Radioactive material may be suddenly or steadily introduced into the environment as a result of various human activities (industrial, medical, military, scientific) and is also naturally present throughout the earth and the atmosphere. Such material consists of unstable isotopes of various chemical elements (for example: carbon, hydrogen, iodine, strontium) called radio-nuclides, whose atoms undergo transformation into atoms of a different element, sometimes also unstable, at a known constant rate. Because they are chemically indistinguishable from their stable isotopes, radio-nuclides behave chemically like non-radioactive nuclides. They are thus similarly distributed among the various components of the environment and, through ingestion of food or inhalation of air containing them, may be deposited in various tissues of the human body, depending on the properties of the chemical compounds of which they are part.
The ionizing radiation that radio-nuclides emit during radioactive decay is what causes biological damage, whether the radiation reaches human tissues from inside or outside the body. The resulting effects depend on the amount of energy imparted by radiation per gramme of a specific tissue, a measurable quantity called the absorbed dose.
Radioactive contamination is regarded as the number one environmental problem in Russia. In 1992, up to 2.7 million people still lived in the areas affected by the 1986 nuclear power plant explosion at Chernobyl. A total of 1.3 million people were registered in hospital as suffering from diseases related to radiation exposure from Chernobyl by that time. In other areas affected by nuclear radiation, many people became invalid, suffering from headaches, bleeding, anaemia and leukaemia.
In 1993, it was estimated that for every year of operation of a proposed new nuclear processing plant at Sellafield in the UK, around 200 deaths from cancer would be caused worldwide. This would be mainly due to emission of two very long-lived radionuclides, iodine-129 and krypton-85 which circulated globally and therefore irradiate large numbers of people. Incidence of childhood leukaemia in the area is already up to 10 times the national average.
Some 85 per cent of the average total radiation dose to UK individuals comes from natural radiation sources such as radon, gamma and cosmic radiation. Radon accounts for half of the total average population dose. Artificial radiation accounts for the remaining 15 per cent of total average population dose, most of which comes from medical sources. Less than 0.1 per cent of total population exposure from artificial radiation results from discharges from nuclear installations. High level radioactive waste results from the processing of nuclear fuel. Stocks stored at Sellafield and Dounreay fell by 3 per cent between 1991 and 1994. Intermediate level radioactive waste includes, for example, nuclear reactor components and metal cladding for nuclear fuel. Stocks stored at UK nuclear installations increased by 19 per cent between 1991 and 1994.
It was revealed in 1998 that the Israeli El Al cargo jet, that plowed into a low-income housing complex near Amsterdam in 1992, contained 270 kilograms of depleted uranium, used for ballast in the tail section of the older aircraft. That kind of uranium emits a low-level alpha radiation and is not hazardous unless ingested, but can be toxic if burned at high temperatures. Although more than half of the uranium was recovered, it was still not known what had happened with the rest.