IN-VITRO DETERMINATION OF HT OXIDATION ACTIVITY AND TRITIUM CONCENTRATION IN SOIL AND VEGETATION DURING THE CHRONIC HT RELEASE EXPERIMENT AT CHALK-RIVER

The oxidation activity of molecular tritium (HT) in soils and vegetati on collected in experimental plots during the 1994 chronic HT release experiment at Chalk River was determined in in vitro laboratory experi ments after the release. HT oxidation activity was highest in surface soils in the natural plot, about 3-4 times that in soils in the cultiv ated plots. HT oxidation activity in weeds and Komatsuna leaves was ab out 2 and 0.4 % of that in the cultivated soil, respectively The numbe r of HT-oxidizing bacteria isolated from soils was highest in the surf ace soil (0-5 cm) in the natural plot. The viable cell numbers in surf ace soils in the cultivated and natural plots were almost the same. Th e total occurrence rates of HT-oxidizing bacteria in the surface soils were 22 % in the natural plot, and 7.5 % in the cultivated plot. The occurrence rates of HT-oxidizing airborne bacteria during the release on two culture media were 4.2 and 1.9 %.