Impact of natural organic matter on the physicochemical properties of aqueous C60 nanoparticles

Existing toxicity data indicate that industrial-scale production of C60 fullerene poses a potential threat to the environment. Evaluating the environmental impact of C60 requires careful characterization of its physicochemical properties in the natural aqueous environment. Our study aims to determine the effects of aquatic natural organic matter (NOM) on the physicochemical properties of aqueous C60 nanoparticles, nC60. Stable nC60 suspensions were formed using three different solvent exchange protocols. They were thoroughly characterized for particle size, morphology, and electrophoretic mobility in the absence or presence of two model NOM components, Suwannee River humic acid and fulvic acid. NOM caused disaggregation of nC60 crystals and aggregates under typical solution conditions of natural water, leading to significant changes in particle size and morphology. Such effect increased with increasing NOM concentration. The changes in nC060 size and morphology strongly depended on the nC60 formation pathway. Results from this study indicate that NOM may play a critical role in the transport and toxicity of C60 in the natural aqueous environment.     

Enhanced transport of 2,2',5,5'-polychlorinated biphenyl by natural organic matter (NOM) and surfactant-modified fullerene nanoparticles (nC60)

Stable colloidal suspensions of buckminsterfullerene (nC(60)) in aqueous environments can significantly affect the fate and transport of hydrophobic organic contaminants by serving as a contaminant carrier. In this study, we examined enhanced transport of 2,2',5,5'-polychlorinated biphenyl (PCB) in saturated sandy soil columns by a variety of nC(60) samples, including an nC(60) sample prepared by the typical solvent exchange method, as well as eight natural organic matter (NOM) or surfactant-modified nC(60) samples, prepared by phase-transferring C(60) from toluene to an NOM or a surfactant solution. Whereas the NOM- and surfactant-modified nC(60) samples have mobility similar to the unmodified nC(60), their contaminant-mobilizing capabilities are significantly greater: breakthrough of PCB increases by 47.2 to 227% with the surfactant-modified nC(60) samples and by 233 to 370% with the NOM-modified nC(60) samples. The significantly enhanced contaminant-mobilizing capability of the modified nC(60) is likely due to a combined effect of increased adsorption affinities and increased tendency of desorption nonequilibrium, likely caused by the changes of nC(60) aggregation properties induced by the presence of NOM or surfactant. Findings in this study indicate that nC(60) formed in different processes might have vastly different effects on contaminant fate and transport.     

C₆₀ oxide as a key component of aqueous C₆₀ colloidal suspensions

Stable aqueous fullerene colloidal suspensions (nC(60)) are demonstrated to rely on the [6,6]-closed epoxide derivative of the fullerene (C(60)O) for stability. This derivative is present, though often unrecognized, in small quantities in nearly all C(60) starting materials due to a reaction with air. The low-yield formation of nC(60) from organic solvent solutions results from a preferential partitioning and thus enrichment of C(60)O in the colloidal particles. This partitioning is significantly retarded in the nC(60) synthesis method that does not involve organic solvent solutions: long-term stirring in water. Instead, this method relies on trace levels of ozone in the ambient atmosphere to produce sufficient C(60)O at the surfaces of the nC(60) particles to allow stable suspension in water. Controlled-atmosphere syntheses, deliberate C(60)O enrichment, light scattering measurements, and extraction followed by HPLC analysis and UV-visible absorption spectroscopy support the above model of nC(60) formation and stabilization.     

Transport and retention of colloidal aggregates of C60 in porous media: effects of organic macromolecules, ionic composition, and preparation method

The physical-chemical behavior of the fullerene C60 in environmental and physiological media is of interest for understanding the potential transport, exposure, and impacts of these materials on organisms and ecosystems. We considerthe role of electrolyte composition and concentration, the effect of organic macromolecules, and the mode of preparation of colloidal aggregates of C60 (nC60) on the deposition of these colloids in a porous medium such as a groundwater aquifer or a water treatment filter. Results for nC60 deposition are qualitatively consistent with trends anticipated by theory. Deposition was found to increase with increasing ionic strength, the presence of polysaccharide-type organic matter, and lower Darcy velocities. Factors that will tend to decrease the retention of these materials in porous media include a low ionic strength and the presence of humic-like substances, while the ionic strengths typical of many natural waters and the presence polysaccharide-based natural organic matter, as may be produced by algae or bacteria, will tend to favor deposition and reduced potential for exposure. Variability in the method of preparing colloidal aggregates of fullerenes was observed to yield significant differences in nC60 properties and transport behavior.     

