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The addition of activated carbon (AC) to sediments is a relatively new approach to remediate contaminated sites. Activated carbon strongly sorbs hydrophobic organic contaminants, thereby reducing their bioavailability and uptake in organisms. Because of its high sorption capacity, AC might, however, also sorb other chemicals that are not contaminants but instead have ecological functions. Examples of such compounds are infochemicals or pheromones (i.e., compounds serving as chemical inter- and intraspecies information vectors). The present study investigated the sorption of 2 known infochemicals, hypoxanthine-3-N-oxide (H3NO) and pyridine-N-oxide (PNO), to 5 different powdered ACs. Sorption isotherms of these low-molecular-weight, polar fish kairomone substances appeared highly nonlinear, with logarithmic Freundlich sorption coefficients of up to 7.6. At physiologically relevant concentrations, sorption was up to 7 to 9 orders of magnitude stronger than expected on the basis of hydrophobic forces only (i.e., the compounds' log octanol-water partition coefficient, being approximately -1), indicating exceptionally strong binding to specific sites. This binding effectively reduced the bioavailability of H3NO to Sarasa goldfish, as was shown in a behavioral assay. The present study demonstrates the previously unrecognized potential of AC to sorb ecologically relevant chemicals. Whether this potential may lead to subtle, unwanted ecological effects in the field will have to be investigated in more detail during future research.

The variation among bioconcentration factors (BCFs) available in the literature is commonly ascribed to experimental parameters and metabolic capacity. Though bioconcentration is generally considered to be governed by partitioning processes and therefore to depend on the composition of the partition phases, the effect of lipid composition on BCFs measured for hydrophobic organic chemicals has largely escaped attention. The reason may be that the effect cannot easily be studied separately in a conventional BCF test setup and that any subtle effects will often be obscured by the variation normally observed when working with living organisms. In the present study, this variation was circumvented by substituting biota with biological homogenates, which allowed measuring chemical partitioning in a fashion that has proved successful for many other environmental matrixes (e.g., sediments, soils, carbonaceous materials). The appropriateness of using a homogenate as a representation of the organism from which it was derived was demonstrated by a good agreement between homogenate-water partition coefficients (or necroconcentration factors; NCFs) and actual BCFs for PCBs and aquatic worms. Subsequent experiments focused on the intra- and interspecies differences in lipid-normalized NCFs. Intraspecies variation was studied for aquatic worms and sticklebacks, which were acclimatized at different temperatures (5-24 °C), whereas interspecies variation was investigated by determining NCFs for eight different aquatic species. Although temperature-induced intraspecies differences were subtle (0.16 log units), interspecies differences among lipid-normalized NCFs were as high as 0.9 log units, with homogenates of "simple" organisms showing a lower sorption capacity than those of the more "complex" species. These results suggest that the variation observed in the literature BCFs may partly be caused by differences in lipid composition and contest the usefulness of the common practice of applying generic BCFs in risk assessment of chemicals.

It is unknown whether carbonaceous geosorbents, such as black carbon (BC) affect bioturbation by benthic invertebrates, thereby possibly affecting sediment–water exchange of sediment-bound contaminants. Here, we assess the effects of oil soot on polychlorinated biphenyl (PCB) mass transfer from sediment to overlying water, for sediments with and without tubificid oligochaeta as bioturbators. PCB levels were so low that toxicity to the oligochaeta played no role, whereas soot levels and binding affinity of PCBs to soot were so low that pore water PCB concentrations were not significantly affected by binding of PCBs to soot. This setup left direct effects of BC on bioturbation activity as the only explanation for any observed effects on mass transfer. Mass transfer coefficients (KL) for benthic boundary layer transport were measured by a novel flux method using Empore™ disks as a sink for PCBs in the overlying water. For the PCBs studied (logKow 5.2–8.2), KL values ranged from 0.2 to 2 cm × d-1 in systems without tubificids. Systems with tubificids showed KL values that were a factor of 10–25 higher. However, in the presence of oil soot, tubificids did not cause an increase in mass transfer coefficients. This suggests that at BC levels as encountered under field conditions, the mechanism for reduction of sediment–water transfer of contaminants may be twofold: (a) reduced mass transfer due to strong binding of the contaminants to BC, and (b) reduced mass transfer of contaminants due to a decrease in bioturbation activity. Highlights We measured sediment to water fluxes for polychlorobiphenyls (PCBs). ¿ PCB fluxes were induced using Empore disks as a sink in the overlying water. ¿ PCB fluxes were higher in the presence of bioturbators. ¿ PCB fluxes were not higher in the presence of black carbon and bioturbators.

