Competitive sorption of pyrene, phenanthrene, and naphthalene on multiwalled carbon nanotubes

Knowledge of toxic chemical sorption by carbon nanotubes (CNTs) is critical for environmental application of CNTs as superior sorbents and for environmental risk assessment of both CNTs and toxic chemicals. Single-solute sorption results were reported in the literature, however, they cannot be used for predicting pollutant sorption by CNTs in wastewater and natural water systems where multiple organic contaminants are present. In this study, competitive sorption of pyrene, phenanthrene, and naphthalene on a multiwalled CNT material was investigated. All isotherms in single-, bi-, and tri-solute systems were fitted well by the Dubinin-Ashtakhov (DA) model. The isotherm of a given primary solute changed from being significantly nonlinear to nearly linear when competitors were added. The observed competitive sorption depended on the relative equilibrium concentrations of both primary and cosolutes. Significant competition was observed at relatively low concentrations of primary solute and high concentrations of competitors, while competition was much weaker in the case of relatively high concentrations of primary solute and low competitor concentrations. When the relative concentration of primary solute (Ce/Cs) approached 1, competition by other solutes seemed to disappear. Sorption and competition of three polycyclic aromatic hydrocarbons (PAHs) on CNTs could not be explained with either pore-filling or partition-adsorption mechanisms. A Polanyi-based surface adsorption mechanism was proposed to interpret the observed sorption and competition.     

Strong sorption of phenanthrene by condensed organic matter in soils and sediments

The nonhydrolyzable carbon (NHC) and black carbon (BC) in three contaminated soils and seven sediments from the Pearl River Delta and Estuary, China, were isolated upon treatments with an acid hydrolysis method and with a combustion method at 375 degrees C, respectively, and their sorption isotherms for phenanthrene (Phen) were established. It was found that NHC is chemically and structurally different from the biopolymer and humic substances and consists mainly of aliphatic and aromatic carbon using elemental analysis, 13C nuclear magnetic resonance spectroscopy (13C NMR), and Fourier transformed infrared spectroscopy (FTIR). All the sorption isotherms are nonlinear and are well fitted by the Freundlich model. The single-point organic carbon-normalized distribution coefficient (K(oc)) measured for the isolated NHC is 1.3-7.7 times higher than that for the bulk samples at the same aqueous concentration of Phen. The NHC fractions play a dominant role to the overall sorption in the bulk samples. The bulk soils and their NHC fractions have lower sorption capacity than the bulk sediments and their NHC fractions, relating to the different source of organic matter between soils and sediments. The Phen sorption capacity in the NHC samples is related significantlyto H/C ratios and aliphatic carbon, but negatively to aromatic carbon, demonstrating the important role of aliphatic carbon to the Phen sorption and the fate in the investigated soils and sediments.     

Adsorption and hysteresis of bisphenol A and 17alpha-ethinyl estradiol on carbon nanomaterials

Adsorption of 17alpha-ethinyl estradiol (EE2) and bisphenol A (BPA) on carbon nanomaterials (CNMs) was investigated. Single point adsorption coefficients (K) showed significant relationship with specific surface areas of CNMs for both chemicals, indicating surface area is a major factor for EDC adsorption on CNMs. BPA adsorption capacity is higher than EE2 on fullerene and single-walled carbon nanotubes (SWCNT). Our molecular conformation simulation indicated that BPA has a unique ability to adsorb on the curvature surface of CNMs because of its "butterfly" structure of two benzene rings. The higher adsorption capacity of BPA over EE2 is well explained by considering helical (diagonal) coverage of BPA on the CNMs surface and wedging of BPA into the groove and interstitial region of CNM bundles or aggregates. The comparison of K(HW) (hexadecane-water partition coefficient) normalized adsorption coefficients between EDCs and several polyaromatic hydrocarbons indicates that pi-pi electron donor--acceptor system is an important mechanism forthe adsorption of benzene-containing chemicals on CNMs. The high adsorption capacity and strong desorption hysteresis of both chemicals on SWCNT indicate that SWCNT is a potential adsorbent for water treatment.     

