Organic Carbon-normalized Distribution Coefficients Research Articles

Quantifying the sediment sorption of organic ultraviolet filter chemicals using solvophobic theory

Hydrophobic organic chemicals (HOCs) that enter the aquatic environment often negatively impact organisms, endangering aquatic biodiversity. Understanding sediment sorption equilibria for these chemicals can properly direct mitigation efforts. In addition, many HOCs of environmental concern lack sufficient environmental fate data to adequately assess their risk to ecosystems and humans. In this study, a sorption method addressing solvophobic effects was used to quantify the sorption of an HOC of current environmental concern, OD-PABA (padimate O, 2-ethylhexyl-4-(dimethylamino)benzoate), to a variety of sediments. OD-PABA is an organic ultraviolet filter chemical used in commercial sun protection products; it has been shown to exhibit cytotoxic effects and is known to photochemically transform under natural sunlight conditions. Given its commercial use, it enters the aquatic environment via recreational use and wastewater treatment plant effluent. OD-PABA is strongly hydrophobic; to mitigate the adsorption of OD-PABA to the container walls during sorption experiments, a precise concentration of methanol was used to avoid solvophobic effects. This sorption method was used to determine the sorption capacities for OD-PABA of four sediment samples, each with unique geochemical characteristics. Sediment-water distribution coefficients (Kd) were quantified and were normalized to various sediment characteristics to assess the main driving force(s) for sorption of OD-PABA. Organic carbon content was found to be a main driving force, with organic carbon-normalized distribution coefficients (log Koc) ranging from 4.4 to 4.6 for sediments with total organic carbon (TOC) > 10%); the clay fraction was also found to be important, especially for sediments with low TOC. The sorption of para-aminobenzoic acid (PABA), a water-soluble analog of OD-PABA was also investigated to assess the experimental approach, yielding a log Koc of 2.1 for the sediment with the greatest TOC.

Perfluoroalkyl acids in the aquatic environment of a fluorine industry-impacted region: Spatiotemporal distribution, partition behavior, source, and risk assessment

The present study investigated the temporal and spatial distributions, partition behaviors, sources, and risks of 14 perfluoroalkyl acids (PFAAs) in the aquatic environment of a fluorine industry-impacted region. The total concentrations of 14 PFAAs (ΣPFAAs) were 118.10–2235.4 ng/L, 40.00–2316.1 ng/g dw, and 6.90–180.5 ng/g dw in dissolved, suspended particle matter (SPM), and sedimentary phases, respectively. The predominant pollutants in the dissolved and SPM phases were perfluoroalkyl carboxylic acids (PFCAs) with carbon chain lengths <9, whereas C13 and C14 PFCAs accounted for a large proportion in the sedimentary phase. The dry season exhibited the highest concentration of ΣPFAAs in the dissolved phase (500.9 ± 350.2 ng/L), while the wet season showed the highest concentrations of ΣPFAAs in the SPM and sedimentary phases (591.6 ± 469.1 ng/g dw and 59.7 ± 35.5 ng/g dw, respectively). Significantly higher concentrations of PFAAs have been found in sewage plant and industrial areas. The concentration of PFAAs in the Xupu water source area (XPS) was slightly higher than that in other water source areas of the Yangtze River, which were either not affected or were less affected by the fluorine industry. The log KD-SPM (distribution coefficient between SPM and water), log KD-SED (distribution coefficient between sediment and water), and log KOC-SED (the organic carbon normalized distribution coefficient) of PFAAs showed significant differences between the wet season and dry season, which may also be affected by carbon chain length. Source identification results showed that industries, wastewater discharge, and nonpoint sources were the main sources of PFAAs in this region. The ecological risk posed by long-chain PFAAs in aquatic organisms cannot be ignored, especially in areas with intensive industrial and agricultural activities. Health risks may exist for local toddlers with long-term exposure to perfluorooctanoic acid (PFOA) through drinking water intake and dermal contact.