Aquasols: on the role of secondary minima

Experiments are presented that test the hypothesis of deposition into and reentrainment from secondary minima during flow through porous media. The release of deposited particles following a decrease in ionic strength is inconsistent with deposition in the primary minimum of either simple DLVO interaction energy curves (which suggest that deposition is irreversible) or Born-DLVO interaction energy curves (which create a finite primary minimum that deepens with decreasing ionic strength). The observed release of particles is, on the other hand, consistent with deposition in the secondary minimum because this energy minimum decreases and can disappear with decreasing ionic strength. The implications for colloid transport of a reversible deposition process in the secondary minimum are very different from those of a process involving irreversible deposition in the primary minimum. First, particles that are continually captured and released will travel much farther in the subsurface than might be expected if the classic irreversible filtration model is applied. Second, and perhaps more significantly, deposition in the secondary well can increase with increasing particle size. Although particle transport by convective diffusion increases as particle size decreases, particle "attachment" in secondary minima decreases with decreasing particle size. Thus, smaller particles (those with diameters in the order of a few tens of nanometers) would be more effective in the facilitated transport of highly sorbing contaminants such as hydrophobic organic molecules, metals, and radionuclides. Other contaminants are themselves particles, such as viruses (tens of nanometers in diameter) and bacteria (near 1 microm in diameter). Due to this difference in size, viruses could be transported over much larger distances than bacteria. Third, the transport of colloids and, hence, the transport of contaminants associated with them, depends on the Hamaker constant of the particle-water-aquifer media system. Colloids of lower Hamaker constant are likely to be transported farther than colloids of higher Hamaker constant. The extent of adsorption of specific contaminants and the Hamaker constant for the particle-aquifer system are both characteristics of the particles and contribute to the effectiveness of colloid-facilitated transport. Finally, the solution chemistry of the pore waters (through pH, ionic strength, types of solutes, and the valence of the ions) ultimately controls the deposition and release of colloidal particles in porous media. The pH determines the charge density and surface potential of the surfaces. When the surfaces are similarly charged, their interaction can be unfavorable, with an energy barrier and secondary minimum. The ionic strength and valence of the ions determines the shape of the interaction energy curve, including the presence and height of the energy barrier and the presence and depth of the secondary well. Since the subsequent release of a particle depends on the mode in which the particle is deposited (primary or secondary), these factors are particularly important in determining the extent of colloid transport in the subsurface.     

Size-exclusive nanosensor for quantitative analysis of fullerene C60

This paper presents the first development of a mass-sensitive nanosensor for the isolation and quantitative analyses of engineered fullerene (C??) nanoparticles, while excluding mixtures of structurally similar fullerenes. Amino-modified beta-cyclodextrin (β-CD-NH?) was synthesized and confirmed by 1HNMR as the host molecule to isolate the desired fullerene C??. This was subsequently assembled onto the surfaces of gold-coated quartz crystal microbalance (QCM) electrodes using N-dicyclohexylcarbodiimide/N-hydroxysuccinimide (DCC/NHS) surface immobilization chemistry to create a selective molecular configuration described as (Au)-S-(CH?)2-CONH-beta-CD sensor. The mass change on the sensor configuration on the QCM was monitored for selective quantitative analysis of fullerene C?? from a C??/C?? mixture and soil samples. About ~101?-101? C?? particles/cm2 were successfully quantified by QCM measurements. Continuous spike of 200 μL of 0.14 mg C?? /mL produced changes in frequency (-Δf) that varied exponentially with concentration. FESEM and time-of-flight secondary-ion mass spectrometry confirmed the validity of sensor surface chemistry before and after exposure to fullerene C??. The utility of this sensor for spiked real-world soil samples has been demonstrated. Comparable sensitivity was obtained using both the soil and purified toluene samples. This work demonstrates that the sensor has potential application in complex environmental matrices.     

