Aging effects on cadmium transport in undisturbed contaminated sandy soil columns.

Limited information is available on the effects of contaminant aging (i.e., the contact time of Cd with the soil) on Cd transport in soils. We conducted displacement experiments in which indigenous Cd and freshly applied Cd were leached simultaneously from undisturbed samples of three Spodosol horizons. Sorption of Cd was described using Freundlich isotherms, whereas transport was described as a convection-dispersion process. Parameter optimization analysis using a mobile-immobile transport model applied to nonsorbing tracer displacement data showed that 16 to 22% of the water in the columns was immobile. The low dimensionless mass transfer coefficients in the mobile-immobile model were indicative of diffusion-limited transfer between mobile and immobile water, and hence physical nonequilibrium. A two-site kinetic sorption model could be fitted closely to breakthrough curves of the non-aged Cd for three soil horizons. No conclusive evidence was found that contaminant aging in soil affects cadmium transport. On the one hand, predictions of aged Cd leaching, using parameters estimated from displacement experiments with nonaged Cd, differed from those for the aged Cd in the E horizon. On the other hand, no meaningful differences in transport behavior between aged and non-aged Cd were found for the humus Bh and Bh/C horizons. The two-site kinetic rate coefficient alphac was found to depend on water flux, further indicating that mass transfer between sorption sites and the liquid is limited by diffusion rather than by kinetic sorption.

[1]  Tammo S. Steenhuis,et al.  MECHANISM FOR FINGER PERSISTENCE IN HOMOGENEOUS, UNSATURATED, POROUS MEDIA: THEORY AND VERIFICATION , 1989 .

[2]  H. Flühler,et al.  Cadmium Transport in an Unsaturated Stony Subsoil Monolith , 1996 .

[3]  P. Jardine,et al.  Quantifying the diffusive mass transfer of nonreactive solutes in columns of fractured saprolite using flow interruption , 1996 .

[4]  M. Close,et al.  Field-scale physical non-equilibrium transport in an alluvial gravel aquifer , 1999 .

[5]  E. Smolders,et al.  Cadmium fixation in soils measured by isotopic dilution , 1999 .

[6]  W. Inskeep,et al.  Nonequilibrium Transport of Atrazine through Large Intact Soil Cores , 1995 .

[7]  Mark L. Brusseau,et al.  Reply [to Comment on Modeling the transport of solutes influenced by multiprocess nonequilibrium , 1989 .

[8]  G. R. Babu,et al.  A Proposed Method for the Measurement of Coupled Microstrip Line Parameters , 1975 .

[9]  Albert J. Valocchi,et al.  Validity of the local equilibrium assumption for modeling sorbing solute transport through homogeneous soils , 1985 .

[10]  S. van der Zee,et al.  A SCALED SORPTION MODEL VALIDATED AT THE COLUMN SCALE TO PREDICT CADMIUM CONTENTS IN A SPATIALLY VARIABLE FIELD SOIL , 1992 .

[11]  G. Vachaud,et al.  Solute Transfer, with Exchange between Mobile and Stagnant Water, through Unsaturated Sand1 , 1977 .

[12]  J. W. Biggar,et al.  On the Equivalence of Two Conceptual Models for Describing Ion Exchange During Transport Through an Aggregated Oxisol , 1984 .

[13]  Daniel Hillel,et al.  Laboratory Tests of a Theory of Fingering during Infiltration into Layered Soils , 1990 .

[14]  P. Seuntjens,et al.  Full uncertainty calculation on quantitative determination of tracer (111Cd) cadmium and natural cadmium in soil column effluents with ICP-MS , 1999 .

[15]  W. Chardon.  Mobiliteit van cadmium in de bodem , 1984 .

[16]  T. H. Christensen.  Cadmium soil sorption at low concentrations: I. Effect of time, cadmium load, pH, and calcium , 1984 .

[17]  S.E.A.T.M. van der Zee,et al.  Transport of reactive solute in spatially variable soil systems , 1987 .

[18]  T. H. Christensen.  Cadmium soil sorption at low concentrations , 1989 .

[19]  G. Gillman.  A proposed method for the measurement of exchange properties of highly weathered soils , 1979 .

[20]  K. Kung.  Laboratory observation of funnel flow mechanism and its influence on solute transport , 1993 .

[21]  M. Vanclooster,et al.  Determining local-scale solute transport parameters using time domain reflectometry (TDR) , 1993 .

[22]  J. W. Biggar,et al.  Modeling tritium and chloride 36 transport through an aggregated oxisol , 1983 .

[23]  J. W. Biggar,et al.  Diffusion effects in miscible displacement occurring in saturated and unsaturated porous materials , 1960 .

[24]  J. Wit,et al.  Analytical Isotherm Equations for Multicomponent Adsorption to Heterogeneous Surfaces , 1994 .

[25]  L. Ma,et al.  Modeling the Transport and Retention of Cadmium in Soils: Multireaction and Multicomponent Approaches , 1992 .

[26]  J. Francis.  Statistica for Windows , 1995 .

[27]  L. Lapidus,et al.  Mathematics of Adsorption in Beds. VI. The Effect of Longitudinal Diffusion in Ion Exchange and Chromatographic Columns , 1952 .

[28]  M. V. Genuchten,et al.  Mass transfer studies in sorbing porous media. I. Analytical solutions , 1976 .

[29]  P. Gassman,et al.  Cobalt, Cadmium, and Lead Sorption to Hydrous Iron Oxide: Residence Time Effect , 1994 .

[30]  F. D. Haan,et al.  Speciation and calcium competition effects on cadmium sorption by sandy soil at various pHs , 1995 .

[31]  P. Seuntjens,et al.  Derivation of functional layers in a podzol toposequence for simulating cadmium transport , 1999 .

[32]  T. H. Christensen.  Cadmium soil sorption at low concentrations: II. Reversibility, effect of changes in solute composition, and effect of soil aging , 1984 .

[33]  H. Selim,et al.  Transport of zinc and cadmium in soils: experimental evidence and modeling approaches , 1994 .

[34]  Jan M. H. Hendrickx,et al.  Preferential flow mechanism in a water repellent sandy soil , 1993 .