Effects of Tritiated Water on Germ Cells in Medaka Embryos

Abstract

Embryos of medaka, Oryzias latipes, were exposed to tritiated water and 137Cs gamma rays continuously from the one-cell stage until hatching (10 days at 26 degrees C). Germ cells in the gonads of newly hatched fry were counted in histological sections and compared with controls. The accumulated dose for 50% survival of germ cells was 195 rad for tritium beta rays and 350 rad for 137Cs gamma rays. Female progeny were produced using Yamamoto's method. The 50% survival doses for female germ cells treated in a manner similar to that described above were 140 rad for beta rays and 305 rad for gamma rays. When embryos of medaka were irradiated with gamma rays below an accumulated dose of 475 rad or treated with tritiated water at a concentration of 0.2 mCi/ml or lower, the dose response of the germ cells showed an exponential relationship. It appeared that there was no threshold or significant dose-rate effect for either beta or gamma rays on germ cell survival, and that tritium beta rays were more effective than 137Cs gamma rays in germ cell killing.

Effects of in vivo exposure to tritium: a multi-biomarker approach using the fathead minnow, Pimephales promelas

“…Strand et al (1982) showed mortality and malformations in trout eggs after 21 days of HTO exposure at 12 µGy/h (total dose of 6 mGy). In medaka, the number of germ cells changed in embryos exposed to 7080 µGy/h for 10 days (total dose of 1.7 Gy) (Etoh &Hyodo-Taguchi 1983), and the number of primary spermatogonia (Hyodo Taguchi &Egami 1977), vertebral malformations and fecundity (Hyodo-Taguchi &Etoh 1986, 1993 were affected at 1200 µGy/h in adult fish exposed for 30 days (total dose of 864 mGy). In the puffer fish, Fugu niphobles, HTO induced a decrease of egg hatching at 12100 µGy/h following a 130 h exposure period (total dose of 1.54 Gy) (Ichikawa &Suyama 1974).…”

Cellular Responses to Tritium Exposure in Rainbow Trout: Hto- And Obt-Spiked Feed Exposure Experiments

“…In fact, very few studies regarding the effects of tritium exposure in fish have been published to date. Most studies were conducted using a single fish species, e.g., medaka (Oryzias latipes) [2][3][4]. The medaka studies reported detrimental effects of tritium on developmental and reproductive endpoints at dose rates that are much higher than the ones used in the present studies.…”

“…This study was primarily designed to evaluate tritium (particularly the organically bound fraction) uptake, under controlled conditions, in edible fish [5]. As none of the previously cited studies reported biological effects and because biological effect studies in fish exposed to tritium have generally been conducted at higher doses than the present study [2][3][4], some tissues were reserved for this purpose.…”

Impacts of temperature, morpholine, and chronic radiation on the embryonic development of round whitefish (Prosopium cylindraceum)

“…Using a 137 Cs source also had its challenges: although the doses used in our study were some of the lowest achievable, the lowest dose used (0.10 mGy/d) was >300 times the discharge limit of radioactive substances from nuclear power plants (Bruce Power, 2014). Even if tritium is more biologically effective than gamma radiation (Etoh and Hyodo-Taguchi 1983;Bellamy and Eckerman 2013), the fact that no mortality or sublethal effects were observed even at the highest doses tested suggests that radiation from once-through cooling processes alone is unlikely to significantly affect round whitefish embryonic development or survival.…”

“…Annual releases of tritium by nuclear power plants from cooling water discharge into surrounding lakes and streams are typically <40 Bq L À1 , which is well under the Ontario provincial drinking water limit of 7000 Bq L À1 (Bruce Power 2014). Based on previous work by Etoh and Hyodo-Taguchi (1983), 7000 Bq L À1 tritium would be equivalent to a dose of <0.5 mGy/d (Orient 2014). Ionizing radiation can be described as either directly (e.g., tritium, emitting beta particles) or indirectly ionizing (e.g., 137 Cs, emitting gamma rays; Hall and Giaccia 2012).…”