Uptake of HTO by human body

The interaction of atmospheric HTO with vegetation and soil has several time scales. After a short release, airborne HTO is deposited to land or sea by vapour diffusion with a vg of about 10 mm s-1 (Garland, 1980). From land, about 75% of the HTO returns to the atmosphere within days or weeks depending on climate. At sea, HTO mixes downwards and only a small fraction re-enters the atmosphere within the radioactive life of tritium. 

When atmospheric HTO remains at a more or less constant level for months, water in soil and surface run-off approaches equilibrium with the atmosphere. In 1963, tritium in US surface water averaged 3000 pCi l-1 (110 Bq l-1) (NCRP, 1979), equivalent to 920 TU and rather greater than the level in oceanic rains (Fig. 4.2). 

The dose to tissue from HTO is low, because the energy of decay is low and the distribution uniform. In the 1960s, the average dose to man in the northern hemisphere from tritium reached a peak of 2 /uGy a-1, about 0.2% of natural background radiation. 

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