Tritium Uptake and Loss in Grass Vegetation Which Has Been Exposed to an Atmospheric Source of Tritiated Water

Abstract

Rates of uptake and loss of tritiated water (HTO) were measured in grass vegetation in the field after the plants had been exposed to an atmosphere containing HTO. Uptake of H T O from the atmosphere by leaves required 66 min to achieve 50% equilibrium activity while stems required 1970 min. Loss of HTO from leaves and stems during daylight however took place at rapid and comparable rates. The half time for loss in stems was 25 min while in leaves it was 35 min. Delabeling of contaminated leaves and sterns in darkness took place at much reduced rates. The half time for delabeling of leaves in the dark was 400 min while for stems it was 2180 min. Rapid labeling and delabeling of plant tissue after exposure from the atmosphere takes place through leaf stomata and by direct transfer through the epidermis. Loss of HTO from plants is primarily dependent on transpiration. In the event of accidental HTO release to the atmosphere near the ground rapid contamination of vegetation could be expected. When the atmospheric source is dissipated, rapid decontamination could also be expected during periods of normal plant transpiration but not at night or other times when transpiration flow is not taking place.

Apports de la surveillance du centre CEA-Valduc sur la connaissance des transferts de l’eau tritiée atmosphérique dans les différents compartiments de l’environnement

“…L'eau libre des feuilles se charge puis se décharge assez rapidement en tritium, avec une demi-vie biologique de l'ordre de quelques heures pendant la journée, lorsque les végétaux sont temporairement placés dans une atmosphère contenant de la vapeur d'eau tritiée (Kline et Stewart, 1974 ;Dinner et al, 1980 ;Guenot et Belot, 1984 ;Spencer, 1984 ;Choi et al, 2002 ;Davis et al, 2002). Ceci révèle une diffusion de l'eau de l'air vers l'eau contenue dans la plante, principalement à travers les stomates, malgré un flux d'eau essentiellement sortant.…”

Tritium levels in Chinese cabbage and radish plants acutely exposed to HTO vapor at different growth stages

“…It is well established that sunlight stimulates stomata to open so that a vapor exchange can easily occur between the inside and outside of the plant leaves (Diabate´and Strack, 1997; Kline and Stewart, 1974;Noggle and Fritz, 1976). For radish, this seems to partly explain the highest percentage for exposure R1 and the lowest percentage for exposure R3 because the light intensity was highest during exposure R1 and lowest during exposure R3, as shown in Table 1.…”

“…The water contents of their fresh plants are very high. Some amount of 3 H (tritium, T), a beta-emitting radionuclide, is released in the form of tritiated water vapor (HTO) from nuclear installations such as nuclear power plants, reprocessing plants and, in the future, fusion reactors (Kline and Stewart, 1974;Okada and Momoshima, 1993). The HTO vapor in the atmosphere easily passes through the stomata of growing crop plants to enter into their water pools (Belot et al, 1979;Diabate´and Strack, 1990;Kline and Stewart, 1974).…”

“…Some portion of TFWT is incorporated into organically bound tritium (OBT) mainly by photosynthesis and partly by a metabolic process involved in respiration (Belot, 1986;Diabate´and Strack, 1993). It is well documented that the TFWT concentration, in contrast to the OBT concentration, decreases very rapidly from the end of the plant exposure to HTO vapor (Brudenell et al, 1997;Choi et al, 2002;Guenot and Belot, 1984;Kline and Stewart, 1974). In addition, OBT is known to be two to three times more radiotoxic to humans than TFWT (Diabate´and Strack, 1990;IAEA, 1996).…”

Accumulation and retention of Tritium (tritiated water) inRhodopseudomonas spheroides under aerobic condition

“…Hence, the quantitative and qualitative studies on the bound T incorporated from THO is necessary for reliable estimation of the toxicity of THO. Specific activity ratio of organic bound T to environmental THO (R value) was 0.1-1 in heterotrophic organisms such as mammals [3,5,10,34], fish eggs [32] and Artemia [11] and 0.5-0.7 in autotrophic organisms such as plants [15], diatom [11] and algae [14,39].…”