Understanding the interactions between organic contaminants and carbon nanomaterials is essential for evaluating the materials' potential environmental impact and their application as sorbent. Although a great deal of work has been published in the past years, data are still limited in terms of compounds, concentrations, and conditions investigated. We applied a passive sampling method employing polyoxymethylene (POM-SPE) to gain a better understanding of the interactions between polycyclic aromatic hydrocarbons (PAHs) and multiwalled carbon nanotubes (CNTs) over a 6 orders of magnitude wide concentration range. In the low-concentration range (pg-ng L(-1)), sorption of phenanthrene and pyrene was linear on a nonlogarithmic scale. Here, sorption could thus be described using a single sorption coefficient. Isotherm fits over the entire concentration range showed that (i) monolayer sorption models described the data very well, and (ii) the CNTs sorption capacity was directly related to their surface area. Sorption coefficients for 13 PAHs (11 of which have not been reported to date) were also measured at environmentally relevant low concentrations. No competition seemed to occur in the low-concentration range and sorption affinity was directly related to the solubility of the subcooled liquid of the compounds.

Several experimental methods have been developed to assess the bioavailability of individual organic compounds. So far none of them has however been applied to complex mixtures, such as oil (petroleum hydrocarbons), which is an ubiquitous pollutant. In the present study, we tested the potential of five of these experimental methods and that of a model approach to predict bioaccumulation of oil in the aquatic worm Lumbriculus variegatus exposed to 14 field-contaminated sediments. Actual and predicted bioaccumulation were compared in terms of both total bioaccumulative petroleum hydrocarbon concentrations and the relative distribution pattern of separate boiling point fractions (hydrocarbon blocks). None of the experimental methods was able to directly assess bioaccumulation in L. variegatus and correction factors were needed to match predicted and actual concentrations. These factors appeared concentration-dependent for solid phase micro extraction (SPME) and extractions with Tenax and cyclodextrin, most probably due to artifacts. Moreover, the hydrocarbon block pattern produced by these methods considerably differed from the pattern observed for worms; an additional reason for disqualification also applying to headspace-SPME. In contrast, the pattern produced by polyoxymethylene solid phase extraction (POM-SPE) closely mimicked the worm pattern and a sediment, hydrocarbon block, and concentration-independent correction factor (17) could be derived, based on which actual bioaccumulation could be predicted within a factor of 3. Finally, the model predicted bioaccumulation directly within a factor of 2. The accompanying hydrocarbon block pattern however deviated significantly more from the worm pattern than the POM-SPE pattern did. We therefore conclude that POM-SPE may be the overall best approach for predicting bioaccumulation of complex hydrocarbon mixtures in aquatic worms, all the more since an experimental approach will implicitly capture all factors determining bioavailability, which may prove difficult through a modeling approach.