Reaction of water-stable C60 aggregates with ozone

While the reactivity of C60 has been described in a variety of organic solvents, little information is available regarding aqueous-based reactions due to solubility limitations. In this study, a reaction between C60, as a nanoscale suspension, and dissolved ozone in the aqueous phase was investigated. Findings indicate a facile reaction occurs, resulting in aggregate dissolution concurrent with formation of water-soluble fullerene oxide species. Product analyses, including 13C NMR, MS (LDI), FTIR, UV-Vis, and XPS, indicate highly oxidized fullerene with an average of approximately 29 oxygen additions per molecule, arranged in repeating hydroxyl and hemiketal functionalities. These findings are significant in that they (1) demonstrate the feasibility of other aqueous-based fullerene chemistries, including those for alternative synthesis routes, which might otherwise be considered prohibitive on the basis of solubility limitations, and (2) imply that the aqueous reactivity of fullerene-based materials must be considered appropriately for accurate assessment of their transport, fate, and potential risk(s) in environmental systems.     

Approaches to mitigate the impact of dissolved organic matter on the adsorption of synthetic organic contaminants by porous carbonaceous sorbents

Adsorption of trichloroethylene (TCE) and atrazine, two synthetic organic contaminants (SOCs) having different optimum adsorption pore regions, by four activated carbons and an activated carbon fiber (ACF) was examined. The selected adsorbents had a wide range of pore size distributions but similar surface acidity and hydrophobicity. Single solute and preloading (with a dissolved organic matter (DOM)) isotherms were performed. Single solute adsorption results showed that (i) the adsorbents having higher amounts of pores with sizes about the dimensions of the adsorbate molecules exhibited higher uptakes, (ii) there were some pore structure characteristics, which were not completely captured by pore size distribution analysis, that also affected the adsorption, and (iii) the BET surface area and total pore volume were not the primary factors controlling the adsorption of SOCs. The preloading isotherm results showed that for TCE adsorbing primarily in pores < 10 angstroms, the highly microporous ACF and GACs, acting like molecular sieves, exhibited the highest uptakes. For atrazine with an optimum adsorption pore region of 10-20 angstroms, which overlaps with the adsorption region of some DOM components, the GACs with a broad pore size distribution and high pore volumes in the 10-20 angstroms region had the least impact of DOM on the adsorption.     

Material and energy intensity of fullerene production

Fullerenes are increasingly being used in medical, environmental, and electronic applications due to their unique structural and electronic properties. However, the energy and environmental impacts associated with their commercial-scale production have not yet been fully investigated. In this work, the life cycle embodied energy of C(60) and C(70) fullerenes has been quantified from cradle-to-gate, including the relative contributions from synthesis, separation, purification, and functionalization processes, representing a more comprehensive scope than used in previous fullerene life cycle studies. Comparison of two prevalent production methods (plasma and pyrolysis) has shown that pyrolysis of 1,4-tetrahydronaphthalene emerges as the method with the lowest embodied energy (12.7 GJ/kg of C(60)). In comparison, plasma methods require a large amount of electricity, resulting in a factor of 7-10× higher embodied energy in the fullerene product. In many practical applications, fullerenes are required at a purity >98% by weight, which necessitates multiple purification steps and increases embodied energy by at least a factor of 5, depending on the desired purity. For applications such as organic solar cells, the purified fullerenes need to be chemically modified to [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM), thus increasing the embodied energy to 64.7 GJ/kg C(60)-PCBM for the specified pyrolysis, purification, and functionalization conditions. Such synthesis and processing effects are even more significant for the embodied energy of larger fullerenes, such as C(70), which are produced in smaller quantities and are more difficult to purify. Overall, the inventory analysis shows that the embodied energy of all fullerenes are an order of magnitude higher than most bulk chemicals, and, therefore, traditional cutoff rules by weight during life cycle assessment of fullerene-based products should be avoided.     

Comparison of electrokinetic properties of colloidal fullerenes (n-C60) formed using two procedures

In this study we report on the electrokinetic behavior of colloidal aggregates of C60fullerenes (n-C60) produced through two different techniques: solvent exchange and extended mixing with water. In the first technique, used to produce colloidal materials in several recent toxicity and transport studies, an organic solvent such as tetrahydrofuran (THF) is used to dissolve the C60 before mixing with water. The second technique is more indicative of conditions that might occur in natural aquatic systems. Both types of n-C60 were observed to be negatively charged under a variety of solution chemistries; however, the n-C60 formed using THF was more strongly charged. We conclude that n-C60 likely acquires charge through charge transfer from the organic solvent (when present) and surface hydrolysis reactions. Nevertheless, C60 is capable of acquiring charge and becoming dispersed as n-C60 in water without the aid of organic solvents, a pathway that may be important in determining the mobility of fullerenes in natural systems. These findings also show that n-C60 made using THF retains a portion of the solvent in the cluster structure, subsequently influencing the characteristics of the n-C60 and possibly requiring a re-interpretation of results from recent studies on n-C60 toxicity using THF-derived materials.     