Distributed reactivity model for sorption by soils and sediments. 15. High-concentration co-contaminant effects on phenanthrene sorption and desorption

Soil and sediment materials having organic matter matrixes of different geochemical character were examined with respect to their sorption and desorption of phenanthrene in the presence of order-of-magnitude larger concentrations of trichloroethylene (TCE) and dichlorobenzene (DCB). These co-contaminants depressed phenanthrene sorption in the lowest residual solution phase concentration ranges of that target solute investigated, whereas in its highest residual concentration regions phenanthrene sorption was either not affected or was actually enhanced. In both concentration ranges, the effects observed varied with the hydrophobicity and relative concentration of the co-contaminant and with the geological maturity and associated degree of condensation and aromatization of the soil/sediment organic matter (SOM). Desorption isotherms for phenanthrene indicate the occurrence of increased hysteresis in the presence of high concentrations of DCB and TCE, the effect increasing with increased degree of associated organic condensation. Tests in which high concentrations of DCB and TCE were added after completion of the phenanthrene desorption experiments show clear evidence of partial displacement of sorbed phenanthrene to the solution phase. The results of the work support the concept of SOM glass-transition concentrations, above which matrix deformation occurs and so-called "conditioning effects" are observed.     

Derivation of an aquatic predicted no-effect concentration for the synthetic hormone, 17 alpha-ethinyl estradiol

17alpha-Ethinyl estradiol (EE2) is a synthetic estrogen widely used in combination with other steroid hormones in oral contraceptives and in the contraceptive patch. EE2 has been detected in sewage treatment plant effluents in the low nanogram -per-liter range and occasionally in surface waters in the U.S., U.K., Canada, Brazil, Germany, and elsewhere. The mode of action is receptor-mediated, and estrogen receptors exist in mammals and other vertebrates. A large number of studies on the effects of EE2 on aquatic organisms exist. One hundred English language studies published between 1994 and 2007, one as yet unpublished study, and findings published in conference proceedings (in German) were compared to published data quality criteria to identify the most relevant studies for deriving a predicted no-effect concentration (PNEC). Reproduction in fish was identified as the most sensitive end point in aquatic species. A species sensitivity distribution was constructed using no observed effect concentrations (NOECs) for reproductive effects from 39 papers in 26 species, resulting in a median hazardous concentration at which 5% of the species tested are affected (HC5,50) of 0.35 ng/L. After comparing this HC5,50 to all of the laboratory and field-derived toxicity information available for EE2, we recommend using 0.35 ng/L as the PNEC for EE2 in surface water. This PNEC is below 95% of the existing NOECs for effects on reproduction and is also below virtually all of the NOECs for vitellogenin induction in the key fish reproduction studies.     

A distributed reactivity model for sorption by soils and sediments. 14. Characterization and modeling of phenanthrene desorption rates

Rates and extents of phenanthrene desorption were studied for more than 250 days as functions of sorbent type, initial loading level, and aging. Apparent first-order desorption rate constants for the slowly desorbing fraction were found to (i) range from 0.00086 to 0.148 days-1 for geosorbents that contain geologically mature kerogen and less rigid humic-type soil organic matter, respectively, (ii) decrease by as much as an order of magnitude with decreasing initial sorbed solid-phase phenanthrene concentration, (iii) decrease by a factor of 2 with increasing aging time for a humic topsoil but remain unaffected by aging time beyond 3 months for a shale, and (iv) be 1-2 orders of magnitude lower than rate constants for the rapidly desorbing phenanthrene fractions for any given contaminated sample. Six models were used to fit the desorption rate data. Biphasic diffusion and biphasic first-order models with three fitting parameters possess broad utility and are potentially useful in a variety of environmental applications. Disadvantages of a five-parameter triphasic first-order desorption model, a two-parameter gamma-function model, and a one- or two-parameter pore diffusion model are also discussed.     

