Download - SW—Soil and Water: Transport of Particulate and Colloid-sorbed Contaminants through Soil, Part 1: General Principles

Biosystems Engineering (2002) 83 (3), 255–273doi:10.1016/S1537-5110(02)00192-7, available online at http://www.idealibrary.com onSW}Soil and Water

REVIEW PAPER

Transport of Particulate and Colloid-sorbed Contaminants through Soil, Part 1:General Principles

M.B. McGechan; D.R. Lewis

Environment Division, SAC, Bush Estate, Penicuik EH26 0PH, UK; e-mail of corresponding author: [email protected]

(Received 14 September 2001; accepted in revised form 1 August 2002)

Literature is reviewed describing through soil colloid-facilitated transport of contaminants such asphosphorus, pesticides and other agrochemicals, plus a range of biological microorganisms. Smallermicroorganism (viruses and bacteria) are transported mainly (like chemical contaminants) by adsorption ontootherwise harmless mobile colloidal clay particles or soil organic matter. Potential impediments to movementof colloids through soil can be subdivided into straining and filtration, depending on whether a particle has adimension similar to pores (leading to physical trapping) or much smaller. Filtration mechanisms, includinginterception, diffusion and sedimentation, have been compared to those described in the extensive engineeringliterature on deep bed filtration. Sorption processes are discussed, both those to static components of the soilmatrix and onto mobile colloids. The chemical influences of ionic strength and pH to colloid transport arereviewed, as well as the double diffusion layer as a mechanism linking particles to surfaces.Numerous reported studies using column experiments to measure colloid or contaminant transport throughsoil have been reviewed. Many indicate the importance of macropore flow which allows rapid unrestrictedtransport of contaminant carrying colloids. Some experiments determine a filtration coefficient for a simplefiltration equation representing straining and filtration processes. The few existing models (incorporating thisfiltration equation), both for column experiments and for the field situation, are reviewed as background tofurther development of a field-scale model representing colloid-facilitated transport of a range of chemical andmicrobiological contaminants. # 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved

1. Introduction

Many contaminants move through the soil inparticulate or colloidal form, either because they areinherently particulate (sometimes due to low solubility),or because they are sorbed onto otherwise harmlessmobile particles which are present in the soil. However,unlike soluble contaminants which can move freely withsoil water movements, there are various restrictions onthe movement of particulate contaminants, includingboth capture mechanisms and sorption by staticcomponents of the soil. This paper discusses themovement and restrictions on movement of suchparticulate and colloidal contaminants, and the mechan-isms which control them. There appear to be two maintypes of physical capture mechanisms restricting colloidmovement in soil and other porous media: straining,where the physical size of the pore is smaller than theparticle so the particle is unable to pass; and filtration,

1537-5110/02/$35.00 255

which covers a range of mechanisms by which particlesare captured in pores with dimensions larger than theparticles. Other restrictions on movement includesorption and various electrostatic charge mechanismsincluding the ‘diffuse double layer’ (DDL). An expandeddiscussion of capture mechanisms relating particle sizesto pore sizes is presented in Part 2 (McGechan, 2002a),making use of various theoretical and mathematicalconcepts.

2. Three-phase representation of contaminant transport

In many previous studies of contaminant transport,only a two-phase approach has been used, in whichcontaminants are partitioned between an immobile solidphase and a mobile aqueous phase. In such a two-phasesystem which is most appropriate to soluble contami-nants, the rate of overall migration can be significantly

# 2002 Silsoe Research Institute. Published by

Elsevier Science Ltd. All rights reserved

M.B. MCGECHAN; D.R. LEWIS256

A Hamaker constant in London–van der Waals’attractive force equations, J

As Parameter correcting particle capture by asingle isolated collector for capture within apacked porous medium

B(s) Dynamic blocking functionc Mass concentration of colloids in solution,

kg kg�1

cn Suspended colloid number concentrationper unit volume of packed bed, m�3

dm diameter of mobile particle, mdp diameter of collector grain, mDh hydrodynamic dispersion coefficient for colloi-

dal particles, m2 s�1

Dp particle diffusivity in Brownian motion, m2 s�1

f collector surface area per unit volume of packedbed, m2 m�3

F filtration sink term, g m�3 h�1

g acceleration due to gravity, m s�1

I rate of colloid capture per grain, s�1

k Boltzman constant, J K�1

kd colloid deposition rate coefficient, s�1

kps equilibrium solid–liquid partition coefficientbetween dissolved solute and solute sorbedonto immobile soil matrix

kpcs equilibrium solid–liquid partition coefficientbetween dissolved solute and solute sorbedonto colloids

kp biochemical transformation rate for dissolvedsolute, s�1

kr colloid release rate coefficient, s�1

ks biochemical transformation rate for solutesorbed onto immobile soil matrix, s�1

kcs biochemical transformation rate for dissolvedsolute sorbed onto colloids, s�1

kt particle transfer coefficient, m s�1

mc average mass of colloidal particles, kgnf empirical exponentp0 clean bed porosity, fractionP Parameter related to media porositys Fraction of collector surface covered by

particlessm Deposited colloidal particles per unit mass

of the porous media, kg kg�1

sj jamming limit slopeSmax maximum fractional coverage by deposited

colloidal particless1 hard sphere jamming limitt time, sT absolute temperature, KU fluid velocity, m s�1

v pore water velocity, m h�1

vref pore water velocity at which fref is measured,m h�1

vp velocity of colloidal particles in porous mediam s�1

vs particle settling velocity, m s�1

z distance, ma volume of collector grains in array, m3

ae particle attachment efficiencyb excluded area parameter, kg kg�1

y soil porosity, m3 m�3

lf filtration coefficient, m�1

lref reference filtration coefficient, m�1

l0 clean bed filtration coefficient, m�1

m fluid dynamic viscosity, N s m�2

rb solid matrix bulk density, kg m�3

rf, rp fluid and particle densities, kg m�3

Notation

slower than the rate at which the water flows, becausereactive contaminants tend to be absorbed onto theimmobile solid phase. However, colloids in water canact as a third mobile solid phase (McCarthy & Zachara,1989), which can sorb contaminants in a similar fashionto the immobile solid phase, and can migrate at ratessimilar to or even greater than the mobile aqueousphase. A three-phase approach is therefore necessary toaccurately simulate the migration of sorbing contami-nants. McDowell-Boyer et al. (1986) also discuss theimplications of this mobile colloid third phase, referringto experiments by Vinten et al. (1983c) and Jury et al.(1986) which first challenged the then accepted view thatstrongly sorbing compounds would be completelyimmobilised by sorption onto the static soil componentalone. Mills et al. (1991) describe mobile and immobile

phases for both colloids and chemical contaminants(Fig. 1).

The mobile solid phase consists of colloidal (orparticulate) particles in the size range from 1 nm to1 mm (Buddemeier & Hunt, 1988), although otherauthors state the upper size limit as 10 mm. Theseparticles move mainly under the influence of Brownianmotion (i.e. due to bombardment by fluid moleculesmoving with a random thermal nature). Ibaraki andSudicky (1995a) have introduced the distinction between‘true colloids’ and ‘pseudo-colloids’. True colloids aregenerated from contaminants such as radionuclideswhich are precipitated when their concentration exceedstheir solubility. Pseudo-colloids originate from non-contaminant sources, such as clay particles, which dueto their small particle size and large specific surface area,

Chemical

Dissolvedsolute

Adsorbed

Adsorbed

solute

solute

(immobile soil matrix)

(colloidal solids)

Colloids

Mobilecolloids

Immobilisation Mobilisation

Immobile colloids

Generation

Immobilesoil

matrix

kp

kps

kpcs

kcs

ks

Fig. 1. Framework of phases for colloid facilitated contaminanttransport (based on Mills et al., 1991); lines with single arrowsdenote kinetic processes; lines with two arrows denote equili-brium processes; ks, kcs, kp, biochemical transformation rates;

kps, kpcs, equilibrium solid-liquid partition coefficientsFig. 2. Water and contaminant movement in soil matrix poresand macropores; soil matrix flow leads to straining or filtrationof particulate (colloid-sorbed) contaminants; macropore flowoccurs when inter-aggregate pore spaces are water-filled,particulate contaminants pass rapidly through soil without

restrictions

TRANSPORT OF CONTAMINANTS THROUGH SOIL 257

become contaminants due to sorption of something elseonto their surface. In the former case the process ofcolloid transport is the main focus, whereas in the lattercase (which is most common in agricultural applica-tions) both colloid transport and the sorption of thecontaminants onto the colloids are important.

3. Role of macropores and fractures in particulatecontaminant transport

A number of researchers have discussed the impor-tance of macropores and fractures in subsurface layersfor fast relatively unrestricted transport of colloidalcontaminants; e.g. Rahe et al. (1978) observed very fastmovements of E. coli organisms through some soilhorizons which could only be attributed to macroporeflow. Macropores arise in agricultural soils for a numberof reasons, including worm holes, channels created byplant roots which have since died and withered away,cracks in dry clay soil, and inter-aggregate spaces which

become water-filled in wet soil conditions (Fig. 2). Someauthors such as Ibaraki and Sudicky (1995a, 1995b) andGwo et al. (1998) use the term ‘fractures’ rather thanmacropores, particularly with reference to contaminantsreaching groundwater aquifers after passing throughdeep subsurface layers as well as the soil profile.However, whether described as macropores or fractures,the mathematics of water and contaminant transportthrough them are the same. Jarvis et al. (1999) quoteMcDowell-Boyer et al. (1986) to suggest that macro-pores are the only pathways by which suspended mattercan pass through the unsaturated zone, since suchparticles are efficiently retained by physical filtrationprocesses when moving through the more tortuous soilmatrix pores (Fig. 2). A similar conclusion was reachedby Kretzschmar et al. (1994). Macropore or fractureflow generally needs to be studied experimentally under


field conditions, since any attempt to extract, transportor reconstitute soil cores for laboratory experimentstends to alter or destroy the macropore structure.However, Abu-Ashour et al. (1998) managed to workin the laboratory with reconstituted soil columns inwhich macropores had been created artificially, demon-strating fast movement of bacteria out the bottomthrough the macropores compared to nothing comingthrough columns without the macropores.

4. Nature and size of particulate and colloidallytransported contaminants

4.1. Chemical pollutants

The main agriculturally derived chemical substanceswhich pollute water and are transported through the soilin particulate or colloidal form are phosphorus arisingfrom mineral fertiliser or manure applications, and somepesticides. The important mechanism by which thesesubstances are transported is by molecules beingadsorbed onto small but otherwise harmless particlesor colloids, such as clay components of soil or organicmaterial from the soil or from manure. This mechanismappears to be of far greater importance than anymovement of precipitated insoluble phosphorus com-pounds or pesticides. The physical size and othercharacteristics of the carrier particles or colloid aretherefore the important determinants for the movementof such chemical pollutants.

