Abstract: Samples of polyethylene pellets were collected at 30 beaches from 17 countries and analyzed for organo-chlorine compounds. PCB concentrations in the pellets were highest on US coasts, followed by western Europe and Japan, and were lower in tropical Asia, southern Africa and Australia. This spatial pattern reflected regional differences in the usage of PCBs and was positively correlated with data from Mussel Watch, another monitoring approach. DDTs; showed high concentrations on the US west coast and in Vietnam. In Vietnam, DDT was predominant over its metabolites (DDE and DDD), suggesting the principal source may be current usage of the pesticide for malaria control. High concentrations of pesticide HCHs were detected in the pellets from southern Africa, suggesting current usage of the pesticides in southern Africa. This study demonstrates the utility and feasibility of the International Pellet Watch approach to monitor POPs at a global scale. (C) 2009 Elsevier Ltd. All rights reserved.
Abstract: A partitioning tracer test based on gas-phase diffusion in the vadose zone yields estimates of the residual nonaqueous phase liquid (NAPL) saturation.The present paper investigates this technique further by studying diffusive tracer breakthrough curves in the vadose zone for a heterogeneous NAPL distribution. Tracer experiments were performed in a lysimeter with a horizontal layer of artificial kerosene embedded in unsaturated sand. Tracer disappearance curves at the injection point and tracer breakthrough curves at some distance from the injection point were measured inside and outside of the NAPL layer. A numerical code was used to generate independent model predictions based on the physicochemical sand, NAPL and tracer properties. The measured and modeled tracer breakthrough curves were in good agreement confirming the validity of important modeling assumptions such as negligible sorption of chlorofluorocarbon (CFC) tracers to the uncontaminated sand and their fast reversible partitioning between the soil air and the NAPL phase. Subsequently, the model was used to investigate different configurations of NAPL contamination. The experimental and model results show that the tracer disappearance curves of a single-well diffusive partitioning tracer test (DPTT) are dominated by the near-field presence of NAPL around the tip of the soil gas probe. In contrast, breakthrough curves of inter-well tracer tests reflect the NAPL saturation in between the probes, although there is no unique interpretation of the tracer signals if the NAPL distribution is heterogeneous. Numerical modeling is useful for the planning of a DPTT application. Simulations suggest that several cubic meters of soil can be investigated with a single inter-well partitioning tracer test of 24-hour duration by placing the injection point in the center of the investigated soil volume and probes at up to I m distance for the monitoring of gaseous tracers. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: Plastic pellets have been characterized as toxic pollutant carriers throughout the world oceans and coastal zones. However, their sorptive properties are not yet well understood. In the present study, virgin pellets and plastic eroded pellets (PEP) are used to elucidate their distribution characteristics through distribution kinetic studies. Distribution occurs through diffusion into the pellet for all materials (polyethylene, polyoxymethylene, and PEP) except polypropylene (PP). Although diffusion into the polymer happens with similar rates for both freshwater and saltwater external solutions, apparent diffusion is dependent on the solution salinity because it results in higher equilibrium distribution coefficients. Distribution coefficient into the PEP is higher and diffusion is slower than into the virgin materials. This is attributed to increased crystallinity of the PEP due to weathering. PP demonstrates diffusion rates that are increased by salinity and is apparently faster than into the other polymers suggesting a surface diffusion process. (C) 2007 Elsevier Ltd. All rights reserved.
