Sorption of organic contaminants by biopolymers: role of polarity, structure and domain spatial arrangement

Sorption behavior of hydrophobic organic contaminants (HOCs) (i.e., pyrene, phenanthrene and naphthalene) by native and chemically modified biopolymers (lignin, chitin and cellulose) was examined. Lignins (native and treated) showed nonlinear sorption for all compounds studied, emphasizing their glassy character. Chitins and celluloses had linear isotherms for phenanthrene and naphthalene, illustrating the dominance of partitioning, while pyrene yielded nonlinear isotherms. Sorption capacity (K(oc)) of HOCs was negatively correlated with the polarity [(O+N)/C] of the biopolymers. Aromatic and alkyl+aromatic C percentages, rather than alkyl C content, demonstrated a better correlation with K(oc) values, indicating the importance of aromatic structures for HOC affinity. Hydrophobicity (K(ow))-normalized K(oc) values decreased sharply with increasing percentage of O-alkyl C versus total aliphatic C (O-alkyl C/total aliphatic C) or with polar C/(alkyl+aromatic C) ratio of the biopolymers until their values reached 80% and 4, respectively, illustrating the effect of surrounding polar groups on reducing affinity for HOCs. Overall, the results of this study highlight the role of spatial arrangement of domains within biopolymers in sorption of HOCs, and point to sorbent properties, such as functionality, polarity and structure, jointly regulating the sorption of HOCs in biopolymers.     

Evaluation of impacts of soil fractions on phenanthrene sorption

Phenanthrene sorption to soils and soil fractions was investigated using two contrasting soils with different clay mineral and organic carbon (OC) contents in an attempt to evaluate the contribution of each soil fraction to phenanthrene sorption and the applicability of the carbon-normalized distribution constant (K(OC)) in soils. Sorbents were characterized using surface analysis, solid-state (13)C NMR analysis, and glass transition temperature (T(g)) analysis to gain a insight into the chemical nature of OC in soils. Dissolved organic carbon (DOC) in the soil solution impeded the phenanthrene sorption, while humins accounted for the predominant phenanthrene sorption in soils. The contribution of OC to phenanthrene sorption in soil would be overestimated if only a K(OC)-approach was adopted, since clay minerals could account for much of the sorption, especially when OC was low in soils. Nitrogen gas was shown to be inappropriate for probing non-polar sorption capacity. The results obtained highlight the importance of clay minerals in governing the sorption of phenanthrene in soil, and emphasize the inapplicability of the carbon-normalized distribution coefficient K(OC) in soils.     

Separating the effects of organic matter-mineral interactions and organic matter chemistry on the sorption of diuron and phenanthrene

Even though it is well established that soil C content is the primary determinant of the sorption affinity of soils for non-ionic compounds, it is also clear that organic carbon-normalized sorption coefficients (K(OC)) vary considerably between soils. Two factors that may contribute to K(OC) variability are variations in organic matter chemistry between soils and interactions between organic matter and soil minerals. Here, we quantify these effects for two non-ionic sorbates-diuron and phenanthrene. The effect of organic matter-mineral interactions were evaluated by comparing K(OC) for demineralized (HF-treated) soils, with K(OC) for the corresponding whole soils. For diuron and phenanthrene, average ratios of K(OC) of the HF-treated soils to K(OC) of the whole soils were 2.5 and 2.3, respectively, indicating a substantial depression of K(OC) due to the presence of minerals in the whole soils. The effect of organic matter chemistry was determined by correlating K(OC) against distributions of C types determined using solid-state (13)C NMR spectroscopy. For diuron, K(OC) was positively correlated with aryl C and negatively correlated with O-alkyl C, for both whole and HF-treated soils, whereas for phenanthrene, these correlations were only present for the HF-treated soils. We suggest that the lack of a clear effect of organic matter chemistry on whole soil K(OC) for phenanthrene is due to an over-riding influence of organic matter-mineral interactions in this case. This hypothesis is supported by a correlation between the increase in K(OC) on HF-treatment and the soil clay content for phenanthrene, but not for diuron.     