Impact of deashing treatment on biochar physicochemical properties and sorption mechanisms of naphthalene and 1-naphthol

To elucidate the mechanisms controlling mineral effects of biochars on sorption of organic pollutants (OPs), sorption kinetics and isotherms of naphthalene and 1-naphthol on both pristine and deashed rice straw-derived biochars obtained at 200, 400 and 600 ºC were investigated. The organic carbon-normalized distribution coefficients (Koc) and equilibrium sorption capacity (Qe) of naphthalene and 1-naphthol by biochars generally increased after deashing. This was principally because mineral removal caused less exposure of polar groups, especially the O-alkyl components, on biochar surfaces and enhancement of hydrophobic sorption domains, thus mainly facilitating hydrophobic interactions between the compounds and aromatic components within biochars relative to the alkyl carbon components. The removal of minerals in biochars, which reduced the surface polar groups, promoted diffusion of naphthalene molecules toward the surface hydrophobic domains, thereby increasing its sorption rate constant for the fast-sorbing fraction on biochars (kfast). In contrast, the kfast values of 1-naphthol decreased after deashing, which could be ascribed to the weakened fast sorption via H-bond between 1-naphthol and mineral O-containing surfaces or polar groups on biochar surfaces. Both compounds exhibited lower rate constants for the slowly sorbing fraction (kslow) on deashed biochars, which had higher aromaticity and larger porosity and surface area than the raw biochars and inhibited the diffusion of sorbates into condensed organic moieties and pores. Results of this work are critical for better understanding on the impact of minerals, bulk/surface polarity, and sorption domain arrangement of biochars on their efficacy for OPs removal and predicting the fate and risk of OPs.

Characterization of adsorption and desorption of lawn herbicide siduron in heavy metal contaminated soils

Siduron is a widely used herbicide in urban lawn and has been frequently detected in urban and suburban surface water. However, characteristics of its environmental behavior in soil are seldom reported. The combined pollution of heavy metals, especially for Cu, Pb, Cd, Zn and siduron would be common because of the widely existence of heavy metal pollution in urban soils. In this study, four soils with similar physicochemical properties but different levels of preexisting heavy metals were selected to investigate the adsorption and successive desorption of siduron using batch experiments. The results revealed a low sorption of siduron to all the tested soils. The organic carbon normalized distribution coefficient (Koc) of siduron in the studied soils ranged from 117 to 137 L kg−1 and was not significantly correlated to heavy metal levels. No apparent desorption hysteresis was observed with the hysteresis index (HI) ranging from 0.921 to 1.11. More than 50% of the sorbed siduron was readily released into soil solution. Results suggested that siduron was highly mobile and bioavailable in the studied soils. Significant correlation was found between adsorption/desorption parameters and soil organic carbon (SOC) in four soils. soil organic matter was thus considered as the dominant factor determining the adsorption and desorption of siduron in soils. Different from most of reported studies conducted by laboratory-amended soils, the influence of preexisting heavy metals on the adsorption-desorption of siduron was not significant in this work.

Application of SPME-GC/MS to Study the Sorption of Organophosphate Esters on Peat Soil

Organophosphate esters (OPEs) are classified as re-emerging pollutants, and studies on their environmental fate, e.g., sorption behavior on soil are still limited. In this paper, three OPEs, triphenyl phosphate (TPP), tris (1,3-dichloro-2-propyl) phosphate (TDCP), and tris (1-chloro-2-propyl) phosphate (TCPP) were selected, and their sorption characteristics on peat soil with high organic matter were investigated by direct immersion solid phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC/MS). The sorption kinetics of TPP, TDCP, and TCPP was found to confirm to the pseudo-second-order model, and intra-particle diffusion was not the only rate-controlling step for the sorption process. Linear, Freundlich, and Dubinin-Radushkevich isotherm models were used to analyze the sorption equilibrium data, and the best correlation was achieved by the linear isotherm model. The organic carbon normalized distribution coefficients (logK oc ) were calculated to be 3.45 for TPP, 2.83 for TDCP, and 2.23 for TCPP. Thermodynamics showed that the sorption of TPP, TDCP, and TCPP on Peat soil was spontaneous, exothermic, and physical in nature.

