Radiation effects
Ionising radiation transports energy. When this radiation energy hits biological tissue - for example in the human body - it is taken up (absorbed) by the tissue. The absorbed energy may produce manifold effects. If and to what extent the radiation exposure of an organism leads to health damage depends on the absorbed radiation dose, the type of radiation and which organ or body tissue is mainly affected. If the radiation dose is very high, tissue or even the entire organism may die. Radiation damage can, however, also be repaired. But, if repair is faulty, the long-term result may be the development of cancer or leukaemia, for instance.
When ionising radiation hits a cell, the radiation energy is taken up (absorbed) by the molecules of the cell. This energy has the effect of ejecting electrons from the molecules (ionisation) or breaking bonds in the molecules. The resulting molecule types (radicals) are very reactive chemically and can be electrically charged or electrically neutral. These radicals react with the other molecules inside the cell which may then directly or indirectly lead to cell damage.
Ionising radiation can cause cancer and leukaemias. Both types of disease belong to the malignant neoplasms. Whereas cancer includes malignant neoplasms affecting an organ, leukaemia is a disease of the blood-forming system that has an effect on the whole organism. Much the same applies to lymphomas, malignant neoplasms of the lymphatic system which also affect the whole organism.
Radon can accumulate in the ambient air of closed rooms. Particularly harmful are its short-lived progeny which can deposit in the respiratory tract. Alpha radiation that accrues during decay can promote lung cancer. According to statistical risk calculations, nearly 1,900 deaths yearly are due to indoor radon in Germany. Within the European Union, 20,000 deaths yearly can be attributed to indoor radon.
It is highly controversial, whether low doses of ionising radiation may possibly have a positive effect on biological systems. The positive effects seen sporadically but often just claimed are gathered under the term "hormesis". The manifestations of these positive effects are manifold and variable. These effects cannot be observed regularly in studies conducted under almost identical conditions.
The International Atomic Energy Agency's (IAEA) criteria for health consequences of radiation accidents are summarized in "Planning the medical response to radiological accidents", Vienna, IAEA, 1998.
When ionising radiation acts upon gonads or germ cells, it may cause damage to the genetic material (mutations) which can lead to genetically induced diseases (hereditary defects). These may result in malformations, metabolic disorders, immune deficiencies etc. in the children or grandchildren of exposed individuals or may only become apparent after many generations.
Epidemiology (derived from Greek epi "on, upon", demos "people", logos "study") is a scientific discipline studying the distribution of diseases in a population (descriptive epidemiology) and the factors influencing this distribution (analytical epidemiology).
The manifestations of diseases and damages (e.g. cancer) caused by ionising radiation cannot be distinguished from so-called spontaneously occurring diseases. Possible causation by radiation can only be established when the diseases consistently occur statistically significantly more frequently in groups of individuals exposed to radiation and over different groups of individuals than in non-exposed control groups.
