Transport Of Hydrophobic Organic Compounds Research Articles

Surfactant-modified fatty acid composition of Citrobacter sp. SA01 and its effect on phenanthrene transmembrane transport

The effects of the surfactants, Tween 80 and sodium dodecyl benzene sulfonate (SDBS) on a membrane’s fatty acid composition and the transmembrane transport of phenanthrene were investigated. The results indicated that both surfactants could modify the composition of fatty acids of Citrobacter sp. Strain SA01 cells, 50mgL−1 of both surfactants changed the composition of the fatty acids the most, increasing the amount of unsaturated fatty acids. The comparison of fatty acid profiles with diphenylhexatriene fluorescence anisotropy, a probe for plasma membrane fluidity, suggested that an increased amount of unsaturated fatty acids corresponded to greater membrane fluidity. In addition, increased unsaturated fatty acids promoted phenanthrene to partition from the extracellular matrix to cell debris, which increased reverse partitioning from the cell debris to the cytochylema. The results of this study were expected in that the addition of a surfactant is a simple and effective method for accelerating the rate-limiting step of transmembrane transport of hydrophobic organic compounds (HOCs) in bioremediation.

Effect of Combined Bacillus subtilis on the Sorption of Phenanthrene and 1,2,3‐Trichlorobenzene onto Mineral Surfaces

In the natural environment, minerals are often associated with coexisting microorganisms. These interactions have profound impacts on the fate of a wide variety of contaminants. However, little information is available on the sorption of hydrophobic organic compounds (HOC), such as polycyclic aromatic hydrocarbons and chlorinated benzenes, onto the composites of minerals with bacteria, and knowledge of the influence of combined bacteria on HOC sorption to minerals is limited. In our study, sorption isotherms of phenanthrene (Phen) and 1,2,3-trichlorobenzene (TCB) onto Bacillus subtilis, minerals (kaolinite, montmorillonite, and goethite), and mineral-B. subtilis composites were studied to determine the role of B. subtilis in sorption. For pure mineral systems, the order of Phen and TCB sorption affinity was montmorillonite > kaolinite > goethite. For mineral-B. subtilis composites, the trend was montmorillonite > goethite > kaolinite, consistent with that of their ability to combine with bacteria. The coating of B. subtilis with minerals enhanced the sorption due to the strong sorption of Phen and TCB onto B. subtilis cells and the increase of total organic carbon of minerals. With increasing B. subtilis concentration, sorption of Phen and TCB on pure B. subtilis cells decreased, but sorption on kaolinite surface increased. Sodium azide can greatly reduce sorption capacity but increases sorption linearity for B. subtilis and mineral-B. subtilis composites. Compared with TCB, Phen had higher sorption affinity due to its high hydrophobicity. Our results may be useful for understanding the role of bacteria in regulating the distribution and transport of HOCs in the environment.

Comparative sorption of benzo[α]phrene to different humic acids and humin in sediments

Sediment/soil organic matter (SOM) is the predominant sorbents for hydrophobic organic compounds (HOCs). The identification and comparison of sorption characterization of HOCs by different organic matter fractions are essential to predict the fate and transport of HOCs in soils and sediments. The objectives of this paper are to compare the sorption of benzo[α]phrene (BaP) to the humic acid (HA) and humin (HM) extracted from different sediments. The HA and HM were extracted with 0.1 M NaOH from five sediments in different areas in China, and their sorption isotherms for BaP were determined. All sorption isotherms were nonlinear and nonlinearity increased in the order HA < sediment < HM. BaP sorption capacities on the HA fractions were significantly related to their aliphaticity, but negatively correlated to aromatic carbon. However, more aromatic carbon in HM fractions can result in higher K oc values of BaP than HA. This implied the importance of both aliphatic and aromatic groups in BaP sorption. HM contributed to 54–92% of the total sorption depending on initial concentrations, clearly indicating the dominance of HM in BaP sorption by the sediments.

