INTRODUCTION

1. (a) (b) (a) (b) -♦-EC = 68 μ S/cm -●-EC = 6 μ S/cm -♦-EC = 18 μ S/cm Total Metal Concentration (C/C0) C/C0 -●-EC = 6 μ S/cm C/C0 LSBC -♦-EC = 12 μ S/cm -●-EC = 4 μ S/cm LSBC 0 min 0 min 30 min 30 min 1 hour 1 hour 2 hour 2 hour 4 hour 4 hour 8 hour 8 hour 24 hour 24 hour ADBC pH 4 pH 8 Percent Colloid in Suspension 0 5 10 15 20 Fig. 6. Mean total metal loads (Cu, Zn, Pb) eluted with smectitic, mixed, and kaolinitic nanocolloids from Argiudoll soil monoliths. Percent Colloid in Suspension Total Pb Control ADBC Percent Colloid in Suspension Fig 12. Soil nanocolloid transport model. PMBC pH 120 Smectitic Mixed Kaolinitic PMBC 100 Fig 1. Mean settling rates of smectitic, mixed, and kaolinitic nanocolloids eluted from Argiudoll soil monoliths. 80 60 Fig 2. Mean settling rates of LSBC (lime-stabilized), ADBC (aerobically digested ), and PMBC (poultry manure) nanocolloids eluted from Argiudoll soil monoliths. 40 Fig 3. Mean settling rates of LSBC, ADBC, and PMB nanocolloids eluted from Argiudoll soil monoliths at different EC levels. (a) C/C0 Soluble Metal Concentration (C/C0) (b) Fig. 5. Mean breakthrough curves of ADBC, LSBC, and PMBC nanocolloids eluted from Argiudoll (a) and Udifluvent (b) soil monoliths. Fig. 7. Mean soluble metal loads (Cu, Zn, Pb) eluted with smectitic, mixed, and kaolinitic nanocolloids from Argiudoll soil monoliths. (a) (b) C/C0 1.0 PMBC 0.8 Fig 4. Mean breakthrough curves for smectitic, mixed, and kaolinitic nanocolloids eluted from Argiudoll soil monoliths. 0.6 0.4 0.2 0.0 Pore Volume Soluble Pb Fig. 8. Mean total and soluble Cu loads eluted with LSBC, ADBC, and PMBC nanocolloids from Argiudoll (a) and Udifluvent (b) soil monoliths. Fig. 9. Mean total and soluble Zn loads eluted with LSBC, ADBC, and PMBC nanocolloids from Argiudoll (a) and Udifluvent (b) soil monoliths. Fig. 10. Mean total and soluble Pb loads eluted with LSBC, ADBC, and PMBC nanocolloids from Argiudoll (a) and Udifluvent (b) soil monoliths. b a Composition and Transport Behavior of Soil Nanocolloids in Natural Porous Media A. D. Karathanasis Department of Plant & Soil Sciences, University of Kentucky • INTRODUCTION • Natural nanoparticles and nanocolloids are ubiquitous in soil environments playing important roles in many environmental processes, including soil genesis, nutrient cycling, dispersion/flocculation, sorption, precipitation, dissolution, contaminant transport, biogeochemical transformations, bioavailability, and various remediation practices (Christian et al., 2008). • They can travel very long distances but their transport potential is dictated by the colloidal stability imposed by the dispersion media and the ionic environment. While the small size of the nanoparticles implies considerable stabilization potential, their high surface energy may also induce multiple inter-particle collisions and significant agglomeration, particularly under elevated ionic concentrations (Bradford et al., 2007). • Their stability, mobility, and reactivity behavior is of particular interest in environmental pollution and remediation processes because their presence in large quantities may cause a significant deterioration of water quality and their association with organic and inorganic pollutants may adversely affect the integrity of sensitive ecosystems and pose a great contamination risk for ground water supplies (Karathanasis et al., 2007; Wigginton et al., 2007). • OBJECTIVES • The objective of this investigation was to examine the composition and behavior of environmental nanocolloids infused to undisturbed soil monoliths, evaluate their interaction with selected metals and herbicides, and assess their potential to facilitate contaminant transport in soil environments. • CONCLUSIONS • Although these mesocosm scale experiments cannot accurately assess the magnitude and variability of nanocolloid generation and transport behavior within field-scale natural environments, the findings provided unquestionable evidence for increased nanocolloid stability with the potential to migrate great distances through natural porous media, and a significant role as potential carriers and/or transport facilitators of organic and inorganic pollutants to groundwater aquifers. • In all cases involving mineral or bio-nanocolloids, their composition, size, and surface properties were the primary parameters controlling their stability, mobility, and co-transportability of metals and herbicides. • Decreases in mean nanocolloid diameter, and increases in surface charge, surface area, and electrophoretic mobility drastically enhanced nanocolloid stability and mobility through undisturbed soil monoliths, even at relatively high ionic strength levels, and significantly increased (up to 11-fold) metal and herbicide co-transportability. • Substantial increases