Acetamiprid, carbendazim, diuron and thiamethoxam sorption in two Brazilian tropical soils

Sorption of acetamiprid ((E)-N1-[(6-chloro-3-pyridyl)methyl]-N2-cyano-N1-methylacetamidine), carbendazim (methyl benzimidazol-2-ylcarbamate), diuron (N-(3,4-dichlorophenyl)-N, N-dimethyl urea) and thiamethoxam (3-(2-chloro-thiazol-5-ylmethyl)-5-methyl-[1,3,5]oxadiazinan-4-ylidene-N-nitroamine) was evaluated in two Brazilian tropical soils, Oxisol and Entisol, from Primavera do Leste region, Mato Grosso State, Brazil. To describe the sorption process, batch experiments were carried out. Linear and Freundlich isotherm models were used to calculate the K(d) and K(f) coefficients from experimental data. The K(d) values were utilized to calculate the partition coefficient normalized to soil organic carbon (K(oc)). For the pesticides acetamiprid, carbendazim, diuron and thiamenthoxan the K(oc) (mL g(- 1)) values ranged in both soils from 98 - 3235, 1024 - 2644, 145 - 2631 and 104 - 2877, respectively. From the studied pesticides, only carbendazim presented correlation (r(2) = 0.82 and p < 0.01) with soil organic carbon (OC) content. Acetamiprid and thiamethoxam showed low sorption coefficients, representing a high risk of surface and ground water contamination.     

Sorption of polar and nonpolar aromatic compounds to four surface soils of eastern China

Improved predictions on the fate of organic pollutants in surface environments require a better understanding of the underlying sorption mechanisms that control their uptake by soils. In this study, we monitored sorption of nine aromatic compounds with varying physicochemical properties (hydrophobicity, electron-donor/acceptor ability and polarity), including two polycyclic aromatic hydrocarbons, two chlorobenzenes, two nitroaromatic compounds, dichlobenil, carbaryl and 2,4-dichlorophenol in aqueous suspension of four surface soils of eastern China. The tested soils were characterized with respect to organic carbon (OC) content, black carbon content, mineralogy, morphology and size fraction to assess the role of the diverse soil characteristics in sorption. The results of this study show that not only the solute hydrophobicity and the OC content of soil are important to the retention of organic pollutants, but also the solute molecular structure and the soil nature.     

Sorption of phenanthrene by soils contaminated with heavy metals

The fate of polycyclic aromatic hydrocarbons (PAHs) in soils with co-contaminants of heavy metals has yet to be elucidated. This study examined sorption of phenanthrene as a representative of PAHs by three soils contaminated with Pb, Zn or Cu. Phenanthrene sorption was clearly higher after the addition of heavy metals. The distribution coefficient (K(d)) and the organic carbon-normalized distribution coefficient (K(oc)) for phenanthrene sorption by soils spiked with Pb, Zn or Cu (0-1000 mg kg(-1)) were approximately 24% larger than those by unspiked ones, and the higher contents of heavy metals added into soils resulted in the larger K(d) and K(oc) values. The enhanced sorption of phenanthrene in the case of heavy metal-contaminated soils could be ascribed to the decreased dissolved organic matter (DOM) in solution and increased soil organic matter (SOM) as a consequence of DOM sorption onto soil solids. Concentrations of DOM in equilibrium solution for phenanthrene sorption were lower in the case of the heavy metal-spiked than unspiked soils. However, the decreased DOM in solution contributed little to the enhanced sorption of phenanthrene in the presence of metals. On the other hand, the sorbed DOM on soil solids after the addition of heavy metals in soils was found to be much more reactive and have far stronger capacity of phenanthrene uptake than the inherent SOM. The distribution coefficients of phenanthrene between water and the sorbed DOM on soil solids (K(ph/soc)) were about 2-3 magnitude larger than K(d) between water and inherent SOM, which may be the dominant mechanism of the enhanced sorption of phenanthrene by soils with the addition of heavy metals.     

