ENVIRONMENT

Hong Kong’s background radiation levels ‘astounding’, says former top official

Former official takes readings almost a third higher than world average

PUBLISHED : Monday, 30 March, 2015, 3:32am
UPDATED : Monday, 30 March, 2015, 5:42pm

"Astounding" levels of background radiation measured in some of the city's poorly ventilated urban areas were almost a third higher than the world average, a former environmental protection official has revealed.

Dr Mamie Lau May-ming, who retired as principal officer last year, measured background radiation with a Geiger counter at around a dozen points across the city last year, including Sham Shui Po, Sai Kung and Central.

At one covered pedestrian bridge in Nam Cheong, radiation levels hit 0.32 microsieverts per hour and above - 36 per cent higher than the global average of about 0.25.

Roughly the same readings were taken from the stairwells of an old Tai Kok Tsui primary school and a poorly ventilated office building corridor in Central.

By contrast, recordings at the abandoned Japanese city of Tomioka-machi, near the tsunami disaster-hit Fukushima Daiichi nuclear plant, were 0.65 as of September, she said.

Lau, a former member of the city's Radiation Board, said the results were "astounding".

"Background radiation is a problem and few people are aware of it," Lau told the Post. She said building clusters in close proximity could elevate the radiation levels considerably.

The source was likely to be granite building materials including some concretes which contain traces of gamma radiation-emitting minerals such as radon, uranium and thorium.

Although Lau said levels were not life-threatening - 0.23 microsieverts per hour is equivalent to 2 millisieverts (mSv) a year, or roughly one cranial CT scan - constant exposure in small doses could have cumulative effects.

In Lau's new book, Healing Tree, she points to the Petkau effect, which proves cell membranes are damaged much more readily by long-term exposure to low-level radiation than brief exposure at the same dose.

The health risks to urban dwellers were also compounded by stress, imbalanced diets and unhealthy lifestyles, she said.

About 38 per cent of the city's background radiation comes from the air in the form of radon, a gas which enters the lungs as particles and cannot come out.

Citing a 1988 study by City University physics professor Peter Yu Kwan-ngok, she said 13 per cent of deaths from lung cancer - the city's biggest killer - could be attributed to long-term radon exposure. "We should raise public awareness that good ventilation with intake of fresh air in homes and offices is important," said Lau. "With so many illness-causing factors, it is wise to minimise the risks as best we can."

She urged the government to strengthen management of indoor radon including using less radioactive materials for construction and giving more consideration to radon issues at the planning stage when redeveloping old areas.

The Observatory, which monitors the city's ambient radiation, says the level of background radiation in the city does not pose a high risk to human health.

"We're talking about microsieverts, which is a very small amount," said Observatory scientific officer Leung Wai-hung. "The average person absorbs 2 to 3 millisieverts in a year just from the natural environment."

A Department of Health spokesman said in addition to man-made sources, ionising radiation came from natural sources in the soil, water and air.

He added that even the International Atomic Energy Agency had no definite conclusion as to whether exposure to background radiation carried a health risk, "though it has been demonstrated at a level a few times higher".

The Buildings Department said it did not measure radioactive materials used in construction, nor did it have any regulations on their use.

"It is believed the source of low-level radiation in buildings, if any, comes from the aggregate of the concrete," a spokesman said.