Radiocontamination of the environment and its effects on the mother and fetus—III: Part I—Retention of cesium 137 during pregnancy: An inter-laboratories study

Abstract

The determination of cesium 137 and strontium 90 in human placments was carried out in different laboratories in Japan and Canada, in order to standardize the radioassay procedures. Placentas from normal term deliveries were collected and measured for a period of 12–16 months in the Tokyo and Osaka areas in Japan and in the Montreal area in Canada. Two procedures required the ashing of the entire placenta prior to radioassay. In the Tokyo group, the ashed organ was placed in a two NaI crystal system, in an almost 4π geometry, and the γ radiation was measured. The Osaka group continues the chemical separation of cesium by precipitation with chloroplatinate; the β radiation is then further measured with an anticoincidence system. These procedures are not adequate for a large series of measurements, since the ashing of the placenta is time-consuming and frequently leads to errors due to loss of material during the ashing. Another procedure avoids the ashing and compresses the fresh placentas to a semi-dry cake; the method is more rapid and avoids losses of radionuclides or radiocontamination during the manipulation. The samples are then measured in a two NaI crystal system, with a geometry close to 4π. The average content of cesium 137 is closely similar in Japanese and Canadian placentas, regardless of the differences in the dietary habits and potassium intake in the two racial groups. However, some organs exhibit a markedly higher level, sometimes 3–4 times the average of 23–24 μμCi/kg tissue; even at this concentration, the total amount of placental cesium 137 accounts for only a small fraction of the irridiation produced by potassium 40 in the same organ. The amount of absorbed energy produced by both radionuclides is well below the danger level. These data compare well with the former measurements in placentas obtained from women of the Hiroshima region, some of whom had been in that city during the war.