Evaluation of sewage sludge and slow pyrolyzed sewage sludge-derived biochar for adsorption of phenanthrene and pyrene

The present study investigated the sorption of phenanthrene (PHE) and pyrene (PYR) by sewage sludges and sewage sludge-derived biochars. The organic carbon normalized distribution coefficient (logKOC for Cw=0.01 Sw) for the sewage sludges ranged from 5.62Lkg−1 to 5.64Lkg−1 for PHE and from 5.72Lkg−1 to 5.75Lkg−1 for PYR. The conversion of sewage sludges into biochar significantly increased their sorption capacity. The value of logKOC for the biochars ranged from 5.54Lkg−1 to 6.23Lkg−1 for PHE and from 5.95Lkg−1 to 6.52Lkg−1 for PYR depending on temperature of pyrolysis. The dominant process was monolayer adsorption in the micropores and/or multilayer surface adsorption (in the mesopores), which was indicated by the significant correlations between logKOC and surface properties of biochars. PYR was sorbed better on the tested materials than PHE.

Effect of Ionic Strength and Index Cation on the Sorption of Phenanthrene

Sorption characteristics of phenanthrene were studied in batch equilibrium experiments with 32 Australian soils that varied widely in physicochemical properties. Sorption of phenanthrene varied widely among the soils and was generally nonlinear, with the nonlinearity index (n) of the Freundlich isotherm varying from 0.62 to 1.01. Simple regression analyses revealed that total organic carbon (TOC) accounts for about 68 % of the variation in the partition coefficient (K′f) for sorption among the soils at an equilibrium concentration (Ce) of 0.05 mg/L. The organic carbon normalized distribution coefficient (KOC), varied considerably between soils with >70 % of the variance of logKOC being accounted for by logTOC, clay and log dissolved organic carbon (DOC). These results show that the phenanthrene Ce is influenced by both TOC as well as the DOC in soil suspensions. The effects of ionic strength (IS) and index cation were investigated using four contrasting soils. Results show that with an increase in IS from 0.03 to 0.15 M sorption of phenanthrene generally increased in CaCl2 background solutions, whereas the effect was less significant and variable in NaCl background solutions. Sorption of phenanthrene was slightly higher at low IS (0.03 M) with Na+ as index cation compared with that of Ca2+, whereas an opposite trend was observed at higher IS (0.15 M). For two soils high in TOC, the flocculation of endogenous DOC in the presence of Ca2+ reduced the influence of background electrolyte and resulted in a more linear sorption isotherm as well as higher sorption capacity. This trend was more significant with Ca2+ relative to Na+.

Occurrence and Transport of Perfluoroalkyl Acids (PFAAs), Including Short-Chain PFAAs in Tangxun Lake, China

Short-chain perfluoroalkyl acids (PFAAs), which have less than seven fluorinated carbons, have been introduced as substitutes for eight-carbon homologue products. In this study, water, sediment, and biological samples (fish and plant) were collected from Tangxun Lake, which is located near a production base of the fluorochemical industry in Wuhan, China. Perfluorobutane sulfonate (PFBS) and perfluorobutanoic acid (PFBA) were the predominant PFAAs in surface water, with average concentrations of 3660 ng/L and 4770 ng/L, respectively. However, perfluorooctane sulfonate (PFOS) was the most abundant PFAA in sediments, with an average concentration of 74.4 ng/g dw. The organic carbon normalized distribution coefficients (KOC) indicated that short-chain PFAAs (CF2 < 7) tended to have lower adsorption potentials than PFOS, perfluorooctanoic acid (PFOA), and longer perfluoroalkyl chain compounds. PFBS and PFBA could transport to a farther distance in the horizontal direction along the water flow and infiltrate into deeper depths in the vertical direction. However, levels of PFOS and PFOA in water dropped exponentially along the current, and their proportions were decreased gradually with the increasing depth in sediment cores. Furthermore, values of log bioconcentration factor (BCF) of the short-chain PFAAs were all relatively low (<1), indicating no bioaccumulation potentials for short-chain PFAAs in aquatic species.

