Effects of ionizing radiation on the boreal forest: Canada's FIG experiment, with implications for radionuclides

The Field-Irradiator Gamma (FIG) experiment chronically irradiated a section 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 berbaceous plant community thrived at dose rates up to 65 mGy·h-1. Irradiation resulted in the establishment of four zones of vegetation: a herbaceous community, a shrub community, a narrow zone of dying trees, and a zone with no apparent impacts. Concentrations of 14C, 99Tc, 129I, 137Cs and 226Ra that could cause a dose rate of 0.1 mGy·h-1 within vegetation were calculated. Chemical toxic effects on plants would be caused by 99Tc and 129I before radiological effects are predicted to occur. The calculated 226Ra concentration is about a factor of 10 greater than that measured at some natural sites. Sufficiently high concentrations of 14C and 137Cs to cause an impact are unlikely unless a site is severely contaminated. (author)