EFFECTS OF IONIZING-RADIATION ON THE BOREAL FOREST - CANADA FIG EXPERIMENT, WITH IMPLICATIONS FOR RADIONUCLIDES

The Field-Irradiator Gamma (FIG) experiment chronically irradiated a s ection of the Canadian boreal forest over a period of 14 years. Forest trees were affected at dose rates > 0.1 mGy.h-1, but a herbaceous pla nt community thrived at dose rates up to 65 mGy.h-1. Irradiation resul ted in the establishment of four zones of vegetation: a herbaceous com munity, a shrub community, a narrow zone of dying trees, and a zone wi th no apparent impacts. Concentrations of C-14, Tc-99, I-129, Cs-137 a nd Ra-226 that could cause a dose rate of 0.1 mGy.h-1 within vegetatio n were calculated. Chemical toxic effects on plants would be caused by Tc-99 and I-129 before radiological effects are predicted to occur. T he calculated Ra-226 concentration is about a factor of 10 greater tha n that measured at some natural sites. Sufficiently high concentration s of C-14 and Cs-137 to cause an impact are unlikely unless a site is severely contaminated.