铜绿假单胞菌对萘和菲降解特性研究

研究不同pH和温度条件下,铜绿假单胞菌（Pseudomonas aeruginosa）对多环芳烃中萘和菲的降解效果。结果表明,以活性炭为吸附载体,多环芳烃为唯一碳源,将此菌株培养48 h后,pH值为7.0时,萘的降解率可达25.68%,脱氢酶活性达到33.42 （μg/mL）·h;菲的降解率可达41.9%,脱氢酶活性达到37.44 （μg/mL）·h。当温度为37 ℃时,萘的降解率可达27.7%,脱氢酶活性达到33.60 （μg/mL）·h;菲的降解率可达34.5%,脱氢酶活性达到39.96 （μg/mL）·h。     

Micellar solubilization of naphthalene and phenanthrene from nonaqueous-phase liquids

The equilibrium partitioning of the polycyclic aromatic hydrocarbon (PAH) compounds naphthalene and phenanthrene, from nonaqueous-phase liquids (NAPLs) into micellar solutions of five different nonionic polyethoxylated surfactants, is evaluated in this study. A series of synthesized NAPLs, comprised of naphthalene and/or phenanthrene dissolved in hexadecane at varying concentrations, were equilibrated with surfactant solutions in well-mixed batch systems. It was observed that the extent of micellar partitioning of PAH compounds increases linearly with their relative abundance in the NAPLs. A theoretical liquid-liquid partitioning framework that describes PAH equilibrium partitioning between the NAPL, aqueous, and the liquid-like micellar phases is presented. Although the maximum solubilization capacity of micelles is generally higher for naphthalene as compared to phenanthrene, results indicate that with certain NAPLs phenanthrene may be solubilized to a similar extent as naphthalene, even when equal mole fractions of the compounds are present in the NAPLs. Selective solubilization of naphthalene over phenanthrene into micellar solutions of Brij 35 was observed in systems where naphthalene and phenanthrene were both present. The extent of micellar partitioning of phenanthrene was decreased by approximately 18% in the presence of naphthalene, while naphthalene partitioning was unaffected by the presence of phenanthrene.     

Importance of unburned coal carbon, black carbon, and amorphous organic carbon to phenanthrene sorption in sediments

The aim of this paper was to estimate the contribution to total phenanthrene sorption from unburned coal and black carbon (BC; soot and charcoal) in sediment. We determined sorption isotherms for five Argonne Premium Coal standards over a wide concentration interval (0.01-10 000 ng/L). The coals showed strong and nonlinear sorption (carbon-normalized K(F) = 5.41-5.96; nF = 0.68-0.82). Coal sorption appeared to become more nonlinear with increasing coal maturity. The coal's specific surface area appeared to influence K(F). On the basis of the current coal sorption observations combined with earlier petrographic analyses and BC sorption experiments, we calculated for one particular sediment that coal, BC, and "other" OC were all important to PHE sorption in the environmentally relevant nanogram per liter range. This indicates that it is important to consider strong sorption to coal in the risk assessment of coal-impacted geosorbents (e.g., river beds) where coal is mined/shipped and manufactured gas plant sites.     

Aluminum control of phosphorus sorption by lake sediments

Release of reactive (phosphate-like) phosphorus (P) from freshwater sediments represents a significant internal P source for many lakes. Hypolimnetic P release occurs under reducing conditions that cause reductive dissolution of ferric hydroxide [Fe(OH)3]. This hypolimnetic P release may be naturally low or artificially reduced by sediment with naturally high or artificially elevated concentrations of aluminum hydroxide [Al(OH)3]. We presentfield and laboratory data for a common extraction analysis of sediments from 43 lakes differing in trophic status, pH regime, climate, and P loading. The results indicate that a simple sequential extraction of sediment may be a useful predictor of sediment's ability to release P. Sequential extractions of sediment P, Al, and Fe by water (H2O), bicarbonate-dithionite (BD), and NaOH (at 25 degrees C) showed that negligible amounts of P would be released from lake sediments during hypolimnetic anoxia if either (1) the molar Al(NaOH-25):Fe(BD) ratio is > 3 or (2) the molar Al(NaOH-25):P(H2O+BD) ratio is > 25. These ratios can be used as operational targets for estimation of sediment P release potential and Al dosing of P-rich sediment to prevent hypolimnetic P release under anoxic conditions.     

