ASTANA — Thirty-five years after Kazakhstan closed the Semipalatinsk nuclear test site, researchers and community advocates say its legacy still shapes health, science and policy. As evidence becomes more precise, experts say the focus is shifting toward how that knowledge can better support affected communities.
The Aug. 29, 1991, closure ended more than four decades of Soviet nuclear testing at the site in eastern Kazakhstan. Between 1949 and 1989, 456 nuclear tests were conducted there, including 116 atmospheric explosions, some of which sent radioactive fallout over surrounding populated areas.
The date later gained international significance when the United Nations General Assembly, at Kazakhstan’s initiative, designated Aug. 29 as the International Day against Nuclear Tests. The anniversary now marks both the historic closure and continuing questions surrounding the long-term effects of exposure.
Radiation exposure was far from uniform. Doses could differ significantly depending on the test, the path of radioactive fallout, where a person lived, their age, activities and diet. Reconstructing individual exposure decades later is particularly difficult because personal radiation measurements were generally unavailable at the time.
Vladimir Drozdovitch. Photo credit: National Cancer Institute In a comment for this story, Vladimir Drozdovitch, a staff scientist in the Radiation Epidemiology Branch of the United States National Cancer Institute’s Division of Cancer Epidemiology and Genetics, said researchers therefore combine historical environmental data with information about individual circumstances.
“Even when exposure occurred 60-75 years ago and individual radiation measurements were not made at the time, scientists can reconstruct doses by combining many different types of historical evidence,” Drozdovitch told The Astana Times. “For the Semipalatinsk population, this includes archival measurements of radiation exposure rates in air made after the nuclear tests, information about the nuclear tests and radioactive fallout, measurements of residual radionuclides in soil and, where available, retrospective physical dosimetry using materials such as bricks and tooth enamel,” he said.
Researchers must then establish where people lived during individual tests, whether they were temporarily away, their age and occupation, housing conditions and, for internal exposure, their consumption of locally produced food. Milk and dairy products were particularly relevant because radioactive iodine deposited on pasture could enter the food chain.
A 2026 study by Drozdovitch and an international team estimated external whole-body doses for 14,789 people from 15 settlements affected by fallout between 1949 and 1962. Such estimates allow epidemiologists to examine whether disease risk changes with radiation dose rather than treating everyone living near the test site as a uniformly exposed population.
“Dose reconstruction tells us who was exposed, how much they were exposed, and why some people received much larger doses than others,” said Drozdovitch. That evidence can help distinguish possible radiation effects from other influences on health and inform how decades of research might translate into healthcare today.