Robust Prediction of Kd from Soil Properties for Environmental Assessment

ABSTRACT

Soil solid/liquid partition coefficients (Kd) are commonly used in quantitative environmental assessments as a means to predict retention of contaminant metals and radionuclides in soils. There are Kd data for most elements in the literature, and they can be measured for specific sites. However, there is also a need for robust, defensible relationships to predict the variation in Kd as a function of soil characteristics. This article reports relationships for As, Cd, Ce, Cl, Co, Cr, Cs, Cu, Fe, Ho, I, La, Mn, Mo, Nb, Nd, Ni, Np, Pa, Pb, Pu, Ra, Sb, Se, Sm, Sn, Sr, Tc, Th, Tl, Tm, U, W, and Yb, most based on a wide range of soil properties. Soil pH, clay content, and organic carbon content were the independent variables considered in all cases, and methodology variables were invoked for Cs, Mn, and Ni. The underlying Kd data were considered representative of steady state conditions: most were measured by desorption of the indigenous element at realistic field moisture contents. The equations, developed by forward or backward stepwise regression, were all statistically highly significant. Estimates from the equations were compared to data for seven site-specific soils and generally were within 95th percentile bounds.

Key Words:

• retention
• retardation
• partition coefficient
• nuclear
• metal
• desorption

ACKNOWLEDGMENTS

The author is grateful for financial and technical support from the Swedish Nuclear Fuel and Waste Management Co. (Svensk Kärnbränslehantering AB), Stockholm. B. Sanipelli of ECOMatters Inc. assisted with the literature review. G. Sohlenius of Sveriges geologiska undersökning, Uppsala conducted the field sampling and characterization of Swedish soils used in this study.

Notes

^a Ashworth et al. 2008; Cao et al. 2001; Covelo et al. 2004; Dhillon and Dhillon 1999; Echevarria et al. 1998, 2003; Fernandez et al. 2006; Hellerich and Nikolaidis 2005; Jalali and Moharrami 2007; Lee et al. 1998; MacDonald and Hendershot 2006; Nakamaru and Uchida 2008; Rabie Ahmed Usman 2008; Roussel-Debet 2005; Sanchez et al. 2002; Sastre et al. 2006; Sauve et al. 2003; Schimmack et al. 1987; Shan et al. 2002; Sheppard and Hawkins 1991; Skipperud et al. 2000; Staunton 2004; Twining et al. 2004; van den Hoop 1995; Vandenhove and Van Hees 2007; Vandenhove et al. 2007; Vega et al. 2006; Wang and Liu 2005; Watmough et al. 2005; Yin et al. 2002.

^aFor desorption of indigenous Cs the Kd values will be 4.2-fold higher than predicted by the equation, and for sorption of new ¹³⁷Cs, they will be 4.2-fold lower.

^bFor desorption of indigenous Mn the Kd values will be 4.0-fold higher than predicted by the equation, and for sorption of new ⁵⁴Mn, they will be 4.0-fold lower.

^cFor desorption of indigenous Ni the Kd values will be 6.2-fold higher than predicted by the equation, and for sorption of new Ni, they will be 6.2-fold lower.