Sorption of phenanthrene by nonhydrolyzable organic matter from different size sediments

Nonhydrolyzable organic carbon (NHC) and sorption isotherms of phenanthrene (Phen) on six size-fractionated NHC fractions in two sediments from the Pearl River and Estuary, South China, were investigated. It was found that NHC including ancient organic carbon, black carbon, resistant aquatic organic carbon, and aged soil organic carbon consists mainly of aliphatic and aromatic carbon using 13C nuclear magnetic resonance spectroscopy. The sorption isotherms of Phen by the size-fractionated NHC fractions are nonlinear and are well-fitted to the Freundlich model. For the estuary sediment, the NHC contents and the organic carbon-normalized distribution coefficients (Koc) in the size fractions increase with decreasing particle size. The clay NHC fraction contributes to 70% of the Phen sorption by the bulk NHC isolate. However, for the contaminated river sediment, the NHC contents and the Koc values exhibit no regular variations among the size fractions. The Phen sorption capacities on the size-fractionated NHC fractions of the two sediments are significantly related to their H/C ratios and aliphatic carbon, but negatively to aromatic carbon. The fine-particle NHC fractions with high aliphatic carbon and H/C ratio play a very important role in the sorption, transport, and fate of Phen by the investigated sediments.     

Chemical extractions affect the structure and phenanthrene sorption of soil humin

Humin is a major fraction of soil organic matter and strongly affects the sorption behavior and fate of organic contaminants in soils and sediments. This study evaluated four different extraction methods for soil humins in terms of their organic carbon structural changes and the consequent effects on phenanthrene sorption. Solid-state 13C NMR demonstrated that 0.1 M NaOH exhaustively extracted humin and humin extracted with 6 M HF/HCl at 60 degrees C had a relatively high amount of aliphatic components as compared with 1 M HF-extracted humin. The treatment of 6 M HF/HCl at 60 degrees C greatly reduced carbohydrate components (50-108 ppm) from humin samples, i.e., more than 50% reduction. In addition, the humin from this 6 M HF/HCl treatment contained relatively more amorphous poly(methylene) domains than the humins extracted by other methods. With the respect to phenanthrene sorption, the linearity of sorption isotherm (N) and sorption affinity (Koc) varied markedly among the humin samples extracted by different methods. The NaOH exhaustively extracted humin had the most nonlinear sorption isotherm and the HF-extracted humin had the lowest Koc. It is concluded that humin samples from different extraction procedures exhibited substantial differences in their organic carbon structure and sorption characteristics, even though they were from the same soil. Therefore, one needs to be cautious when comparing the structural and sorption features of soil humins, especially when they are extracted differently. The 6 M HCl/HF extraction at elevated temperature is not encouraged, due to the modifications of chemical structure and physical conformation of organic matter.     

Improved approaches for modeling the sorption of phenanthrene by a range of plant species

Equilibrium sorption of phenanthrene and its relationship with plant lipid contents were investigated using roots and shoots of alfalfa, ryegrass, tomato, potato, carrot, cucumber, zucchini, and pumpkin. Lipid extractions using chloroform and hexane were compared, and the influence of dechlorophyllization on lipid determinations was evaluated. The sorption isotherms were close to linear (R2 > 0.923, P < 0.05) and the plant-water partition coefficients (K(pl)) of phenanthrene obtained from the isotherms exhibited significant and positive correlations with plantlipid contents (R2 > 0.664, P < 0.05). The correlations were more significant (R2 > 0.906, P < 0.001) when dechlorophyllization was included in the lipid extraction. The measured sorption was higher than that estimated using the octanol-water partition coefficient (K(ow)) but was very close to the estimate using the triolein-water partition coefficient (K(tw)). This study leads us to conclude that dechlorophyllization is necessary for plant lipid determination and that K(tw) is more accurate as a substitute for the lipid-water partition coefficient (K(lip)) than K(ow). These novel approaches may provide substantial improvements in the application of partition-limited models for the estimation of plant uptake of organic contaminants.     

Pyrene and phenanthrene sorption to model and natural geosorbents in single- and binary-solute systems

Sorption of pyrene and phenanthrene to model (illite and charcoal) and natural (Yangtze sediment) geosorbents were investigated by batch techniques using fluorescence spectroscopy. A higher adsorption of phenanthrene was observed with all sorbents, which is related to the better accessibility of smaller molecules to micropores in the molecular sieve sorbents. In addition, pyrene sorption in binary-solute systems with a constant initial concentration of phenanthrene (0.1 μmol L(-1) or 2 μmol L(-1)) was studied. A 0.1 μmol L(-1) concentration of phenanthrene causes no competitive effect on the pyrene sorption. A 2 μmol L(-1) concentration of phenanthrene significantly suppresses the sorption of pyrene, especially in the low concentration range; nonlinearity of the pyrene sorption isotherms thus decreases. The competitive effect of 2 μmol L(-1) phenanthrene on the pyrene sorption is overestimated by the ideal adsorbed solution theory (IAST) using the fitted single sorption results of both solutes. An adjustment of the IAST application by taking into account the molecular sieve effect is proposed, which notably improves the IAST prediction for the competitive effect.     