Abstract: Plastic pellets (small granules, 1-5 millimeters in diameter) are widely distributed in the ocean and coastal zones all over the world. They are an industrial raw material for the plastic industry and are unintentionally released to the environment both during manufacturing and transport. These pellets are highly persistent and because of their hydrophobic nature they have being identified as carriers of toxic chemicals in the marine environment. Several marine organisms accumulate plastic particles in their stomach. A positive correlation between the mass of ingested plastic and PCBs in fat tissues has been documented. Also, plastic pellets are proposed as indicators of organic pollution in the sea. However, the sorption mechanisms of organic contaminants onto plastic pellets are not yet well understood. For this reason we collected such pellets from various beaches in Lesvos island. Since this material is highly heterogeneous we also obtained, from plastic manufacturers, virgin pellets made from polyethylene and polypropylene. Phenanthrene was used as the model sorbate. It is a compound with high toxicity and abundance in the environment and relatively easy to use in the laboratory. Also, there are many publications dealing with phenanthrene sorption onto different materials and our results are easily compared with previous research. Batch experiments were performed to determine the sorption kinetics of the pellets. Factors under investigation included pellet material, degree of pellet erosion, and sorption kinetic behavior. All of the five beaches in Lesvos island investigated had plastic pellets on the sand surface. All of these plastic pellets were eroded and 2/3 of them had similar appearance to virgin polyethylene pellets obtained from plastic manufacturers. Pellet color is not indicative of erosion that will lead to varying sorption kinetic behavior. Pellet density could not be used to identify pellets sampled from the beach. Apparent sorption coefficient increases with time for all pellets investigated. Thus, sorption into plastic pellets is limited by diffusion in the polymer phase. 2/3 of the plastic eroded pellets demonstrate sorption kinetics similar to virgin polyethylene pellets after 38 days.
Abstract: Activated carbon (AC) is used for the removal of organic compounds from freshwater and saltwater systems. The effect of salinity on the sorption of organic compounds by sorbents with pores such as AC is not yet well understood. Phenanthrene sorption equilibrium and kinetic experiments are performed in the present work. An EPA granular AC bed model is employed to demonstrate the effect the salinity has on the breakthrough curves at different phenanthrene initial concentrations. At high relative to the solubility phenanthrene concentrations (20050 mu g/L), sorption is higher in the saltwater than in the freshwater solutions. At low relative to the solubility phenanthrene concentrations (3 mu g/L), sorption is lower in the saltwater than in the freshwater solutions. Activated carbon is less efficient in removing phenanthrene from saltwater than from freshwater solutions when phenanthrene is present at low relative concentrations (<10 mu g/L).
Abstract: The relationship between phenanthrene sorption properties and petrography of low rank organic particles was investigated to aid in understanding sorption mechanisms, and confirm the previously observed impact of inertinite. Sorption experiments, using phenanthrene as the model organic chemical, were conducted on peat and lignite, of matrix and xylite-rich lithotypes, that have significant differences in inertinite content. Both peat and lignite samples display non-linear isotherms described by the Freundlich model. in general, the sorption isotherm linearity decreases from peat to lignite, and lignite samples show higher sorption capacities (K-fr = 4.2 - 10(4) -4.5 x 10(5)) than peat (K-fr=8.4x 10(3) -3 x 10(4)). Regression analysis applied to the maceral data and sorption parameters showed a strong correlation between inertinite and the variability of isotherm non-linearity. This correlation implies the significant impact of oxidized tissues to the heterogeneity of sorption sites. Moreover, the organic carbon normalized sorption coefficient (K-oc), at low phenanthrene concentrations, is related to the inertinite content, as well as to the organic carbon content (on dry, ash-free basis). The degree of inertinite effect on sorption (at low C-e) is higher in lignites than in peat or better, that it increases for samples with increasing organic carbon content (on dry, ash-free basis). This probably suggests that the inertinite content could be a measure of sorption non-linearity and affinity only among samples that have undergone common humification and/or coalification pathways. (C) 2006 Elsevier B.V. All rights reserved.
