Competitive sorption between 17alpha-ethinyl estradiol and naphthalene/phenanthrene by sediments

Steroid hormones such as 17alpha-ethinyl estradiol (EE2) have been frequently detected at various levels in surface waters downstream of many municipal wastewater treatment facilities. Their fate, transport, and environmental risk are currently not well characterized. This study examined the competitive sorption between EE2 and two aromatic hydrocarbon compounds, phenanthrene and naphthalene, by three sediments. The sorption isotherms of phenanthrene and naphthalene were measured at 22 +/- 0.5 degrees C using a batch technique with initial aqueous concentrations (Co) of EE2 at 0, 100, 500, and 2000 microg/L. Competitive sorption varied between EE2 and phenanthrene or naphthalene on the sediments. The linearity of the naphthalene sorption isotherm was found to increase as a function of the cosorbate EE2 concentration from 0 to 2000 microg/L. The single-point naphthalene KD value at equilibrium aqueous-phase naphthalene concentration (Ce) of 25 microg/L was reduced by 19-26% and 27-48% at Co (EE2) = 100 and 500 microg/L, respectively. The sorption of phenanthrene at its low Ce range was similarly affected by EE2, but to a much less extent, possibly because phenanthrene is more hydrophobic than EE2. At high phenanthrene Ce, no measurable change was observed even at CO (EE2) = 2000 microg/L. While the effect of naphthalene on EE2 sorption was insignificant, the competitive effect on the sorption of EE2 by phenanthrene was very significant at low EE2 concentrations. The measured single-point EE2 KD values decreased as much as 35% as the phenanthrene Ce increases from below 10 microg/L to slightly above 100 microg/L. This study suggests that the fate and transport of emerging pollutants such as EE2 could be affected in the presence of more hydrophobic pollutants in aquatic systems.     

Phenanthrene and pyrene sorption and intraparticle diffusion in polyoxymethylene, coke, and activated carbon

We report sorption isotherms and uptake kinetics for phenanthrene and pyrene with three organic model sorbents: polyoxymethylene (POM), coke, and activated carbon. We combine batch equilibration and kinetic experiments with the direct observation of the long-term diffusion of phenanthrene and pyrene as measured within cross-sectioned particles using microprobe laser-desorption laser-ionization mass spectroscopy (muL2MS). For POM pellets, the intraparticle concentration profiles predicted from kinetic batch experiments and a polymer diffusion model with spherical geometry are in agreement with the independent muL2MS measurements. For coke particles, the apparent diffusivities decreased with smaller particle size. These trends in diffusivities were described by a sorption-retarded pore diffusion model with a particle-size-dependent solid-water partitioning coefficient obtained from apparent equilibrium observed in the kinetic batch studies. For activated carbon, the muL2MS measurements showed faster radial diffusion of phenanthrene and pyrene into the particle interior than predicted from diffusion models based on a single sorption domain and diffusivity. A branched pore kinetic model, comprising polycyclic aromatic hydrocarbon (PAH) macropore diffusion with kinetic exchange of PAH between macroporous and microporous domains, fits the experimental observations better. Because of parallel macro- and microdiffusion processes, nonlinear sorption isotherms, and a concentration-dependent diffusivity, it is not possible to make independent parameter estimations for intraparticle diffusion in activated carbon using our present procedures.     

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.     

Roles of acetone-conditioning and lipid in sorption of organic contaminants

Sorption of phenanthrene and 1-naphthol by a peat soil (PS) and its humic acid fractions (HAs) and humin (HM) was examined. Both phenanthrene and 1-naphthol consistently had decreased isotherm nonlinearity in the order PS > HA1 (first fraction) > HA7 (seventh fraction), due to decreased heterogeneity of soil organic matter (SOM). High isotherm nonlinearity of HM was attributed to the condensed structure of SOM in it. Acetone-conditioning increased sorption affinity and isotherm nonlinearity of HAs and HM for phenanthrene, and the conditioning effect was more pronounced at low solute concentrations. However, sorption of 1-naphthol by PS, HAs, and HM was insignificantly affected by acetone-conditioning, suggesting that 1-naphthol could have disparate distribution of sorbed sites from phenanthrene due to their structure and hydrophobicity difference. Lipid removal further increased sorption of phenanthrene and 1-naphthol by acetone-conditioned PS, HAs, and HM, due to increased accessibility of high-energy sites in SOM. Nonlinearity of phenanthrene and 1-naphthol also increased after lipid removal from the acetone-conditioned sorbents. In 1-naphthol- and phenanthrene-lipid competitive sorption systems, lipid had strong competition with phenanthrene, whereas 1-naphthol exhibited cooperative sorption with lipid on lipid-free PS, HAs, and HM, again showing the different sorption characteristics between phenanthrene and 1-naphthol.     

