Twenty years after being exposed to radiation at a 1957 Nevada neclear weapons test nicknamed Smoky, nine of 22 rhesus monkeys developed cancer, according to an Atlanta, Ga., researcher.
The same type of delayed incidence of a cancer has turned up in ex-GI's who were exposed to far less radiation at the Smoky. A study by the federal Center for Disease Control in Atlanta has found that eight Smoky veterans have developed leukemia, a cancer of the blood, twice the number normally expected.
Altogether, according to Dr. Harold M. McClure of the Yerkes Regional Primate Center, 11 of the 22 Smoky monkeys have turned up with cancer and seven have died from the disease.
Normally, McClure said in a telephone interview yesterday, about 2 percent of a rhesus monkey colony would be expected to develop cancer.
The monkeys were one of many joint military-civilian experimental efforts that accompanied almost every nuclear weapons test in the 1950s.
After the 1957 test was completed, the Air Force maintained the monkeys at the School of Aerospace Medicine at Brooks Air Force Base, Tex.
Sometime after 1960, however, the job of tracking these particular 22 animals for any long-term health effects was given to the Yerkes Center in Atlanta with financial support from the National Cancer Institute.
Yesterday, no one at the Pentagon or at Brooks could recall if any other monkeys from the 1950s' tests had been placed with other research institutions.
"I thought all the monkeys at the tests were killed by the explosions," was the way one veteran Pentagon official recalled the experiments.
The monkeys were placed in cages less than three miles from the 44-kiloton Smoky shot. The bomb dropped on Hiroshima was 12.5 kilotons, equivalent to 12,500 tons of TNT.
According to McClure, the monkeys received radiation doses measured at from 221 rems to 597 rems. In humans, a single dose of 450 rems is expected to cause half those exposed to die of radiation poisoning within 30 days.
One monkey, which took a reported 530 rem dose is still alive, McClure said. But another, which received 221, is among the ones that died of cancer.
Since the CDC study turned up the apparently excessive number of leukemia cases among the Smoky GIS, attempts have been made to locate other participants in the tests to determine if the low-level exposures in 1957 caused the cancer more than 20 years later.
Recently, the Defense Nuclear Agency sponsored a study that attempted to reconstruct the radiation levels to which a sample of 55 soldiers at Smoky were exposed.
By reconstructing the position of this particular maneuver group throughout the test period, the scientists suggested the average does was less than one rem. In addition they concluded from their calculations that most of that dose came from residual radiation left over from shots prior to Smoky.
The low dosage, however, has not stopped speculation that the Smoky exposure was connected somehow with the later appearance of cancer.
McClure's findings, that cancers do not appear for 20 years or more in monkeys with much higher radiation exposure, may add to the belief by some that despite long latent periods, radiation has an effect at any level.
A second group of monkeys McClure inherited from the Air Force seems to support that thesis.
In 1954, according to Yerkes, a group of five rhesus monkeys were exposed to neutrons in an experimental laboratory. This time the doses were from 16 rem to 64 rem.
More than 20 years later, three of the five have died of cancer -- a much higher rate than expected, though the sample is small.
McClure said, however, "that the neutron looks like an even higher source of cancer than" radiation from a normal atomic bomb.
In a third experimental group, the Air Force in 1958 exposed 15 rhesus monkeys to radioactice cobalt. This time the doses were given in short spurts and added up to from 200 rem to 1,000 rem. Despite the higher total dose levels, only five of the 15 have turned up with cancer tumors.
These findings give support to those who say there is some repair to cells damaged by radiation and that a single shot is more hazardous than the same dose spread over a period of time.
McClure said yesterday he is in the process of writing up his work of the past 14 years with the monkeys.
Though McClure said it is dangerous to extrapolate from the monkey experiments, he added that the rhesus is "physiologically" more closely related to humans than any other type of animal.