of both total metal and soluble metal loads in the presence of nanocolloids suggested the influence of strongly interactive chemical and physical processes between nanocolloid surfaces and soil matrices in controlling the co-transport behavior. • Although the increased chemisorption affinity of the nanocolloid surfaces for the pollutants may be the dominant mechanism facilitating co-transport, organic complexation and physical exclusion processes may have also increased the magnitude of the transported contaminant loads. • These findings emphasize the importance of investing more advanced technology resources towards in situ monitoring of environmental nanocolloid generation and transport processes as well as their improved characterization so that we can obtain a more realistic understanding of their role and behavior under natural conditions as potential pollutants or remediators. • SELECTED REFERENCES • Bradford S A, Torkzaban S, and Walker S L (2007) Coupling of physical and chemical mechanisms of colloid straining in saturated porous media. Water Res. 41:3012-3024. • Christian P, Von der Kammer F, Baalousha M, and Hofmann T (2008) Nanoparticles: structure, properties, preparation, and behaviour in environmental media. Ecotoxicology, 17: 326-343. • Karathanasis A, Johnson C, and Matocha C (2007) Subsurface transport of heavy metals mediated by biosolid colloids in waste-amended soils. P. 175-201, in Frimmel F H, Von der Kammer F, and Fleming H C (eds), Colloidal Transport in Porous Media, Springer, Berlin. • Wigginton, N S, Haus K L, and Hochella Jr. M F (2007) Aquatic environmental nanoparticles. J. Environ. Monitor. 9:1306-1316. • METHODOLOGY • Leaching Soil Media • Duplicated, undisturbed soil monoliths (20 cm diameter by 36 cm length) consisted of A-Bt or A-C horizons of a fine-silty, mixed, mesic Typic Argiudoll and a sandy, mixed, mesic Typic Udifluvent, respectively. • Colloid Preparation • Water dispersible mineral colloids were fractionated from upper Bt horizons of three Kentucky soils with smectitic, mixed, and kaolinitic mineralogy. • Water dispersible biosolid colloids were fractionated from one agricultural (poultry manure, PMBC) and two municipal (lime stabilized, LSBC and aerobically digested, ADBC) biosolid wastes. • The colloid fractionation was accomplished by mixing 10 g of material with 200 mL of de-ionized water, shaking overnight, and centrifuging at 130 x g for 3.5 min. • Colloid Characterization • Physicochemical colloid properties were determined according to procedures of the National Soil Survey Laboratory Manual. Mineralogical compositions were assessed with X-ray diffraction and thermal analyses. • Electrophoretic mobility was determined with a Delsa 440 Doppler Light Scattering Analyzer and the mean colloid diameter via a Beckman Coulter N5 Submicron Particle Size Analyzer. • Monolith Leaching Experiments • Mineral colloid suspensions of 300 mg/L spikedwith 10 mg/L of Cu, Zn, or Pb-chloride salts and 2 mg/L of atrazine or metolachlor herbicides were infused into undisturbed soil monoliths at a rate of 2.2 cm/hr, sustaining unsaturated flow conditions for a continuous 7 pore volume leaching cycle. • Biosolid colloid suspensions of 200 mg/L spiked with 10 mg/L of the same metal chloride salts were also infused into undisturbed soil monoliths at a rate of 0.7 cm/hr, sustaining unsaturated flow conditions for a continuous 16 pore volume leaching cycle. • Leaching cycles with a conservative tracer (CaCl2), de-ionized water and metal solutions without colloids were used as controls. • Leaching outputs were monitored continuously with respect to eluent volume, and colloid, metal, and herbicide concentrations. All leaching experiments were duplicated with an acceptable standard error level of < 15%. • Colloid Elution & Characterization • Eluent colloid concentrations were determined gravimetrically and turbidimetrically by measuring the optical density of the colloid suspensions at 540 nm with a Bio-Tec instruments microplate reader. • Metal concentrations were measured via inductively coupled plasma spectrometry. Herbicide levels were determined using liquid chromatography. FINDINGS Colloid Characteristics INF – infused colloids; EL – eluted colloids; LSBC – lime-stabilized biosolid colloids; ADBC – aerobically digested colloids; PMBC – poultry manure biosolid colloids; NOM – natural organic matter; SM – smectite; HI – hydroxy-interlayered smectite/vermiculite; K – kaolinite; Q – quartz; FE – iron oxyhydroxide; CC – calcium carbonate; CA - calcium hydroxide; MCD – mean colloid diameter; SA – surface area; CEC – cation exchange capacity; EM – electrophoretic mobility. Fig. 11. Mean BTCs for atrazine (a) and metalochlor (b) eluted with smectitic, mixed, and kaolinitic nanocolloids from Argiudoll soil monoliths.