Adsorption of Polycyclic Aromatic Hydrocarbons by Carbon Nanomaterials

Carbon nanomaterials are novel manufactured materials, having widespread potential applications. Adsorption of hydrophobic organic compounds (HOCs) by carbon nanomaterials may enhance their toxicity and affect the fate, transformation, and transport of HOCs in the environment. In this research, adsorption of naphthalene, phenanthrene, and pyrene onto six carbon nanomaterials, including fullerenes, single-walled carbon nanotubes, and multiwalled carbon nanotubes was investigated, which is the first systematic study on polycyclic aromatic hydrocarbons (PAHs) sorption by various carbon nanomaterials. All adsorption isotherms were nonlinear and were fitted well by the Polanyi-Manes model (PMM). Through both isotherm modeling and constructing "characteristic curve", Polanyi theory was useful to describe the adsorption process of PAHs by the carbon nanomaterials. The three fitted parameters (Q0, a, and b) of PMM depended on both PAH properties and the nature of carbon nanomaterials. For different PAHs, adsorption seems to relate with their molecular size, i.e., the larger the molecular size, the lower the adsorbed volume capacity (Q0), but higher a and b values. For different carbon nanomaterials, adsorption seems to relate with their surface area, micropore volume, and the volume ratios of mesopore to micropore. Quantitative relationships between these sorbent properties and the estimated parameters of PMM were obtained. These relationships may represent a first fundamental step toward establishing empirical equations for quantitative prediction of PAH adsorption by carbon nanomaterials and possibly other forms of carbonaceous (geo-) sorbents, and for evaluating their environmental impact. In addition, high adsorption capacity of PAHs by carbon nanotubes may add to their high environmental risks once released to the environment, and result in potential alteration of PAHs fate and bioavailability in the environment.

Quantifying the Effect of Medium Composition on the Diffusive Mass Transfer of Hydrophobic Organic Chemicals through Unstirred Boundary Layers

Unstirred boundary layers (UBLs) often act as a bottleneck for the diffusive transport of hydrophobic organic compounds (HOCs) in the environment. Therefore, a microscale technique was developed for quantifying mass transfer through a 100-microm thin UBL, with the medium composition of the UBL as the controllable factor. The model compound fluoranthene had to (1) partition from a contaminated silicone disk (source) into the medium, (2) then diffuse through 100 microm of medium (UBL), and finally (3) partition into a clean silicone layer (sink). The diffusive mass transfer from source to sink was monitored over time by measuring the fluoranthene content of the source and sink disks. The diffusive flux of fluoranthene was slightly higher for air than for water. Cyclodextrin, humic acids, and micelles of sodium dodecyl sulfate (SDS) enhanced the diffusive flux of fluoranthene in water by more than 1 order of magnitude. These results demonstrate that medium constituents, which normally are believed to bind hydrophobic organic chemicals, actually can enhance the diffusive mass transfer of HOCs in the vicinity of a diffusion source (e.g., contaminated soil particles). The technique can be used to evaluate the effect of natural fluids on diffusive mass transfer, as it integrates the different processes, partitioning and diffusion, in one laboratory model.

Oxygenated fuel induced cosolvent effects on the dissolution of polynuclear aromatic hydrocarbons from contaminated soil

The cosolvent-induced dissolution of polynuclear aromatic hydrocarbons (PAHs) from contaminated soil caused by oxygenated fuel spills was studied. Oxygenated fuel induces a solvent flushing effect on the contaminated soil due to the high content of oxygenated compounds (i.e., methanol, ethanol, and methyl tert butyl ether (MTBE)). The miscible displacement techniques were applied to evaluate the increased potential for secondary contamination in an impacted site. Significant solubility enhancement of the 18 PAHs monitored during fuel spill simulation and cosolvent flushing is clearly evident when compared to normal water dissolution. The breakthrough concentration profile for each PAH constituent was integrated over the cumulative effluent volume (i.e., the zeroth moment) to determine the total PAH mass removed during the experiment. The removal efficiency of PAHs ranges from 46.6% to 99.9% in three oxygenated fuels (i.e., M85, E85, and oxygenated gasoline) during the fuel spill. Several factors including hydrophobicity of compounds, nonequilibrium dissolution due to nonuniform coal tar distribution, and heterogeneous media properties affect the oxygenated compound-induced dissolution process. This study provides a basis to predict the facilitated transport of hydrophobic organic compounds from subsurface environment due to the cosolvent effects of oxygenated fuels.