Sorption of Eu(III) on humic acid or fulvic acid bound to hydrous alumina studied by SEM-EDS, XPS, TRLFS, and batch techniques

To identify the effect of humic acid (HA) and fulvic acid (FA) on the sorption mechanism of Eu(III) on organic--inorganic colloids in the environment at a molecular level, surface adsorbed/ complexed Eu(III) on hydrous alumina, HA-, and FA-hydrous alumina hybrids were characterized by using X-ray photoelectron spectroscopy (XPS) and time-resolved laser fluorescence spectroscopy (TRLFS). The experiments were performed in 0.1 mol/L KNO3 or 0.1 mol/L NaClO4 under ambient conditions. The pH values were varied between 2 and 11 at a fixed Eu(III) concentration of 6.0 x 10(-7) mol/L and 4.3 x 10(-5) mol/L. The different Eu(III)/FA(HA)/hydrous alumina complexes were characterized by their fluorescence emission spectra ((5D0-F1)/ (5D0 --> 7F2)) and binding energy of Eu(III). Inner-sphere surface complexation may contribute mainly to Eu(III) sorption on hydrous alumina, and a ternary surface complex is formed at the HA/ FA-hydrous alumina hybrid surfaces. The sorption and species of Eu(III) in ternary Eu-HA/FA-hydrous alumina systems are not dominated by either HA/FA or hydrous alumina, but are dominated by both HA/FA and hydrous alumina. The results are important for understanding the sorption mechanisms and the nature of surface adsorbed Eu(III) species and trivalent chemical homologues of Eu(III) in the natural environment.     

Facilitating effects of metal cations on phenanthrone sorption in soils

Effects of metal cations (Na+, Ca2+, and Al3+) on phenanthrene sorption were investigated using two soils with contrasting organic carbon (OC) contents. The presence of the polyvalent cations (i.e., Ca2+ or Al3+) at a concentration of 0.01 mol/L significantly increased the capacity and nonlinearity of phenanthrene sorption to soils compared with the monovalent Na+. The effects were governed by the content of soil OC. Rubbery OC (i.e., soft, amorphous OC including dissolved organic carbon (DOC)) tended to become condensed on soil surfaces as evidenced by a decrease in the signals of the 1H NMR spectra of DOC and an increase in the glass transition temperature (Tg) of the soils when the polyvalent cations were present. Increasing Ca2+ concentration led initially to an effect similar to that of the polyvalent cations in the low cation concentration range, and the effect was gradually attenuated as Ca2+ concentration further increased. These findings lead us to propose that the modifications in the physical configuration and chemical characteristics of OC resulting from the presence of metal cations account for the increase in the capacity and nonlinearity of phenanthrene sorption to the soils. This study points to an important role of metal cations in the sorption and fate of phenanthrene in the soil environment.     

Adsorption and desorption of phenanthrene on carbon nanotubes in simulated gastrointestinal fluids

Adsorption of phenanthrene on carbon nanotubes (CNTs) and bioaccessibility of adsorbed phenanthrene were studied in simulated gastrointestinal fluids. Adsorption of phenanthrene on CNTs was suppressed in pepsin (800 mg/L) solution (gastric) and bile salt (500 and 5000 mg/L) fluids (intestinal). In addition to competitive sorption, pepsin and high-concentration bile salt (5000 mg/L, above critical micelle concentration) solubilized phenanthrene (3 and 30 times of the water solubility, respectively), thus substantially reduced phenanthrene adsorption on CNTs. Pepsin and bile salts also increased the rapidly desorbing phenanthrene fraction from CNTs. The rapidly desorbing phase lasted less than 1 h for all CNTs. Further, 43-69% of phenanthrene was released from CNTs after desorption in the simulated gastric and intestinal fluid at low bile salt concentration while 53-86% was released in the gastric and intestinal fluid at high bile salt concentration. These findings suggest that the release of residual hydrophobic organic compounds from CNTs could be enhanced by biomolecules such as pepsin and bile salts in the digestive tract, thus increasing the bioaccessibility of adsorbed phenanthrene and possibly the overall toxicity of phenanthrene associated CNTs.     

