Journal of Environmental Radioactivity 53 (2001) 257–264 Short note Effect of pH on the sorption of uranium in soils Guillaume Echevarria a, *, Marsha I. Sheppard b , JeanLouis Morel a a Laboratoire Sols et Environnement, ENSAIA-INRA/INPL, BP 172, F-54505 Vandœuvre-le  s-Nancy Cedex, France b ECOMatters, PO Box 430, Pinawa, MB, ROE 1L0, Canada Received 20 December 1999; received in revised form 20 April 2000; accepted 4 May 2000 Abstract This work was undertaken to study the influence of soil type and chemical composition on uranium sorption ratios (SR in l kg 1 ) in order to reduce the uncertainty associated with this parameter in risk assessment models. Thirteen soil samples were collected from three different locations in France under different geological conditions. Clay content varied from 7.0 to 50.0%, pH ranged from 5.5 to 8.8 and organic matter content from 1.0 to 4.6%. Soils were incubated at room temperature in polyethylene packets for 28 days in the presence of 1 mg U kg 1 soil. Sorption ratio values varied from 0.9 to 3198 for all soils with no significant effect of soil texture or of organic matter. However, soil pH was highly linearly correlated with (log SR) as a probable consequence of the existence of different uranium complexes as a function of soil pH. The sorption behaviour differences between UO 2þ 2 and UO 2þ 2 -carbonate complexes are so great that any other effect of soil properties on U sorption is hidden. Thus, soil pH should be the focus variable for reduction of the uncertainty associated with the soil K d value used in environmental risk assessments, even for reducing the uncertainty in site- specific K d values. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Uranium; Soil; Sorption; Distribution coefficient; K d 1. Introduction Uranium is one of the radioelements whose mobility in soils may vary strongly depending on soil type and physico-chemical properties. Soil:solution distribution coefficients, K d , that describe the mobility of elements in soils and rocks range in *Corresponding author. Tel.: +33-3-83595792; fax: +33-3-83595791. E-mail address: guillaume.echevarria@ensaia.inpl-nancy.fr (G. Echevarria). 0265-931X/00/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII:S0265-931X(00)00116-8