A distributed reactivity model for sorption by soils and sediments 13. Simulated diagenesis of natural sediment organic matter and its impact on sorption/desorption equilibria

Subcritical water treatment was used to effect rapid compositional and functional changes to peat organic matter that mimic those of the natural diagenesis process. Elemental, solid state 13C NMR, FTIR, and calorimetry analyses all indicated that the organic matter of the artificially aged peat was chemically similar to that of geologically mature coal kerogens. This paper extends the work of the previous paper in this series, which investigated the effects of subcritical water treatment of humic topsoil on subsequent phenanthrene sorption and desorption equilibria. As opposed to the previous study, however, changes in sorptive reactivity herein were unequivocally related to changes in organic matter rather than other soil constituents, and organic matter functional changes due to the simulated diagenesis were more accurately characterized. Phenanthrene sorption capacity and isotherm nonlinearity both increased with increasing degrees of artificial aging, supporting the viewpoint that hydrophobic organic contaminant sorption equilibrium properties can be directly related to the degree of diagenesis of geosorbent organic matter. In addition, this work investigated effects of subcritical water treatment of a geologically mature, kerogen-containing shale sample. In contrast to the peat, the functional characteristics of the shale were unchanged by this treatment, and subsequent phenanthrene sorption equilibria were altered far less.     

Mechanisms and factors affecting sorption of microcystins onto natural sediments

The sorption of microcystins (MCs) to fifteen lake sediments and four clay minerals was studied as a function of sediment/clay properties, temperature, and pH through well-controlled batch sorption experiments. All sorption data for both sediments and clays are well described by a nonlinear Freundlich model (n(f) varies between 0.49 and 1.03). The sorption process for MCs exhibited different adsorptive mechanisms in different lake sediments mainly dependent on the sediment organic matter (OM). For sediments with lower OM (i.e., less than 8%), the sorption of MCs decreases with increasing OM and is dominated by the competition for adsorption sites between MCs and OM. In contrast, MC sorption to organic-rich (i.e., more than 8%) sediments increases with increasing OM and is dominated by the interaction between MCs and adsorbed OM. The sorption thermodynamics of MCs onto sediments showed that MC sorption is a spontaneous physisorption process with two different mechanisms. One mechanism is an exothermic process for sediment with lower OM, and the other is an endothermic process for sediment with higher OM. Furthermore, the sorption of MCs onto sediments is pH dependent (sorption decreased with increasing pH). These results provide valuable informations for a better understanding of the natural abiotic attenuation mechanisms for MCs in aquatic ecosystems.     

Effect of temperature and salinity on phosphate sorption on marine sediments

Our previous studies on the phosphate sorption on sediments in Florida Bay at 25 °C in salinity 36 seawater revealed that the sorption capacity varies considerably within the bay but can be attributed to the content of sedimentary P and Fe. It is known that both temperature and salinity influence the sorption process and their natural variations are the greatest in estuaries. To provide useful sorption parameters for modeling phosphate cycle in Florida Bay, a systematic study was carried out to quantify the effects of salinity and temperature on phosphate sorption on sediments. For a given sample, the zero equilibrium phosphate concentration and the distribution coefficient were measured over a range of salinity (2-72) and temperature (15-35 °C) conditions. Such a suite of experiments with combinations of different temperature and salinity were performed for 14 selected stations that cover a range of sediment characteristics and geographic locations of the bay. Phosphate sorption was found to increase with increasing temperature or decreasing salinity and their effects depended upon sediment's exchangeable P content. This study provided the first estimate of the phosphate sorption parameters as a function of salinity and temperature in marine sediments. Incorporation of these parameters in water quality models will enable them to predict the effect of increasing freshwater input, as proposed by the Comprehensive Everglades Restoration Plan, on the seasonal cycle of phosphate in Florida Bay.