Identification and characterization of sorption domains in soil organic matter using strucuturally modified humic acids

The sorption of phenanthrene was examined in humic acids (HAs) from different sources: a compost, a peat soil, and a mineral soil. Sub-samples of each HA were subjected to bleaching or hydrolysis to remove predetermined chemical groups from their structures. Bleaching successfully removed a large percentage of rigid, aromatic moieties, whereas hydrolysis removed the mobile, carbohydrate components. Phenanthrene sorption by all HAs was nonlinear (N < 1). However, the phenanthrene isotherms of the bleached HAs were more linear than those of the untreated HAs, whereas the removal of the carbohydrate components by hydrolysis produced more nonlinear isotherms. The introduction of pyrene to the phenanthrene sorption system yielded more linear isotherms for all the HAs, indicative of competitive sorption. Proton spin-spin (1H T2) relaxation determined by nuclear magnetic resonance (NMR) was used to identify separate rigid (condensed) and flexible (expanded) 1H populations and to determine their distribution. These 1H domains were highly sensitive to temperature and correlated well with reported glass transition temperatures for HAs. In combination with the chemical treatments, sorption, and spectroscopic data, we were able to observe some significant relationships among chemical groups, sorption behavior, and structural characteristics.     

Competitive sorption of pyrene on wood chars

Sorption isotherms of pyrene on original and heat-treated wood chars were examined to understand its sorption behavior. Pyrene in single-solute systems had nonlinear isotherms. Polanyi-based dual-domain model fit sorption data well, and the model results showed that the adsorption component dominated pyrene sorption by original char at all aqueous concentrations. In contrast, this adsorption component contributed a much lower fraction to the total sorption by the heat-treated char, and dominated only at low solute concentrations; with increasing concentration, partitioning became a predominant contributor to the total sorption. Competitive effect of four cosolutes, phenanthrene (Phen), benzo[a]anthracene (BaA), 2,2-methylene-bis (4-methyl-6-tert-butylphenol) (MMBP), and phenol on pyrene sorption by original and treated chars was examined to understand the underlying mechanism of competition. Hydrophobicity (adsorbability) and molecular size of competitors played an important role in competition with pyrene by both chars, suggesting the direct competition for sorption sites and pore blockage mechanism. Competitive sorption results indicated that the fate and transport of hydrophobic organic chemicals (e.g., pyrene) could be strongly affected in the presence of coexisting organic contaminants with high hydrophobicity and large molecularsize,thereby, enhancing the mobility and leachability of these chemicals.     

石墨烯电化学传感器法快速测定植物油中的苯并（a）芘

利用新型纳米材料石墨烯与聚合物材料壳聚糖构建纳米电化学传感器,研究苯并（a）芘（benzo(a)pyrene,BaP）的电化学性质,并建立一种植物油中BaP的快速灵敏检测方法。BaP在该纳米电化学传感器上的循环伏安图表明在1.0?V处出现了一个形状良好的氧化峰,无还原峰,为一种不可逆的氧化还原过程;优化纳米电化学传感器法快速测定植物油中BaP的实验条件,结果表明：壳聚糖-石墨烯（1∶2,V/V）混合溶液作为修饰液,修饰量5?μL、电解质LiClO4浓度0.2?mol/L、硫酸浓度0.1?mol/L、富集时间15?min,在此条件下,BaP的氧化还原峰电流与其浓度在0～100?nmol/L之间具有良好的线性关系,校正曲线方程为：Ip=0.116?2CBaP＋22.926?2（R2=0.997?8）,其检测限为0.103?nmol/L（RSN=3）。利用该法对香油样品中的BaP进行检测,其加标回收率为98.51%～100.57%,检测结果与高效液相色谱法基本一致,并且具有良好的稳定性和重复性,样品预处理简单、检测时间短、速度快、成本低。     

Sorption mechanisms of phenanthrene, lindane, and atrazine with various humic acid fractions from a single soil sample