Sorption of monoaromatic compounds to heated and unheated coals, humic acid, and biochar: Implication for using combustion method to quantify sorption contribution of carbonaceous geosorbents in soil

Batch sorption isotherms of two nonpolar compounds (1,3-dichlorobenzene and 1,3,5-trichlorobenzene) and two polar compounds (1,3-dinitrobenzene and 1,3,5-trinitrobenzene) to heated (at 375°C for 24h) and unheated coals (lignite and anthracite) were compared with those to a soil humic acid and a maize stalk derived biochar. For all test compounds, unheated lignite and anthracite exhibited much stronger sorption than humic substances (the organic carbon-normalized distribution coefficient was up to 2–3 orders of magnitude larger), but lower sorption than biochar. This sorption trend is consistent with the degree of sorbent condensation (biochar>coal>humic acid). The results indicate that sorption of the test sorbates (regardless of the difference in polarity) to soils would be dominated by carbonaceous geosorbents. Notably, the organic carbon contents of the coals were pronouncedly lowered by the heat treatment, from 47.4% to 7.3% for lignite, and from 80.1% to 58.1% for anthracite. Moreover, the heat treatment markedly decreased organic carbon-normalized distribution coefficient to coals (up to one order of magnitude), attributable to the decreased hydrophobicity of sorbents due to increased O-containing groups from oxidation. An important implication is that heat treatment, which is commonly used to quantify the content of carbonaceous geosorbents in soil and sediment, may cause significant underestimation of sorption contribution of carbonaceous geosorbents due to the combined effect of reduced organic carbon content and decreased hydrophobicity of less graphitized carbonaceous geosorbents (coals). This was illustrated using a widely adopted dual-component model that combines linear partition to humic substances (represented by humic acid) and nonlinear adsorption on condensed geosorbents (represented by biochar and coal).

Effect of salting out on the desorption-resistance of polycyclic aromatic hydrocarbons (PAHs) in coastal sediment

The effects of “salting out” on the sorption and desorption of polycyclic aromatic hydrocarbons (PAHs) in coastal sediment were investigated. The sorption and desorption isotherms of three PAHs (naphthalene, phenanthrene and pyrene) in coastal sediment were linear. The distribution coefficients of sorption (Kd,s) and desorption (Kd,d) increased with salinity and hydrophobicity (logKow). A three-dimensional model was proposed to explain the combined effects of solubility (S), logKow and the organic-carbon normalized partition coefficient (logKoc). The sequential desorption of phenanthrene at different salinities of 0–30ppt from sediment was conducted after sequential sorption at 0 and 30ppt, respectively. The desorption data was fitted to a biphasic desorption model including linear labile fraction and non-linear desorption-resistant fraction. The linear distribution coefficient (Kdlab) for the labile desorption fraction was affected by the salinity in the previous sequential sorption stage, whereas the desorption-resistance parameters such as the maximum capacity of the desorption-resistant fraction (qmaxres, mg/kg) and the organic carbon-normalized distribution coefficient in the desorption-resistant fraction (Kocres, L/kg-OC), were affected by the salinity in the current desorption stage. In conclusion, the salinity increased the sorbed capacity of PAH as well as the desorption-resistance (as indicated by both qmaxresand Kocres) due to the “salting out effect”.