Abstract: Surfactant-modified sorbents have been proposed for the removal of organic compounds from aqueous solution. In the present study, one cationic (HDTMA) and three anionic (DOWFAX-8390, STEOL-CS330, and Aerosol-OT) surfactants were tested for their sorptive behavior onto different sorbents (alumina, zeolite, and Canadian River Alluvium). These surfactant-modified materials were then used to sorb a range of hydrophobic organic chemicals (HOCs) of varying properties (benzene, toluene, ethylbenzene, 1,2-dichlorobenzene, naphthalene, and phenanthrene), and their sorption capacity and affinity (organic-carbon-normalized sorption coefficient, K-oc) were quantified. The HDTMA-zeolite system proved to be the most stable surfactant-modified sorbent studied because of the limited surfactant desorption. Both anionic and cationic surfactants resulted in modified sorbents with higher sorption capacity and affinity than the unmodified Canadian River Alluvium containing only natural organic matter. The affinities of the surfactant-modified sorbents (K-oc) for most HOCs are lower than octanol/water partition coefficient (K-ow) normalized to the organic carbon content (f(oc)) and the density of octanol (K-oc octanol); naphthalene and phenanthrene are the exceptions to this rule. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: A certain amount of wood char or soot in a soil or sediment sample may cause the sorption of organic compounds to deviate significantly from the linear partitioning commonly observed with soil organic matter (SOM). Laboratory produced and field wood chars have been obtained and analyzed for their sorption isotherms of a model solute (phenanthrene) from water solution. The uptake capacities and nonlinear sorption effects with the laboratory wood chars are similar to those with the field wood chars. For phenanthrene aqueous concentrations of 1 mugl(-1), the organic carbon-normalized sorption coefficients (log K-oc) ranging from 5.0 to 6.4 for field chars and 5.4-7.3 for laboratory wood chars, which is consistent with literature values (5.6-7.1). Data with artificial chars suggest that the variation in sorption potential can be attributed to heating temperature and starting material, and both the quantity and heterogeneity of surface-area impacts the sorption capacity. These results thus help to corroborate and explain the range of log K-oc values reported in previous research for aquifer materials containing wood chars. (C) 2004 Elsevier Ltd. All rights reserved.
Abstract: An emplaced hydrocarbon source field experiment was conducted in the relatively homogeneous sandy geology of the vadose zone at Airbase V ae rlose, Denmark. The source (10.2 1 of NAPL) consisted of 13 hydrocarbons (n-, iso- and cyclo-alkanes and aromates) and CFC-113 as a tracer. Monitoring in the 107 soil gas probes placed out to 20 m from the centre of the source showed spreading of all the compounds in the pore air and all compounds were measured in the pore air within a few hours after source emplacement. Seven of the fourteen compounds were depleted from the source within the 1 year of monitoring. The organic vapours in the pore air migrated radially from the source. The CFC-113 concentrations seemed to be higher in the deeper soil gas probes compared with the hydrocarbons, indicating a high loss of CFC- 113 to the atmosphere and the lack of degradation of CFC-113. For the first days after source emplacement, the transport of CFC- 113, hexane and toluene was successfully simulated using a radial gas-phase diffusion model for the unsaturated zone. Groundwater pollution caused by the vadose zone hydrocarbon vapours was only detected in the upper 30 cm of the underlying groundwater and only during the first 3 months of the experiment. Only the most water-soluble compounds were detected in the groundwater and concentrations decreased sharply with depth (approximately one order of magnitude within 10 cm depth) to non-detect at 30 cm depth. The groundwater table varied more than 1 m within the measurement period. However that did not influence the direction of the groundwater flow. Approximately 7 months after source emplacement the groundwater table rose more than 1 m within 1 month. That did not cause additional pollution of the groundwater. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: 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 laserdesorption laser-ionization mass spectroscopy (mu (LMS)-M-2). 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 mu (LMS)-M-2 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 particlesize-dependent solid-water partitioning coefficient obtained from apparent equilibrium observed in the kinetic batch studies. For activated carbon, the mu (LMS)-M-2 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.
Abstract: Petroleum products involve mixtures of different volatile organic compounds (VOCs) that may represent a risk for groundwater after a spill to the unsaturated zone. However, the majority of the published approaches and codes for unsaturated zone modeling handle only either a single or a limited number of compounds in order to cope with the complexity of processes involved in VOC attenuation. This work aimed at simulating complex VOC scenarios using a grouping procedure, which results in the definition of a small number of effective pseudospecies with carefully specified effective properties. Grouping criteria are developed for a hypothetical scenario that involves a mixture of seven VOCs with properties covering a wide range of values. These criteria are assessed through a comparison of group-based calculations with rigorous calculations using the individual components. Groups of species with similar solubility resulted in concentration profiles that compared very satisfactorily with the rigorous results. The approach is validated with data from a large-scale lysimeter experiment. The simulation results compare satisfactorily with the experimental data for several days and for the vast majority of the mixture components. The agreement was significantly improved when temporally varying solubility values were used, justified by the difference in the compound volatility and the concomitant alteration of the VOC mixture composition with time. (C) 2003 Elsevier Ltd. All rights reserved.
