Sequential extraction of fallout radiocesium from the soil: Small scale and large scale spatial variability

The reproducibility, the small scale as well as the large scale variability of Cs-137 extracted sequentially from the soil by using a modified Tessier procedure was investigated sit several grassland sites in Bavaria/Germany and in the Chemobyl area. Because undisturbed grassland soils are never homogeneous with respect to their soil properties, all sequential extractions at the German sites were carried out at each plot separately for different soil layers (e.g., 0-2, 2-5, 5-10, 10-15, 15-20 and 20-30 cm). The results show that the coefficients of variation (CV) for the reproducibility of the extraction procedure for Cs-137 was (with some exceotions) around 10-20% for all fractions. For the small scale variability of Cs-137 (samples within an area of 10 x 10 m(2)) the values for the CV were (again with a few exceptions) in the same range. Compared to that, the large scale variability of extractable Cs-137 (random soil samples within an area of 100 x 200 km(2)) was higher for all fractions, even though only moderately. The implications of these results with respect to a sampling design are discussed.