The biology and radiobiology of in utero development in relation to radiological protection.

Aspects of intrauterine development relevant to radiological protection but not considered in the recently revised Recommendations of ICRP (1991a) include (i) recently acquired evidence on the totipotency of cells of the morula with implications for dosimetry and risk in the first week of human development in utero; (ii) much older evidence on the earliest stages of myelo- and lymphopoiesis in the human subject that bears on radiosensitivity to leukaemia induction in utero; (iii) much older evidence on species differences that may affect the application to the human of experimental work on radionuclide transport from mother to embryo and fetus; (iv) recent proposals of alternative mechanisms for localization of functions in the developing mammalian forebrain with implications for risk of mental impairment caused by low level irradiation in utero, and (v) a recent demonstration that UNSCEAR (1977) was mistaken when concluding that a high radiosensitivity for teratogenesis is characteristic of the embryo and of preimplantation irradiation. The 1990 Recommendations of ICRP (1991a) to limit exposure of the fetus to radionuclides by reference to the occupation ALI for adults, i.e. women of reproductive age, seems to be a serious mistake.