Chernobyl: emerging data on accident.

Chernobyl: Emerging data on accident

As low-level radioactive fallout from the catastrophic accident at the Chernobyl Nuclear Power Station began wafting over the West Coast of the United States on Monday, the Soviets began releasing their first, brief descriptions of what crippled a reactor in the Ukraine one week earlier. The accident began at 1:23 a.m. on Saturday, April 26, when a chemical explosion ripped apart structural elements in the building housing the reactor, said Soviet officials this week. At a press conference in Moscow on Tuesday, those officials said the accident, which occurred during a planned shutdown in the plant, was a result of "several highly improbable and therefore unforeseen failures.'

No mention was made of what caused the initial explosion or of the status of a graphite fire, which Western scientists suspect is still burning in the damaged number-4 reactor's core. Although the Soviets reported on Monday that some 26,000 Chernobyl-area residents had been evacuated "in a strict and organized fashion,' taking only four hours, they added at the Moscow press conference the following day that the evacuation did not begin until about 36 hours after the accident. That is long after many would have sustained substantial and potentially lethal radiation doses, Western scientists believe. First Deputy Health Minister Yevgeny Vorobyev told reporters on Tuesday that 204 had been hospitalized for "radiation disease'--18 suffering from "extreme radiation exposure.' In addition, Soviet officials reported that by May 5, radiation levels at Chernobyl had been reduced "by two- to three-fold' since April 27, to 10 to 15 milliroentgens per hour--an hourly exposure that would be equivalent to one-half to two-thirds of a chest X-ray.

Sources outside the Soviet Union continue to accumulate data on the Chernobyl accident, and last week the White House established a U.S. government interagency task force to analyze the growing body of information. Extrapolating radiation-monitoring data collected in the Stockholm area by the Swedish government, for example, the task force estimates that the whole-body radiation doses that might have been absorbed by persons in the immediate area of the plant range from 20 to hundreds of rems during the two days when radiation releases were likely highest. (A rem is a unit of absorbed radiation dose that takes into account the type of radiation.) The task force says these doses are "sufficient to produce severe physical trauma, including death.'

Atomic bomb and laboratory data have indicated that thousands of rems cause the central nervous system to fail, killing within hours or days. No treatment is possible at such doses. According to radiation expert Herbert L. Abrams of Stanford University, at 700 to 1,200 rems death comes within days to weeks as a result of gastrointestinal damage. From a few hundred to 700 rems, the first medical intervention--in the form of bone marrow transplantation--is possible. Without successful transplantation, death could come within a month, usually from the destruction of the blood-cell-forming bone marrow. Exposures of 200 to 400 rems kill half the people exposed within a month, by Abrams's estimate; 100 to 200 rems injure the immune system and carry a long-term risk of cancer. Fewer than 100 rems can cause nausea and vomiting, with the cancer risk decreasing as the exposure decreases.

The immediate medical recommendation for people exposed to radioactive particles is to shed contaminated clothing, wash their skin and avoid ingesting anything radioactive. In terms of intervention, at the low end of the exposure scale iodide can be ingested to prevent the body from incorporating radioactive iodine. But neither iodide nor bone marrow transplantation is a panacea. Iodide can cause side effects ranging from allergy to thyroid problems, and pregnant women taking iodide can harm their fetuses. Though iodide was distributed in Poland after the accident, several U.S. experts told SCIENCE NEWS that, at least from the data they saw in the press, the action was not warranted. And bone marrow transplantation is a complex, difficult and risky procedure. Bone marrow transplant specialist Robert Gale, of the University of California at Los Angeles, went to the USSR a week after the accident and, joined later by several colleagues, was reported to have begun performing transplants there. Such a procedure needs to be done within one to two weeks after exposure, notes Andrew Yeager, a bone marrow transplant specialist at Johns Hopkins University in Baltimore. Following the transplant, the patient has to be completely isolated from infection while the new marrow takes root.

Knowing which radioisotopes contributed to the dose is important in estimating the severity of exposure because certain isotopes, such as krypton, aren't absorbed by the body. With so few data available on the exposure levels within the USSR, calculating the long-term health effects is guesswork at best. At the moment, says H. Jack Geiger of the City University of New York and president of Physicians for Social Responsibility, "the major long-term meaning of this event is the need for international cooperation.'

For the United States, the international aspect of the accident became more immediate on Monday, when the National Oceanic and Atmospheric Administration reported its first measurements of very dilute Chernobyl fallout in the U.S. atmosphere--above the Oregon-Washington coast and the Gulf of Alaska. There is no danger within the United States from these near-background levels of radiation entering the atmosphere via the jet stream, according to U.S. radiation-health experts. Some of that fallout was also detected at ground level in rain. The 500 picocuries per liter of iodine-131 measured in Washington state "pose no danger,' the task force reported Tuesday.

However, health experts recommend that Europeans nearer Chernobyl avoid food and water contaminated by radioactivity. U.S. radiation-monitoring teams were dispatched last week to Moscow, Bucharest and Warsaw to measure possible radiation exposures that the U.S. diplomatic corps might receive. According to the State Department, initial readings indicate "there is no reason for significant health concerns.'

The State Department and the interagency task force both noted early this week that the raging graphite fire at Chernobyl's unit-4 reactor, detected in aerial photos last week, may still be burning. The task force said it could not confirm news reports--generated by Swedish analysis of commercial-satellite survey photos--that a second reactor might be burning. However, at a task force briefing this week, Harold Denton, director of the Nuclear Regulatory Commission's office of reactor regulation, did report indications that a second reactor at the Chernobyl complex might be having trouble cooling--a suggestion that it might not proceed safely to full, "cold' shutdown.

Many Western scientists expect that a better picture of the accident may be forthcoming now that three members of the International Atomic Energy Agency --a Swedish, a Soviet and a U.S. nuclear scientist--have been invited to discuss the accident with Soviet officials.