Abstract: Typical contaminants found in the unsaturated zone (diesel oil, unleaded gasoline, etc.) are mixtures of several volatile organic compounds (e.g., toluene, xylene, etc.) having variable properties. A large number of models and codes dealing with the description of contaminant attenuation in the subsurface have appeared in the literature. In the present work, several representative codes capable of unsaturated zone modeling are presented. Only a limited number of these codes consider vapor phase diffusion, despite its significance in practical applications. These codes are discussed here in more detail. Three of these codes treat contaminants as mixtures of more than one compound with variable properties. However, only two of them include degradation, which is also an important attenuation mechanism. New approaches trying to overcome code limitations-in terms of compound number they can handle-are also discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.
Abstract: Using composite constituents to simulate the average behavior and fate of groups of individual hydrocarbons in the subsurface may provide the means for dealing with mixtures of tens or hundreds of individual hydrocarbons while reducing the computational cost. There are two additional sources of uncertainty associated with this technique, namely, the time dependence of the effective properties of a composite constituent due to temporal composition changes, and the approximation in determining their effective property values. In this work, an approach to limit these sources of uncertainty is described and certified with published experimental data, that involved an artificially mixed kerosene. An inverse analysis is used to estimate the effective property values of composite constituents, and a methodology is introduced for optimizing component grouping, based on the minimization of an objective function. Aqueous solubility is found to be the optimal grouping criterion for the multicomponent organic mixture considered here. Under the assumption of equilibrium partitioning among phases, the effective property values of the composite constituents are expressed in terms of the property values of the member components using a step-wise inverse analysis. Simple arithmetic averages are found to provide poor approximations to the effective group properties and alternative schemes are proposed, based on experimental data. (C) 2002 Elsevier Science Ltd. All rights reserved.
Abstract: Organic petrography has been proposed as a tool for characterizing the heterogeneous organic matter present in soil and sediment samples. A new simplified method is proposed as a quantitative means of interpreting observed sorption behavior for phenanthrene and different soils and sediments based on their organic petrographical characterization. This method is tested under singe solute conditions and at phenanthrene concentration of 1 mug/L. Since the opaque organic matter fraction dominates the sorption process, we propose that by quantifying this fraction one can interpret organic content normalized sorption distribution coefficient (K-oc) values for a sample. While this method was developed and tested for various samples within the same aquifer, in the current study the method is validated for soil and sediment samples from different sites that cover a wide range of organic matter origin, age, and organic content. All 10 soil and sediment samples studied had log K-oc values for the opaque particles between 5.6 and 6.8. This range of K-oc values illustrates the heterogeneity of opaque particles between sites and geological formations and thus the need to characterize the opaque fraction of materials on a site-by-site basis.
