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Discharge of 137Cs and 90Sr by Finnish rivers to the Baltic Sea in 1986-1996.

The total amounts of 137Cs and 90Sr transported from Finland by rivers into the Gulf of Finland, Gulf of Bothnia and Archipelago Sea since 1986 were estimated. The estimates were based on long-term monitoring of 137Cs and 90Sr in river and other surface waters and on the statistics of water discharges from Finnish rivers to the above sub-areas of the Baltic Sea. The total amounts of 137Cs and 90Sr removed from Finland into the Baltic Sea during 1986-1996 were estimated to be 65 and 10 TBq, respectively. The results show that, although the deposition of 137Cs was much higher than that of 90Sr after the Chernobyl accident, the amount of 137Cs removed from Finland is only six times as high as that of 90Sr. This emphasizes the importance of 90Sr while considering radiation doses from surface waters and 137Cs while estimating doses via pathways from catchment soil, lake sediments and biota after a fallout situation.

Cesium Radioisotopes↗

Ecological half-time of radiocesium from Chernobyl debris and from nuclear weapons fallout as measured in a group of subjects from the south of Sweden.

From 1960 to 1980 and between 1987 and 1994 the whole-body content of 17Cs, and when possible also 134Cs, was measured in a group of subjects living in the city of Lund, Sweden (55.7 degrees N, 13.2 degrees E). The results have been analyzed to estimate the effective ecological half-time of fallout radiocesium in humans living in the area. The Lund area (The Province of Skåne) was subjected to a deposition of about 2 kBq m(-2) of pre-Chernobyl 137Cs from nuclear weapons testing and 1 kBq m(-2) of 137Cs from Chernobyl fallout in May 1986. The radiocesium from the nuclear weapons tests in the 1950's and 1960's still gave a significant contribution to the total 137Cs levels in humans in the post-Chernobyl study period (1987-1994) of about 0.4 Bq per kg body weight, which was about 10% of the peak post-Chernobyl concentration level of 137Cs (3.5-4 Bq kg(-1)) in 1987. The effective ecological half-time for 137Cs from Chernobyl was found to be 1.8 +/- 0.2 y. The aggregate transfer factor from deposition to mean activity concentration in man was estimated to be 3.6 Bq kg(-1)/kBq m(-2). These values may be compared with an effective ecological half-time of 1.3 y found in the reference group in the 1960's, and an aggregate transfer factor of 10 Bq kg(-1)/kBq m(-2). This difference is largely explained by the continuous nature of the global fallout leading to contamination on growing crops whereas the Chernobyl fallout occurred just prior to the South Swedish growing season, leading to less efficient transfer to crops and to human diet. The average committed individual effective dose (50 y) from ingested 137Cs from the Chernobyl fallout was estimated to be 0.02 mSv and from the nuclear weapons fallout (1945-1995) to be 0.20 mSv.

Adult↗

Mapping of 137Cs deposition over eastern France 16 years after the Chernobyl accident.

We observed the relationship between present-day 137Cs surface activity and the rainfall in May 1986 to establish a relevant map of 137Cs deposition over eastern France. This study was performed in an area of the lower Rhône valley where clayey soils are assumed to trap caesium efficiently. Based on the rainwater/airborne activity ratio deduced from this relationship, we verified that present-day activities, measured in clayey soils of this type, are relatively representative of the initial depositions. The interlocked contaminated areas of the resulting map can be related to rainfall occurrences, as is the case for all countries affected by the Chernobyl fallout. This map can be reasonably compared with those obtained for countries bordering France in terms of both activity levels and extent of homogeneous activity areas. Lastly, we demonstrate that it would not be possible to produce a coherent map of initial fallout by extending the campaign over the whole of the eastern territory based on present-day soil activity measurements alone. Hence, only the relationship between 137Cs deposition and the rainfall of the first week of May 1986 can be used to construct a map depicting the Chernobyl fallout over eastern France.

Cesium Radioisotopes↗