Abstract
The conversion of atmospheric molecular tritium (HT) to tritiated water in soils was examined. The oxidation rate of HT varied with soil depth, temperature and soil water content. Among three sandy loam soils, rate constant was highest in the top section (0-5 cm) of grassy forest soil, 0.196/min, and in lower sections with soil depths of 5 to 10 cm and 10 to 15 cm, the rate constants were one fourth and one eighth, respectively, of that of the top section. The rate constants of the top sections of paddy and upland fields were 0.038/min and 0.058/min. Oxidation occurred over a broad temperature range from 0 to 75°C. Optimal water content for HT oxidation ranged from 10 to 25% of soil dry weight. The addition of KCN or NaN3 to the soil partially decreased HT oxidation and pretreatment with chloroform or acetone (20%) reduced the oxidation rate by a half. HT oxidation activity in the surface soil (0-5 cm) under anaerobic conditions was somewhat less than that under aerobic conditions, but below this depth, the activity was essentially the same under either condition.