Persistent organic pollutants in soil density fractions: distribution and sorption strength

The sorption strength of persistent organic pollutants in soils may vary among different soil organic matter (SOM) pools. We hypothesized that polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were unevenly distributed and had different soil organic carbon (SOC)-water partition coefficients (K(OC)) among soil density fractions. We determined the concentrations and K(OC) values of 20 PAHs and 12 PCBs in bulk samples and three density fractions (light, <2.0, medium, 2.0-2.4, and heavy, >2.4 g cm(-3)) of 11 urban topsoils (0-5 cm) from Bayreuth, Germany. The K(OC) values were determined using sequential extraction with methanol-water mixtures (35% and 65% methanol) at 60 degrees C. The sum of 20 PAH concentrations in bulk soil ranged 0.4-186 mg kg(-1), and that of 12 PCB concentrations 1.2-158 microg kg(-1). The concentrations of all PAHs and PCBs decreased in the order light>medium>heavy fraction. When normalized to the SOC concentrations, PAH concentrations were significantly higher in the heavy than in the other density fractions. The K(OC) values of the PAHs in density fractions were 3-20 times higher than those of the PCBs with similar octanol-water partition coefficients (K(OW)). The K(OC) values of individual PAHs and PCBs varied up to a factor of 1000 among the studied soils and density fractions. The K(OC) values of 5- and 6-ring PAHs tended to be highest in the heavy fraction, coinciding with their enrichment in this fraction. For the other PAHs and all PCBs, the K(OC) values did not differ among the density fractions. Thus, there is no relationship between sorption strength and distribution among density fractions, indicating that density fractionation is not a suitable tool to distinguish among differently reactive PAH and PCB pools in soils.     

Clear effects of soil organic matter chemistry, as determined by NMR spectroscopy, on the sorption of diuron

Organic matter has long been recognized as the main sorbent phase in soils for hydrophobic organic compounds (HOCs). In recent times, there has been an increasing realization that not only the amount, but also the chemical composition, of organic matter can influence the sorption properties of a soil. Here, we show that the organic carbon-normalized sorption coefficient (K(OC)) for diuron is 27-81% higher in 10 A11 horizons than in 10 matching A12 horizons for soils collected from a small (2ha) field. K(OC) was generally greater for the deeper (B) horizons, although these values may be inflated by sorption of diuron to clays. Organic matter chemistry of the A11 and A12 horizons was determined using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. K(OC) was positively correlated with aryl C (r2=0.59, significance level 0.001) and negatively correlated with O-alkyl C (r2=0.84, significance level <0.001). This is only the second report of correlations between whole soil K(OC) and NMR-derived measures of organic matter chemistry. We suggest that this success may be a consequence of limiting this study to a very small area (a single field). There is growing evidence that interactions between organic matter and clay minerals strongly affect K(OC). However, because the soil mineralogy varies little across the field, the influence of these interactions is greatly diminished, allowing the effect of organic matter chemistry on K(OC) to be seen clearly. This study in some way reconciles studies that show strong correlations between K(OC) and the chemistry of purified organic materials and the general lack of such correlations for whole soils.     

Fluorescence of sediment humic substance and its effect on the sorption of selected endocrine disruptors