Considering the importance of bioaccumulation factors (BAFs) in risk assessment of chemicals and the ethical issues and complexity of the determination of these factors in standard tests with living organisms, there is a need for alternative approaches for predicting bioaccumulation. In this study, liposome-water partitioning coefficients as determined by using solid-phase microextraction (SPME) were evaluated for the cause of assessing bioaccumulation potential of hydrophobic organic chemicals (HOCs). To this end, the SPME method was mapped (in terms of mass balance, mode of spiking, kinetics, and reproducibility) and validated against literature data. Furthermore, the robustness of liposomes as partitioning phase was investigated (in terms of chemical loading, and pH and ionic strength of the medium), and finally liposome-water partition coefficients (K(lipw)) determined for polycyclic aromatic hydrocarbons (PAHs; 4.5logK(ow)7.2) were compared with literature BAF values for several aquatic species. The results indicated that (i) SPME is a valid, fast, and reproducible method for measuring K(lipw) values; (ii) liposomes provide a very robust partitioning phase; and (iii) K(lipw) values agreed very well with literature PAH BAF values. SPME-derived K(lipw) values therefore seem a very promising predictor of bioaccumulation potential of HOCs. By including model- or in vitro-derived biotransformation rates, bioaccumulation potential estimates might be converted into surrogate BAFs, thereby extending the applicability of K(lipw) values to metabolizable chemicals and species with more advanced biotransformation capacity.

Activated carbon (AC) addition is a recently developed technique for the remediation of sediments and soils contaminated with hydrophobic organic chemicals. Laboratory and field experiments have demonstrated that the addition of 3-4% of AC can reduce aqueous concentrations and the bioaccumulation potential of contaminants. However, one aspect of the technique that has hardly received any attention is the possible occurrence of secondary, eco(toxico)logical effects, i.e., effects of AC addition on the health, behavior, and habitat quality of local organisms. In the present study, several ecotoxicological effects were investigated in AC-water and AC-enriched (0-25%) sediment systems. It was demonstrated that (i) powdered activated carbons can be toxic to aquatic invertebrates (Lumbriculus variegatus, Daphnia magna, and Corophium volutator) based on different mechanisms and preferably should be washed prior to application; (ii) Asellus aquaticus and Corophium volutator may physically avoid AC-enriched sediments; (iii) exposure of Lumbriculus variegatus to AC-enriched sediments lead to a time and dose-dependent reduction in the worms' lipid content, which was most probably caused by the observation that (iv) worm egestion rates decreased drastically upon AC addition, indicating that the presence of AC disturbed feeding behavior; and (v) there were no obvious effects on the microbiological community structure. All in all, these results suggest potential ecotoxicological effects of powdered AC addition and stress the need for a detailed further investigation of secondary effects of the technique, prior to any large-scale field application.

Petroleum hydrocarbons (oil) are common environmental contaminants. For risk assessment purposes, their concentrations in environmental matrixes, such as biota and soils/sediments are frequently determined by solvent extraction and subsequent analysis with gas chromatography (GC) equipped with flame ionization detection (FID) or mass spectrometry (MS). Because the total GC detector response is labeled as total petroleum hydrocarbon (TPH) concentration and matrix compounds (lipids, organic matter) will contribute to this response, proper extract clean-up is crucial. Still, the choice for a specific clean-up material during open column chromatography often seems arbitrary, since no comparative study on clean-up agents for TPH analysis is available. Here, such a study is described and it is demonstrated that none of the commonly used agents fulfills the requirements of complete matrix compound removal and TPH recovery. A novel column filled with (top-down) 1g of 33% (w/w) 1 M NaOH-impregnated and 2.2g of 7% (w/w) H(2)SO(4)-impregnated silica gel is recommended for cleaning-up biota extracts, as it fully removes extracted lipids and yields acceptable TPH recoveries of around 90%, based on a certified oil reference standard. For sediment extracts, most columns tested resulted in a negligibly low contribution of matrix compounds to the overall detector response, but 5% deactivated Florisil or 10% deactivated aluminum oxide are preferable, because these materials yield the highest (approximately 95%) TPH recoveries.

Soils from former manufactured gas plant (MGP) sites are often heavily contaminated with polycyclic aromatic hydrocarbons (PAHs). Current risk assessment methods that rely on total PAH concentrations likely overstate adverse effects of such soils since bioavailability is ignored. In this study, solid-phase microextraction (SPME) was applied to estimate bioavailable PAH concentrations and toxicity in earthworms exposed to 15 MGP soils. In addition, PAH sorption to all soils (K0o values) was determined. The results showed a several orders of magnitude variation in Koc values, demonstrating that generic organic carbon-normalized sorption coefficients will typically be overconservative at MGP sites. SPME-predicted bioaccumulation generally was within a factor of 10 of measured bioaccumulation (in earthworm bioassays), in contrast to current risk assessment model estimates that overpredicted bioaccumulation 10-10 000 times. Furthermore, on the basis of estimated total body residues of narcotic PAHs, SPME correctly predicted worm mortality observed during bioassays in the majority of cases. For MGP sites where current risk assessment procedures indicate concerns, SPME thus provides a useful tool for performing a refined, site-specific assessment.

