Objective: To assess the effect of radioactive nuclides of uranium and thorium on the morphometric characteristics of human placentaMaterials and methods: The present study was performed on 67 placentas (Group Ⅰ) of women with a normal pregnancy (38-41 weeks) living in the town of Mayluusuu (12-17 km downstream the uranium biogeochemical zone, where uranium ores were extracted for 22 years) and 48 placentas of women (Group Ⅱ- control) living in ecologically-pure zone. Placentas were weighed on electronic scales, followed by length measuring. To detect the concentration of uranium and thorium, placentas were burned in a porcelain dish in muffle furnace at 400 - 600°C. X-ray spectrometry was used to analyze concentrations of uranium and thorium in the ashes. Results: In Group Ⅰ, uranium and thorium were detected in all specimens of placenta. Uranium concentration levels ranged from 0.01 to 2.26 mg / kg (average concentration 0.73 ± 0.4), thorium - from 0.01 to 0.63 mg / kg (average concentration 0.25 ± 0.2), P ＜0.001. No traces of uranium or thorium were found in specimens of placenta in control group. Considering the fact that placental weight depends on the number of births, three groups were distinguished: primipara, secundipara and multipara. In Group Ⅰ, placental weight was 477 ± 59 g (P ＜0.001) in primipara and 607 ± 164 g in multipara. In Group Ⅱ - 415.12± 16.2 g and 478.35± 13.3 g (P ＜0.001), respectively. Besides, the weight of placenta was dependent on the concentration of uranium and thorium in placenta.Conclusion: Thus, the weight of human placenta containing radioactive nuclides is higher than that of placenta free from radioactive nuclides, i.e. even small concentrations of radioactive nuclides in placenta, possessing "excess" energy create conditions for accelerated cell division, and as a result, increased weight of placenta.
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