A large and startling increase in the incidence of thyroid cancer, perhaps a legacy of the 1986 Chernobyl nuclear reactor accident, has been observed in Belarus children, according to scientists.
"The overall incidence rose from an average of just four cases per year from 1986 to 1989 inclusive, to 56 cases in 1991, and is projected to be not less than 60 in 1992," a Belarus team said in a letter to the science journal Nature.
World Health Organization scientists wrote a separate report to appear in the journal today. Belarus, north of the Ukrainian reactor, was the first place hit by the radioactive cloud that escaped in the explosion.
"The occurrence of this increase in thyroid cancer in children within a few years of exposure to radioactive isotopes of iodine is unexpected but real," they said. "We believe the only realistic explanation . . . is that it is a direct consequence of the accident at Chernobyl."
The Belarus team is headed by Dr. Vassili S. Kazakov of the Belarus Ministry of Health, in Minsk. The team said that the cause of thyroid cancer is probably iodine 131, a byproduct from operation of a nuclear reactor. The half-life of iodine 131 is quite short -- only eight days -- so the danger should decrease relatively quickly.
Stephen Musolino, a health physicist at the Brookhaven National Laboratory in New York, said that the time between exposure and emergence of tumors seems too short. He speculated that the increased reports of cancer may be attributable to better surveillance and reporting of cases.
According to radiation physicist Keith Baverstock, at the World Health Organization's European Center for Environment and Health, in Rome, it is also surprising that "the disease, which is normally rather easily treatable, is aggressive and is leading to metastases" [spreading to other parts of the body].
It is not a surprise to see some thyroid cancer, he added, but
"it's a surprise that it has come so early" after the reactor accident. Normally, the cancer takes a decade or two to arise.
The Belarus team reported that one of the children died at age 7, and "10 others are seriously ill." Of the reported cases, 55 show signs of tumor growth into other tissues, and "six are distant metastases, mostly in the lungs."
Mr. Baverstock noted in a phone interview that the increase in thyroid cancer is quite uneven from region to region. In the cities of Minsk, Mogilev and Vitebsk, for example, no significant increase has been seen. And in areas where there was little ground contamination, the incidence is abnormally high.
"So it [the cancer] may not be due to ground deposition" of radioactive materials, "but instead to their being exposed to the cloud of radioactivity that crossed Belarus immediately after the accident," Mr. Baverstock said.
When the power plant at Chernobyl caught fire in 1986, it spit tons of radioactive particles into the air over Belarus, western Russia and Ukraine. About 80 percent of the particles were short-lived isotopes of iodine and most of the rest were cesium isotopes.
Most of the radioactive iodine that people ingested came from cows' milk. The iodine dropped onto plants that were eaten by cows. From there it entered their milk. When people drank this milk, the iodine concentrated in the thyroid gland.
Cesium, in contrast, spreads throughout the body, so that no one organ has anything like the dose of radioactivity that the thyroid receives from iodine isotopes.