Abstract: Diffusion, sorption and biodegradation are key processes impacting the efficiency of natural attenuation. While each process has been studied individually, limited information exists on the kinetic coupling of these processes. In this paper, a model is presented that couples nonlinear and nonequilibrium sorption (intraparticle diffusion) with biodegradation kinetics. Initially, these processes are studied independently (i.e., intraparticle diffusion, nonlinear sorption and biodegradation), with appropriate parameters determined from these independent studies. Then, the coupled processes are studied, with an initial data set used to determine biodegradation constants that were subsequently used to successfully predict the behavior of a second data set. The validated model is then used to conduct a sensitivity analysis, which reveals conditions where biodegradation becomes desorption rate-limited. If the chemical is not pre-equilibrated with the soil Drier to thc onset of biodegradation, then fast sorption will reduce aqueous concentrations and thus biodegradation rates. Another sensitivity analysis demonstrates the importance of including nonlinear sorption in a coupled diffusion/sorption and biodegradation model. While predictions based on linear sorption isotherms agree well with solution concentrations, for the conditions evaluated this approach overestimates the percentage of contaminant biodegraded by as much as 50%. This research demonstrates that nonlinear sorption should be coupled with diffusion/sorption and biodegradation models in order to accurately predict bioremediation and natural attenuation processes. To our knowledge this study is unique in studying nonlinear sorption coupled with intraparticle diffusion and biodegradation kinetics with natural media. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: Alluvial aquifer samples from the same depth but different locations and from different depths at the same location were characterized and evaluated both for the nature of their organic matter and their sorption properties. Both equilibrium and kinetic sorption were evaluated using batch studies with phenanthrene. Organic petrology was used both qualitatively and quantitatively to explain and predict the patterns of sorption for each sample. Organic carbon content values varied by 1 order of magnitude, and sorption capacities varied by 2 orders of magnitude within a given depth and location for these samples. The sorption isotherms ranged from nonlinear to virtually linear. The organic content-normalized distribution coefficients (K-oc) varied significantly between organic matter subgroups as did the time to reach equilibrium. We were able to correlate these Variations in sorption behavior with the organic matter type in subgroups. K-oc values were assigned to each organic matter subgroup and were used along with the fraction of each organic matter subgroup to predict the composite K-oc values. Close agreement between predicted and measured K-oc values validated this approach. Using the subgroup K-oc values and literature fraction organic carbon (f(oc)) values, the sorption distribution coefficients were also predicted within the 95% confidence intervals for the measured values. Our results also demonstrate that opaque organic matter fractions dominate the sorption process and that quantifying this fraction alone can virtually predict the sample K-oc value.
Abstract: Sediment organic matter heterogeneity in sediments is shown to impact the sorption behavior of contaminants. We investigated the sorptive properties as well as the composition of organic matter in different subsamples (mainly grain size fractions) of the Canadian River Alluvium (CRA). Organic petrography was used as a new tool to describe and characterize the organic matter in the subsamples. The samples studied contained many different types of organic matter including bituminous coal particles, Differences in sorption behavior were explained based on these various types of organic matter. Subsamples containing predominately coaly, particulate organic matter showed the highest K-oc, the highest nonlinearity of sorption isotherms and the slowest sorption kinetics. Soil subsamples with organic matter present as organic coatings around the quartz grains evidenced the lowest K-oc, the most linear sorption isotherms and the fastest sorption kinetics, which was not limited by slow intraparticle diffusion. Due to the high sorption capacity of the coaly particles even when it is present as only a small fraction of the composite organic content (<3%) causes K-oc values which are much higher than expected for soil organic matter (e.g. K-oc - K-ow relationships). The results show that the identification and quantification of the coaly particles within a sediment or soil sample is a prerequisite in order to understand or predict sorption behavior of organic pollutants.
Abstract: Phenanthrene was used as a model chemical to study the sorption properties of Canadian River Alluvium aquifer material. Both equilibrium and kinetic sorption processes were evaluated through batch studies. The bulk sample was divided into subsamples with varying properties such as particle size, organic content, equilibration time, etc, in order to determine the effect of these properties on resulting sorption parameters. The data have been interpreted and the effect of experimental variables was quantified using the Freundlich isotherm model and a numerical solution of Fick's 2(nd) law in porous media. Microscopic organic matter characterization proved to be a valuable tool for explaining the results. Different organic matter properties and sorption mechanisms were observed for each soil subsample. Samples containing coal particles presented high Koc values. Samples with organic matter dominated by organic coatings on quartz grains presented low Koc values and contained a high percentage of fast sorption sites. The numerical solution of Fick's 2(nd) law requires the addition of two terms (fast and slow) in order to fit the kinetics of these heterogeneous samples properly. These results thus demonstrate the need for soil organic matter characterization in order to predict and explain the sorption properties of a soil sample containing heterogeneous organic matter and also the difficulty and complexity of modeling sorption in such samples. (C) 1999 Elsevier Science Ltd. All rights reserved.
