Diffusion experiments for estimating radiocesium and radiostrontium sorption in unsaturated soils from Spain: comparison with batch sorption data.

As sorption data obtained from batch tests are often used to estimate pollutant transport in unsaturated soils, comparison between sorption data obtained in the two conditions is required to ensure a correct risk assessment. With this aim, radiostrontium and radiocesium apparent diffusion coefficients (D(a)) were quantified in nine unsaturated soils, and the derived distribution coefficients (K(d)) were compared with K(d) data from batch experiments. The D(a)(Sr) and the D(a)(Cs) ranged from 1.8x10(-11) to 1.5x10(-10) m(2) s(-1), and from 1.0x10(-13) to 5.9x10(-11) m(2) s(-1), respectively. The D(a)(Sr) varied according to both soil packing parameters and properties governing Sr interaction. For Cs, the soil sorption properties explained the variation on D(a)(Cs). The K(d) values derived from D(a) (from 0.014 to 1.8 L kg(-1) for Sr; from 0.55 to 942 L kg(-1) for Cs) were lower than from batch tests (from 1 to 97 L kg(-1) for Sr; from 10 to 14,600 L kg(-1) for Cs), thus indicating that batch data may not accurately describe radionuclide transport in unsaturated soils. However, the two sets of data correlated well, thus suggesting that radionuclide transport can be estimated from batch tests, which are faster than diffusion experiments.