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Concern remains over the potential effect on human health from radiation leaks at the stricken Fukushima Daiichi nuclear plant.

A 20km (12 mile) evacuation zone affecting about 70,000 people has been imposed around the plant, and is being extended to five communities outside the zone to the north west of the plant, where radioactive contamination is most significant.

Residents living within 30km (18 miles) have been advised to leave the area, or to stay indoors, and try to make their homes airtight.

Experts believe that swift action of this sort should have minimised the risk to human health, but there are worries about the level of radiation to which emergency workers have been exposed, and about possible contamination of food and water supplies.

What are the immediate health effects of exposure to radiation?

How is radiation sickness treated?

How does radiation have an impact on health?

What are the most likely long-term health effects?

Are children at greater risk?

What risk does Fukushima pose currently?

What radioactive materials have been released?

How can the Japanese authorities minimise the cost to human health?

Is there evidence that food has been contaminated?

What is the threat to Tokyo residents from contaminated tap water?"

Is it safe to bathe or wash food in contaminated tap water?

What about contaminated seawater?

How does Fukushima compare to Chernobyl?

What if the situation deteriorates?