4.2. Carrier particles and colloids

Soil particles are generally categorised as ‘clay’ (ratherthan silt or sand) if they have a diameter of less than2 mm. McCarthy and Zachara (1989) suggest a size rangeof 0.1–10 mm for various soil mineral derived colloids,including clays, iron (hydr)oxides, silica and lime.Pilgrim and Huff (1983) measured sediments in a largermean size range 4–8 mm diameter in subsurface flowsfollowing storms of low to moderate intensity, whichthey attribute to detachment on the surface andtransport through the soil via macropores. Soil organicmatter and organic particles from manure and slurryhave a wide range of physical sizes, but particles at thesmall end of the range have the highest surface area tovolume ratio, so provide the largest number of sites forsorption of pollutants. Matthews et al. (1998) haverecently analysed the quantity of phosphorus sorbedonto colloidal particles in various size ranges beingtransported in water flowing either by combined over-land and inter-flow or through mole drains. This showedthat a high proportion of the phosphorus was sorbed

onto particles much smaller than 2 mm. Voice et al.(1983) and Gschwend and Wu (1985) have described animportant role played by non-settling microparticles andorganic macromolecules as carriers for hydrophobicorganic pollutants. Thurman et al. (1982) analysedaquatic humic substances, concluding that some hadhigh molecular weights within the colloidal size range.Atteia and Kozeel (1997) measured size distributions forparticles and colloids in Karstic aquifers. They con-sidered particles up to 4 mm to be contaminant carryingcolloids, which although accounting for a small propor-tion of the mass of suspended material, had a very highproportion of the area of sorbing surfaces. McCarthyand Shevenell (1998) carried out a similar analysis ofcolloids in aquifers, also examining chemical composi-tions of colloids and carried contaminants.

4.3. Biological pollutants

Information in the literature about biological pollu-tants, particularly pathogens in livestock wastes (includ-ing faeces deposited by grazing animals), and theirpotential for movement through the soil to causeenvironmental pollution, have been reviewed byMawdsley et al. (1995). This review categorises micro-organisms in ascending size order as viruses, bacteria(including E. coli and salmonella) and protozoa(including Cryptosporidium and Giardia), but no sizesare stipulated for viruses or bacteria. A size range of 20–200 nm for viruses is stated by Bitton (1975), althoughviruses can form aggregates under certain conditions asdescribed by Floyd and Sharp (1978a, 1978b) and Floyd(1979). McCarthy and Zachara (1989) suggest a sizerange of 1-100 nm for viruses and 0.5–3 mm for bacteria.Kretzschmar et al. (1999) describe graphically the sizeranges for viruses and bacteria, alongside those forcarrier colloids (Fig. 3). Mawdsley et al. (1995) describecryptosporidium as consisting of transmissive oocystswith a diameter of about 4–6 mm (although they maycoagulate to an unknown degree to form larger units),and the most commonly studied out of three species ofGiardia having infective cysts with diameter 7–14 mm(also shown in Fig. 3). Similar size ranges for the maintypes of microorganisms and colloids are described byStumm (1977), who also discusses how such sizes can bechanged by coagulation processes.

5. Sources of colloidal material

Carrier particles and colloids are either added to thesoil surface along with other substances in land spreadwastes, or are created within the soil by particles being

Fig. 3. Size ranges of colloids and microorganisms (adaptedfrom Kretzschmar et al., 1999)


detached from the static soil matrix. Slurry, manure andother organic wastes contain large quantities of parti-culate and colloidal material with a wide range ofparticle sizes, of which the smaller particles will alreadybe carrying a high load of sorbed pollutants (such asphosphorus and microorganisms) when applied to thesoil. In contrast, clay and other colloidal mineralparticles plus some organic colloids are created bydetachment. A number of authors have suggested thatsome detachment of such particles takes place as waterpasses through the macropores and soil matrix pores ofthe soil profile. Kaplan et al. (1993), Govindaraju et al.(1995) and Jacobsen et al. (1997) all measured thisprocess in laboratory soil columns or lysimeters, andGovindaraju et al. (1995) used their results to calibrate amodel of detachment, transport and deposition of clayparticles. Ryan and Gschwend (1990) analysed colloidsin groundwater aquifers attributable to detachment inwater passing through subsurface layers. However,Jarvis et al. (1999) have expressed the opinion thatdetachment within the pores will be dwarfed by a muchmore extensive detachment occurring when raindropsimpinge on the soil surface, the classical erosion process,and eroded particles then enter pores in the soil profile(as described also by Pilgrim and Huff, 1983). There isextensive literature on erosion, some authors relating theextent of erosion to kinetic energy of raindrops(e.g. Rose et al., 1983), giving higher levels of erosion

for a given rainfall quantity in short-lasting, heavy,thundery rain than more continuous gentle rain. Otherauthors including Miller and Baharuddin (1986),Shainberg et al. (1992), Brubaker et al. (1992), Curtinet al. (1994) and Lieffering and McLay (1996) measuredvariations in dispersivity (a measure of erodability)amongst different soils in relation to their differingcomposition and chemistry. Quirk and Schofield (1955),Rowell et al. (1969), Frenkel et al. (1978) and Moutieret al. (1998) investigated an effect where an electrolytesolution in soil water causes some clay soils to hydrateand swell (reducing the size of large soil pores and henceconductivity), and this results in an increase indispersivity of small clay particles.

6. Interactions with surfaces

6.1. Sorption

6.1.1. General principles of sorption mechanisms and

processes

Sorption is the process by which reactive substancesincluding contaminants attach themselves to surfaces ofotherwise harmless solids. A finely divided solid such asclay has a high sorption capacity due to its small particlesize and large specific surface area. Sorption sites in soiloccur both in the static soil matrix and on mobile soil(mainly clay) particles. Sorption is the mechanism bywhich a reactive solute combines with an otherwiseharmless colloid to become a ‘pseudo-colloid’ contami-nant.

The extent of sorption varies between differentreactive solutes and between solid materials, and formobile colloids in relation to the particle size distribu-tion. The term ‘isotherm’ is commonly used for theequation relating the concentration of a substance onsorption sites to its concentration in water. Isothermstend to be non-linear, as energy levels vary betweendifferent binding sites on the solid surfaces, high-energysites becoming occupied before low-energy sites. Somecommonly used sorption isotherm equations, withalternatives for instantaneous equilibrium and for akinematic, time-dependent approach to equilibrium,have been described by McGechan and Lewis (2002).

6.1.2. Sorption of contaminants in soil

The extensive literature on sorption of phosphorusonto soil particles (mainly in relation to the static soilmatrix), e.g. Barrow (1973,1974) and Barrow and Ellis(1986), has been reviewed in detail by McGechan andLewis (2002) and McGechan (2002b). An example ofexperimentally derived isotherms for phosphorus from

Fig. 4. Freundlich isotherms for phosphorus sorption in silty clayloam soil for a range of soil depths at Crichton Royal Farm,Dumfries, logarithmic plot (above) and linear plot (below).From Hooda et al. (1999); , 0-0.1 m; , 0.1-0.2 m;

, 0.2-0.3 m; , 0.3-0.45 m; , 0.45-0.6 m


Hooda et al. (1999) is shown in Fig. 4, based on theFreundlich equation with different coefficients for lowand high phosphorus concentrations below and above abreak-point. There are many studies of sorption ofcontaminants onto static soil components (e.g. Knight &Tomlinson, 1967; Faust & Zarins, 1969; Gonzalez &Ukrainczyk, 1999), a process which locks up thecontaminants and reduces water pollution in the shortterm. The kinetics of time-dependent desorption (thereverse of sorption) of sorbed uranium from the staticcomponent of soils is described by Braithwaite et al.(1997).

6.1.3. Sorption of contaminants onto colloids

In contrast to work on sorption onto static soilcomponents, there is very little published informationon sorption to mobile colloids, the process whichaggravates pollution. Karickhoff et al. (1979) studiedsorption of various hydrophobic pollutants (mainlyorganic liquids) onto natural sediment particles, fittinglinear or logarithmic isotherms to their data. Voice et al.(1983) measured sorption of hydrophobic pollutants,

but concluded that results were complicated by thepresence of microparticles at the small end of the colloidsize range. Gschwend and Wu (1985) also experimentedwith sorption of hydrophobic organic pollutants ontosediments, concluding that the process could bedescribed by a simple partition coefficient, equivalentto a linear isotherm with complete and instantaneousreversibility. In contrast, Penrose et al. (1990) concludedthat radionucleides are almost irreversibly sorbed ontocolloidal material in the size range 0�025–0�45� 10�6 m.O’Connor and Connolly (1980) studied the effect oforganic matter content and clay content on the partitionof contaminants between the dissolved phase and thesorbed phase for a number of pesticides and heavy metalcompounds.

6.2. Colloidal particles interacting with soil surfaces

6.2.1. Sorption of microorganisms

Marshall (1971) and M .uuller and Hickisch (1970) havereviewed the subject of sorption of microorganisms onsoil particles, and further information on sorption ofbacteria by clay minerals is presented by Filip (1973).Filip (1973) also observed that the growth of somemicroorganisms could be enhanced where other sub-stances which inhibit growth are removed from solutionby sorption onto clay particles. However, Bitton (1975)reviewing the subject of sorption of viruses indicated alack of information about sorption for these organisms.Burge and Enkiri (1978) measured virus sorption by fivedifferent soils. Goyal and Gerba (1979) observed largevariations in the extent of adsorption between differenttypes and strains of viruses under the same conditions.Moore et al. (1982) describe the mechanisms by whichviruses are sorbed in soil, and measured variations insorption capacity of a range of soil minerals. Murrayand Parks (1980) measured sorption of poliovirus onoxide surfaces in soil, showing that the ionic strength,pH and composition of the soil solution had a majoreffect. Vilker and Burge (1980) and Vilker (1981) havedescribed a mass transfer model of transport of virusesthrough soil which includes sorption according to theFreundlich isotherm equation, but for sorption by thestatic soil matrix only.

6.2.2. Surface charge effects

Charged colloids within soils originate from a multi-tude of sources, ranging from small mineral clays,organic breakdown products, to small living organismssuch as coliforms or viruses. These colloids can often beconsidered as behaving like charged particles, interact-ing strongly with soils through a variety of surface


reactions. An important feature of colloid transport isthus the nature and occurrence of surface charge in soils(Brady & Weil, 1996).

