Uptake of Heavy Water and Loss by Tangerine in the Heavy Water Vapor Release Experiment in a Greenhouse as a Substitute for Tritiated Water

Tritiated water (HTO) uptake and loss in maize plant after short-term exposure of atmospheric HTO vapor at daytime and nighttime

Maize plants were exposed to atmospheric tritiated water (HTO) in the field for 1 h during the day and night under different growth periods. The uptake of HTO vapor by leaves and tissue free water tritium (TFWT) loss in maize plants were investigated. Rate constants of uptake of HTO from the atmosphere by maize leaves were 0.10 ± 0.02-0.21 ± 0.01 h^-1 during the daytime exposure and 0.035 ± 0.001-0.13 ± 0.01 h^-1 in the nighttime exposure. The uptake rate tended to decrease as the exposure increased and harvest neared. At the end of exposure, the TFWT concentration was highest in the leaf and lowest in the ear, the TFWT concentration in different parts of maize varied by a factor of 3-28 for daytime release and 2-30 for nighttime release. After the end of every exposure, TFWT was lost rapidly from different maize tissues for one day and then at a much slower rate until to harvest. At harvest, the TFWT concentrations varied with different maize tissues by factors of 1-4. The decrease was by factors of 4-351 for daytime exposure and 6-605 for nighttime exposure. The reduction of TFWT varied with the exposure time by the factors of 1-10 depending on plant parts. The reduction factor was lowest in kernel. This result suggests that the HTO vapor uptake rates in maize leaves and TFWT loss rates in the ear may be lower than those in C₃ plants.

An overview of organically bound tritium experiments in plants following a short atmospheric HTO exposure

The need for a less conservative, but reliable risk assessment of accidental tritium releases is emphasized in the present debate on the nuclear energy future. The development of a standard conceptual model for accidental tritium releases must be based on the process level analysis and the appropriate experimental database. Tritium transfer from atmosphere to plants and the subsequent conversion into organically bound tritium (OBT) strongly depends on the plant characteristics, seasons, and meteorological conditions, which have a large variability. The present study presents an overview of the relevant experimental data for the short term exposure, including the unpublished information, also. Plenty of experimental data is provided for wheat, rice, and soybean and some for potato, bean, cherry tomato, radish, cabbage, and tangerine as well. Tritiated water (HTO) uptake by plants during the daytime and nighttime has an important role in further OBT synthesis. OBT formation in crops depends on the development stage, length, and condition of exposure. OBT translocation to the edible plant parts differs between the crops analyzed. OBT formation during the nighttime is comparable with that during the daytime. The present study is a preliminary step for the development of a robust model of crop contamination after an HTO accidental release.