Dose-rate effects on adaptive response induced by tritiated water in human blood lymphocytes

The present study examined the question whether adaptive response concerning micronucleus induction in lymphocytes can be elicited by low-level pre-irradiation from tritiated water and can be influenced by the modification of the dose rate. Lymphocytes previously exposed in vitro to (HOH)-H-3 (0.2 - 6.6 MBq/ml) and subsequently irradiated with 1 Gy gamma-rays showed micronuclei frequency significantly lower than the sum of the yield induced by (HOH)-H-3 and gamma-rays separately. The degree of the radioresistance induced by HTO pre-treatments became higher with decreasing dose-rate for a rather similar total adapting dose. The yield of observed micronuclei decreased until 40%-45% of the expected number. This limit is already reached at dose rate of 0.05 cGy/h.