The emission of black carbon is known to cause major environmental problems. Black carbon particles contribute to global warming, carry carcinogenic compounds and cause serious health risks. Here, we show another side of the coin. We review evidence that black carbon may strongly reduce the risk posed by organic contaminants in sediments and soils. Extremely efficient sorption to black carbon pulls highly toxic polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, polybrominated diphenylethers and pesticides into sediments and soils. This increased sorption is general, but strongest for planar (most toxic) compounds at environmentally relevant, low aqueous concentrations. Black carbon generally comprises about 9% of total organic carbon in aquatic sediments (median value of 300 sediments), and then may reduce uptake in organisms by up to two orders of magnitude. This implies that current environmental risk assessment systems for these contaminants may be unnecessarily safe.

Evidence is accumulating that sorption of organic chemicals to soils and sediments can be described by "dual-mode sorption": absorption in amorphous organic matter (AOM) and adsorption to carbonaceous materials such as black carbon (BC), coal, and kerogen, collectively termed "carbonaceous geosorbents" (CG). Median BC contents as a fraction of total organic carbon are 9% for sediments (number of sediments, n approximately 300) and 4% for soils (n = 90). Adsorption of organic compounds to CG is nonlinear and generally exceeds absorption in AOM by a factor of 10-100. Sorption to CG is particularly extensive for organic compounds that can attain a more planar molecular configuration. The CG adsorption domain probably consists of surface sites and nanopores. In this review it is shown that nonlinear sorption to CG can completely dominate total sorption at low aqueous concentrations (10(-6) of maximum solid solubility). Therefore, the presence of CG can explain (i) sorption to soils and sediments being up to 2 orders of magnitude higher than expected on the basis of sorption to AOM only (i.e., "AOM equilibrium partitioning"), (ii) low and variable biota to sediment accumulation factors, and (iii) limited potential for microbial degradation. On the basis of these consequences of sorption to CG, it is advocated that the use of generic organic carbon-water distribution coefficients in the risk assessment of organic compounds is not warranted and that bioremediation endpoints could be evaluated on the basis of freely dissolved concentrations instead of total concentrations in sediment/soil.

Combustion-derived PAHs are strongly sorbed to their particulate carrier (i.e., soot, charcoal), and therefore, very slow desorption kinetics of the chemicals might be anticipated. Measurements are however lacking, because conventional methods (Tenax, XAD, gas-purging) fail to accurately determine desorption kinetics due to practical problems. In this study, we used a mild supercritical fluid extraction (SFE) method, which mimics desorption into water and circumvents these problems, to quantify desorption kinetics of 13 native PAHs from pure charcoal, coal, and four types of soot. The results show that generally only very small PAH fractions are released. Desorption behavior was, however, not related to common sorbent/sorbate characteristics. Two-site model-derived "fast desorbing fractions" were

Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van der Waals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polycholorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported methodRecent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van der Waals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polychlorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method. The variation in maximum adsorption capacities could be explained by the variation in sorbent specific surface area, sorbent organic carbon content, and the sorbent-sorbate contact area. Furthermore, increasing sorbate thickness was related to a decrease in maximum adsorption capacities, which points to adsorption in micropores. Maximum adsorption capacities decreased by 1-2 orders of magnitude as the contact area increased by 50%. This points to adsorption sites being hardly larger than sorbates.