Humic substances (HS) have a critical influence on the sorption of organic contaminants by soils and sediments. This paper describes investigations into the sorption behavior of three representative endocrine disruptors, bisphenol A (BPA), 17beta-estradiol (E2), and 17alpha-ethynylestradiol (EE2), onto sediments and HS extracted sediments using a batch technique. The organic carbon-normalized partition coefficients (K(oc)) for the extracted HS (K(oc)(hs)) were calculated, and the fluorescence spectra of the HS extraced from different sediment samples were gained using excitation/emission matrix (EEM). Particular attention was paid to the correlations between the fluorescence characteristics of HS and the log K(oc)(hs) of selected endocrine disruptors. The results show that the log K(oc)(hs) values range from 3.14 to 4.09 for BPA, from 3.47 to 4.33 for E2, and from 3.65 to 4.32 for EE2. Two characteristic excitation-emission peaks were observed for HS samples extracted from sediments. They are located at Ex/Em=250-260 nm/400-450 nm (peak alpha') and Ex/Em=310-330 nm/390-400 nm (peak alpha) respectively. The alpha' and alpha peak relative intensities I(alpha')/I(alpha) vary from 0.46 to 1.64 for different extracted HS samples. The similarity between fulvic acids (FA) Ex/Em pairs and those observed for HS indicates that FA is the predominant fraction of HS extracted from sediments. Moreover, the log K(oc)(hs) values of BPA, E2, and EE2 have a negative linear correlation to I(alpha')/I(alpha) values. Peak alpha is often attributed to relatively stable and high molecular weight aromatic fulvic-like matter. Therefore, the result presented here reveals that the abundance of aromatic rings in HS molecular structure plays a critical role in the sorption of selected endocrine disruptors.     

Sorption of imidacloprid and its metabolites on tropical soils

The sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolid-inimine ) (IMI) and its metabolites imidacloprid-urea (1-[(6-chloro-3-pyridinyl)-methyl]-2-imidazol-idinone) (IU), imidacloprid-guanidine (1-[(6-chloro-3-pyridinyl)-methyl]-4,5-dihydro-1H-imidazol-2-amine) (IG), and imidacloprid-guanidine-olefin (1-[(6-chloro-3-pyridinyl)methyl]-1H-imidazol-2-amine) (IGO) was determined on six typical Brazilian soils. Sorption of the chemicals on the soil was characterized using the batch equilibration method. The range and order of sorption (Kd) on the six soils was IG (4.75-134) > or = IGO (2.87-72.3) > IMI (0.55-16.9) > IU (0.31-9.50). For IMI and IU, Kd was correlated with soil organic carbon (OC) content and CEC, the latter due to the high correlation between OC and cation exchange capacity (CEC) (R2 = 0.98). For IG and IGO, there was no correlation of sorption to clay, pH, OC or CEC due to the high sorption on all soils. Average Koc values were IU = 170, IMI = 362, IGO = 2433, and IG = 3500. Although Kd and Koc values found were consistently lower than those found in soils developed in non-tropical climates, imidacloprid and its metabolites were still considered to be slightly mobile to immobile in Brazilian soils.     

Sugarcane straw management and soil attributes on alachlor and diuron sorption in highly weathered tropical soils

This research evaluated the effects of the new sugarcane harvesting system (without straw burning) and soil attributes on the organic carbon (OC) accumulation and sorption of alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide) and diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in highly weathered Brazilian soils. Alachlor was more likely to leach (K _d,app = 1.0–7.0 L kg^?1 and mean K _oc,app = 174 L kg^?1) than diuron (K _d,app = 6.2–116.3 L kg^?1 and mean K _oc,app = 1789 L kg^?1). The sorption coefficient (K _d,app) values correlated better with soil OC contents, but the Fe-oxides also played an important role in these highly weathered soils. Sorption was enhanced in the areas without straw burning mostly due to OC accumulation that was higher in the clayey soils, but it was not enough to change their mobility classification.     