Velocity effects on fullerene and oxide nanoparticle deposition in porous media

Products of nanochemistry have been proposed in a number of applications ranging from soil stabilization and cosmetics to groundwater remediation. A fundamental understanding of the transport properties of these materials is essential to assess their efficacy and environmental impact in such applications. In this work, we consider the effect of flow on nanoparticle transport and deposition in porous media. The transport of three aqueous suspensions of fullerenes in a well-characterized porous medium is compared with that of two oxide nanomaterials at two flow rates. Despite significant differences in surface chemistry and size, the fullerenes exhibited an unexpected and similar breakthrough behavior at the higher flow rate. A striking characteristic of the fullerene breakthrough curves obtained at the higher Darcy velocity was an initial enhancement in nanoparticle deposition shortly after the passage of the first pore volume of suspension, followed by an increase in passage. This velocity-sensitive "affinity transition" in the initial deposition of nanoparticles in the porous medium was observed for fullerene-based materials only at the higher velocity and was in no case observed for silica or titania nanoparticles. The removal of fullerene-based nanoparticles was observed to converge to a level that was independent of flow velocity, suggesting that under these conditions time scales for attachment or reorganization on the surface are greater than the time scale for transport to collector surfaces.     

The effect of water temperature on the adsorption equilibrium of dissolved organic matter and atrazine on granular activated carbon

The influence of water temperature on the adsorption of natural dissolved organic matter (DOM) on activated carbon has not been investigated intensively yet. In this study, batch experiments with granular activated carbon (GAC) have been carried out at three temperatures (5 degrees C, 20 degrees C, 35 degrees C) using a humic acid model water and different types of surface water (lake, river, canal). Furthermore, the adsorption of an anthropogenic contaminant, atrazine, was quantified in the absence and presence of DOM. The results indicate a significant influence of water temperature on the adsorption equilibrium of DOM and atrazine. Contrary to expectations, DOM and atrazine adsorption in surface water tends to be increased with increasing water temperature, whereas the extent of this effect is dependent on the type and concentration of DOM. Furthermore, the temperature effect on atrazine adsorption is controlled by competition of DOM and atrazine on adsorption sites. Some assumptions are proposed and discussed for explaining the temperature effects observed in the batch studies.     

Bacteriophage inactivation by UV-A illuminated fullerenes: role of nanoparticle-virus association and biological targets

Inactivation rates of the MS2 bacteriophage and (1)O(2) generation rates by four different photosensitized aqueous fullerene suspensions were in the same order: aqu-nC(60) < C(60)(OH)(6) ≈ C(60)(OH)(24) < C(60)(NH(2))(6). Alterations to capsid protein secondary structures and protein oxidation were inferred by detecting changes in infrared vibrational frequencies and carbonyl groups respectively. MS2 inactivation appears to be the result of loss of capsid structural integrity (localized deformation) and the reduced ability to eject genomic RNA into its bacterial host. Evidence is also presented for possible capsid rupture in MS2 exposed to UV-A illuminated C(60)(NH(2))(6) through TEM imagery and detection of RNA infrared fingerprints in ATR-FTIR spectra. Fullerene-virus mixtures were also directly visualized in the aqueous phase using a novel enhanced darkfield transmission optical microscope fitted with a hyperspectral imaging (HSI) spectrometer. Perturbations in intermolecular extended chains, HSI, and electrostatic interactions suggest that inactivation is a function of the relative proximity between nanoparticles and viruses and (1)O(2) generation rate. MS2 log survival ratios were linearly related to CT (product of (1)O(2) concentration C and exposure time T) demonstrating the applicability of classical Chick-Watson kinetics for all fullerenes employed in this study. Results suggest that antiviral properties of fullerenes can be increased by adjusting the type of surface functionalization and extent of cage derivatization thereby increasing the (1)O(2) generation rate and facilitating closer association with biological targets.     

