The Unification Ministry has found evidence of severe radiation exposure in 10 North Koreans who defected from the vicinity of North Korea's defunct nuclear test site in Punggye-ri.

The ministry tested them and found radioactivity levels in their bodies exceeding 250 mSv, which is enough to trigger chromosomal abnormalities.

One 48-year-old woman showed 1,386 mSv of radiation, which drastically raises the chances of cancer. Nuclear industry workers can only be allowed to be exposed to around 50 mSv of radiation a year.

The ministry tested the defectors in September of last year but has still not officially announced the results a year later. Bareun Mirae Party lawmaker Choung Byoung-gug had to obtain them under a freedom-of-information request.

The tests also showed between seven and 59 chromosomal mutations in five of the defectors, with radiation levels of 279-1386 mSv. The 48-year-old woman with the highest contamination lived just 23 km away from Punggye-ri, where the North conducted three nuclear tests from 2006 to 2013.

In a similar test of 30 North Korean defectors in 2017, four showed radioactive contamination exceeding 250 mSv. The natural amount of radiation people are exposed to in a year during their daily routines is 2.4 mSv.

Jeong Yong-hoon at the Korea Advanced Institute of Science and Technology said, "There is no way these levels of radiation exposure could happen under normal conditions. The reason must be that a tunnel at the test site collapsed, so it is urgent to check how the site is being managed."

Experts fear the six nuclear tests have contaminated the soil and ground water table in Punggye-ri.

Kim Tae-woo, the former head of the Korea Institute for National Unification, said "Residents of Kilju county and other areas near the test site get their drinking water from underground springs emanating from Mt. Mantap. I believe a lot of the exposure to radiation comes from the drinking water."

There have been numerous accounts from defectors from the region describing deformed babies being born over the past years. One former intelligence official said a spring that starts on Mantap Mountain flows into the East Sea after passing through Kilju and added, "We need to conduct a thorough investigation on the possible impact on [South] Korea as the current flows through the ocean."

But a ministry official claimed, "A study in 2017 found no relationship between [the nuclear tests] and radioactive contamination. Additional tests conducted last year showed similar results as the previous one, so we decided there was no need to make a separate announcement."

That contrasts with the extra caution with which the government has treated Japan's handling of radioactive debris from the Fukushima nuclear power plant, where levels are now down to an average of 1 mSv or the same as Seoul.

Even after the 2011 meltdown levels never exceeded 100 mSv. "The radioactive levels found in North Korean defectors is hundreds of times higher than normal and can only be the result of exposure to severe radiation," said Joo Han-gyu at Seoul National University.

Most of the defectors who were tested were suffering from headaches, blurred vision, blunted senses, heart pain, reduced white blood cell counts and aching bones and joints.