Bioaccumulation of hydrophobic organic chemicals from sediments containing soot or sootlike materials has been hypothesized to be limited by strong sorption of the chemicals to the soot matrixes. To test this hypothesis, we quantified bioaccumulation of 11 polychlorinated biphenyls (PCBs) into the aquatic oligochaete Limnodrilus sp. exposed to spiked sediment with and without the sootlike materials coal and charcoal. In addition, sorption experiments with sediment containing varying amounts of coal or charcoal were performed to elucidate the accumulation mechanism. Results showed that coal and charcoal (at realistic levels of 1.5% on a dry-wt basis) reduced PCB accumulation in worms 1.2 to 8.5 times when expressed oil a mass basis. Moreover, whereas bioaccumulation from pure sediment increased with molecular planarity of the PCBs (toxic potency), it decreased in case of sediments containing coal and charcoal. In contrast to this advantageous effect, it was hypothesized that coal and charcoal had an adverse influence on the habitat quality of oligochaetes: Organisms inhabiting sediment containing coal or charcoal had significantly reduced lipid contents as compared to organisms from pure sediment. Because of these reduced lipid contents, lipid-normalized PCB concentrations in worms and biota-to-sediment accumulation factors (BSAFs) for most PCBs were higher in sediments containing the sootlike materials as compared to those for reference sediment. Also, measured BSAFs for coal- and charcoal-containing sediments appeared to be much higher than estimated on the basis of equilibrium partitioning theory. Sorption experiments revealed that this was caused by much weaker sorption to the sediment-coal/charcoal mixture than calculated assuming linear additivity of sorption capacities of the distinct phases. It was hypothesized that this weaker sorption resulted from competition between PCBs and dissolved organic carbon molecules for sorption sites on coal/charcoal. This points to a sorption process that is much more complicated than generally assumed.

Oil is ubiquitous in aquatic sediments and may affect partitioning and bioavailability of hydrophobic organic chemicals (HOCs). In contrast to other sedimentary hydrophobic carbon phases (natural organic matter, soot-like materials), oil residues have hardly received any attention as far as it concerns effects on HOC sorption. This paper describes experimental work dealing with such effects of oil on polycyclic aromatic hydrocarbon (PAH) sorption to sediments. Three different oils were spiked to a marine sediment in concentrations between 0 and 100 g/kg. Sediment-water distribution coefficients (Kd) for six deuterated PAHs were then determined either directly after spiking the oil or after a semi-natural weathering process in the lab (lasting for more than 2 yr). Resulting Kd values demonstrated sorption-reducing (competitive) effects at relatively low oil concentrations and sorption-enhancing effects at high oil concentrations. The latter effects only occurred above a certain threshold [i.e., ca. 15% (w/w) of oil on a sedimentary organic carbon basis] marking the oil concentration at which the hydrocarbon mixture presumably starts forming separate phases. Assuming a two-domain (organic carbon + oil) distribution model, oil-water distribution coefficients (K(oil)) for PAHs were estimated. For fresh oils, log K(oil) values appeared to be very similar for different types of oils, proportional to log K(OW) values and indistinguishable from log K(OC) values. For weathered oils, K(oil) values were also rather independent of the type of oil, but the affinity of low molecular weight PAHs for weathered oil residues appeared to be extremely high, even higher than values reported for most types of soot. Because affinities of high molecular weight PAHs for oils had not changed upon weathering, sorption of all PAHs studied (comprising a log K(OW) range of 4.6-6.9) to the weathered oil residues appeared to be more or less constant (averaged log K(oil) = 7.0 +/- 0.24). These results demonstrate that it is crucial to take the presence of oil and its weathering state into account when assessing the actual fate of PAHs in aquatic environments.

During the past few years, the presence of soot in sediments has received growing interest. Soot is thought to serve as a strong partitioning medium for specific organic contaminants (PAHs). The precise extent of sorption to this material, however, is poorly known because soot/water distribution coefficients for native PAHs have not been determined yet. Measuring these coefficients using existing partitioning methods is problematic due to the nature of soot. Therefore, the objective of this study was to develop a method for the determination of distribution coefficients for organic contaminants in soot/water (but also sediment/water) systems. The method is based on solid phase extraction (SPE) of chemicals onto the plastic polyoxymethylene (POM). Sorption experiments with POM showed monophasic sorption kinetics, linear isotherms covering several orders of magnitude, and a linear relationship between distribution coefficients for POM and the octanol/water distribution coefficient. Therefore, the sorption process can be considered to be true partitioning. Application of POM for the determination of distribution coefficients for soot and sediment (POM-SPE method) resulted in highly reproducible values. The method was validated by comparing values for sediment with results for the same sediment determined using the cosolvent method. This comparison resulted in an almost 1:1 relationship, proving the method's validity.