Flux decline during nanofiltration of organic components in aqueous solution

Flux decline due to interaction of the membrane with the feed solution is a major drawback for the use of nanofiltration in environmental applications. This paper studies different mechanisms of flux decline for the nanofiltration of aqueous solutions containing organic compounds. The resistance model for flux decline is used: different mechanisms contribute through an increase of the resistance of the membrane against mass transport. The focus in this research is on pore blocking and adsorption inside the membrane pores. Osmotic pressure is also taken into account as it decreases the driving force. The nanofiltration membranes used were NF70 (Dow), UTC-20 and UTC-60 (Toray Ind.), and NTR 7450 (Nitto-Denko). Experiments with different organic components in aqueous solution showed that adsorption resulted in a strong decrease of the water flux. The results of the flux decline as a function of the concentration could well be fitted with the Freundlich equation for adsorption. The components that showed the largest effect had the highest polarity (permanent dipole moment or polarizability), which indicates that adsorption is favored by the polarity of the components in solution. Moreover, the molecules with a size similar to the pore size had a stronger effect on the water flux than other molecules. This can be explained by blocking of the pores by adsorbed compounds.     

Adsorption of polar and nonpolar organic chemicals to carbon nanotubes

Understanding adsorptive interactions between organic contaminants and carbon nanotubes is critical to both the environmental application of carbon nanotubes as special adsorbents and the assessment of the potential impact of carbon nanotubes on the fate and transport of organic contaminants in the environment. The adsorption of organic compounds with varied physical-chemical properties (hydrophobicity, polarity, electron polarizability, and size) to one single-walled carbon nanotube (SWNT) and two multiwalled carbon nanotubes (MWNTs) was evaluated. For a given carbon nanotube, the adsorption affinity correlated poorly with hydrophobicity but increased in the order of nonpolar aliphatic < nonpolar aromatics < nitroaromatics, and within the group of nitroaromatics, the adsorption affinity increased with the number of nitrofunctional groups. We propose that the strong adsorptive interaction between carbon nanotubes and nitroaromatics was due to the pi-pi electron-donor-acceptor (EDA) interaction between nitroaromatic molecules (electron acceptors) and the highly polarizable graphene sheets (electron donors) of carbon nanotubes. Additionally, we attribute the stronger adsorption of nonpolar aromatics compared to that of nonpolar aliphatics to the pi-electron coupling between the flat surfaces of both aromatic molecules and carbon nanotubes. For tetrachlorobenzene, the bulkiest adsorbate, adsorption affinity (on a unit surface area basis) to the SWNT was much stronger than to the two MWNTs, indicating a probable molecular sieving effect.     

Fullerene-Enhanced Accumulation of p,p'-DDE in Agricultural Crop Species

The effect of C(60) fullerene exposure on the accumulation of dichlorodiphenyldichloroethylene (p,p'-DDE; DDT metabolite) by Cucurbita pepo L. (zucchini), Glycine max L. (soybean), and Solanum lycopersicum L. (tomato) was determined. The plants were grown in 125 mL jars of vermiculite amended with 0 or 40 mg of C(60) fullerenes. Prior to planting, the jars were amended with 40 mL solution containing 100 ng/mL of p,p'-DDE with 0 or 100 mg/L humic acid. During three weeks of growth, plants were watered with the same p,p'-DDE containing solutions. Total shoot p,p'-DDE levels in nonfullerene exposed tomato, soybean, and zucchini were 26.9, 131, and 675 ng, respectively; total root DDE content for the three plants was 402, 5970, and 5830 ng, respectively. Fullerenes increased the shoot p,p'-DDE content of zucchini by 29%; contaminant levels in soybean shoots were decreased by 48% but tomato shoot content was unaffected. The root and total plant p,p'-DDE content of all three species was significantly increased by fullerene exposure; enhanced contaminant uptake ranged from 30 to 65%. Humic acid, regardless of fullerene presence or plant type, significantly decreased the p,p'-DDE uptake. Fullerenes were detected in the roots of all plants but were not detected in plant shoots in the initial study. In a follow up study with zucchini designed to maximize biomass for extraction, over half the analyzed stems contained fullerenes at 60.5 to 4490 ng/g. These findings show that the carbon-based nanomaterials may significantly alter the accumulation and potentially the toxicity of cocontaminants in agricultural systems.     

Transport of fullerene nanoparticles (nC60) in saturated sand and sandy soil: controlling factors and modeling

Understanding subsurface transport of fullerene nanoparticles (nC(60)) is of critical importance for the benign use and risk management of C(60). We examined the effects of several important environmental factors on nC(60) transport in saturated porous media. Decreasing flow velocity from approximately 10 to 1 m/d had little effect on nC(60) transport in Ottawa sand (mainly pure quartz), but significantly inhibited the transport in Lula soil (a sandy, low-organic-matter soil). The difference was attributable to the smaller grain size, more irregular and rougher shape, and greater heterogeneity of Lula soil. Increasing ionic strength and switching background solution from NaCl to CaCl(2) enhanced the deposition of nC(60) in both sand and soil columns, but the effects were more significant for soil. This was likely because the clay minerals (and possibly soil organic matter) in soil responded to changes of ionic strength and species differently than quartz. Anions in the mobile phase had little effect on nC(60) transport, and fulvic acid in the mobile phase (5.0 mg/L) had a small effect in the presence of 0.5 mM Ca(2+). A two-site transport model that takes into account both the blocking-affected attachment process and straining effects can effectively model the breakthrough of nC(60).     