A negative soil surface charge in inorganic matter isthe result of isomorphic substitution in the matrix orbonds broken at the surface of oxides, etc. withdissociation of ions passing into solution, while fororganic matter a negative charge is produced when e.g.hydroxyl groups become attached to polymer chains.Apart from the first case of isomorphic substitution,these reactions are usually pH dependent.

6.2.3. Diffuse double layer

Physiochemical surface reactions affecting colloidsinclude the filtration processes discussed later andthe concept of the ‘diffuse double layer’ (DLL). Thislayer arises from the finite spatial arrangement of ionsdissociated from a charged surface. Such ions aresubjected to two opposing forces: an adsorptionforce from the electric field generated by the chargedsurface, and a diffusive force from concentrationgradients acting to equilibrate the ion concentrationsthroughout the solution (Brady & Weil, 1996). Ions in the ‘bulk’ solution, outside of the DLL, arenot influenced by the charges of the soil solids.Consideration of the DDL facilitates our under-standing of the behaviour of colloidal material withinsoils.

The original Gouy–Chapman theory of DDL, men-tioned in Shaw (1999), assumes that the distribution ofions around a charged surface follows the Boltzmann-Maxwell distribution and the resulting electric potentialis determined by the Poisson equation. According to thistheory, there will be an exponential accumulation ofcations within the layer when there is a negative chargeon the surface, and the anionic concentration willdecrease from the bulk solution to the solid surface.There are several more complex theories for DDLbehaviour involving different ion and solid surfacedistributions (Shaw, 1999), but the essentials areencapsulated by the Gouy–Chapman theory.

An important characteristic of a DDL is the thick-ness, which can be determined by the three variables,logarithm of the bulk soil solution concentration,valence of the cations and the soil water content. Thelayer thickness is large (10 mm) for monovalent cationscombined with low electrolyte concentrations undersaturated conditions. Correspondingly this layer is thin(0.1 mm) for multi-valent ions, high electrolyte concen-trations and unsaturated conditions. Within the DDL,charged colloids, nutrients, etc. can be held, and releasedslowly when needed by cation exchange to the bulksolution.

7. Transport, straining and filtration of colloidalcontaminants in soil

Following their description of types and sizes ofmicroorganisms (Section 4.3), the review by Mawdsleyet al. (1995) continues to discuss factors influencingmicrobial movement (both horizontal and vertical)through the soil, including soil type, soil water content,soil water flow, intensity and type of rainfall, surfaceproperties of microorganisms and presence of plantroots. They quote literature sources which suggest thatsoil pore size will significantly affect movement ofbacteria and protozoa through the soil, but not virusesbecause of their smaller size, and that movements will begreater in coarse-textured than in fine-textured soils.They quote a paper by Griffin and Quail (1968) thatmovement of rod-shaped bacteria will be severelyrestricted in pores of less than 1–1�5 mm diameter. Theyalso discuss adsorption of microbes onto soil material(in a similar manner sorption of phosphorus orpesticides), particularly the higher sorptive capacity ofclay and organic material compared to other soilparticles. Sorption is particularly important for viruses,being the main mechanism for their retention in soil(Goyal & Gerba, 1979; Bitton, 1975). However,Mawdsley et al. (1995) regard high contents of clayand organic material in soil as a factor retardingmovement of microbes, ignoring the possibility ofsorption onto mobile colloids which move with the soilwater. They also mention the importance of macroporesfor transport of protozoal cysts in particular because oftheir largest size. Further studies reviewed by Mawdsleyet al. (1995) indicate increased movements of bacteriaand viruses in soils with high water contents, includingdetection of bacteria in water flowing out through fielddrains when animal manure is spread at times of highrainfall. Both Evans and Owens (1972) and Patni et al.(1984) observed that rainfall increased concentrations ofbacteria in drains from fields with grazing animals orafter slurry spreading, the higher mobility of bacteria inwetter soil more than offsetting any dilution effect of therainfall.

Vinten and Nye (1985) discuss transport and deposi-tion of colloidal particles in soil by a number ofmechanisms (Fig. 5), while other authors includingMcDowell-Boyer et al. (1986), Hunt et al. (1987),McCarthy and Zachara (1989) and Ibaraki and Sudick-ey (1995a) discuss transport through ‘porous media’ inrelation to contaminants reaching groundwater viavarious subsurface layers. Corapcioglu and Haridas(1984) discuss these processes theoretically for micro-organisms as the contaminant. All these authors quotethe extensive literature on filtration (in relation toindustrial rather than agricultural applications and

Fig. 5. Particle capture mechanisms. From Vinten and Nye,(1985); F, flow streamline; D, diffusion; I, interception; ST,

straining; SD, sedimentation


covering filtration of air as well as liquids), such as Ives(1975) and Tien and Payatakes (1979).

8. Colloid capture processes

8.1. Transport equation

Assuming steady-state saturated flow conditions, thetransport of colloidal particles through granular porousmedia can be described by an advection–dispersiontransport equation with terms for colloid deposition andrelease (Kretzschmar et al. 1999):

@c

@t¼ Dh

@2c

@z2� vp

@c

@z�

rb

y@sm

@tð1Þ

and

rb

y@sm

@t¼ kdc �

rb

ykrsm ð2Þ

These equation describe the evolution in time t of thecolloidal mass or number concentration c in suspension,

and the colloidal amount deposited per unit mass of theporous matrix sm. Here, Dh is the hydrodynamicdispersion coefficient for colloidal particles, rb thematrix bulk density, y the porosity and np the averagevelocity of colloidal particles over a distance z. Thecolloidal deposition and release rate coefficients aregiven by kd and kr respectively.

8.2. Straining

Capture by straining, where a colloidal particle isphysically larger than a pore or pore restriction it isattempting to pass through, is discussed in detail in Part2 (McGechan, 2002a).

8.3. Restriction on colloid movements by filtration

8.3.1. Introduction

McDowell-Boyer et al. (1986), Hunt et al. (1987) andIbaraki and Sudickey (1995a) describe a range ofcapture processes as ‘filtration’, including retention ofcolloidal particles through attraction to porous materialsurfaces, fracture surfaces and trapping in pores.Referring to the literature on filtration, they describesurface (mechanical) filtration as occurring when colloi-dal particles are too large to flow into a porous mediumand consequently form a surface mat (cake) over theporous material; however, other authors call this processstraining (as discussed above and in Part 2, McGechan,2002a). Deep bed filtration is described as occurringwhen colloids are small enough to enter the porousmedia and are transported and deposited within it. Twotypes of deep bed filtration are also described: mechan-ical filtration of large particles in the matrix (whichagain is in effect straining as discussed in Part 2) andphysicochemical filtration of small particles throughmolecular forces. For industrial purposes, deep bedmechanical filtration is not a practical option as the filterrapidly becomes clogged, but the theory is neverthelessdiscussed by Tien and Payatakes (1979), and bothforms of deep bed filtration are relevant to filtration bysoil. Equations which include the filtration coefficient lf

are appropriate to either of the deep bed filtrationprocesses.

Ives (1975) describes physicochemical deep bedfiltration as being the capture of fine particles insuspension by filtration through a porous medium,and divides the process into three steps: transport,attachment and (in some situations only) detachment.Particles tend to be mainly transported with the flowstreamlines, but to become attached they must moveacross the streamlines for one or more reasons


including: interception where the particle passes closerthan one particle radius from the solid surface andelectrostatic forces come into play; inertia where thestreamline takes a curved path around an obstructionbut the particle tends to keep going in a straight line;gravitational forces causing sedimentation; diffusioncaused by bombardment by water molecules undergoingBrownian motion; and hydrodynamic action where oneside of the particle is in a faster moving streamline thanthe other causing the particle to rotate and inducingpressure differences. Attachment can take place whenparticles intercept or come into close proximity with thepore surface due to a combination of electrostatic forcesand ‘London–van der Waals’ forces. Kretzschmar et al.(1997) have described the process of colloid filtration insoil, where particles are much smaller than the pores inwhich they become trapped. Vinten (1981) also studiedthis process, describing details of the forces leading toattachment. The extent of all the filtration mechanismsdepends on a range of factors including the relative sizesof particles and pores. Ives (1975) concluded thatsedimentation is likely to be unimportant since sedi-mentation velocities can be calculated as beingextremely low for clay particles due to their smalldiameter; also, sedimentation will be almost zero forbiological pollutants which have a density near to thatof water.

8.3.2. Basic filtration equations

The basic equation used in all filtration theory torepresent removal of particles (mass concentration c)with distance z was first empirically observed by Iwasaki(1937) to be a first-order relationship with suspendedparticle concentration:

�@c

@z

� �¼ lf c ð3Þ

Subsequent studies have shown that the filtrationcoefficient lf is a function of the deposited particles(Hunt et al., 1987) and various other factors. Vinten andNye (1985) suggest that these factors include packinggeometry, particle size, flow rate, electrolyte composi-tion and surface potentials of both particles and poresurfaces (as reviewed by Spielman, 1977). Assuming thattransport by dispersion can be neglected, then in termsof the deposition rate coefficient, kd, the filtrationcoefficient lf can also be expressed as lf= kd/vp.

Classical particle capture theories can be used toidentify some of the above dependencies. These theoriesfocus on collection by a representative element such asspherical porous medium grains. Interpretation offiltration experiments then requires relating capture bya representative element to the assemblage that com-prises the porous matrix (Spielman, 1977). If we

consider a bed of collecting grains perpendicular to themean flow (of velocity U), the change in suspendedparticle number concentration dcn over depth dz is givenby:

�U dcn ¼ I6apd3

p

!dz ð4Þ

where: 6a=pd3p is the ratio of the volume fraction of

grains in the array to the grain volume (diameter dp),and the rate of particle capture per grain is given by I.The dimensionless grain capture efficiency is conven-tionally defined as Z ¼ 4I=pd2

p Ucn and the clean bedfiltration coefficient by l0 ¼ 6aI=pd3

p Ucn: A clean bedfiltration coefficient assumes that particle retentionoccurs on a clean medium without deposited particlesaltering the medium surface or fluid flow.