Investigation of Sorption Behavior between Pyrene and Colloidal Organic Carbon from Activated Sludge Processes

The sorption behavior of pyrene for different size fractions of colloidal organic carbon (COC) originating from two biological wastewater treatment facilities (a full-scale activated sludge system (FSAS) and a membrane bioreactor (MBR)) was investigated by fluorescence quenching. Fluorescence lifetime measurements demonstrated a dynamic quenching component in all samples, including the colloidal-free filtrates. COC sorption coefficients (Kcoc) for pyrene ranged from <1 x 10(3) L/kgcoc to 80 x 10(3) L/kgcoc and were comparable to values obtained in the literature for natural organic matter. Both linear and nonlinear behaviors were observed in the Freundlich-described converted isotherms (n = 0.89-2.1). The aromatic content of COC was quantified by the molar extinction coefficient at 280 nm (e280). Good correlations were observed between COC-pyrene sorption coefficients and e280 coefficients, suggesting that e280 may be a useful tool for predicting colloidal transport of hydrophobic organic compounds (HOCs) from activated sludge systems. The removal of COC from treated effluents may appreciably reduce the concentrations of HOCs discharged to receiving streams.

Sorption and transport behavior of naphthalene in an aggregated soil.

Soil solution chemistry influences the sorption and transport behavior of hydrophobic organic compounds (HOCs) in soil. We used both batch and column studies to investigate the influence of ionic strengths (0.03 and 1.5 M) and flow velocities (12 and 24 cm h-1) on sorption and transport of naphthalene (NAP) in aggregated soil. Sorption parameters such as the Freundlich coefficient (Kf) and exponent (n) calculated from batch studies and column experiments were also compared. Retardation of NAP transport was greater at higher solution ionic strength, which may be attributed to greater sorption affinity due to enhanced aggregation of the sorbent. The effect of ionic strength on sorption of NAP observed in the batch study was consistent with the results from the column study. The Kf and n values obtained from the batch study for the two ionic strengths ranged from 7.8 to 13.7 and 0.68 to 0.80, respectively, whereas the Kf and n values obtained from the column study ranged from 7.9 to 9.9 and 0.73 to 0.85, respectively. The effluent breakthrough curve (BTC) of NAP at a flow rate of 24 cm h-1 showed significant chemical and physical nonequilibrium behavior, implying that a considerable amount of sorption in aggregated soil was time dependent when flow was relatively fast. The BTCs calculated with the parameters determined from batch studies compared poorly with the measured BTCs. The potential for nonequilibrium transport should be incorporated in models used for predicting the fate and transport of HOCs. Furthermore, caution is required when extrapolating the results from batch studies, especially for aggregated soils.

Sorption of phenanthrene by reference smectites.

Fate and behavior of nonionic hydrophobic organic compounds (HOCs) in the environment is mainly controlled by their interactions with various components of soils and sediments. Due to their large surface area and abundance in many soils, smectites may greatly influence the fate and transport of HOCs in the environment. We used phenanthrene as a probe to explore the potential of reference smectites to sorb HOCs from aqueous solution. Batch experiments were used to construct phenanthrene sorption isotherms, and possible sorption mechanisms were inferred from the shape of the isotherms. Our results demonstrate that smectites can retain large amounts of phenanthrene from water. Phenanthrene sorption capacities of the reference smectites investigated in this study were comparable to those of soil clays containing a considerable amount of organic matter. Hectorite exhibited the highest sorption affinity and capacity followed by Panther Creek montmorillonite. The lack of correlation between Freundlich sorption constants (K'f) and indices of charge or hydrophobicity suggests that sorption of phenanthrene by smectites is primarily a physical phenomenon. Capillary condensation into a network of nanoor micropores created by quasicrystals is likely to be a dominant mechanism of phenanthrene retention by smectites.