The sorption behavior of organic compounds (phenanthrene, lindane, and atrazine) to sequentially extracted humic acids and humin from a peat soil was examined. The elemental composition, XPS and (13)C NMR data of sorbents combined with sorption isotherm data of the tested compounds show that nonspecific interactions govern sorption of phenanthrene and lindane by humic substances. Their sorption is dependent on surface and bulk alkyl carbon contents of the sorbents, rather than aromatic carbon. Sorption of atrazine by these sorbents, however, is regulated by polar interactions (e.g., hydrogen bonding). Carboxylic and phenolic moieties are key components for H-bonding formation. Thermal analysis reveals that sorption of apolar (i.e., phenanthrene and lindane) and polar (i.e., atrazine) compounds by humic substances exhibit dissimilar relationships with condensation and thermal stability of sorption domains, emphasizing the major influence of domain spatial arrangement on sorption of organic compounds with distinct polarity. Results of pH-dependent sorption indicate that reduction in sorption of atrazine by the tested sorbents is more evident than phenanthrene with increasing pH, supporting the dependence of organic compound sorption on its polarity and structure. This study highlights the different interaction mechanisms of apolar and polar organic compounds with humic substances.     

Dynamic behavior of semivolatile organic compounds in indoor air. 2. Nicotine and phenanthrene with carpet and wallboard

The surface interactions of nicotine and phenanthrene with carpet, painted wallboard, and stainless steel were investigated in a room-sized environmental test chamber. Adsorption kinetics were tested by flash evaporating a known mass of each compound into a sealed 20 m3 chamber containing one or more of the tested sorbents. In each experiment, one or more emissions were performed after the gas-phase concentration had reached an apparent plateau. At the end of each experiment, the chamber was ventilated and resealed to monitor reemission of the compound from the sorbents. Kinetic sorption parameters were determined by fitting a mass-balance model to the experimental results. The sorption capacity of stainless steel was of similar magnitude for nicotine and phenanthrene. Sorption of nicotine on carpet and wallboard was much stronger, with equilibrium partitioning values 2-3 orders of magnitude higher. The sorption capacities of phenanthrene on carpet and wallboard were smaller, approximately 10-20% of the stainless steel values. The rates of uptake are of similar magnitude for all sorbate--sorbent pairs and are consistent with the limit imposed by gas-phase boundary-layer mass transport. The rates of desorption are much faster for phenanthrene than for nicotine. Model simulations predict average nicotine levels in a typical smoking residence that are consistent with published data.     

Effects of competitor and natural organic matter characteristics on the equilibrium sorption of 1,2-dichlorobenzene in soil and shale

The competitive sorption behaviors of 1,2-DCB in binary solute systems in four natural sorbents having natural organic matter (NOM) matrixes of different physicochemical characters were investigated in batch reactors. Specifically, the study focused on investigating how the extent of 1,2-DCB competitive sorption depends on (i) the rigidity of NOM matrixes as assessed by the efficiency of chemical oxidation and (ii) the closeness of competitor structure to that of the primary solute. The chemical oxidation and elemental composition results suggest that the shale NOM is the most reduced and condensed, the peat was the most oxidized and amorphous, and two surface soils had intermediate NOM structures. Four chlorinated benzenes and phenanthrene were used as competing solutes. All five chemicals exhibited competition against 1,2-DCB in all sorbents, including the peat, but the extent of competition varied significantly. Little difference in the extent of competition with 1,2-DCB was observed for the various chlorinated benzenes even though some were liquids and some were solids at the experimental temperature. All of the chlorobenzenes were more effective competitors than phenanthrene. The shale showed markedly different competition features from the other sorbents, with a much smaller competitive effect at a given sorbed volume of competitor. However, normalizing sorbed competitor volumes by the capacity of the adsorption domain in the Polanyi-Manes single-solute partition-adsorption model (V0) produced qualitatively similar competitive behavior for each solute; displacement of 1,2-DCB increased with increasing sorbed competitor volumes up to V0, and little additional competition occurred beyond that point. The extent of competition was positively correlated with the maximum adsorption capacity and the fraction of "hard" and "soot" carbon contents as assessed by chemical and thermal oxidation methods. These findings indicate that competition is associated with voids in the NOM structure, that these voids are likely present within the condensed ("hard" plus "soot") carbon domain, and therefore that diagenetic alteration of NOM plays a central role in determining competitive sorption characteristics for hydrophobic contaminants.     

