[Late sequelae of small doses of ionizing radiation in humans]

Toxic effects of low doses of ionizing radiation, below 100 rads, may appear within up to 20 years after irradiation. These effects include: increased incidence of leukaemias, pulmonary neoplasms, tumours of the thyroid, stomach and liver. The younger is the organism at the time of radiation exposure the shorter is the latency period of tumour development. Children irradiated in utero with low doses of X-rays exhibit delayed mental development. The period of particular fetal risk is 8-15 weeks of intrauterine life. In the first generation of irradiated males no chromosomal changes were revealed. The free-radical theory of tumour aetiology and the role of factors which may attenuate tumour development on the free-radical pathway are discussed.