Biological effects of low dose radiation from the cobalt-60 source at Ås, Norway, and of natural background radiation at the thorium-rich area in Telemark, Norway : studies with the model plant Arabidiopsis Thaliana
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- Master's theses (IPM) 
Several studies exist on radiation effects on organisms. Although most of the interest has been on humans, during the last few years increasing attention has been directed to other organisms, focusing on an ecosystem perspective with the intention of defining ‘safe’ levels of radiation. Recent nuclear power plant explosions at Fukushima have also heightened public interest in low dose effects. In Norway, interest in developing the thorium resource in Telemark has also been an issue in relation to low dose radiation effects. In this study, we looked at low dose effects of gamma radiation on Arabidopsis at the Co-60 source at Ås, analyzing parameters such as seed germination, primary root growth (1 week), seedling mortality and seedling weight. Seed germination was not affected in any of the treatments, including the highest exposure rates of 384 mGy/h. When measured 1 week after sowing seed, we found no effect of continuous gamma exposure as high as dose rates of 270 mGy/h on primary root growth or on seedling weight. Two weeks continuous exposure gave no plant mortality and no obvious growth effects except for a small increase in seedling weight at 0.08 mGy/h (13 mGy total dose). Continuous exposure for 3 weeks resulted in significant effects on plant mortality and seedling weights, even at dose rates as low as 0.01 mGy/h. When seedlings received a 5 or 10 day exposure of radiation followed by several days growth without exposure, we saw effects at the end of a 21-24 day experiment on plant mortality and seedling weights. Both low dose rates (0.01 mGy/h for 10 days, 2.4 mGy total dose) and very high dose rates (270 mGy/h for 5 days, 32 Gy) gave final seedling weights significantly higher than controls. We incubated plants at the Fen site in Telemark for 1 month (dose rate exposure on site of 3.5 mGy/h), then produced seed from 1 plant at Ås. A comparison of seedlings growth from the Fen-exposed plant with control seedlings showed no difference. Similarly, we found no difference in seedling growth with control seedlings grown over soil samples from Fen compared to controls not grown over Fen soil. We conclude that Arabidopsis shows effects in response to so-called ‘safe’ doses rates of radiation (e.g. 0.01 mGy/h) and that these effects are not apparent before approximately 3 weeks after the start of exposure.