Oral administration of tritiated water (HTO) in mouse. II. Tumour development

Previously we reported haematopoietic death as an effect of tritiated water (HTO) in drinking water in the concentration range from 5.92 × 10¹¹ to 1.85 × 10¹⁰ Bq/dm³. In the present study the effects of HTO in a lower concentration range from 9.25 × 10⁹ Bq/dm³ (0.240 Gy/day) to 3.70 × 10⁸ Bq/dm³ (0.096 Gy/day) are reported. Female (C57BL/6N and C3H/He)F₁ mice were maintained on drinking water containing various levels of HTO. Mice survived for > 150 days with a high incidence of tumour development (70 to 80%). In the dose-rate range from 9.25 × 10⁹ Bq/dm³ (0.240 Gy/day) to 1.85 × 10⁹ Bq/dm³ (0.048 Gy/day) the main cause of death was thymic lymphoma. However, at a dose-rate of 9.25 × 10⁸ Bq/dm³ (0.024 Gy/day) the incidence of thymic lymphoma sharply decreased, while the incidence of other tumours increased. The tumour types became more diverse at lower concentrations of HTO. The latent period of tumour development was shorter and the life-shortening effect was more marked by ³H βirradiation in this study than by X- or γirradiation reported in other investigations.