Dispersion state and humic acids concentration-dependent sorption of pyrene to carbon nanotubes

Sonication and humic acids (HA) are known to disperse carbon nanotube (CNT) suspensions, but potential effects on sorption of chemicals to CNTs remain poorly understood. We applied a passive sampling method to investigate the influence of dispersion/aggregation on sorption of pyrene to CNTs. Sonication broke down CNT aggregates and increased pyrene sorption affinity by up to 1.39 orders of magnitude. Sorption surfaces newly exposed by sonication remained available to pyrene even after reaggregation occurred, suggesting an irreversible effect of sonication. The presence of HA decreased sorption of pyrene to CNTs, but at the highest HA concentration investigated (200 mg/L), sorption affinity was still 1.90 orders of magnitude larger than sorption of pyrene to HA alone. Specific interactions between pyrene and CNTs were thus still taking place, in spite of the presence of a HA coating on the CNTs' surface. A greater suppression of sorption by CNTs occurred when the HA addition was combined with a sonication pretreatment. Sorption isotherm fitting indicated that the maximum sorption capacity, sorption affinity, and heterogeneity of the CNT surface were all affected by sonication and the presence of HA at a concentration as low as 1 mg/L. The present results contribute to an improved understanding of the sorption behavior of CNTs in both natural and wastewater systems.     

Desorption kinetics of phenanthrene in aquifer material lacks hysteresis

Desorption experiments were carried out in flow through columns following long-term sorption batch experiments (up to 1010 days at 20 degrees C; Rügner, H.; Kleineidam, S.; Grathwohl, P. Long-term sorption kinetics of phenanthrene in aquifer materials. Environ. Sci. Technol. 1999, 33, 1645-1651) to elucidate sorption/desorption hysteresis phenomena of phenanthrene in aquifer materials. Most of the sorbents employed in this study (homogeneous lithocomponents separated from aquifer sediments or fresh rock fragments) showed highly nonlinear sorption isotherms because of coal particles embedded inside the grains. Because sorption capacities were high, sorption equilibrium was not reached in most of the sorbents during the initial sorptive uptake experiments lasting up to 1010 days. Desorption was studied up to 90 days at 20 degrees C. The temperature was raised after that stepwise from originally 20 to 30, 40, 50, and finally to 70 degrees C for selected samples to estimate activation energies of desorption. A numerical intraparticle pore diffusion model was used to fit sorptive uptake data and subsequently for pure forward prediction of the release rates in the desorption column experiments. Desorption was initially fast followed by extended tailing which in other studies is fitted by using multirate first-order models. Our results demonstrate that the retarded intraparticle pore diffusion model can predict the desorption rates with a single diffusion rate constant obtained independently from the long-term batch sorption experiment. No evidence for hysteresis was found, suggesting that many hysteresis phenomena reported earlier are experimental artifacts resulting from nonequilibrium effects and "nonphysical" models. The different temperature steps allowed one to additionally calculate activation energies of desorption (45-59 kJ mol(-1)), which were in reasonably good agreement with results from earlier studies for a retarded pore diffusion process. In addition, equilibrium sorption isotherms were determined at 20 and 40 degrees C to compare sorption and desorption enthalpies. Both were in good agreement, confirming that desorption was not significantly different from sorption.     

紫甘薯花青素体外抑制α-糖苷酶活性研究

为了研究紫甘薯花青素体外对α-糖苷酶活性的影响,采用HPLC和LC-MSn对紫A19(ZA1)和京薯(JS6)中花青素的含量和组分进行对比分析。结果表明：两种紫甘薯花青素含量分别为52.44mg/g和39.46mg/g,其组分基本一致,不同的是ZA1另含牵牛花色素类色素,而JS6另含天竺葵色素类色素;这两种紫甘薯花青素对α-糖苷酶活性都有抑制效果,但ZA1的抑制效果最佳,当加入质量浓度为0.1mg/mL 600μL(即抑制剂ZA1占总反应体积的18%)、抑制时间15min、抑制温度40℃时对α-糖苷酶活性抑制率可达50%以上,用Lineweaver-Burk双倒数作图考察其抑制类型,根据曲线可判定为竞争性抑制,抑制常数Ki=5.43×10-2mmol/L,vmax=1.71μmol/(L ·min)。     

Sorption of aromatic organic contaminants by biopolymers: effects of pH, copper (II) complexation, and cellulose coating

