Studies on soil to grass transfer factor (F_v) and grass to milk transfer coefficient (F_m) for cesium in Kaiga region

摘要

Detailed studies were carried out to establish site-specific soil to grass transfer factors (F_v) and grass to cow milk transfer coefficients (F_m) for radioactive cesium (~(137)Cs) and stable cesium (Cs) for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of ~(137)Cs and stable Cs to evaluate the soil to grass F_v values. The milk samples from the adopted cows were analyzed for the ~(137)Cs and stable Cs concentrations to evaluate F_m values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of F_v were found to be 1.1 × 10~(-1) and 1.8 × 10~(-1) for ~(137)Cs and stable Cs, respectively. The F_m of ~(137)Cs had geometric mean values of 1.9 × 10~(-2) d L~(-1) and 4.6 × 10~(-2) d L~(-1) respectively, for adopted Cows 1 and 2; 1.7 × 10~(-2) d L~(-1) for the cows of local farmers, and 4.0 × 10~(-3) d L~(-1) for the dairy farm cows. The geometric mean values of F_m for stable Cs were similar to those of ~(137)Cs. The F_m value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The F_m values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher F_m values were identified. The correlation between F_v and F_m values for ~(137)Cs and stable Cs and their dependence on the potassium content (~(40)K and stable K) in the soil and grass were also studied. In order to estimate the ingestion dose accurate data of the dietary habits of the population was necessary and this data was collected through a well planned demographic survey. The internal doses to a child due to the ingestion of ~(137)Cs along with the milk of the local cows and from the dairy farm were found to be 0.29 μSv y ~(-1) and 0.04 μSv y~(-1),while that to an adult were 0.39 μSv y~(-1) and 0.05 μSv y~(-1), respectively.