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Thirty-one people were killed instantly. Based on the official reports, close to 8,400,000 people in Belarus, Ukraine and Russia were exposed to the radiation to varying degrees.
These three countries were the worst affected, but radioactive material was also deposited widely across Europe, in some cases hundreds of kilometres beyond ground zero.
The people who received the highest radiation were 240 000 of the 600 000 ‘liquidators’ (involved in clean-up and containment activities within the 30km zone of the reactor).
116 000 people were evacuated from the area around the reactor in 1986, to non-contaminated areas. Another 230 000 people were relocated later.
Health effects of exposure to nuclear radiation
Chernobyl and Hiroshima were like ghastly real-life experiments of the effects of nuclear radiation on human body. The aftermath of both has been studied – and continues to be studied - intensively , but there is still a lot of uncertainty and controversy about the results. Such ‘experiments’ involve large numbers of people, vast areas and many additional factors that could contribute to the diseases being researched.
The following are the main health effects that have been studied with regard to Chernobyl, and are likely to be seen with similar nuclear events:
Radiation sickness
People who receive very high doses of radiation, such as some of the Chernobyl ‘liquidators’ (involved in clean-up and containment activities within the 30km zone of the reactor), are at risk of acute radiation sickness (ARS), the result of damage to the body’s tissues and immune system.
Immediate ARS symptoms include nausea, diarhea and fatigue. This may be followed by symptoms such as hair loss, bleeding under the skin and mouth inflammation.
In severe cases death may occur within two to four weeks. Those who survive for six weeks after a large dose may generally be expected to recover.
Long-term effects
Radiation can also cause little understood changes to the body's genes, which can cause the development of diseases such as cancer later in life.
Radiation-related illnesses tend to emerge about 10 to 15 years after a radiation disaster. The most notable such illness attributable to Chernobyl is thyroid cancer: a large increase in incidence – nearly 5000 cases diagnosed - has been recorded among people in the most contaminated areas who were younger than 18 at the time of the accident.
There is considerable uncertainty about many of the other possible health effects attributable to radiation from Chernobyl. The health effects of lower radiation doses are not well understood. The following effects are suspected, however:
Leukaemia (a cancer of the blood): a doubling of the incidence among the most highly exposed Chernobyl liquidators
Breast cancer: a small increase in pre-menopausal incidence in the most contaminated areas
Cataracts: these are known to result from radiation doses of about 2 Sv. .Chernobyl cataract studies suggest that cataract formation may begin to occur from doses as low as 250 mSv.
Cardiovascular disease: A study of emergency workers has suggested an increased risk of death from cardiovascular disease in highly exposed individuals.
Mental illness
Depression and post-traumatic stress disorder are well-established risks for survivors of natural and man-made disasters.
In the case of Chernobyl, evacuation and relocation proved deeply traumatic to many people in the contaminated zone. People were uprooted from their homes, lost the support of social networks and in many cases suffered economically. This was compounded by the social stigma associated with being an "exposed person", and the anxiety of not knowing what health problems they could be facing.
Information sources:
Health Effects of the Chernobyl Accident and Special Health Care Programmes: Report of the UN Chernobyl Forum Health Expert Group World Health Organization, Geneva, 2006.
Health24, April 2007
