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Is it safer for pregnant women to leave northern Japan?

Thomson Reuters Foundation - Fri, 29 Apr 2011 15:45 GMT
Author: Gabrielle Babbington
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HONG KONG - To be afraid or not to be afraid is the question that has haunted millions of people as radioactivity leaks from a Japanese nuclear plant battered by last month’s earthquake and tsunami. 

Officials say health risks are minimal outside evacuation areas, but in the absence of detailed advice, many in northern Japan have fled.

Expectant mothers are particularly worried, not least because pregnant women are routinely advised to avoid x-rays, lest the radiation harms the developing foetus or leads to childhood cancers. 

"When we heard prefectures near Tokyo had ten times the normal level of radiation, I booked my ticket for Singapore and flew out the next morning,” said one Australian expat who is five months pregnant with her first child.

“Nobody really knows what’s going on and it just wasn’t worth the risk,” added the woman who didn’t want to be named because of employment sensitivities. 

She is among several thousand foreigners who left Japan after a 9.0 magnitude earthquake and tsunami hit the northeast coast on March 11. Explosions at the Fukushima Daiichi Nuclear Power Station in the aftermath have led to increased radiation levels in many areas.

Did she and other pregnant women like her overreact? 

Not necessarily, according to Dr Edward Lazo, deputy division head for radiation protection at the Organisation for Economic Cooperation and Development’s Nuclear Energy Agency, who said avoiding radiation exposure is especially important for pregnant women, because developing foetuses are the most vulnerable group.

"The urgent phase of the accident is not yet over,” he added.

However, evacuating is not officially recommended and comes with its own travel-related risks and the stress of upheaval, he said. Ultimately, the choice is an individual judgment call. 

The clouds of steam coming from the damaged Fukushima reactors contain - several radioactive particles, including radioactive iodine (iodine-131).

These particles cause two main problems. The first is what happens when they enter the body - by being inhaled, or ingested via contaminated farm produce or water. 

The second is what happens when they remain in the external environment and emit gamma ionizing radiation.

Because the clouds of radioactive particles disperse on the wind, there is far less chance of inhaling or ingesting them than of being exposed to the ionizing radiation the particles emit when they remain in the environment, Lazo said.

To protect against some of the effects of inhaling or ingesting iodine-131, people can take potassium iodide tablets – and avoid contaminated tap water and food.

But there is nothing they can take to reduce the impact of gamma radiation and there’s no way to avoid exposure. It passes through the human body and, when absorbed, causes a destructive process in tissues that can lead to cell death and increase the risk of cancer.

It also gets into homes, as it would take thick walls of concrete or lead to stop it, Lazo said. 


How much ionizing radiation the body absorbs over time is called a dose rate and is measured in sieverts per hour. A millisievert (mSv) is one thousandth of a sievert and a microsievert is one millionth of sievert.

“Most experts in the field of radiation research agree that there are no definitive data showing foetal harm at dose levels below about 20 millisievert,” radiological physicist Robert Barish, wrote in the journal of the American College of Obstetrics and Gynecologists 2004.

But childhood cancers, particularly leukemia, are still a concern at in utero exposures below 20 mSv, Barish wrote.

Experts assume there is a linear relationship between radiation dose and adverse effects – the one increases in line with the other.

However, scientists simply don’t have enough data to know for sure, because large groups of people are rarely exposed to radiation above normal background levels.

Barish, speaking in a phone interview, cited more recent information from U.S. authorities.

Exposure to acute radiation doses above 50 mSv in the first trimester of pregnancy may result in major malformations, growth retardation, a reduction in IQ of up to 15 points and mental retardation, depending on dose.

But from about 16 weeks gestation, non-cancer health effects from acute doses below about 500 mSv are unlikely.

Based on mathematical modeling, the ‘best guess’ for childhood cancer risk is that it will occur in 0.3 percent of those exposed to normal background radiation levels in utero; rising to 1 percent of those exposed to acute doses of up to 50 mSv in utero, and so on.

Because of the data shortage, policy makers err on the side of caution. The United States and Europe recommend maximum exposure of 1 mSv over a 40-week pregnancy.

In Tokyo, radiation levels have been consistently elevated since March 21 – at daily maximums of about 0.08 to 0.15 microsieverts per hour.

A back-of-envelope calculation suggests it would take about 40 weeks at these levels to reach the 1 mSv limit for pregnancy.

But 1 mSv is the equivalent of 10 chest x-rays.

International guidelines discourage radiological examinations during pregnancy unless there is a pressing medical need.

However, Barish said radiation doses delivered over long periods don’t have the same impact on the body’s normal healing mechanisms as acute doses delivered in minutes or less.

And Lazo pointed out that Tokyo’s radiation levels are naturally very low. The Fukushima incident has brought them up to par with everyday levels in Hong Kong and several other cities around the world.

But there’s no question of pregnant women leaving Hong Kong, where the natural radiation from rocks and soil is part of life, Lazo said.

When it comes to relatively low levels of radiation, it’s not a matter of what is safe or unsafe, it’s a matter of what you can control and whether or not you can justify a risk by the offsetting benefits, he added.

Lazo suggested pregnant women consider leaving areas with annual radiation exposures between 1 and 20 mSv (constant readings between 0.1 and 2.3 microsieverts per hour), if it’s not overly inconvenient. He unequivocally supported their decision to leave areas with exposures above this level.

The public can check radiation readings on this Japanese government website and on a site called, which collates radiation data from diverse sources.     

It was not possible to get a comment from the Japanese Ministry of Health, Welfare and Labour.  And the World Health Organisation has not made specific recommendations for pregnant women.

Lazo said areas with minimal increases in radiation would soon return to normal, once the Fukushima incident was resolved.

That should take a few weeks to a few months, as the wind and rain wash away the nuclear contamination – and the fear. 

Gabrielle Babbington is a freelance medical journalist based in Hong Kong.

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