The findings are based on 2024 tests conducted by the National Radiation Emergency Medical Center under the Korea Institute of Radiological and Medical Sciences. The study examined 35 defectors from eight cities and counties surrounding the Punggye-ri nuclear test site, where North Korea carried out all six of its nuclear tests.
Of those tested, 12 individuals — about 34 percent — showed chromosomal changes in a “stable chromosome aberration test,” a biological dosimetry method used to estimate cumulative lifetime radiation exposure. All 12 recorded levels above the minimum detection threshold of 0.25 gray.
By contrast, an “unstable chromosome aberration test,” which detects more recent exposure within the past three to six months, found no values above the detection limit in any subject, suggesting that any potential exposure occurred earlier.
Officials cautioned that the results do not establish a direct connection to nuclear testing. Chromosomal abnormalities may arise from other sources, including medical radiation such as CT scans or exposure to harmful chemicals, including smoking.
North Korea conducted nuclear tests at Punggye-ri between 2006 and 2017, releasing radioactive isotopes such as iodine-131, cesium-137, strontium-90 and plutonium-239, which can enter the body through contaminated air, water or food and potentially cause genetic damage.
Despite the findings, none of the 12 individuals identified with possible abnormalities has been diagnosed with cancers typically associated with radiation exposure, according to the ministry.
The latest results build on earlier screenings. In 2023, 15 out of 59 defectors showed similar signs, bringing the three-year total to 44 out of 174 individuals — about 25 percent of those tested who had lived near Punggye-ri since North Korea’s first nuclear test in October 2006.
The ministry said establishing a definitive link would require environmental sampling of soil and water near the test site — currently impossible without cooperation from Pyongyang. Comparative analysis with the general South Korean population could also help clarify any correlation.
About 800 defectors in South Korea are believed to have originated from the eight regions surrounding the test site.
The Unification Ministry said it will continue testing, aiming to examine 50 additional individuals this year, though the program has slowed, with only 94 people tested over the past two years and no new results publicly released since 2024.
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