Sorption kinetics of 2,4-D and carbaryl in selected agricultural soils of northern Iraq: application of a dual-rate model

Agriculture in northern Iraq (Kurdistan) relies on the widespread use of pesticides to promote crop performance. Over-application of many pesticides is commonplace, however, and may compromise soil and water quality, and ultimately human health, within the region. The aim of this study was to investigate the sorption-desorption kinetics and equilibrium partitioning of two selected pesticides in agricultural soils from northern Iraq. This was achieved by fitting a dual-rate sorption-desorption model to time-dependent data obtained from batch experiments. 2,4-D and carbaryl were selected for scrutiny since both are in common use in the region. Six agricultural soils, sampled around the city of Erbil, were investigated. These were low in organic carbon (OC) compared with many agricultural soils from more temperate regions. However, there was still a clear trend of increasing sorption of both 2,4-D and carbaryl with increasing % OC. In the case of both compounds, fast and slow adsorption rate coefficients and 48 h experimental K(d) values were positively correlated with % OC. It was assumed that K(OC) would provide a simple and reliable predictor of K(d). However, while this assumption holds true for short-term (48 h) experimental data, longer-term sorption in some soils (as indicated by theoretical K(d) values estimated from kinetic parameters in our study) appears to be under-predicted by K(OC) alone. The data presented here provide a useful starting point for further site-specific investigations of pesticide impacts in the Kurdistan region of Iraq.     

Hydrolysis and soil sorption of insecticide pyraclofos

The hydrolysis of the insecticide pyraclofos in buffered solutions at pH 5.0, 7.0 and 9.0, and its sorption on four soils of different physicochemical properties were investigated. The results showed that the degradation of pyraclofos in buffered solutions followed pseudo-first-order kinetics. At 40 degrees C, the rate constants for the hydrolysis of pyraclofos at pH 5.0, 7.0 and 9.0 were 0.0214, 0.1293, and 2.1656 d(-1), respectively. Pyraclofos was relatively stable under both acidic and neutral conditions, while it was readily hydrolyzed under basic conditions. The sorption of pyraclofos on four soils was well described by the Freundlich equation. The sorption constant, K(f), increased with an increase in soil organic carbon content, suggesting that organic carbon content was an important factor affecting sorption. The K(oc) values for Xiaoshan clay loam soil, Hangzhou I clay loam soil, Hangzhou II soil, and Fuyang silt loam soil were 30.4, 6.7, 5.3, and 7.1, respectively. These results suggest that the sorption of pyraclofos on the tested soils was relatively weak.     

Influences of preparative methods of humic acids on the sorption of 2,4,6-trichlorophenol

Humic acids (HAs) are a major component of soil organic matter which strongly affects the sorption behavior of organic contaminants in soils. To assess the sorption-desorption characteristics of organic compounds on HAs, the organic adsorbent is usually isolated using an acid-base extraction method followed by air-drying or freeze-drying. In this study, a peat soil from the Yangming mountain area of Taiwan was sampled and repeatedly extracted followed by either air-drying or a non-drying treatment (denoted DHAs and NDHAs, respectively). The sorption of 2,4,6-TCP on HAs was evaluated using the batch method. Kinetic sorption results indicated that DHAs exhibited a two-step first-order sorption behavior, involving a rapid sorption followed by a slow sorption. The slow sorption may be attributed to the diffusion of 2,4,6-TCP through the condensed aromatic domains of HAs. On the contrary, the sorption of 2,4,6-TCP on NDHAs was extremely rapid, and the sorption data did not fit existing kinetic models. Each HA sample exhibited a nonlinear sorption isotherm. Sorption nonlinearity (represented by Freundlich N values) and K(oc) had a positive relationship with aliphaticity for DHAs; however, nonlinearity and K(oc) correlated positively with aromaticity when NDHAs adsorbents were used. We conclude that the air-drying technique may artificially create a more condensed area, which strongly affects the sorption characteristics of HAs. Thus, an incorrect evaluation of the sorption capacity and its relationship with the chemical composition of HAs would arise following use of the air-drying method.     

