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Rising radiation levels have been recorded at Chinese monitoring stations close to the North Korean border. Photo: AP

China detects rising radiation levels in areas close to North Korean nuclear blast site

Monitoring stations record upward trend, but expert says it could be explained by natural causes

Chinese scientists are considering whether a small but gradual increase in environmental radiation picked up by monitoring stations close to the border with North Korea is related to the nuclear test carried out over the weekend.

The changes could be down to environmental factors and unrelated to the nuclear test, but the trend was “worthy of attention”, said a scientist who sits on a panel that advises the Chinese government on emergency responses to radioactive hazards.

The radiation level in Changbai Korean autonomous county – the closest Chinese urban area to the Punggye-ri test facility – climbed gradually from an average of 104.9 nanograys per hour immediately after the test on Sunday to 108.5 on Tuesday, according to figures released by China’s environment ministry.

By Wednesday morning the average level in the county, which lies about 80km west of the blast site, had risen to 110.7 with a peak of 112.5.

Nanograys per hour is the standard unit for measuring the absorption of radiation by human tissue.

Similar upward trends were reported by monitoring stations in other regions, including in Antu county at the foot of Changbai Mountain and in Yanbian Korean autonomous prefecture further north.

At Punggye-ri, the estimated 100 kiloton blast triggered several large landslides, according to satellite images released on Wednesday by the US-based Johns Hopkins School of Advanced International Studies.

Earlier, a research team at the University of Science and Technology of China traced the locations of the five most recent tests carried out by North Korea to a single mountain, which they warned was now at risk of imploding. In such an event, the radioactive material currently trapped underground would be released.

Guo Qiuju, a professor of radiation protection at the school of physics at Peking University, said it was too early to be certain what had caused the rising trend at the monitoring stations as radiation levels change over time even under normal conditions.

The public had no need to panic as no suspicious trace elements were detected by the government on Tuesday, she said.

“If something bad had happened I would be one of the first to be informed,” she said. “I have not received the call so far.”

The current radiation levels were far below anything that could be regarded as a risk to people’s health, she said, “but if the figures keep going up it may require a closer look”.

Guo explained that it was considered normal for readings to fluctuate within a 20 nanogray range due to the effects of wind, rain and cosmic rays.

For instance, radioactive materials floating high in the atmosphere could be carried down into the soil by rain, she said.

Several regions close to the test site had recorded rain in the past few days, according to Chinese weather authorities.

Despite Guo’s reassurances, the owner of a restaurant in Changbai close to a monitoring station said the blasts had left many of the county’s near 100,000 residents scared.

“After the jolt on Sunday the street has been quiet. People prefer to stay indoors with their mobile phones, expressing their fears on WeChat,” he said.

“We hope that heaven will hear our prayers and keep the devil away from our land.”

This article appeared in the South China Morning Post print edition as: Elevated radiation levels close to nuclear test site