Soil–water interfacial adsorption of phenanthrene along a Chinese climatic gradient of soils with and without the addition of black carbon

Sorption isotherms for a hydrophobic solute probe, phenanthrene, were determined in 16 Chinese soils. They were sampled along a climatic gradient, and amended, or not, with charcoal (0.2%, 0.5%, and 1%), a form of black carbon (BC). Within the concentration range of added phenanthrene (0.2–0.8mgl−1), most of the adsorption isotherms of the unamended soils were non-linear. Both the Freundlich equation and the Dual Reactive Domain Model (DRDM) model closely fitted the data, indicating that phenanthrene sorption in these soils was site-specific and demonstrated capacity-limited adsorption in a condensed organic domain. Correlations between the Freundlich model capacity factor (KF) and soil physico-chemical properties showed that the total soil organic C (TOC) concentrations, cation exchange capacities and silt had a cumulative effect on phenanthrene sorption, indicating that organic and inorganic components interacted in this process. The soils studied also indicated that humic acid carbon (HAC) concentration may be a further relevant factor that should be considered. The soils covered a wide range of physical and chemical properties, in particular organic C and the organic carbon-normalized distribution coefficients (KOC) demonstrated a large range of variation. Therefore, KOC values may be poor predictive parameters for phenanthrene sorption by soils. Addition of BC not only enhanced the sorption of phenanthrene but also altered the sorptive characteristics of the soils studied.

Visualization of transport pathways for organic compounds in undisturbed soil monoliths

Small amounts of organic compounds are often found at much larger depths than expected from their organic carbon normalized distribution coefficient (Koc). In this study the food dye Brilliant Blue (BB) was used to visualize the (preferential) transport pathways in undisturbed soil monoliths taken from an Orthic Luvisol and from a Eutric Cambisol. After spiking the monoliths with 1.0MBq of either 14C-labeled benazolin (leacher) or 14C-labeled benzo[a]pyrene (BaP, nonleacher), they were intermittently irrigated under free-draining conditions twice weekly with 4mm of rain water for 17weeks. BB (4gL−1) was added to the rain water during the last 4weeks. After irrigation, the monoliths were sliced and photographs were taken from horizontal cross-sections. Soil was dried and incinerated to measure total 14C-activity. The mean travel depth for benazolin (6–7cm) was larger than for BaP (2cm), which is in line with their Koc values, although BaP was much more mobile than expected from the Koc value. BB patterns, arbitrarily classified into five intensity classes, showed that large parts of the monolith were bypassed below the completely stained upper two to five centimeter. Furthermore, BB patterns indicated the locations of strongly sorbing compounds in the deeper soil layers and are therefore a helpful tool to selectively sample the soil for these compounds. A continuously stained root channel below the 20-cm depth contained substantial amounts of BaP, indicating that soil structure cannot be neglected to assess the fate of nonleachers in undisturbed soils.

High Affinity Sorption Domains in Soil Are Blocked by Polar Soil Organic Matter Components

Reported correlations between organic contaminant sorption affinity and soil organic matter (OM) structure vary widely, suggesting the importance of OM physical conformation and accessibility. Batch equilibration experiments were used to examine the sorption affinity of bisphenol A, atrazine, and diuron to five soils of varying OM composition. (13)C cross-polarization magic angle spinning NMR spectroscopy was used to characterize the organic carbon chemistry of the soil samples. High sorption by a soil low in O-alkyl components suggested that these structures may block high affinity sorption sites in soil OM. As such, soil samples were subjected to acid hydrolysis, and NMR results showed a decrease in the O-alkyl carbon signal intensity for all soils. Subsequent sorption experiments revealed that organic carbon-normalized distribution coefficient (K(OC)) values increased for all three contaminants. Before hydrolysis, K(OC) values correlated positively with soil aromatic carbon content and negatively with polar soil O-alkyl carbon content. While these correlations were weaker after hydrolysis, the correlation between K(OC) values and soil alkyl carbon content improved. This study suggests that hydrolyzable O-alkyl soil OM components may block high affinity sorption sites and further highlights the importance of OM physical conformation and accessibility with respect to sorption processes.