Sorption of hydrophobic organic compounds (HOCs) (i.e., pyrene, phenanthrene, naphthalene, and 1-naphthol) by original and coated biopolymers was examined. Lignin yielded nonlinear isotherms due to its glassy character. Except for pyrene, cellulose showed linear isotherms for other compounds, indicating a partitioning dominant mechanism. Sorption of 1-naphthol by lignin decreased with increasing pH, attributed to both the increased pi e theta-pi e theta repulsion and weakened hydrogen bonds, while the affinity reduction of cellulose for 1-naphthol with increasing pH resulted from only the decrease in H-bonding due to its absence of benzene ring. Complexation of lignin with Cu2+ increased the sorption affinity for phenanthrene (2.6 times) and slightly enhanced its isotherm nonlinearity. For 1-naphthol, lignin-Cu2+ complex had a much higher sorption capacity (7 times)than the original lignin, accompanied bythe increased isotherm nonlinearity. Cellulose-coated lignin showed increased sorption affinity and more pronounced nonlinearity for 1-naphthol than the lignin-Cu2+ complex. In comparison, cellulose coating exhibited little effect on sorption affinity for phenanthrene relative to the lignin-Cu2+ complex. Isotherm nonlinearity of coated lignins increased with increasing cellulose coating, indicating more condensed domains produced, supported by an increase (from 68.9 degrees C for the original lignin to 82.4 degrees C for the highest cellulose coating level) in glass transition temperature (Tg). Results of this study highlightthe importance of structure, polarity, surface O-containing functional groups, and surface charges of biopolymers in controlling HOC sorption.     

Solubility-normalized combined adsorption-partitioning sorption isotherms for organic pollutants

Equilibrium sorption isotherms were measured for five different low-polarity organic compounds (benzene, trichloroethene, 1,2- and 1,4-dichlorobenzene, and phenanthrene) over a wide concentration range. The investigated sorbents can be grouped into the following three classes: (1) humic soil organic matter, which shows linear sorption isotherms (solely partitioning, as observed in the peat sample); (2) carbon materials, which were thermally altered (due to their natural history or industrial production) and thus contain a high specific surface area and exhibit nonlinear isotherms, and (3) pure engineered microporous materials (e.g., zeolites and activated carbon), where adsorption is solely due to a pore-filling process. Sorption of all compounds was fitted very well by the Polanyi-Dubinin-Manes (PDM) model, which for sorbents containing humic organic matter (e.g., peat) was combined with linear partitioning. Both the partitioning and the Polanyi-Dubinin-Manes model predict unique sorption isotherms of similar compounds if the solubility-normalized aqueous concentration is used. In addition, an inverse linear relationship between the distribution coefficient (Kd) and water solubility, which was very well confirmed by the data, is obtained. This also leads to unit-equivalent Freundlich sorption isotherms and explains the often observed apparent correlation between sorption capacity at a given concentration (e.g., Freundlich coefficient) and sorption nonlinearity (Freundlich exponent).     

Assessing sequestration of selected polycyclic aromatic hydrocarbons by use of adsorption modeling and temperature-programmed desorption

Sequestration of phenanthrene and pyrene was investigated in two soils--a sandy soil designated SBS and a silt-loam designated LHS--by combining long-term batch sorption studies with thermal desorption and pyrolysis of amended soil samples. The Polanyi-based adsorption volume and the adsorbed solute mass increased with aging for both soils, thus demonstrating the mechanism for observed sequestration. Despite rigorous thermal analysis, 30-62% (SBS sand) and 8-30% (LHS silt-loam) of phenanthrene could not be recovered after 30-270 days of sorption, with the increase in desorption resistance showing greater significance in SBS sand. For both soils, these values were 20-65% of adsorbed phenanthrene mass. Activation energies estimated from the temperature-programmed desorption (TPD) of sorbed phenanthrene at < or = 375 degrees C were 51-53 kJ/mol, consistent with values derived for desorption of organic compounds from humic materials. The activated first-order model fitting of observed TPD data supports the conclusion that the desorption-resistant fraction of phenanthrene has become sequestered onto condensed organic domains and requires temperatures exceeding 600 degrees C to be released. The work demonstrates the use of thermal analysis in complementing the Polanyi-based adsorption modeling approach for assessing the mechanistic basis for sequestration of organic contaminants in soils.