Tritiated Water Movement in Semiconfined Growth Systems

Since its beta radiation will not penetrate the skin, the major hazard of tritium ( 3 H) to man is via the food pathways. This investigation was designed to provide preliminary information on 3 H behavior in the food pathways, which include soils and plants. Each of six semi‐confined growth systems contained four corn (Zea mays L.) plants grown on 0.1 m 3 of a fertilized peat‐sandperlite mixture. The bottom of each container and the surface of the growth medium was covered with plastic to prevent excessive loss of 3 H due to evaporation or mass flow. The growth medium in each system received a single surface application of 3 mCi of tritiated water (HTO), and was kept near field capacity by watering every 2 or 3 days. Pairs of systems were labeled at 7, 10, or 13 weeks maturation of the corn, and the rate of 3 H removal at different stages of plant growth was determined. Residence time of 3 H in the growth medium was short. At maximum rates of withdrawal (transpiration), over 90% of the added 3 H was removed within 1 week. The maximum amount of readily extractable 3 H found in the plants was about 3% of the original application. This occurred 3 days after labeling and decreased to 0.1 to 0.3% in 2 weeks.