Extractability of global fallout Pu from agricultural soils and its potential indication of bioavailability

We present the first investigation of the extractability of global fallout Pu from agricultural soils under natural conditions and its potential for indication of Pu bioavailability. On average, the nominal water soluble and exchangeable Pu fractions in sampled upland field soils were 0.07 +/- 0.07% and 0.02 +/- 0.01%, respectively, while those fractions in the rice paddy soils were 0.10 +/- 0.06% and 0.03 +/- 0.02%, respectively. Sequential extraction results indicated that the dominant sinks of Pu in both upland and paddy soils were the immobile organic matter fraction and the immobile residual fraction. Furthermore, both the water soluble and NH4OAc exchangeable Pu percentages showed a significant negative correlation with the exchangeable Ca2+ concentration in the soils. Regarding the potential plant bioavailability of Pu, we observed a positive correlation (r = 0.549, p = 0.034) between the Pu concentration in rice and the water soluble Pu concentration in the corre-sponding rice paddy soils, and that illustrated the water soluble Pu fraction was likely to be available for rice plant uptake. This bioavailable fraction was further applied in evaluating the available transfer factor (ATF) of Pu by dividing the Pu concentration in rice with the bioavailable Pu concentration in the corresponding soil. The ATFs of Pu from soil to rice plant ranged from 6.9 x 10(-3) to 1.7 x 10(-1). Statistical analysis indicated the ATF data were less discrete compared with the conventional transfer factor (TF). Therefore, we consider the ATF to be more representative than the TF to illustrate the transfer ability of Pu from soil to rice plant.