03 November 2011

Thyroid Cancer Corridor in India and the Chernobyl Iodine Fallout

Cancer is a disease caused by mutation. Some 200 genes out of an estimated 30,000 genes in the human genomes have been linked to cancers. There are four types of cells in our body. These are stem cells, dividing cells, working cells and dead cells. The outer layer of the skin is composed of dead cells. Stem cells are those that will divide some time in future and become adult cells. Sperm and ovum are also stem cells, but they will divide in another body (embryo/fetus). Stem cells that will become blood in future are stored in bone marrow.
Only mutations on the stem cells and dividing cells can cause cancers. According to the current understanding, at least two genes in the same cell need to be mutated to cause cancer. Such mutations can be caused by ionizing radiations, chemicals like benzene and also some virus. Cancer can occur between a few days and several years after the exposures. After a mass exposure like atomic bombing or nuclear accident, a statistically visible increase can be found after two-three years. Then the incidence peaks in 20-25 years and then it declines. Cancers attributable to radiation are still surfacing among the people in Hiroshima-Nagasaki, 65 years after the bombings.
Generally more women suffer from cancer than men. This is because of the cancer proneness of the female reproductive organs. This is also the case with thyroid – an organ present in both sexes. In Kerala for instance, cancer of the thyroid is about 2 to 3% of the total cancer. It is about 6% in women.
The regional cancer centre (RCC) Thiruvananthapuram has a hospital based cancer registry. The registry data is periodically published by the Indian Council for Medical Research (ICMR). We analyzed RCC data for all cancers and thyroid cancers diagnosed during 1984 to 2003. The data was divided into four periods – 1984-93, 1994-98, 1999-2000 and 2001-03 and compared the incidence of all cancers and thyroid cancer across these periods. The results are given in graph below:
The first graph shows thyroid cancer as percentage of thyroid cancer to the total cancer load in men and women during the four periods. There is more or less a parallel increase of thyroid cancer in both sexes.
The second graph shows the percentage increase over the first period (1984-92) of all cancers and thyroid cancer in men and women during 1994-98, 1999-2000 and 2001-03. All cancers registered an increase in both men and women, but the increase cancer of thyroid is dramatic and highly visible.
Similar increases have been reported in the entire Western Ghats region and the Indian Council for Medical Research (ICMR) has named it as the Thyroid Cancer Corridor of India. We named it, but we do not know who sired it.
On 26 April 1986, there was a ‘chemical’ explosion in a 1000 MW nuclear reactor at Chernobyl in Ukraine. About 20% of the radioactive materials inside the reactor escaped to the atmosphere and was lofted to 3 km in the troposphere. The total radioactivity released in the explosion was 1.5E+19 Bq. (If you are not familiar with this language, remove the decimal after 1 and add 18 zeros to the left of 5. You can also say 15 billion billion Becquerel. Becquerel = one nuclear disintegration in a second) Hundreds of radioisotopes were released. But more important from a public health perspective were radioactive iodine and cesium. 131Iodine ( half life – 8.3 days) accounted for 10% of the total release (1.5 billion billion Bq).
Winds in the middle troposphere carried the radionuclides to almost all parts of the Northern hemisphere. On 5th of May 1986, the air samplers at the Indira Gandhi Centre for Atomic Research (IGCAR) showed Chernobyl iodine. Next day, the scientists also found it in the thyroid of goats. (They have been collecting goat thyroid from the butchers around Kalpakkam regularly)
So the Chernobyl iodine and cesium was in the lower troposphere over India during May 1986. Rain is a medium that brings radio-iodine and similar nanoparticles from the air to the ground. Wind also does it, but less efficiently. During mid-May, the Western Ghats region receives the summer showers. The rains also brought in radionuclides. Drinking water and milk were two important medium of transfer of iodine to the population. Detailed data on fallout of Chernobyl radionuclides in different parts of India is not available. Thyroid dose to Children from Chernobyl fallout is given in graph below. India is also there, second from the right. Since the half life of 131 Iodine is 8.3 days, regions that receive South West Monsoon rains during May-June received most of the fallout. Incidentally, this rainfall and fallout was observed in UK and other places in Europe.
Source : Annex J of UNSCEAR, 2000. www.unscear.org
Once inside the mammalian body, radioactive iodine behaves exactly like the stable iodine which is part of the diet. It goes to the thyroid. Cesium is chemically similar to potassium. So it goes to almost all parts of the body. Cancer of the thyroid is very rare in children. The background incidence is about 1 case per million children. A hundred fold increase in thyroid cancer was registered in children in Belarus during 20 years after the accident.
We have not been able to locate any other etiological agent for the sudden and dramatic increase in the incidence of thyroid cancer in Trivandrum and other parts of the Western Ghats. Hence we hypothesize that Chernobyl iodine did it.
-VT Padmanabhan, R Ramesh and V Pugazhendi

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