Aging effects on sorption–desorption behaviors of PAHs in different natural organic matters

The aging effects of sorption–desorption of two polycyclic aromatic hydrocarbons (PAHs), that is, phenanthrene and chrysene on different natural organic matters (NOMs), that is, humic acid, fulvic acid, and humins of different sources were studied. Both organic carbon-normalized distribution coefficients (Koc) and the reversible desorption fractions (frd) were evaluated. Results showed that aging effects were both sorbent and sorbate specific. With increasing aging duration, Kocs of phenanthrene on humins increased, whereas Kocs of chrysene did not change significantly. Significant frd declinations over aging times were observed for all the NOMs, which demonstrated the effects of aging on availability of PAHs. Furthermore, the frd was not only positively correlated with the atomic O/C ratio of NOMs, which represent the geological maturity of NOMs, but also varied with the property of sorbates. We conclude that aging effects of HOCs on NOMs should be a case-specific process and the desorption reversibility depends on the structure and characteristics of both NOMs and sorbates.

Modifications of black carbons and their influence on pyrene sorption

Sorption of pyrene on black carbons (BCs) obtained by heating sawdust at two temperatures (400 and 700 °C, denoted as 400BC and 700BC, respectively), as well as on modified BCs (via oxidation, oximation, and hydrolysis) was studied to investigate the role of BC structural characteristics in sorption of hydrophobic organic compounds. Pyrene was bound strongly by 700BC and 400BC, with organic carbon normalized distribution coefficients ( K oc) of 10 5.04–10 5.86 and 10 4.65–10 5.16, respectively, at equilibrium pyrene concentrations of 10–100 μg L −1. Both chemical composition and pore distribution of the two BCs changed after modifications, which led to changes in their sorption characteristics for pyrene. After modifications, the linearity of pyrene sorption isotherm increased for 700BC but decreased for 400BC. For 700BC, both oxidation and oximation reduced pyrene sorption, with K oc decreasing by 69.1–73.7% and 18.7–33.9%, respectively, whereas hydrolysis did not exert a significant influence. For 400BC, oxidation and hydrolysis reduced K oc by 2.28–25.9% and 29.2–33.9%, respectively, while oximation increased K oc. In most cases, the change in sorption capacity could be explained by the changes in C content and type, polarity, surface area, and micropore volume of the BCs; however, the role of conformation (the accessibility to sorption sites) could not be ignored.

Do Lab-Derived Distribution Coefficient Values of Pesticides Match Distribution Coefficient Values Determined from Column and Field-Scale Experiments? A Critical Analysis of Relevant Literature

In this study, we analyzed sorption parameters for pesticides that were derived from batch and column or batch and field experiments. The batch experiments analyzed in this study were run with the same pesticide and soil as in the column and field experiments. We analyzed the relationship between the pore water velocity of the column and field experiments, solute residence times, and sorption parameters, such as the organic carbon normalized distribution coefficient ( ) and the mass exchange coefficient in kinetic models, as well as the predictability of sorption parameters from basic soil properties. The batch/column analysis included 38 studies with a total of 139 observations. The batch/field analysis included five studies, resulting in a dataset of 24 observations. For the batch/column data, power law relationships between pore water velocity, residence time, and sorption constants were derived. The unexplained variability in these equations was reduced, taking into account the saturation status and the packing status (disturbed-undisturbed) of the soil sample. A new regression equation was derived that allows estimating the values derived from column experiments using organic matter and bulk density with an value of 0.56. Regression analysis of the batch/column data showed that the relationship between batch- and column-derived values depends on the saturation status and packing of the soil column. Analysis of the batch/field data showed that as the batch-derived value becomes larger, field-derived values tend to be lower than the corresponding batch-derived values, and vice versa. The present dataset also showed that the variability in the ratio of batch- to column-derived value increases with increasing pore water velocity, with a maximum value approaching 3.5.

Sorption of bisphenol A, 17α-ethinyl estradiol and phenanthrene on thermally and hydrothermally produced biochars

Thermal and hydrothermal biochars were characterized, and adsorption of bisphenol A (BPA), 17α-ethinyl estradiol (EE2) and phenanthrene (Phen) was determined to investigate the sorption characteristic difference between the two types of biochars. Thermal biochars were composed mostly of aromatic moieties, with low H/C and O/C ratios as compared to hydrothermal ones having diverse functional groups. Single-point organic carbon-normalized distribution coefficients (log K OC) of EE2 and BPA of hydrothermal biochars were higher than thermal biochars, while Phen log K OC values were comparable among them. X-ray diffraction and solid state nuclear magnetic resonance results suggested that hydrothermal biochars consisted of more amorphous aliphatic-C, possibly being responsible for their high sorption capacity of Phen. This study demonstrated that hydrothermal biochars could adsorb a wider spectrum of both polar and nonpolar organic contaminants than thermally produced biochars, suggesting that hydrothermal biochar derived from poultry and animal waste is a potential sorbent for agricultural and environmental applications.