Both McDowell-Boyar et al. (1986) and Hunt et al.(1987) quote a semi-empirical equation, again based onclassical particle capture theory, from Tien and Paya-takes (1979) for the clean bed filtration coefficient l0 fora filter consisting of stationary spherical ‘collectors’.This has three terms, taking account (respectively) ofparticle capture by Brownian motion, interception andgravitational sedimentation, with size dependence in allthree terms:

l0 ¼3

2

1� p0ð Þdm

4A1=3s

Udm

Dp

� ��2�3

þ0�56As

A

md2p U

!1=824

�dp

dm

� �15=8

þ2�4� 10�3As

vs

U

� �1�2 dp

dm

� ��0�4#

ð5Þ

where: p0 is the clean bed porosity, U is the fluidvelocity, m is the fluid dynamic viscosity, and dm and dp

are the collector and mobile particle diameters. Theparameter correcting particle capture As by a singleisolated collector for capture within a packed porousmedium is given by

As ¼1� P5

1� 32P þ 3

2P5 � P6

ð6Þ

and

P ¼ ð1� p0Þ1=3 ð7Þ

The first term (Brownian motion) includes the particlediffusivity Dp given by

Dp ¼ kT=3p mdp ð8Þ

where: k is the Boltzman constant (for waterk=2� 10�20 J) and T is the absolute temperature. Inthe second term (interception), A is the Hamakerconstant from London–van der Waals’ attractive forceequations. The third term (sedimentation) includes the


particle settling velocity vs given by:

vs ¼g

18mrp � rf

� �d2

p ð9Þ

where: g is the acceleration due to gravity and rp and rf

are the particle and fluid densities in kg m�3. Wan et al.(1995) describe the mathematics of sedimentation withan equation similar to Eqn (9).

Johnston (1982) combined Poiseuille’s Law withfiltration theory as a method of determining thespecification of filters to achieve a specified degree offiltration efficiency. However, it should be noted thatfiltration theory such as presented by these authorsapplies to a much less dense porous medium than soil.Changes in hydraulic conductivities of soils due to wasteapplications are discussed in Section 9.

8.3.3. Adaptation of filtration equations for soils

Basic filtration equations have been applied to soils,particularly in relation to macropores, by Chen andWagenet (1992a, 1992b), but in this case relating tosolute rather than particulate transport. Jarvis et al.(1999) have described an adaptation of the MACROtwo-domain contaminant transport model (Jarvis, 1994)to represent colloid-facilitated contaminant transport.Filtration is treated differently in the macropore andmicropore (soil matrix) zones. In the micropores, thestandard filtration equation [Eqn (3)] is applied, forwhich a value of the filtration coefficient lf must bespecified. In the macropores, the filtration equation isadapted to take account of the flow velocity, asfollows:

F ¼ lref nnf

ref v1�nf cy ð10Þ

where: F is the filtration sink term in g m�3 h�1, lref is areference filtration coefficient in m�1, nf is an empiricalexponent, v is the pore water velocity in m h�1 and vref isthe pore water velocity in m h�1 at which lref ismeasured. Determination of parameters for this equa-tion has been described by Villholth et al. (2000) andMcGechan et al. (2002).

8.4. Colloid motility effects

Camesano and Logan (1998) showed that motile andnon-motile status has an important influence onbacterial transport. At low fluid velocities, colloidfiltration theory predicts the number of collisions willincrease, leading to greater retention. However formotile cells, the retention was observed to decrease.They concluded that swimming cells are able to avoidsticking to soil grains at low velocities, but at highvelocities the attachment process is unaffected.

9. Changes in soil characteristics over time due to colloiddeposition

9.1. Clogging of pores due to colloid capture

Deep bed filtration theory (Section 8.2.2) such aspresented by Sakthivadivel et al. (1972) and Tien andPayatakes (1979) takes account of a gradual increase inresistance to fluid flow over time due to particledeposition (clogging up of the filter). Similarly, cloggingof soil pores, leading to reductions in hydraulicconductivity, is an issue discussed by a number ofresearchers, e.g. Daniel and Bouma (1974). Jenny andSmith (1935) describe the formation of a low-conduc-tivity clay pan in subsoil due to deposition of colloidalclay particles mobilised from surface layers. A problemof reduced conductivities in soil used for disposal (andpurification) of water containing contaminants in wasteshas been investigated by Rice (1974), Daniel and Bouma(1974) and Vinten et al. (1983a, 1983b, 1983c). The workof Rowell et al. (1969) and Frenkel et al. (1978) ondispersivity of clay soil particles (as discussed inSection 5), also showed reduced hydraulic conductivitiesof soils due to clogging of pores by these dispersedparticles.

9.2. Colloid deposition dynamics

In determining the dynamics of colloid transport, anaccurate description is required of the transient rate ofcolloid deposition onto the grains (collectors) making upthe porous material. The initial stage of filtration ischaracterised by a constant deposition rate whichbecomes transient as colloidal particles accumulate onthe collectors. This transient rate has been observed toincrease or decrease depending upon the solutionchemistry and chemical characteristics of the colloidsand collector grains (Ryan & Elimelech, 1996).

The dynamics of colloid deposition onto granularporous media has been described successfully byrandom sequential adsorption (RSA) mechanics(Adamczyk et al., 1992; Johnson & Elimelech, 1995).Such models are applicable to irreversible particledeposition onto stationary surfaces, with monolayercoverage maintained by prohibiting particle contact,surface diffusion and surface detachment. The kineticrate equation describing the deposition process has beengiven by Johnson and Elimelech (1995) as

@s

@t¼ ae kt p d2

p cn B sð Þ ð11Þ

where: s is the fraction of collector surface covered byparticles, ae is the particle attachment efficiency, kt is theparticle transfer coefficient, dp is the spherical particle


diameter and cn is the number concentration of colloidalparticles in suspension. The colloid quantity depositedper unit mass sm can be related geometrically to s suchthat

sm ¼f ymc

pd2p pb

s ð12Þ

where: f represents the specific surface area in m2 m�3 ofthe porous medium and mc an average mass for thecolloidal particles in kg. The dynamic blocking functionB sð Þ account for excluded area effects of depositedparticles hindering subsequent attachment of particles.For initially bare collector surfaces B sð Þ ¼ 1; with thefunction declining until the jamming limit occurs wherethe maximum coverage smax is attained and B sð Þ ¼ 0:

This function can be based on either the Langmuiradsorption model or RSA mechanics. For a linearLangmuiran blocking function this gives

BðsÞ ¼smax � s

smax

¼ 1� bs ð13Þ

where b ¼ 1=smax; the excluded area parameter which isa measure of the collector surface area blocked fromsubsequent deposition by a deposited particle. For theRSA dynamic blocking function, expressions can bedetermined for a hard sphere captured onto a flatcollector surface, with a jamming limit s1: A generalexpression for any collector geometry and a soft particledeposition is given by Johnson and Elimelech (1995):

B sð Þ ¼

1� 4s1bs þ 3:308 s1bsð Þ2þ1:4069 s1bsð Þ3

for s40:8smaxð Þ

smax � sð Þ2s2j

3

for 0:8smax5s4smaxð Þ

8>>>>>>><>>>>>>>:

ð14Þ

where sj is the jamming limit slope. This has a value of0�236 for hard spheres depositing on flat surfaces, and isdependent upon solution chemistry and hydrodynamicconditions (Johnson & Elimelech, 1995).

As shown in Eqns (13) and (14), a declining colloiddeposition rate is generally attributed to the reducedavailability of deposition sites on the collector grains asdeposited colloids exclude others from their immediatevicinity. Experimental investigations (Johnson & Elim-elech, 1995; Jewett et al., 1995; Johnson et al., 1996)demonstrate that the excluded area parameter increasesas the ionic strength of the electrolyte decreaseslogarithmically, thus indicating that the area blockedis influenced strongly by the thickness of the DDL.These studies show the very large changes in ionicstrengths needed to significantly influence transportconditions. For the case of an increasing depositionrate, multi-layer coverage of the collectors by deposited

colloids is assumed to occur. This phenomenon istermed ‘ripening’, and arises because previously depos-ited colloids provide a more favourable surface foradhesion than the original soil (Liu et al., 1995;Camesano & Logan, 1998).

9.3. Shear strength effect

Hunter and Alexander (1963) considered that theshear strength of a sol (a colloid suspension in water) ofkaolinite (very fine clay soil particles) had a significanteffect on the ability of the sol to pass through a soilcolumn, which was not attributable to clogging of soilby colloidal particles.

10. Experimental investigations into colloid transport andcapture

There are a number of reported experiments in whichthe passage of colloids or colloidally attached contami-nants through soil has been measured. These havegenerally taken the form of laboratory column experi-ments with water containing colloids and contaminantsbeing passed through samples of soil (or sometimesother porous media). In most instances, materialemerging from the bottom of the column has beenanalysed to produce breakthrough curves for the colloidor contaminant, e.g. Lahav and Tropp (1980), Kretzsch-mar et al. (1997) and Hesketh et al. (1998).

10.1. Column experiments with colloids

Lahav and Tropp (1980) passed suspensions ofsynthetic latex microspheres with diameter 0�12 or0�21 mm through real soil samples observing materialemerging from the bottom of the column. They alsoexamined the soil columns after the experiment, noting ahigh concentration of trapped spheres in surface layers.Seta and Karathanasis (1997) compared characteristicsof suspended soil-derived colloids in water emergingfrom the bottom of a column with those in water appliedat the top, for several soils. They observed more colloidtransport in soils with higher macroporosity, and alsoionic charge effects dependent on the pH values of thecolloid suspension. Toran and Palumbo (1992) com-pared transport of colloids through columns both withand without artificially created ‘fractures’ (similar tomacropores). They concluded that chemical effectsaccounted for a high proportion of colloid capture,since particles were substantially smaller than the pores.Coutts et al. (1986a, 1986b) studied colloid generation at


the surface by rainfall impact, using a radioactive tracerto follow colloid movements.

Hu and Brusseau (1995) carried out experimentspassing organic solutions through porous media (notsoil). Solutions with different sizes of molecules wereused, the larger being of similar size to some colloids.

10.2. Column experiments with radioactive and chemical

contaminants

Buddemeier and Hunt (1988) carried out columnexperiments with radionucleides, concluding that trans-port generally took the form of attachment to otherwiseharmless soil-derived colloidal material. Champlin andEichholz (1968) had concluded in similar experimentsthat colloid attachment accounted for most of thetransport even when a radionucleide was very soluble.Jury et al. (1986) experimented with the moderatelysorbed herbicide naprapamide, concluding that colloid-facilitated transport and macropore flow were importantprocesses. De Jonge et al. (1998) carried out columnexperiments with the pesticide prochloraz, concludingthat some but not all was transported attached tocolloids, and also that macropores had an importantrole in transport of both solute and colloids. Gonzalezand Ukrainczyk (1999) concluded that sorption ontostatic soil components would cause herbicide to betrapped rather than transported. Van der Lee et al.(1994) tested their model (Section 11.1) in columnexperiments, commenting on the lack of informationabout colloid sorption parameters.

