The danger of radiation leaks from the nuclear plant in Japan is rising after explosions at the site, but the health effects of radiation were poorly understood.

According to World Health Organization, the nuclear plant leakage materials are iodine-131 and caesium-137, and they can damage the thyroid gland and the blood system. The body parts most vulnerable to radiation damage are the blood and immune systems, reproductive organs, and the stomach and intestinal tract. Exposure to more than 2,000 millisieverts - equivalent to more than 180 CT scans - can have long-term and genetic effects.

Exposure levels:

The radiation dose is expressed in units called a sievert (Sv). On average, a person is exposed to about 3.0 millisieverts a year. The radiation from a CT scan amounts to about 11 mSv.

Phase	Symptom	Exposure (Sv)
		1–2Sv	2–6Sv	6–8Sv	8–30Sv	>30Sv
Immediate	Nausea and vomiting	5–50%	50–100%	75–100%	90–100%	100%
	Time of onset	2–6h	1–2h	10–60m	<10m	immediate
	Duration	>24h	24–48h	<48h	<48h	48h–death
	Diarrhea	None	Slight (10%)	Heavy (10%)	Heavy (90%)	Heavy (100%)
	Time of onset	—	3–8h	1–2h	>1h	<30m
	Headache	Slight	Mild (50%)	Moderate (80%)	Severe (80–90%)	Severe (100%)
	Time of onset	—	4–24h	3–4h	1–2h	<1h
	Fever	Slight–None	Moderate (50%)	High (100%)	Severe (100%)	Severe (100%)
	Time of onset	—	1–3h	>1h	>1h	>30m
	CNS function	No impairment	Cognitive impairment 6–20 h	Cognitive impairment <20 h	Rapid incapacitation	Seizures, Tremor, Ataxia
Latent Period		28–31 days	7–28 days	>7 days	none	none
Overt illness		Mild Leukopenia; Fatigue; Weakness	Leukopenia; Purpura; Hemorrhage; Infections; Epilation	Severe leukopenia; High fever; Diarrhea; Vomiting; Dizziness and disorientation Hypotension; Electrolyte disturbance	Nausea; Vomiting; Severe diarrhea; High fever; Electrolyte disturbance; Shock	Death
	Mortality without medical care	0–5%	5–100%	95–100%	100%	100%
	Mortality with medical care	0–5%	5–50%	50–100%	100%	100%

In a nuclear power plant accident, the general population is not likely to be exposed to doses high enough to cause such effects. Rescuers, first responders and nuclear power plant workers are more likely to be exposed to doses of radiation high enough to cause acute effects.

Long-term effects from radiation exposure:

Exposure to radiation can increase the risk of cancer. Among the Japanese atomic bomb survivors, the risk of leukaemia increased a few years after radiation exposure, whereas the risks of other cancers increased more than 10 years after the exposure.

Radioactive iodine can be released during nuclear emergencies. If breathed in or swallowed, it will concentrate in the thyroid gland and increase the risk of thyroid cancer.

Among persons exposed to radioactive iodine, the risk of thyroid cancer can be lowered by taking potassium iodide pills, which helps prevent the uptake of the radioactive iodine.

The risk of thyroid cancer following radiation exposure is higher in children and young adults.

Treatment

Drugs can stimulate the growth of white blood cells and help people fight off infections. Exposed individuals can also be given capsules containing a dye that binds to thallium and cesium and helps the body get rid of these radioactive elements.