Quantification of solute-solute interactions using negligible-depletion solid-phase microextraction: measuring the affinity of estradiol to bulk organic matter

The interaction of trace organic contaminants with bulk organic matter has implications for the transport and behavior of organic trace contaminants within the aquatic environment as well as water and wastewater treatment processes. Partition coefficients (K(OM)) of the steroidal trace organic contaminant estradiol were quantified for environmentally relevant concentrations of bulk organic matter (12.5 mg C/L) using a full mass balance form of solid-phase microextraction (SPME). The results indicated that the method is successful and can be used at environmental concentrations. Estradiol had the greatest affinity for bulk organic matter that contained phenolic and benzoic acid ester groups, namely tannic acid, compared to organics containing predominately carboxylic functional groups. The solution chemistry (pH) was found to influence the interaction, as estradiol had a lower affinity for negatively charged and hydrophilic bulk organic matter. The partition coefficients determined using SPMEwere consistentwith partition coefficients derived using solubility enhancement and fluorescence quenching measurements, confirming that SPME is a powerful technique to quantify the affinity of estradiol for low concentrations of bulk organic matter and trace contaminants. Further, this novel method can be applied to a range of trace contaminants.     

Simultaneous immobilization of lead and atrazine in contaminated soils using dairy-manure biochar

Biochar produced from waste biomass is increasingly being recognized as a green, cost-effective amendment for environmental remediation. This work was to determine the ability of biochar to immobilize heavy metal Pb and organic pesticide atrazine in contaminated soils. Biochar prepared from dairy manure was incubated with contaminated soils at rates of 0, 2.5, and 5.0% by weight for 210 d. A commercial activated carbon (AC) was included as a comparison. The AC was effective in immobilizing atrazine, but was ineffective for Pb. However, biochar was effective in immobilizing both atrazine and Pb and the effectiveness was enhanced with increasing incubation time and biochar rates. After 210 d, soils treated with the highest rate of 5.0% biochar showed more than 57% and 66% reduction in Pb and atrazine concentrations in 0.01 M CaCl(2) extraction, respectively. Lead and atrazine concentrations in the toxicity characteristic leaching procedure solutions were reduced by 70-89% and 53-77%, respectively. Uptake of Pb and atrazine by earthworms (Eisenia fetida) was reduced by up to 79% and 73%. Phosphorus originally contained in biochar reacted with soil Pb to form insoluble hydroxypyromorphite Pb(5)(PO(4))(3)(OH), as determined by X-ray diffraction, which was presumably responsible for soil Pb immobilization, whereas atrazine stabilization may result from its adsorption by biochar demonstrated by the significant exponential decrease of extractable atrazine with increasing organic C in biochar (r(2) > 0.97, p < 0.05). The results highlighted the potential of dairy-manure biochar as a unique amendment for immobilization of both heavy metal and organic contaminants in cocontaminated soils.     

Buckminsterfullerene's (C60) octanol-water partition coefficient (Kow) and aqueous solubility

To assess the risk and fate of fullerene C60 in the environment, its water solubility and partition coefficients in various systems are useful. In this study, the log Kow of C60 was measured to be 6.67, and the toluene-water partition coefficient was measured at log Ktw = 8.44. From these values and the respective solubilities of C60 in water-saturated octanol and water-saturated toluene, C60's aqueous solubility was calculated at 7.96 ng/L(1.11 x 10(-11) M) for the organic solvent-saturated aqueous phase. Additionally, the solubility of C60 was measured in mixtures of ethanol-water and tetrahydrofuran-water and modeled with Wohl's equation to confirm the accuracy of the calculated solubility value. Results of a generator column experiment strongly support the hypothesis that clusters form at aqueous concentrations below or near this calculated solubility. The Kow value is compared to those of other hydrophobic organic compounds, and bioconcentration factors for C60 were estimated on the basis of Kow.