Extended Kd distributions for freshwater environment

Publication date: December 2018

Source: Journal of Environmental Radioactivity, Volume 192

Author(s): Patrick Boyer, Claire Wells, Brenda Howard

Abstract

Many of the freshwater K_d values required for quantifying radionuclide transfer in the environment (e.g. ERICA Tool, Symbiose modelling platform) are either poorly reported in the literature or not available. To partially address this deficiency, Working Group 4 of the IAEA program MODARIA (2012–2015) has completed an update of the freshwater K_d databases and K_d distributions given in TRS 472 (IAEA, 2010). Over 2300 new values for 27 new elements were added to the dataset and 270 new K_d values were added for the 25 elements already included in TRS 472 (IAEA, 2010). For 49 chemical elements, the K_d values have been classified according to three solid-liquid exchange conditions (adsorption, desorption and field) as was previously carried out in TRS 472. Additionally, the K_d values were classified into two environmental components (suspended and deposited sediments). Each combination (radionuclide x component x condition) was associated with log-normal distributions when there was at least ten K_d values in the dataset and to a geometric mean when there was less than ten values. The enhanced K_d dataset shows that K_d values for suspended sediments are significantly higher than for deposited sediments and that the variability of K_d distributions are higher for deposited than for suspended sediments. For suspended sediments in field conditions, the variability of K_d distributions can be significantly reduced as a function of the suspended load that explains more than 50% of the variability of the K_d datasets of U, Si, Mo, Pb, S, Se, Cd, Ca, B, K, Ra and Po. The distinction between adsorption and desorption conditions is justified for deterministic calculations because the geometric means are systematically greater in desorption conditions. Conversely, this distinction is less relevant for probabilistic calculations due to systematic overlapping between the K_d distributions of these two conditions.

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