Biofilm controlled sorption of selected acidic drugs on river sediments characterized by different organic carbon content

The sorption process of selected non-steroidal anti-inflammatory drugs (ibuprofen, naproxen, ketoprofen, diclofenac) on biofilm covered river sediments were investigated in laboratory. In the course of the experiments, the effect of pH of aqueous phase, the effect of TOC (total organic carbon) content of biofilm on the sorption processes were studied. The determination of concentration of drugs was performed by gas chromatography mass spectrometry (GC-MS) both in liquid and solid phases. The pseudo-first-order rate constant of the sorption was found to be 83 min(-1). The effect of pH on the sorption of diclofenac was significantly lower than the obtained values in case of the other three drugs. The calculated K(d) (sorption coefficient) values increased in the sequence of ibuprofen, naproxen, ketoprofen and diclofenac and varied between 0.1-0.4; 0.2-0.7; 0.2-1.2; 0.2-1.4 kg L(-1) respectively, depending on the characteristics of the sediments. The value of K(d)×f(oc) showed a straight line as function of f(oc) (fraction of organic carbon) therefore, instead of the widely distributed normalization process (K(d)/f(oc)), an empirical equation (K(d)=A/f(oc)+B) was suggested for estimation of the K(d) values in case of different TOC content sediments.     

Sorption of imidacloprid and its metabolites on tropical soils

Abstract

The sorption of imidacloprid (l‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐N‐nitro‐2‐imidazolid‐inimine) (IMI) and its metabolites imidacloprid‐urea (l‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐2‐imidazol‐idinone) (IU), imidacloprid‐guanidine (l‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐4,5‐dihydro‐lH‐imidazol‐2‐amine) (IG), and imida‐cloprid‐guanidine‐olefin ( 1 ‐[(6‐chloro‐3‐pyridinyl)methyl]‐lH‐imidazol‐2‐amine) (IGO) was determined on six typical Brazilian soils. Sorption of the chemicals on the soil was characterized using the batch equilibration method. The range and order of sorption (Kd) on the six soils was IG (4.75–134) > IGO (2.87–72.3) > IMI (0.55 ‐16.9) > IU (0.31–9.50). For IMI and IU, Kd was correlated with soil organic carbon (OC) content and CEC, the latter due to the high correlation between OC and cation exchange capacity (CEC) (R²=0.98). For IG and IGO, there was no correlation of sorption to clay, pH, OC or CEC due to the high sorption on all soils. Average Koc values were IU = 170, IMI = 362, IGO = 2433, and IG = 3500. Although Kd and Koc values found were consistently lower than those found in soils developed in non‐tropical climates, imidacloprid and its metabolites were still considered to be slightly mobile to immobile in Brazilian soils.     

Correlations of nonlinear sorption of organic solutes with soil/sediment physicochemical properties

The estimation of solute sorptive behaviors is essential when direct sorption data are unavailable and will provide a convenient way to assess the fate and the biological activity of organic solutes in soil/sediment environments. In this study, the sorption of 2,4-dichlorophenol (2,4-DCP) on 19 soil/sediment samples and the sorption of 13 organic solutes on one sediment were investigated. All sorption isotherms are nonlinear and can be described satisfactorily by a simple dual-mode model (DMM): q(e)=KpCe+Q0 . bCe/(1+bCe), where Kp (mlg(-1)) is the partition coefficient; Ce (microgml(-1)) is the equilibrium concentration; Q0 (microgg(-1)) is the maximum adsorption capacity; Q0 . b (mlg(-1)) is the Langmuir-type isotherm slope in the low concentration (Henry's law) range and b (mlmicrog(-1)) is a constant related to the affinity of the surface for the solute. Based on these nonlinear sorption isotherms and similar other nonlinear isotherms, it is observed that, for both polar 2,4-DCP and nonpolar phenanthrene, Kp, Q0 and Q0 . b are linearly correlated with soil/sediment organic carbon content (f(oc) in the range of 0.118-53.7%). The results indicate that the nonlinear sorption of organic solutes results primarily from interactions with soil/sediment organic matter. The K*oc K*oc=Kp/f(oc)), Qoc (Qoc=Q0/f(oc)), Loc (Loc=Q0 . b/f(oc)) and b for a given organic solute with different soils/sediments are largely invariant. Furthermore, logK*oc, logb and logLoc for various organic solutes are correlated significantly with the solute logKow or logSw (logKow in the range of 0.9 to 5.13 and logSw in the range of -6.176 to -0.070). A fundamental empirical equation was then established to calculate approximately the nonlinear sorption from soil/sediment f(oc) and solute Sw for a given solute equilibrium concentration.     

