Chernobyl: the final word is yet to be said

Published in The Hindu on April 27, 2006

A radioactive sign hangs on barbed wire outside a café in Pripyat.
Immediate consumption of stable iodine tablets could have prevented thyroid cancer. The thyroid gland absorbs nearly 50 per cent of iodine present in the body, — Photo: Wikipedia

“An accident has occurred at the Chernobyl nuclear power plant. One of the reactors has been ‘damaged.'” These were some of the statements made by the Soviet authorities when confronted with evidence by Sweden. And this came more than 30 hours after the accident had occurred.

Playing it down

The word “damaged” failed to reflect the real magnitude of the accident. Radioactivity discharged from the reactor 4 travelled nearly 1,600 km before reaching Sweden and the radioactivity recorded was twice the background radiation levels in Sweden. Background radiation is the radiation present naturally at a given place. The increased radioactivity was detected in India nearly a month after the accident, first in Rajasthan and last in Chennai. As if concealing the magnitude of the accident was not serious enough, evacuation of the people from Pripyat, which housed the plant staff and located closest to the reactor, started 36 hours after the accident, according to BBC.

Though many radionuclides were discharged from the graphite-moderated light water cooled reactor for ten long days, only iodine-131, iodine134, and ceasium-137 radioisotopes travelled long distances.”Though uranium and plutonium were also thrown out, they were not carried for long distances as they are heavier,” noted Dr. K.S. Parthasarathy, former Secretary of the Atomic Energy Regulatory Board, Mumbai. The greatest damage recorded till date has come from radioactive iodine in the form of thyroid cancer, particularly in children. With a half-life of just eight days, the damage could have been greatly minimised if immediate steps had been taken.

Solution stable iodine

“The thyroid gland takes in about 50 per cent of iodine [compared with breast and stomach]. So providing iodine tablets would have prevented the thyroid gland from absorbing iodine radioisotope,” explained Dr. Parthasarathy. Iodine tablets contain stable iodine unlike radioisotope iodine. With the thyroid gland being only a few grams in weight and having a natural propensity to absorb nearly 50 per cent of any iodine, targeting it makes sense.

Radioactive iodine gets into the body through inhalation and ingestion of foodstuffs particularly milk. “Iodine settles on the ground and grass, and milk from cows that feed on this grass is in turn contaminated,” he explained. “And children are more vulnerable as they drink more milk.” Added to this is the fact that the gland is small in children though it still takes in about 50 per cent of iodine present in the body. The delay in acknowledging the accident meant that many children were put to easily avoidable risk.

Till date, more than 4,000 thyroid cancer cases have been diagnosed during the period 1992-2002 in those who were children at the time of the accident, according to the United Nations Chernobyl Forum report. The Chernobyl Forum report states that residents of Pripyat were given tablets containing stable iodine 6-30 hours after the accident. Dr. Parthasarathy notes that for maximum benefits to be gained, tablets need to be taken within eight hours after an accident.

More cases expected

It is expected that the increase in thyroid cancer incidence from Chernobyl will continue for many more years though the long term risk is difficult to quantify, the report underlines. A paper published online in Nature also points out this uncertainty. It states that early incidence of thyroid cancer was seen in children – the first case was seen in four years’ time.

This put to rest the common perception that it takes about ten years for the cancer to show up. This surprise was essentially because assumptions were made based on adult exposure risks. “The early tumours were clinically aggressive and pathologically unusual. The later ones were more typical and less aggressive,” the Nature paper noted. “… The future epidemiology even for thyroid tumours is unpredictable.” Caesium-137 has a half-life of 30 years and is distributed in the body’s soft tissue. If iodine is spread on the soil and vegetation, caesium, apart from settling on the soil, gets accumulated in wheat, vegetables, mushrooms and lichens, to name a few.

Reindeer, which eat lichens and in turn are consumed by humans for meat, is one route for the radiocaesium to enter the human body. High transfer of such radiocaesium has been seen in the Arctic and sub-Arctic regions. Caesium has a potential to cause leukaemia if present close to the bone marrow. While thyroid cancers show up quite quickly, incidence of leukaemia would be seen later. Solid tumours, on the other hand, would take as much as 30-40 years to show up.

About 20 years after Hiroshima and Nagasaki were bombed, significant increase in thyroid cancer and leukaemia were seen. And it took another ten years before other cancers showed up. “Even today people in Hiroshima and Nagasaki are getting solid tumours,” Dr. Parthasarathy said. Though the Chernobyl Forum report claims that fewer than 50 people were killed, mostly emergency workers, and only nine children have died from thyroid cancer, the final word is yet to be said.

More deaths expected

The report indicates that another 4,000 casualties are estimated during the lifetime of the six lakh people who were living in the immediate vicinity of the reactor. The 600-page report also points out that 5,000-odd people who had lived further away from the reactor and who received relatively smaller doses of radiation would face the same fate.

The report did not look at the risk of people dying from accident-induced radiation in countries in Europe.Only time will tell who is right, the world body or the environmental groups that claim the toll will be several times more than the Forum report.

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