The concentration of 1,2,4-trichlorobenzene that is additionally required within an organism for lethality, after long-term exposure to sediments, is evaluated as an endpoint for risk assessment. This additionally required body burden for lethality after 2 months of exposure to sediments from different locations, was significantly lower in sticklebacks exposed to the more polluted sediments. In two sediments a series of chemicals was analyzed; risk assessment using these data in combination with biota-to-sediment accumulation factors and supposing concentration-addition severely underestimated the ecotoxicological risk. The lethal body burden (LBB) of seawater acclimated sticklebacks did not differ from that of fish acclimated to fresh water. However, the LBB was significantly influenced by temperature. The use of the lethal body burden in risk assessment of sediments is discussed and compared to more conventional techniques.

The addition of activated carbon (AC) to sediments is a relatively new approach to remediate contaminated sites. Activated carbon strongly sorbs hydrophobic organic contaminants, thereby reducing their bioavailability and uptake in organisms. Because of its high sorption capacity, AC might, however, also sorb other chemicals that are not contaminants but instead have ecological functions. Examples of such compounds are infochemicals or pheromones (i.e., compounds serving as chemical inter- and intraspecies information vectors). The present study investigated the sorption of 2 known infochemicals, hypoxanthine-3-N-oxide (H3NO) and pyridine-N-oxide (PNO), to 5 different powdered ACs. Sorption isotherms of these low-molecular-weight, polar fish kairomone substances appeared highly nonlinear, with logarithmic Freundlich sorption coefficients of up to 7.6. At physiologically relevant concentrations, sorption was up to 7 to 9 orders of magnitude stronger than expected on the basis of hydrophobic forces only (i.e., the compounds' log octanol-water partition coefficient, being approximately -1), indicating exceptionally strong binding to specific sites. This binding effectively reduced the bioavailability of H3NO to Sarasa goldfish, as was shown in a behavioral assay. The present study demonstrates the previously unrecognized potential of AC to sorb ecologically relevant chemicals. Whether this potential may lead to subtle, unwanted ecological effects in the field will have to be investigated in more detail during future research.

Passive sampling with nondepletive sorbents is receiving increasing interest because of its potential to measure freely dissolved concentrations of hydrophobic organic compounds (HOCs) at very low concentrations, as well as its potential for both laboratory use and field deployment. However, consistent approaches have yet to be developed for the majority of HOCs of environmental and regulatory interest. In the present study, a passive sampling method was developed which allows the freely dissolved concentrations of 18 parent and 16 groups of alkyl polycyclic aromatic hydrocarbons (PAHs) on the U.S. Environmental Protection Agency (USEPA)'s "PAH-34" target compound list to be measured. Commercially available 76-μm-thick polyoxymethylene (POM) was placed in sediment/water slurries and exposed for up to 126 days, with 28 days found to be sufficient to obtain equilibrium among the sediment, water, and POM phases for the target 2- to 6-ring PAHs. The POM/water partition coefficients (K(POM)) necessary to calculate freely dissolved concentrations for parent PAHs were determined in two separate laboratories (one using pure standards, and the other using coal tar/petroleum-contaminated sediments) and agreed very well. Since the so-called "16" alkyl PAHs on the PAH-34 list actually include several hundreds of isomers for which no standards exist, sediments impacted by coal tar, or spiked with a coal tar/petroleum nonaqueous phase liquid (NAPL) were also used to measure K(POM) values for each alkyl PAH cluster. The log K(POM) values ranged from ca. 3.0 to 6.2 for 2- to 6-ring parent PAHs, and correlated well with SPARC octanol/water coefficients (K(OW)) (correlation coefficient of r(2) = 0.986). However, log K(POM) values for alkyl PAHs deviated increasingly from SPARC log K(OW) values with increasing degree of alkylation. A simple empirical model that incorporates the number of carbon atoms in a PAH gave a better fit to the experimental log K(POM) values, and was used to estimate log K(POM) for alkyl PAHs that could not be directly measured. Detection limits (as freely dissolved concentrations) ranged from ca. 1 part per trillion (ng/L) for the 2-ring PAH naphthalene, down to1 pg/L (part per quadrillion) for the 5- and 6-ring PAHs. Sorption isotherms were linear (r(2)0.99) over at least 4 orders of magnitude.

