occurred within 15 minutes of the exposure. Breathing became extremely difficult and painful because their mucous membranes were severely swollen, dry and ulcerated. These patients had extreme burns from both thermal and beta radiation. The very high dose compromised the production of blood cells in the bone marrow. Within the first few weeks the white blood cells fell dramatically making it nearly impossible to fight off infection and have natural blood clotting activity. 20 of the 21 patients that received 6-16 Gy died in the hospital despite all of the care they were receiving. At exposures lower than 6 Gy vomiting began later and white blood cell counts did not drop as fast. Burns to the skin from beta radiation was still a complicating factor and swollen mucous membranes were difficult to treat. Out of 21 patients that received 4-6 Gy, 14 survived. One out of 55 patients died from receiving 2-4 Gy. No patients out of 140 died from receiving less than 2 Gy. This equals a total of 28 patients that died from acute radiation syndrome and the chances of survival improved under 6 Gy. Therapy to these patients included antibiotics, antifungal agents, bone marrow transplants, blood replacement therapy, and a lot of fluid and electrolytes. Bone marrow transplantation was given to 13 patients who had possibly had irreversible bone marrow damage after doses greater than 4 Gy. All but two of these patients died. The physicians concluded that bone marrow transplantation should play a limited role in treatment because the bone marrow may recover on its own which may lead to future rejection of the transplanted bone marrow. Thermal and beta radiation burns that were not viable were surgically removed. 56 patients had radiation skin burns. Gastro-intestinal syndrome was also a prominent symptom of the acute radiation syndrome patients. Radiation caused oropharyngeal syndrome and consisted of mucosal destruction and absence of lubrication causing it to be severely difficult for the patients to breath and swallow. Between 1987 and 1998, there were 11 deaths among the acute radiation syndrome patients. These deaths were due to different diagnosis including coronary heart disease, myelodysplastic syndrome, liver cirrhosis, lung gangrene, lung tuberculosis, fat embolism, and acute myeloid leukemia. Cataracts and ulcerations are the main disability among the acute radiation syndrome survivors. Fertility was investigated in 1996 and 14 normal children were born to the survivor families.
There were no acute radiation syndrome cases reported in the general public. In Belarus, in the months following the accident it was confirmed in 11,600 people that there were no cases of acute radiation sickness. In regard to late health effects, there has been a rise in the incidence of thyroid cancer. Between 1991-2015 about 20,000 cases of thyroid cancer were diagnosed in patients that were under 18 at the time of the accident. 4,000 cases of thyroid cancer can be attributed to the accidents contamination. UNSCEAR reports 15 fatalities have occurred in those patients. In the International Chernobyl Project, field studies were taken in the late 1990’s on the residents in settlements with a contamination of more than 555 kBq/m2 of cesium. Samples were taken from various age groups over a course of two weeks. No health abnormalities from this study could be contributed to radiation exposure, except for an increase in thyroid cancer. Early on after the accident it became evident that the radioiodines were contributing to thyroid doses in children. The Soviet Union recorded thyroid doses as accurately as possible and reported that some of the population received high doses and had a possibility of being diagnosed with thyroid cancer in the future. Previous studies have shown that thyroid cancer appears six to eight years after radiation exposure, but after the Chernobyl accident the cancer was appearing as early as four years. In the eight year period before the accident, only five cases of childhood thyroid cancer were seen in Minsk, which is “the main Belarussian center for thyroid cancer diagnosis and treatment for children.
“From 1986-1989, 3 to 6 cases of thyroid cancer in children were seen annually in Belarus. In 1990, the number jumped to 31, to 62 in 1991, then to 87 in 1993. By the end of 1998 the total had reached over 600 in Belarus. Nearly 50% of the early (1992) thyroid cancers appeared in children who were aged between one and four years at the time of accident. At the same time 382 were diagnosed in the Ukraine.”
The histology of the cancers showed that they were aggressive and showed local invasion and then distant metastases to the lungs. Since 1996, the incidence of child patients decreased and the number of adult cases continue to increase. Studies have shown that there has been no increase in childhood leukemia since the accident. Iodine concentrates in the thyroid gland. The children in Belarus and Ukraine had a deficiency of iodine in their diet, causing an increase in the risk of absorption of radioactive iodine by the thyroid gland. This uptake of the iodine was mainly from the children drinking contaminated milk. Tens of thousands of children received more than 1 Gy from drinking contaminated milk. WHO reports that the children who drank milk from cows that had eaten the contaminated grass received high doses of iodine to the thyroid gland.
UNSCEAR states that apart from an increase in thyroid cancer, “there is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident”. As the affected population is increasing with age, so is the incidence of thyroid cancer. There has been no evidence of decreased fertility or abnormal births from the radiation. WHO reports that there is a small increase in the incidence of breast cancer that appears to be related to radiation from contaminated areas, but more studies are needed to confirm this. WHO also reported that recent studies show the incidence of leukemia doubling among highly exposed liquidators. WHO revealed that no increase in leukemia had be found in children or adults in the contaminated areas. The main health effects of the Chernobyl accident was in the acute radiation syndrome victims and the children who received heavy iodine exposure to the thyroid gland causing an increase in thyroid cancer