10.3. Column experiments with microorganisms

A number of soil column experiments have beenreported for biological contaminants. White (1985a) andSmith et al. (1985) describe adding suspensions of E. coli

bacteria in column experiments with undisturbedsamples of a range of soils, while White (1985b)discusses the importance of macropores for the resultsobtained. Abu-Ashour et al. (1998) also worked with E.

coli bacteria in column experiments, concluding that soilwater content and the presence of macropores had themost pronounced effect on microorganism transport.Other experiments on transport of bacteria through soilare described by Gannon et al. (1991) and Tan et al.(1992), while Wan et al. (1995) describe bacterialsedimentation experiments using soil columns. McMur-ray et al. (1998) carried out laboratory experiments withpoultry manure spread over intact soil samples subjectedto artificial rain. Water emerging from the bottom of theblocks was analysed for faecal coliforms, and afterwardsthe soil blocks were analysed destructively to determine

the distribution of deposited faecal coliforms. Othercolumn experiments with viruses have been reported byBitton et al. (1974), Dizer et al. (1984) and Lance et al.(1982), while Jin et al. (2000) and Chu et al. (2000)respectively demonstrated the importance of mineralcolloids and buffer solutions for virus transport. Similarexperiments with bacteria have been reported byWollum and Cassel (1978), McCoy and Hagedorn(1979), Trevors et al. (1990), Van Elsas et al. (1991)and Paterson et al. (1993). Column experiments withcryptosporidium parvum oocysts have been reported byMawdsley et al. (1996a, 1996b) and Brush et al. (1999).Bitton et al. (1979) reviewed a number of studies of thetransport of viruses through soil, comparing resultsfrom column experiments with those obtained in thefield. Vilker (1981) has similarly listed a number ofearlier experimental studies of microorganism transport,both with laboratory columns and field soil beds.

10.4. Enhanced colloid migration and other processes

affecting transport

Seta and Karathanasis (1996) evaluated the transportof metolachlor through intact soil columns. Colloidrecovery in the drainage effluent ranged from 54 to 90%,and enhanced metolachlor transport by 22–70%,depending upon colloid type and mobility. Johnsonand Logan (1996) measured the enhanced transport ofbacteria in porous media. Dissolved and sedimentorganic matter were independently added to quartz inmini-columns and retention efficiencies measured. Thelargest decrease in bacterial retention (60%) wasassociated with sediment organic matter in the absenceof dissolved organic matter. Jacobsen et al. (1997)carried out infiltration experiments on intact sandy loamsoil columns, with incident colloid suspensions. Asignificant transport of particles through macroporeswas observed at two soil depths. The particle size in thecollected effluent generally decreased over time follow-ing an irrigation event, but with a relatively constantconcentration of particles of size510 mm. This variationin particle size of the effluent can be explained by thedifferent absorption capacities and exposure to hydrau-lic forces, and by mechanical entrapment. Karanthana-sis (1999) determined the migration rates of copper andzinc in the presence of various water-dispersible soilcolloids (suspensions of montmorillonitic, illitic andkaolintic, with a range of surface properties). Usingundisturbed soil columns (clay, silty clay), the presenceof colloids typically enhanced metal transport by 5–50-fold over the control treatment with no colloids. Zincwas consistently more mobile than copper, with highesttransport occurring with colloids of high negative


surface charge and organic content, and the lowest bycolloids with large particle size, low negative surfacecharge and high iron- and aluminium-hydroxyoxidecontents.

Camesano et al. (1999), demonstrated the blockingeffect (see Section 9.2) for several bacterial colloidalspecies in packed-bed soil column experiments, withexcluded areas ranging from 11 to 24% for Pseudomo-

nas putida. As a practical method for enhancing themobility of colloids in soils, Seaman and Bertsch (2000)used soil column leaching experiments to evaluate theuse of a cationic surfactant as a chemical additive toblock negatively charged deposition sites. Leaching thesurfactant through an iron-oxide-rich column of aquifersediment resulted in the selective dispersion and trans-port of iron-oxide colloids with little column pluggingobserved.

10.5. Hydrophobic and hydrophillic effects

In unsaturated sand column experiments, Schaferet al. (1998) determined that retention of hydrophobicand hydrophillic bacteria is markedly increased at lowwater contents. Strong retention is attributed to theaccumulation of bacteria at the air–water interface, asthe colloidal particles have a high affinity compared withthe solid surface. Trapping of bacteria by the air–waterinterface is thus an important process controllingmobility in unsaturated soils.

For bacteria (Gram-negative rods) moving throughsandy soils, McCaulou et al. (1994) showed thatattachment takes approximately 1 h, and is usuallyreversible, but detachment can take up to several days.Hydrophillic bacteria has slower attachment and de-tachment rates than hydrophobic bacteria, indicatingthat they could move further before being removed byattachment and would be resuspended at a slower rate.Transport studies of Pseudomonas fluorescens andBacillus subtilis bacteria through laboratory columnspacked with silica beads (Kinoshita et al., 1993) showedthat both species were highly retarded with between 20and 94% reductions in initial concentrations. Lessretardation was evident at lower pH and producedlittle change in the electrostatic charge of the bacteria,with the consequence that it was relatively unimportantin determining bacterial retardation. The transportof phages in sandy soils (Kinoshita et al., 1993)showed the predominant effect of hydrophobicity,with a high removal efficiency for hydrophobicphages. Detachment was slow, with an increase inpH having a moderate enhancing effect. Hydrophilicphages tend to act conservatively in low-carbonsandy soils.

10.6. Experiments on colloid deposition

Various experiments have been carried out toinvestigate the interplay between soil water dynamicsand DDL interactions, and their effect on the dynamicsof particle deposition and blocking, as described inSection 9.2. Flow intensity (Camesano & Logan, 1998;Adamczyk & Weronski, 1999), particle sizes (Adamczyket al., 1992; Bohmer et al., 1998) and soil ionic strength(Ryde et al., 1992; Liu et al., 1995; Gross & Logan,1995; Gross et al., 1995) uniquely determine the rate ofblocking and the maximum surface coverage attained oncollectors. Ko and Elimelech (2000) simultaneouslyexamined the above three factors of flow intensity,particle sizes and soil ionic strength, using suspensionsof colloidal latex particles and packed quartz grains incolumn experiments. Their results suggest that the shearcomponent of the fluid flow around collector grainscreates a shadow zone on the collector surfaces, with adeclining gradient of deposited particles. In this zonedeposition rates are substantially reduced, by an extentdetermined by the hydrodynamic interactions andelectrostatic DDL repulsion. Increasing the flow velocityand particle size, and decreasing the solution ionicstrength, result in a larger shadow zone and hence areduced maximum attainable surface coverage ofdeposited colloids.

10.7. Experimental determination of filtration coefficient

The only known studies in which column experimentshave been used to estimate the filtration coefficient lf arepresented by Vinten and Nye (1985) and Kretzschmaret al. (1994). By this means, Vinten and Nye (1985)estimated lf for clay particles (the most importantmineral carrier colloid) labelled with 14C-paraquat, alabel with a very low tendency to desorb into solution,so colloid filtration could be measured independentlyfrom the sorption process.

11. Models of colloid-facilitated contaminant transport

11.1. Models representing transport processes in column

experiments

Enfield and Bengtsson (1988) presented equations fora model (simulating a column experiment) of transportof a hydrophobic contaminant assisted by the presenceof sorbing macromolecules of another substance. Littonand Olsen (1993) use an adaptation of the filtrationequation with an ‘attachment efficiency’ factor (similar


to the filtration coefficient) when testing porous mediafor extracting colloids during wastewater treatment. Vander Lee et al. (1994) describe a model of transport of apollutant sorbed onto a sorbing colloid in a homo-geneous non-sorbing porous medium. Corapcioglu andKim (1995) have described a contaminant transportmodel for the situation where bacteria act as the mobilecolloids onto which contaminants are sorbed. Ouyanget al. (1996) reviewed colloid-enhanced transport modelsand included a section on measurements of the transportof attached chemicals. Knabner et al. (1996) havedescribed a model of reactive solute transport withsorption to mobile and immobile sorbents. They test thismodel using breakthrough data for various contami-nants from column experiments (Totsche et al., 1996).Germann and Beven (1981) describe a statistical modelfor separate representation of macropores and micro-pores, as an alternative to the two-domain adaptation ofthe capillary bundle model approach described by Bevenand Germann (1981). Stagnitti et al. (1999) describe amodel where heterogeneity of soil conductivity (large ina soil with extensive macropores) is described by amathematical distribution function.

11.2. Field scale models

Mills et al. (1991) describe a model (called COMET)of colloid and contaminant processes in subsurface soillayers, with separate equations for the upper unsatu-rated zone and the lower saturated zone. COMET wasintended for investigating the use of land (without fielddrains) for disposal of wastes by surface spreading,where the concern is contamination of the underlyingaquifers. Another model of colloid facilitated transportin a fractured porous medium has been described byIbaraki and Sudicky (1995a). It has been applied to thetransport of contaminants down to deep subsoil layersin clay and sandstone rocks (Ibaraki & Sudicky, 1995b).

The most comprehensive field-scale model incorpor-ating most of the important processes relating tocolloid-facilitated contaminant transport through soilis MACRO. This model simulates contaminant trans-port with ‘dual-porosity’ allowing for different contami-nant concentrations in the soil matrix and themacropores. Pollutant flows both to surface waters viafield drains and to groundwater (aquifers) by deeppercolation are represented. Earlier versions (Jarvis,1994) simulated solute transport with the option ofsorption onto the static soil matrix only. In the mostrecent version (Jarvis et al., 1999), the option of colloid-facilitated contaminant transport has been added, withthree-phase representation of contaminant transport asdescribed in Section 2 (contaminants in solution, sorbed

onto the static soil matrix and sorbed onto mobilecolloidal particles). Two simulation runs must be carriedout for each scenario, the first representing transport ofthe carrier colloid only, the second representing thecontaminant in each of the three phases. In the first run,colloids are generated by detachment caused by rainfallimpact (as discussed in Section 5) or added in ‘irrigation’water (a procedure which can also be used to representspreading of animal manure slurry which contains largequantities of contaminated colloidal material). Colloidsare filtered in both macropores and micropores,according to the equations listed in Section 8.2.3.Colloids are excluded from (but not trapped in) aproportion of the soil pore space (the smallest pores), aphenomenon described by Kretzschmar et al. (1997). Inthe second run, the contaminant is applied in irrigationwater (as a solute, or sorbed onto colloids added in thefirst run). Isotherm equation (Freundlich) parametersare specified for both the static soil matrix and themobile colloid, to give the three contaminant phases asdiscussed in Section 2. MACRO was developed primar-ily for modelling pesticide transport, but it includes mostof the features required for transport of phosphorus andbiological microorganisms. An application for the studyof phosphorus pollutant flows following animal slurryspreading has been described by McGechan et al.

