Dynamics of tritiated water (HTO) uptake and loss by crops after short-term atmospheric release

A knowledge of the dynamics of HTO in crops and soils is required to validate models, such as the UK Ministry of Agriculture, Fisheries and Food STAR-H3, which predict the ingestion dose following release of tritium. Deposition velocities to cabbage, lettuce and soil have been determined. The loss of HTO from cabbage is described by a double exponential decay; the faster component ( 53 min) is attributed to vapour exchange and transpiration, and the slower component ( 15 h) to decontamination of stem and root tissues. Due to the long half-time ( ) of the second component, the loss of the last 5% of the applied HTO would appear to be complete within 48 h. This represents a considerable increase over the 6-h loss period predicted by the current STAR-H3 model. As these components can now be resolved from the above data, this may be a useful addition to the STAR-H3 model. Our data indicate that HTO loss predictions should be more pessimistic than the default STAR-H3 parameters allow. The effect of dark treatment on uptake and loss of HTO has been examined. Pooled data for soils are also well described using a double exponential fit to the loss data.