Sorption nonequilibrium effects on colloid-enhanced transport of hydrophobic organic compounds in porous media

This paper presents the results of modelling and experimental investigations of factors affecting enhanced transport of hydrophobic organic compounds (HOCs) on colloids in porous media, especially effects of nonequilibrium sorption/desorption. Simulations were performed with a model that considers equilibrium and rate-limited exchange of contaminant between the true dissolved phase, the suspended and attached colloids, and the fixed solid phase as well as the advection, dispersion, deposition, and release of colloidal particles from the porous medium. The model was also applied to laboratory column data for colloid-facilitated transport of a common HOC, phenanthrene. Simulations of colloid-enhanced transport and fitting of experimental data indicated that colloid-enhancement of hydrophobic organic contaminant transport can be significant for sufficiently high colloid concentrations, a high partition coefficient of contaminant on colloids with respect to the fixed porous medium, a low deposition efficiency of the colloids on the fixed porous medium surfaces, and a slow desorption rate of contaminant from the colloids. The last of these conditions was identified as probably the most important in enhancing transport distances of contaminants in natural systems with mobile colloids which usually occur at concentrations not exceeding a few mg/l.

Transport of hydrophobic organic compounds by colloids through porous media 3. Diffusion from sediment porewater to overlying water in laboratory microcosms

The diffusion of colloidal organic carbon from the porewater of a local sediment University Lake, Baton Rouge, LA) was studied in laboratory microcosms. The effects of porewater ionic strength on the flux of dissolved organic carbon (DOC) was studied using two different electrolytes, namely NaCl and CaCl 2. The sediment porewater DOC concentration frofiles were used to obtain the effective diffusivities ( D e) in the sediment. The values of D e (0.019 and 0.021 cm 2 d −1) obtained for the sediment sample used in this work indicated low colloid mobility in porewaters. The D e values increased slightly in the presence of electrolytes in the porewaters (0.030 cm 2 d −1 for 1 M CaCl 2 and 0.023 cm 2 d −1 for 0.5 M NaCl). The porewater concentration of colloidal DOC was consistently low in the presence of electrolytes, indicating larger adsorption to the sediment solids. The D e values were found to range from 0.019 to 0.103 cm 2 d −1 for sediments collected from different regions and during different seasons. The effect of ionic strength on the depletion of a hydrophobic organic contaminant (namely pyrene) from the sediment by diffusion was found to be minimal under the conditions of these experiments.

Ground water transport of hydrophobic organic compounds in the presence of dissolved organic matter

AbstractThe effects of dissolved organic matter (DOM) on the transport of hydrophobic organic compounds in soil columns were investigated. Three compounds (naphthalene, phenanthrene and DDT) that spanned three orders of magnitude in water solubility were used. Instead of humic matter, molecularly well‐defined DOM represented by Triton X‐100, a nonionic industrial detergent, and bovine serum albumin protein were used. In batch isotherm studies, the sorption of naphthalene to both model DOMs appeared to be hydrophobic in nature and quantitatively similar to the binding to humic materials. Equations were derived to model the enhanced transport of organic compounds by DOM based on octanol/water partition coefficients, Kow. For a specific soil and DOM level, it was shown theoretically and experimentally that all organic compounds with Kow values above a specific value should move at the same rate in ground water. In some situations, DOM can increase the movement of highly hydrophobic compounds, such as DDT, by a factor of a thousand or more. This enhanced transport in the presence of DOM can either be a problem, as with ground water contaminant spreading, or a benefit, as with contaminated aquifer cleanup.

Facilitated Degradation

Dissolved organic macromolecules have been found to facilitate the transport of hydrophobic organic compounds in the soil. The facilitated transport increases the speed with which toxic and carcinogenic compounds reach the ground water drinking supply. The bacterial degradation of hydrophobic pollutants attached to the dissolved organic macromolecules is unknown. A better understanding is crucial for assessing the importance of the facilitated transport concept for drinking water quality. The degradation of C-14 labelled hexachlorobenzene (HCB) in a saturated soil, with and without 500 mg Blue Dextran/l (BD, model macromolecule) was measured by the amount of radioactive carbon dioxide produced. The soil was contained in stainless steel columns which were purged continuously with sterile air. The lag phase was much shorter in the columns with BD and at the end of the experiment all BD was consumed. In a current batch study with HCB-adapted bacteria the possibility of differentiating between degradation of HCB free in solution and HCB associated with the macromolecule is examined by evaluating three different mathematical models. Model 1 assumes only HCB free in solution is degraded, only by bacteria in solution. Model 2 assumes only HCB associated to BD is degraded, only by associated bacteria. Model 3 assumes associated HCB is degraded by associated bacteria and HCB free in solution is degraded in solution.