(2002). This application represents the only one out ofa number of field-scale phosphorus dynamics models (asreviewed by Lewis & McGechan, 2002) to includerepresentation of through soil colloid-facilitated trans-port of phosphorus.

12. Conclusions

Literature reviewed in this paper indicates that manycontaminants are transported in colloidal form throughthe soil to surface water or groundwater. Thesecontaminants include phosphorus, pesticides and otheragrochemicals, plus a range of biological microorgan-isms. With the exception of the largest category ofmicroorganism, protozoa, most such contaminants aretransported mainly by adsorption onto otherwiseharmless mobile colloidal material such as clay particlesor soil organic matter. There are potential impedimentsto movement of colloids through soil, and these can besubdivided into two main classes: straining (sometimescalled ‘physical filtration’ or ‘mechanical filtration’)where a particle has a dimension larger than the porethrough which it is trying to pass so it becomes trapped,as discussed further in Part 2 (McGechan, 2002a,2002b); true filtration covers a range of mechanismswith the common feature that particle dimensions aremuch smaller than the pores. Such filtration mechanisms


include interception, diffusion and sedimentation,processes akin to those described in the extensiveengineering literature on deep bed filtration. Sorptiononto static components of the soil matrix plays a partin restricting the movement of reactive contaminantsthrough the soil. However, such contaminantsalso readily become sorbed onto colloidal particles,which if mobile aggravate polluting losses to theenvironment.

Capture processes can be represented in models by asimple equation with a filtration coefficient, the value ofwhich can be determined experimentally. However, outof numerous reported studies using column experimentsto measure colloid or contaminant transport throughsoil, very few lead to derivation of such a filtrationcoefficient. The importance of macropore flow, whichleads to rapid unrestricted transport of contaminantcarrying colloids, is widely reported in literature oncolumn experiments and other studies. Such transportdepends on the macropores being water filled, requiringnear-saturation soil water contents, conditions commonin Northern Europe in winter.

There are a few existing models of colloid-facilitatedcontaminant transport processes, both for columnexperiments and for the field situation. They generallyinclude the simple filtration equation (or a slightvariation on it) with sorption of contaminants ontocolloids and static soil components, and separateequations (or coefficient values) for macropores andmicropores where macropore flow is considered. Thematerial presented in this review provides backgroundinformation for further development of a field-scalemodel representing colloid-facilitated transport of arange of chemical and microbiological contaminants.

Understanding contaminant–mineral interactions atthe molecular level has also been shown to be important,and extensive experimentation on individual mineralsystems has provided a foundation for knowledge on thesubject. However, investigations on model mineralsystems cannot be readily extrapolated to complexmineral assemblages in natural systems. Recent studieson phyllosilicate and metal oxohydroxide mineral soilshave elucidated the role of less abundant mineral andorganic substrates as surface chemical modifiers. In suchsystems the surface chemical modifiers control colloidgeneration and transport processes, as well as thetransport of solutes and ionic tracers. Surface chargingmechanisms operating in these complex mineral assem-blages are difficult to predict using only surfacereactivities and other characteristics of their individualmineral components. It is likely that a complete under-standing of the surface chemistry of complex mineralassemblages will be required to assess accurately theenvironmental fate of contaminants.

Acknowledgements

The Scottish Executive Environment and RuralAffairs Department provided funds to carry out thework.

References

Abu-Ashour J; Joy D; M Lee H; Whiteley H R; Zelin S (1998).Movement of bacteria in unsaturated soil columns withmacropores. Transactions of the ASAE, 41, 1043–1050

Adamczyk Z; Siwek B; Zembala M; Weronski P (1992).Kinetics of localized adsorption of colloid particles.Langmuir, 8, 2605–2610

Adamczyk Z; Weronski P (1999). Application of the DLVOtheory for particle deposition problems. Advanced ColloidInterface Science, 83, 137–226

Atteia O; Kozel R (1997). Particle size distributions in watersfrom a karstic aquifer: from particles to colloids. Journal ofHydrology, 201, 102–119

Barrow N J (1973). Relationship between a soil’s ability toadsorb phosphate and the residual effectiveness of super-sulphate. Australian Journal of Soil Research, 11, 57–63

Barrow N J (1974). Effect of previous additions of phosphateon phosphate adsorption by soils. Soil Science, 118, 82–89

Barrow N J; Ellis A S (1986). Testing a mechanistic model. V.The points of zero salt effect for phosphate retention, forzinc retention and for acid/alkali titration of a soil. Journalof Soil Science, 37, 303–310

Beven K; Germann P (1981). Water flow in soil macropores. II.A combined flow model. Journal of Soil Science, 32, 15–29

Bitton G (1975). Adsorption of viruses onto surfaces in soil andwater. Water Research, l9, 473–484

Bitton G; Davidson J M; Farrah S R (1979). On the value ofsoil columns for assessing the transport pattern of virusesthrough soils: a critical outlook. Water Air and SoilPollution, 12, 449–457

Bitton G; Lahav N; Henis Y (1974). Movement and retention ofKlebsiella aerogenes in soil columns. Plant and Soil, 40, 373–380

B.oohmer M R; Van der Zeeuw E A; Koper G J M (1998).Kinetics of particle adsorption in stagnation point flowstudied by optical reflectometry. Journal of Colloid Inter-face Science, 197, 242–250

Brady N C; Weil R R (1996). The Nature and Properties ofSoils, Chapter 8, pp 241–270. Prentice-Hall International(UK) Limited, London.

Braithwaite A; Livens F R; Richardson S; Howe M T; GouldingK W T (1997). Kinetically controlled release of uraniumfrom soils. European Journal of Soil Science, 48, 661–673

Brubaker S C; Holzhey C S; Brasher B R (1992). Estimatingthe water-dispersible clay content of soils. Soil ScienceSociety of America Journal, 56, 1227–1232

Brush C F; Ghiorse W C; Anguish L J; Parlandge J Y; Grimes

H G (1999). Transport of Cryptosporidium parvum oocyststhrough saturated columns. Journal of EnvironmentalQuality, 28, 809–815

Buddemeier R W; Hunt J R (1988). Transport of colloidalcontaminants in the groundwater radionuclide migration atthe Nevada test site. Applied Geo-chemistry, 3, 535–548

Burge W D; Enkiri N K (1978). Virus adsorption by five soils.Journal of Environmental Quality, 7, 73–76


Camesano T A; Logan B E (1998). Influence of fluid velocityand cell concentration on the transport of motile and non-motile bacteria in porous media. Environmental Science andTechnology, 32, 1699–1708

Camesano T A; Unice K M; Logan B E (1999). Blocking andripening of colloids in porous media and their implicationsfor bacterial transport. Colloids and Surfaces A: Physico-chemical and Engineering Aspects, 160, 291–308

Champlin J B F; Eichholz G G (1968). The movement ofradioactive sodium and ruthenium through a stimulatedaquifer. Water Resources Research, 4, 147–158

Chen C; Wagenet R J (1992a). Simulation of water andchemicals in macropore soils. Part 1. Representation of theequivalent macropore influence and its effect on soilwaterflow. Journal of Hydrology, 130, 105–126

Chen C; Wagenet R J (1992b). Simulation of water andchemicals in macropore soils. Part 2. Application of linearfilter thoery. Journal of Hydrology, 130, 127–149

Chu Y; Jin Y; Yates M V (2000). Virus transportthrough saturated sand columns as affected by differentbuffer solutions. Journal of Environmental Quality, 29,

1103–1110Corapcioglu M Y; Haridas A (1984). Transport and fate ofmicroorganisms in porous media: a theoretical investigation.Journal of Hydrology, 72, 149–169

Corapcioglu M Y; Kim S (1995). Modelling facilitatedcontaminant transport by mobile bacteria. Water ResourcesResearch, 31, 2639–2647

Coutts J R H; Kandil M F; Nowland J L; Tinsley J (1986a). Useof radioactive 59Fe for tracing soil particle movement. PartI. Field studies of splash erosion. Journal of Soil Science, 19,311–324

Coutts J R H; Kandil M F; Tinsley J (1986b). Use ofradioactive 59Fe for tracing soil particle movement. Part II.Laboratory studies of labelling and splash displacement.Journal of Soil Science, 19, 325–341

Curtin D; Campbell C A; Zentner R P; Lafond G P (1994).Long-term management and clay dispersibility in twohaploborolls in Saskatchewan. Soil Science Society ofAmerica Journal, 58, 962–967

Daniel T C; Bouma J (1974). Column studies of soil clogging ina slowly permeable soil as a function of effluent quality.Journal of Environmental Quality, 3, 321–326

De Jonge L W; Jacobsen O H; De Jonge L W; Moldrup P

(1998). Particle-facilitated transport of Prochloraz in un-disturbed sandy loam soil columns. Journal of Environ-mental Quality, 27, 1495–1503

Dizer H; Naser A; Lopez J M (1984). Penetration ofdifferent human pathogenic viruses into sand columnspercolated with distilled water, groundwater, or waste-water. Applied and Environmental Microbiology, 47,

409–415Enfield C G; Bengtsson G (1988). Macromolecular transport ofhydrophobic contaminants in aqueous environments.Ground Water, 26, 64–70

Evans M R; Owens J D (1972). Factors affecting andconcentration of faecal bacteria in land-drainage water.Journal of General Microbiology, 71, 477–485

Faust S D; Zarins A (1969). Interaction of diquat and paraquatwith clay minerals and carbon in aqueous solutions. ResidueReviews, 29, 151–170

Filip Z (1973). Clay minerals as a factor influencing thebiochemical activity of soil microorganisms. Folia Micro-biology, Prague, 18, 56–74

Floyd R (1979). Viral aggregation: Mixed suspensions ofpoliovirus and reovirus. Applied and Environmental Micro-biology, 38, 980–986

Floyd R; Sharp D G (1978a). Viral aggregation: quantitationand kinetics of the aggregation of poliovirus andreovirus. Applied and Environmental Microbiology, 35,

1079–1083Floyd R; Sharp D G (1978b). Viral aggregation: effects of salton the aggregation of poliovirus and reovirus at lowpH. Applied and Environmental Microbiology, 35,

1084–1094Frenkel H; Goertzen J O; Rhoades J D (1978). Effects of claytype and content, exchangeable sodium percentage, andelectrolyte concentration on clay dispersion and soilhydraulic conductivity. Soil Science Society of AmericaJournal, 42, 32–39