Pyrethroid sorption to Sacramento River suspended solids and bed sediments

Sorption of pyrethroid insecticides to solid materials will typically dominate the fate and transport of these hydrophobic compounds in aquatic environments. Batch reactor isotherm experiments were performed with bifenthrin and λ-cyhalothrin with suspended material and bed sediment collected from the Sacramento River, California, USA. These batch reactor experiments were performed with low spiking concentrations and a long equilibration time (28 d) to be more relevant to environmental conditions. Sorption to suspended material and bed sediment was compared to examine the role of differential sorption between these phases in the environmental transport of pyrethroids. The equilibrium sorption data were fit to the Freundlich isotherm model and fit with r(2) > 0.87 for all experiments. Freundlich exponents ranged from 0.72 ± 0.19 to 1.07 ± 0.050, indicating sorption nonlinearity for some of the experimental conditions and linearity for others over the concentration range tested. The Freundlich capacity factors were larger for the suspended solids than for the bed sediments, and the suspended material had a higher specific surface area and higher organic carbon content compared to the bed sediment. Calculated organic carbon-normalized distribution coefficients were larger than those previously reported in the literature, by approximately an order of magnitude, and ranged from 10(6.16) to 10(6.68) at an equilibrium aqueous concentration of 0.1 µg/L. Higher than expected sorption of pyrethroids to the tested materials may be explained by sorption to black carbon and/or mineral surfaces.

Sorption ofortho-Phenylphenol to Soils

Conflicting sorption coefficients for ortho-phenylphenol (OPP) have been reported in the literatures, which resulted in the conflicting assessments on OPP mobility in soil. To ascertain the sorption coefficient of OPP, batch experiments were performed based on OECD guideline 106, using three types of soils. Headspace solid-phase microextraction (HS-SPME) and GC-MS were applied to the determination of OPP concentration in the liquid phase. The sorption isotherms obtained for all three soils under equilibrium conditions were described well, assuming linear sorption. The organic carbon normalized distribution coefficients (Koc) ranged from 894 to 1703 L kg−1, which suggested that OPP is moderately mobile in soil. The results also showed that the Koc value of OPP can be predicted precisely from Kow, whereas it was underestimated by one order of magnitude when water solubility is used.

Sorption mechanisms of coexisting PAHs on sediment organic fractions

Sorption of polycyclic aromatic hydrocarbons (PAHs) to natural sediment and isolated organic fractions, including demineralized organic matter (DM), condensed organic matter (COM), and black carbon (BC), was investigated to provide insight into sorption mechanisms. The organic carbon normalized distribution coefficient K(OC) measured for DM was 0.8 to 3.0 times higher than that of bulk sediment, indicating the physical protection of favorable PAH sorption domains by mineral conformation; that is, mineral enwrapping was supposed to prevent physically the accessing process of the sorbate molecules to the sorption domain. Surface area-normalized K(OC) values showed that the differences between COM and BC in the sorption capability were caused largely by their surface areas, additionally indicating the importance of solid physical structure. In considering specific interactions, mature organic fractions with polyaromatic sheets were implied to be affected by π-π interaction, whereas the DM sample that contained the electron-repulsive N-H group hardly sorbed PAHs via this interaction. Besides sorbent characteristics, PAH properties were also assumed to influence the sorption process. The hydrophobicity normalized sorption coefficient increased in the order of fluoranthene> phenanthrene> pyrene> fluorine> acenaphthene, with pyrene showing an exceptional order.