Iodine-131 and various other radionuclides were released into the atmosphere from the damaged Japanese reactors of Fukushima Dai-ichi from 12 to 22 March 2011. The contaminated air mass was detected in France after 24 March; samples of grass, vegetables, and milk have been analyzed for (131)I by the IRSN, considering the fact that few values of iodine-131 transfer parameters have been directly measured in situ, due to the radioactive decay of this isotope. Data are compared with calculated values according to the air iodine concentration. The apparent dry deposition velocity of iodine on grass is therefore estimated to range between 1 × 10(-3) and 5 × 10(-3) m s(-1) from site to site. In addition, the grass to milk transfer factors are 2.8 × 10(-2) and 3.6 × 10(-3) d L(-1) for goat's and cow's milk respectively. These parameters fit well with the current values usually considered for radioecological assessment.
-Geological and climatic diversity leads to significant spatial variability of naturally occurring radioactivity levels, whether in soils, sediments or natural waters. The activity level of Rhône sediments is estimated at 1450 Bq/kg, between the levels observed in the Loire (1925 Bq/kg) and Seine (730 Bq/kg). The largest amounts of radioactive effluent from nuclear facilities concern tritium, for which activity levels are currently 1000 times higher than the sum of artificial gamma emitters discharged. The proportions of naturally occurring 14 C and 3 H in the lower reaches of the River Rhône are estimated at 50 to 70% and <5%, respectively, with the remaining amount coming from nuclear facilities. Long-term records from River Rhône monitoring show that the level of radioactive contamination from artificial sources declined sharply starting in the early 90s, with the level divided by 10 to 100 depending on the element. Radioactivity of natural origin remained unchanged as expected.
-The observations made in Japan in 2011 after the Fukushima-Daiichi accident and those made in France, Italy, Greece and Austria in 1986 after the Chernobyl fallout, show that the development stage of orchard trees at the time of atmospheric deposition is a major factor determining the level of caesium contamination in fruits at harvest. Both data sets are shown to be consistent and enable one to estimate, for mobile elements in plants such as caesium, an aggregated transfer factor (expressed in Bq.kg −1 of fresh fruit per Bq.m −2 deposited on the ground surface) whose value strongly depends on the time elapsed between fallout and harvest. The Fukushima data set also enables one to estimate effective half-lives (expressed in days), which are helpful for predicting the decrease in fruit contamination with time. We found an average value of 200 days for the one-year period after radioactive fallout, which is quite consistent with values estimated from post-Chernobyl surveys.
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