Gannon J T; Mingelgrin U; Alexander M; Wagenet R J (1991).Bacterial transport through homogeneous soil. Soil Biologyand Biochemistry, 23, 1155–1160

Germann P; Beven K (1981). Water flow in soil macropores.III. A statistical approach. Journal of Soil Science, 32,

31–39Gonzalez J; Ukrainczyk L (1999). Transport of nicosulfuron insoil columns. Journal of Environmental Quality, 28,

101–107Govidaraju R S; Reddi L; Kasavaraju S K (1995). A physicallybased model for mobilisation of kaolinite particles underhydraulic gradients. Journal of Hydrology, 172, 331–350

Goyal S M; Gerba C P (1979). Comparative adsorption ofhuman enteroviruses, simian rotavirus, and selected bacter-iophages to soils. Applied and Environmental Microbiol-ogy, 38, 241–247

Griffin D M; Quail G (1968). Movement of bacteria in moist,particulate systems. Australian Journal of BiologicalScience, 21, 570–582

Gross M J; Albinger O; Jewett D G; Logan B E; Bales R C;

Arnold R G (1995). Measurement of bacterial collisionefficiencies in porous media. Water Research, 29, 151–1158

Gross M J; Logan B E (1995). Influence of different chemicaltreatments on transport of Alcaligenes paradoxus in porousmedia. Applied Environmental Microbiology, 61, 1750–1756

Gschwend P M; Wu S C (1985). On the constancy of sediment-water partition coefficients of hydrophobic organic pollu-tants. Environmental Science and Technology, 19, 90–96

Gwo J P; O’Brien R O; Jardine P M (1998). Mass transfer instructured porous media: embedding mesoscale structureand microscale hydrodynamics in a two-region model.Journal of Hydrology, 208, 204–222

Hesketh N; Brookes P C; Addiscott T M (1998). Chlordanetransport in a sandy soil: effects of suspended soil materialand pig slurry. European Journal of Soil Science, 49, 709–716

Hooda P S; Moynagh M; Svoboda I F; Edwards A C; Anderson

H A; Sym G (1999). Phosphorus loss in drainflow fromintensively managed grassland soils. Journal of Environ-mental Quality, 28, 1235–1242.

Hu Q; Brussseau M L (1995). Effect of solute size on transportin structured porous media. Water Resources Research, 31,1637–1646

Hunt J R; McDowell-Boyer L M; Sitar N (1987). Colloidmigration in porous media} an analysis of mechanisms. In:Coupled Processes associated with Nuclear Repositories(Tsang C F, ed), pp 453–472. Academic Press, New York


Hunter R J; Alexander A E (1963). Surface properties and flowbehaviour of kaolinite. Part III: flow of kaolinite solsthrough a silica column. Journal of Colloid Science, 18,

846–862Ibaraki M; Sudicky E A (1995a). Colloid-facilitated contami-nant transport in discretely fractured porous media 1.Numerical formulation and sensitivity analysis. WaterResources Research, 31, 2945–2960

Ibaraki M; Sudicky E A (1995b). Colloid-facilitated contami-nant transport in discretely fractured porous media 2.Fracture network examples. Water Resources Research,31, 2960–2969

Ives K J (1975). The Scientific Basis of Filtration, NATOAdvanced Study Institute Series E, Vol. 2. Noordhoff,Leiden

Iwasaki T (1937). Some notes on sand filtration. Journal of theAmerican Water Works Association, 29, 1591–1602

Jacobsen O H; Moldrup P; Larsen C; Konnerup L; Petersen L

W (1997). Particle transport in macropores of undisturbedsoil columns. Journal of Hydrology, 196, 185–203

Jarvis N (1994). The MACRO model}Technical descriptionand sample simulations. Reports and Dissertations, Vol. 19,51pp. Department of Soil Sciences, Swedish University ofAgricultural Sciences, Uppsala

Jarvis N; Villholth K; Ul!een B (1999). Modelling particlemobilisation and leaching in macroporous soil. EuropeanJournal of Soil Science, 50, 621–632.

Jenny H; Smith G D (1935). Colloid chemical aspects ofclay pan formation in soil profiles. Soil Science, 39,

377–389Jewett D G; Hilbert T A; Bales R C (1995). Bacterial transportin laboratory columns and filters}influence of ionicstrength and pH on collision efficiency. Water Research,29, 1673–1680

Jin Y; Pratt E; Yates M V (2000). Effect of mineral colloids onvirus transport through saturated sand columns. Journal ofEnvironmental Quality, 29, 532–539

Johnston P R (1982). Determining the average pore diameter intubular filter cartridges (candles) from fluid-permeabilitymeasurements. In: Harvesting Theory for Practical Applica-tions, Conference sponsored by The Filtration Society,Vol. II, pp 591–595

Johnson P R; Elimelech M (1995). Dynamics of colloiddeposition in porous media: blocking based on randomsequential adsorption. Langmuir, 11, 801–812

Johnson W P; Logan B E (1996). Enhanced transportof bacteria in porous media by sediment-phase andaqueous-phase natural organic matter. Water Research,30, 923–931

Johnson W P; Martin M J; Gross M J; Logan B E (1996).Facilitation of bacterial transport through porous media bychanges in solution and surface properties. Colloids andSurfaces A: Physicochemical and Engineering Aspects, 107,263–271

Jury W A; Elabd H; Resketo M (1986). Field study ofnapropamide movement through unsaturated soil. WaterResources Research, 22, 749–755

Kaplan D I; Bertsch P M; Adriano D C; Miller W P (1993).Soil-bourne mobile colloids as influenced by water flow andorganic carbon. Environmental Science Technology, 27,1193–1200

Karathanasis A D (1999). Subsurface migration of copper andzinc mediated by soil colloids. Soil Science Society ofAmerica Journal, 63, 830–838

Karickhoff S W; Brown D S; Scott T A (1979). Sorptionof hydrophobic pollutants on natural sediments. WaterResearch, 13, 241–248

Kinoshita T; Bales R C; Yahya M T; Gerba C P (1993).Bacterial transport in a porous medium, retention of bacillusand pseudomonas on silica surfaces. Water Research, 27,1295–1301

Knabner P; Totsche K U; K.oogel-Knabner I (1996). Themodelling of reactive solute transport with sorption tomobile and immobile sorbents. 1. Experimental evidenceand model development. Water Resources Research, 32,

1611–1622Knight B A G; Tomlinson T E (1967). The interaction ofparaquat (1:1-dimethyl 4:4-dipyridylium dichloride) withmineral soils. Journal of Soil Science, 18, 233–243.

Ko C H; Elimelech M (2000). The shadow effect in colloidtransport and deposition dynamics in granular porousmedia; measurement and mechanisms. EnvironmentalScience and Technology, 34, 3681–3689

Kretzschmar R; Barmettler K; Grolimund D; Yan Y D;

Borkovec M; Sticher H (1997). Experimental determinationof colloid deposition rates and collision efficiencies innatural porous media. Water Resources Research, 33,1129–1137

Kretzschmar R; Borkovec M; Grolimund D; Elimelech M

(1999). Mobile subsurface colloids and their role in con-taminant transport. Advances in Agronomy, 66, 121–193

Kretzschmar R; Robarge W P; Amoozegar A (1994). Filterefficiency of three saprolites for natural clay and iron oxidecolloids. Environmental Science and Technology, 28,1907–1915

Lahav N; Tropp D (1980). Movement of synthetic micro-spheres in saturated soil columns. Soil Science, 130, 151–156

Lance J C; Gerba C P; Wang D S (1982). Comparativemovement of different enteroviruses in soil columns. Journalof Environmental Quality, 11, 347–351

Lewis D R; McGechan M B (2002). A review of field scalephosphorus dynamics models (review paper). BiosystemsEngineering Research 82(4), 359–380, doi: 10.1006/bioe.2002.0102

Lieffering R E; McLay C D A (1996). The effect of stronghydroxide solutions on the stability of aggregates andhydraulic conductivity of soil. European Journal of SoilScience, 47, 43–50

Litton G M; Olsen T M (1993). Colloid deposition rateson silica bed media and artifacts related to collectorsurface preparation methods. American Chemical Society,27, 185–193

Liu D; Johnson P R; Elimelech M (1995). Colloid depositiondynamics in flow through porous media: role of electrolyteconcentration. Environmental Science and Technology. 29,2963–2971

Marshall, K C (1971). Sorptive interactions between soilparticles and micro-organisms. In: Soil Biochemistry(McLaren A D; Skujins J J, eds), pp 409-445. MarcelDekker, New York

Matthews R; Preedy N; Heathwaite A L; Haygarth P M (1998).Transfer of colloidal forms of phosphorus in subsurfacehydrological pathways. Proceedings of OECD Workshop‘Practical and Innovative Measures for the Control ofAgricultural Phosphorus Losses to Water’ (Foy R H; DilsR, eds), Antrim

Mawdsley J L; Bardgett R D; Merry R J; Pain B F; Theodorou

M K (1995). Pathogens in livestock waste, their potential for


movement through soil and environmental pollution.Applied Soil Ecology, 2, 1–15

Mawdsley J L; Brooks A E; Merry R J (1996a). Movement ofthe Protozoan Pathogen Cryptosporidium parvum throughthree contrasting soil types. Biology and Fertility of Soils,21, 30–36

Mawdsley J L; Brooks A E; Merry R J; Pain B F (1996b). Useof a novel soil tilting table apparatus to demonstrate thehorizontal and vertical movement of the Protozoan Patho-gen Cryptosporidium parvum in soil. Biology and Fertility ofSoils, 23, 215–220

McCarthy J F; Shevenell L (1998). Processes controllingcolloid composition in a fractured and karstic aquiferin eastern Tennessee USA. Journal of Hydrology, 206,

191–218McCarthy J F; Zachara J M (1989). Subsurface transportof contaminants. Environmental Science Technology, 23,

496–502McCaulou D R; Bales R C; McCarthy J F (1994). Use of short-pulse experiments to study bacteria transport throughporous media. Journal of Contaminant Hydrology, 15, 1–8

McCoy E L; Hagedorn C (1979). Quantitatively tracingbacterial transport in saturated soil systems. Water Airand Soil Pollution, 11, 467–479

McDowell-Boyer L M; Hunt J R; Sitar N (1986). Particletransport through porous media. Water Resources Re-search, 22, 1901–1921

McGechan M B (2002a). Transport of particulate and colloid-sorbed contaminants through soil, Part 2: trapping processesand soil pore geometry (review paper). Biosystems En-gineering, doi:10.1016/S1537-5110(02)00214-3

