The accumulation of Tc by tumbleweed and cheatgrass was measured for five soils at one, two, and three months' harvest times. The initial soil concentration of 1.0 pg 99Tc/g added to the soil as pertechnetate, was traced by 95mTc. At the three month harvest time, uptake of the added Tc ranged from 23 to 82% and 10 to 69% for tumbleweed and cheatgrass respectively. The soil order of percent uptake by tumbleweed was Lickskillet < Burbank < Rupert < Warden < Ritzville. Shoot concentrations of 99Tc ranged from 0.06 to 0.33 and from 0.05 to 0.36 ng/g for tumbleweed and cheatgrass, respectively. Shoot concentration generally decreased with increasing time of harvest. Concentration ratios (CR) were calculated from the estimated average soil concentration during each harvest period. CR values ranged from 76 to 390 and from 54 to 421 for tumbleweed and cheatgrass, respectively. CR values were generally constant with increasing harvest time except for the Lickskillet soil which decreased for both tumbleweed and cheatgrass. 1n a separate experiment, tracer 95mTc was increased in the Burbank and Rupert soils by a tracer activity level factor of 50 over that used in the primary experiment. Good agreement was found when comparing the percent uptake values, shoot concentrations, and CR values between high and low 95mTc tracer concentrations for both soils. This demonstrated that 95mTc was an effective tracer for the 99Tc and that the results were not influenced by either Tc toxicity or radiation effects.
©1978Health Physics Society