Absorption of polycyclic aromatic hydrocarbons to cellulose

Polycyclic aromatic hydrocarbons (PAHs) are widespread toxic chemicals. The environmental fate of these chemicals is in part controlled by sorption to (organic matter in) sediments and soils. One of the most abundant organic matter compounds on earth is cellulose. Remarkably, sorption of PAHs to cellulose has hardly been studied; only two reports on the binding of some low-molecular-weight PAHs exist in the literature. In this study, sorption of PAHs to cellulose was investigated in more detail, by measuring isotherms for a series of 13 PAHs, covering a wide hydrophobicity range. The results indicated that sorption of PAHs to cellulose is a linear partition process for all PAHs investigated (phenanthrene-indeno[1,2,3-cd]pyrene). The affinity of PAHs for cellulose appeared to be about 400 times lower than for octanol and even up to 300000 times lower than for black carbon or coal. Linked to the estimated yearly production of cellulose and black carbon, these results suggest that cellulose is probably not a major environmental sorption domain for PAHs.     

The diffusion and sorption of volatile organic compounds through kaolinitic clayey soils

Laboratory experiments to estimate the effective molecular diffusion coefficient (D(e)) and sorption coefficient (K(d)) for volatile organic compounds through natural clayey soils were conducted using diffusion testing apparatus. The compounds tested were methyl ethyl ketone (MEK), toluene and trichloroethylene (TCE). The D(e) and K(d) values were determined by a curve fitting procedure. The compound losses, and the effects of porous disks used in the apparatus were significant. The transport of MEK was faster than that of TCE and toluene because of the lower sorption to the soils. The D(e) values of all the compounds were of the order of 10(-10) m(2)/s and smaller than the diffusion coefficient in pure aqueous solution at infinite dilution (D(0)), due to the tortuosity of the samples. The effects of the sample thickness on the parameter determination were not significant. Comparison to the K(d) values estimated from batch sorption tests and from organic carbon content (f(oc))-based predictions showed that the diffusion test results were intermediate between those from the other two methods. The diffusion tests use compacted soil samples and should be more relevant to in situ conditions, but the reliability of the tests is affected by large compound losses that cause uncertainties in their interpretation. It is recommended that more than one method be used to assess K(d) values.     

Effect of physical forms of soil organic matter on phenanthrene sorption

The sorption coefficient, K(OC), of phenanthrene (PHE) has been reported to vary with different types of organic matter, leading to uncertainties in predicting the environmental behavior of PHE. Among the studies that relate organic matter properties to their sorption characteristics, physical conformation of organic matter is often neglected. In this work, organic matter samples of different physical forms were examined for their sorption characteristics. Dissolved humic acids (DHA) showed significantly higher K(OC) than the corresponding solid humic acids (SHA) from which the DHAs were made. The K(OC) of DHAs was found to be related to polarity, whereas K(OC) of SHAs increased with aliphatic carbon content. Soil particles were treated with H(2)O(2) to remove organic matter, and humic acid was coated on H(2)O(2)-treated soil particles to make organo-mineral complexes at pH 4, 7 and 10. Although the nonlinear sorption was apparent for SHAs and H(2)O(2)-treated soil particles, the organo-mineral complexes formed using these two components at pH 4, 7 and 10 exhibited relatively linear sorption at organic carbon content, f(OC)>0.5%. These results indicate that organic matter of the same composition may have different sorption properties due to different physical forms (or conformations). Nonlinear sorption for the complexes formed at pH 4 with lower f(OC) (<0.5%) was also discussed.