McGechan M B (2002b). Sorption of phosphorus by soil, Part2: measurement methods, results and model parametervalues (review paper). Biosystems Engineering, 82, 115–130,doi:10.1006/bioe.2002.0068

McGechan M B; Jarvis N J; Hooda P S; Vinten A J A (2002).Parameterisation of the MACRO model to representleaching of colloidally attached inorganic phosphorusfollowing slurry spreading. Soil Use and Management, 18,61–67

McGechan M B; Lewis D R (2002). Sorption of phosphorusby soil, Part 1: principles, equations and models (reviewpaper). Biosystems Engineering, 82, 1–24, doi:10.1006/bioe.2002.0054

McMurray S W; Coyne M S; Perfect E (1998). Fecal coliformtransport through intact soil blocks amended with poultrymanure. Journal of Environmental Quality, 27, 86–92

Miller W P; Baharuddin M K (1986). Relationship of soildispersibility to infiltration and erosion of Southeasternsoils. Soil Science, 142, 235–240

Mills W B; Liu S; Fong F K (1991). Literature review andmodel (COMET) for colloid/metals transport in porousmedia. Gound Water, 29, 199–208

Moore R S; Taylor D H; Reddy M M M; Sturman L S (1982).Adsorption of reovirus by minerals and soils. Applied andEnvironmental Microbiology, 44, 852–859

Moutier M; Shainberg I; Levy G J (1998). Hydraulic gradient,ageing, and water quality effects on hydraulic conductivityof a vertisol. Soil Science Society of America Journal, 62,1488–1496

M.uuller G; Hickisch B (1970). Die Adsorption von Bodenbak-terien an Substrate (Sammelbericht). [The adsorption of soilbacteria on substrates (review paper)]. Zentralblatt Bakteria,124, 271–283

Murray J P; Parks G A (1980). Poliovirus adsorption on oxidesurfaces. Advances in Chemistry Series, 189, 97–133

O’Connor D J; Connolly J P (1980). The effect of concentra-tion of adsorbing solids on the partition coefficient. WaterResearch, 14, 1517–1523

Ouyang Y; Shinde D; Mansell R S; Harris W (1996). Colloid-enhanced transport of chemicals in subsurface environ-ments: a review. Critical Reviews in Environmental Scienceand Technology, 26, 189–204

Paterson E; Kemp J S; Gammack S M; Fitzpatrick E A; Cresser

M S; Mullins C E; Killham K (1993). Leaching of geneticallymodified Pseudomonas fluorescens through intact soilmicrocosms. Biology and Fertility of Soils, 15, 308–314

Patni N K; Toxopeus R; Tennant A D; Hore F R (1984).Bacterial quality of the tile drainage water from manuredand fertilised cropland.Water Research, 18, 127-132

Penrose W R; Polzer W L; Essington E H; Nelson D M;

Orlandini K A (1990). Mobility of plutonium and americiumthrough a shallow aquifer in a semiarid region. Environ-mental Science Technology, 24, 228–234

Pilgrim D H; Huff D D (1983). Suspended sediment in rapidsubsurface stormflow on a large field plot. Earth SurfacesProcesses and Landforms, 8, 451–463

Quirk J P; Schofield R K (1955). The effect of electrolyteconcentration on soil permeability. Journal of Soil Science,6, 163–178

Rahe T M; Hagedorn C; McCoy E L; Kling G F (1978).Transport of antibiotic-resistent Escherichia coli throughwestern Oregon hillslopes under conditions of saturatedflow. Journal of Environmental Quality, 7, 487–494

Rice R C (1974). Soil clogging during infiltration of secondaryeffluent. Journal WPCF, 46, 708–716

Rose C W; Williams J R; Sander G C; Barry D A (1983). Amathematical model of soil erosion and deposition pro-cesses: I. Theory for a plane land element. Soil ScienceSociety of America Journal, 47, 991–995

Rowell D L; Payne D; Ahmad A (1969). The effect of theconcentration and movement of solutions on the swelling,dispersion, and movement of clay in saline and alkali soils.Journal of Soil Science, 20, 176–188

Ryan J N; Elimelech M. (1996). Colloid mobilization andtransport in groundwater (review). Colloids and Surfaces A:Physiochemical and Engineering Aspects, 107, 1–56

Ryan J N; Gschwend P M (1990). Colloid mobilization in twoAtlantic plain aquifers: field studies. Water ResourcesResearch, 26, 307–322

Ryde N; Kihira H; Matijevic M A (1992). Particle adhesionin model systems. 15. Effect of colloid stability in multi-layer deposition. Journal of Colloid Interface Science, 151,421–432

Sakthivadivel R; Thanikachalam V; Seetharaman S (1972).Head-loss theories infiltation. Journal of American WaterWorks Association, 64, 233–238

Schafer A; Ustohal P; Harms H: Stauffer F; Dracos T; Zehnder

A J B (1998). Transport of bacteria in unsaturated porousmedia. Journal of Contaminant Hydrology, 33, 149–169

Seaman J C; Bertsch P M (2000). Selective colloid mobilisationthrough surface-charge manipulation. EnvironmentalScience and Technology, 34, 3749–3755

Seta A K; Karathanasis A D (1996). Colloid-facilitatedtransport of metolachlor through intact soil columns.Journal of Environmental Science and Health, Part B:Pesticide Food Contaminants and Agricultural Wastes, 31,949–968


Seta A K; Karathanasis A D (1997). Stability and transport-ability of water-dispersible soil colloids. Soil Science Societyof America Journal, 61, 604–611

Shainberg I; Levy G J; Rengasamy P; Frenkel J (1992).Aggregate stability and seal formation as affected bydrops impact energy and soil amendments. Soil Science,154, 113–119

Shaw D (1999). Introduction to Colloid and Surface Chemistry(4th Edn.). Butterworth-Heinemann, London

Smith M S; Thomas G W; White R E; Ritonga D (1985).Tranport of E. coli through intact and disturbed soilcolumns. Journal of Environmental Quality, 14, 87–91

Speilman L A (1977). Particle capture from low-speedlaminar flows. Annual Review of Fluid Mechanics, 9,

297–319Stagnitti F; Li L; Allinson G; Phillips I; Lockington D; ZeiliguerA; Allinson M; Lloyd-Smith J; Xie M (1999). A mathema-tical model for estimating the extent of solute- and water-flux heterogeneity in multiple sample percolation experi-ments. Journal of Hydrology, 215, 59–69

Stumm W (1977). Coagulation and filtration in waterand wastewater treatment become more efficient bymodifying the chemical variables to improve the efficiencyof collisions between particles and particles and filtergrains. Environmental Science and Technology, 11,

1066–1070Tan Y; Bond W J; Griffin D M (1992). Transport of bacteriaduring unsteady unsaturated soil water flow. Soil ScienceSociety of America Journal, 56, 1331–1340

Thurman E M; Wershaw R L; Malcolm R L; Pinckney D J(1982). Molecular size of aquatic substances. OrganicGeochemistry, 4, 27–35

Tien C; Payatakes A C (1979). Advances in deep bed filtration.The American Institute of Chemical Engineers, 25,737–759

Toran L; Palumbo A V (1992). Colloid transport throughfractured and unfractured laboratory sand columns. Journalof Contaminant Hydrology, 9, 289–303

Totsche K U; Knabner P; K.oogel-Knabner I (1996). Themodelling of reactive solute transport with sorption tomobile and immobile sorbents. 2. Model discussionand numerical simulation. Water Resources Research, 32,1623–1634

Trevors J T; van Elsas J D; van Overbeek L S; Starodub M-E

(1990). Transport of a genetically engineered Pseudomonasfluorescens strain through a soil microcosm. Applied andEnvironmental Microbiology, 56, 401–408

Van der Lee J; Ledoux E; Marsily G de (1994). Microscopicdescription of colloid transport in fractured or porous

media. In: IAHR/AIRH Symposium: Transport and Re-active Processes in Aquifers, pp 349–355

Van Elsas J D; Trevors J T; Van Overbeek L S (1991).Influence of soil properties on the vertical movement ofgenetically marked Pseudomonas fluorescens through largesoil microcosms. Biology and Fertility of Soils, 10, 249–255

Vilker V L (1981). Simulating virus movement in soils. In:Modelling Wastewater Renovation Land treatment (Iskan-dor I K, ed), pp 223–253, Wiley, New York

Vilker V L; Burge W D (1980). Adsorption mass transfermodel for virus transport in soils. Water Research, 14,

783–790Villholth K G; Jarvis N J; Jacobsen O H; de Jonge H (2000).Field investigations and modelling of particle-facilitatedpesticide transport in macroporous soil. Journal of Envir-onmental Quality, 29, 1298–1309

Vinten A J A (1981). The application and limitations of deepbed filtration theory in the study of dilute colloidalsuspensionmovement through soil. D.Phil. Thesis, Univer-sity of Oxford

Vinten A J A; Mingelgrin U; Yaron B (1983a). The effect ofsuspended solids in wastewater on soil hydraulic conductiv-ity: I. Suspended solids labelling method. Soil ScienceSociety of America Journal, 47, 402–407

Vinten A J A; Mingelgrin U; Yaron B (1983b). The effect ofsuspended solids in wastewater on soil hydraulic conductiv-ity: II. Vertical distribution of suspended solids. Soil ScienceSociety of America Journal, 47, 408–412

Vinten A J A; Yaron B; Nye P H (1983c). Vertical transport ofpesticides into soil when adsorbed on suspended particles.Agricultural and Food Chemistry, 31, 662–664

Vinten A J A; Nye P H (1985). Transport and deposition ofdilute colloidal suspensions in soils. Journal of Soil Science,36, 531–541

Voice T C; Rice C P; Weber Jr W J (1983). Effect of solidsconcentration on the sorptive partitioning of hydrophobicpollutants in aquatic systems. Environmental ScienceTechnology, 17, 513–518

Wan J; Tokunaga K; Tsang C F (1995). Bacterial sedimenta-tion through a porous medium. Water Resources Research,31, 1627–1636

White R E (1985a). The transport of chloride and non-diffusible solutes through soil. Irrigation Science, 6, 3–10

White R E (1985b). The influence of macropores on thetransport of dissolved and suspended matter through soil.Advances in Soil Science, 3, 95–120

Wollum A G; Cassel D K (1978). Transport of microorganismsin sand columns. Soil Science Society of America Journal,42, 72–76

Download - SW—Soil and Water: Transport of Particulate and Colloid-sorbed Contaminants through Soil, Part 1: General Principles

Top Related