Current petroleum risk assessment considers only narcosis as the mode of action, but several studies have demonstrated that oils contain compounds with dioxin-like, estrogenic or antiestrogenic, and androgenic or antiandrogenic activities. The present study is the third in a series investigating the specific toxic effects of 11 crude oils and refined products. By employing recombinant mammalian cells stably transfected with the human estrogen receptor alpha (ERα) or beta (ERβ), and expressing the luciferase protein (ERα-U2OS-Luc and ERβ-U2OS-Luc assay), the estrogenicity or antiestrogenicity of oils was studied. All oils, except for two refined oils and one crude oil, induced estrogenic responses. The calculated estrogenic potencies of the oils were six to nine orders of magnitude lower than the potency of 17β-estradiol (E2). Upon coexposure to a fixed concentration of E2 and increasing concentrations of oils, additive, antagonistic, and synergistic effects were revealed. One nautical fuel oil was tested in the human breast carcinoma cell line MCF-7, in which it induced cell proliferation up to 70% relative to the maximal induction by E2. At its minimum effect concentration of 25 mg/L, the oil was also capable of inducing mRNA expression of the estrogen-dependent protein pS2 by a factor of two. The present results indicate that oils naturally contain potentially endocrine-disrupting compounds that are able to influence the estrogenicity of other compounds and may cause biological responses beyond receptor binding.

Bioaccumulation factors (BAFs) play a key role in risk assessment of chemicals in sediments and soils. For hydrophobic organic chemicals (HOCs), BAFs are, however, difficult to determine and values are mostly obtained by modeling. Apart from a lack of reliable data, the applicability of lab-derived values in the field situation is unknown, as exposure conditions (e.g., temperature, pH, salinity, test species, number of chemicals) are standardized in the lab, whereas they may vary in the field. In this study, the effect of temperature on the bioaccumulation of a series of moderate to very hydrophobic PAHs in aquatic worms was studied by using polydimethylsiloxane (PDMS)-coated solid phase microextraction (SPME) fibers. The results indicated that bioaccumulation of nonmetabolizable HOCs is an exothermic, enthalpy-driven process, thus decreasing with increasing temperature. As such, biotic concentrations may be several times higher in winter than in summertime, which could have ecotoxicological consequences. A two-parameter linear free energy relationship was derived with which PAH bioaccumulation can be predicted from temperature and the chemicals' hydrophobicities. Comparing the determined (thermodynamics of) PAH partitioning into organisms and PDMS indicated that the latter phase cannot be used as a surrogate phase for animal lipids. Still, SPME provides an appropriate analytical tool for the measurement of aqueous concentrations, from which bioaccumulation can subsequently be estimated by using BAFs.

In situ exposure concentrations of chemicals in sediments and their depending risks are determined by site-specific parameters (e.g., sediment organic carbon composition), controlling bioavailability. Over the years, several analytical methods have been developed to assess bioavailable concentrations or fractions. Some of these methods have been successful in the laboratory, but few attempts have been made to test their potential for predicting actual in situ bioavailability. In this study, solid-phase microextraction (SPME)-fibers and aquatic worms (Lumbriculus variegatus) were exposed in situ at three locations. In addition, laboratory-based methods, i.e., methods with which sampling of the bioavailable fraction/concentration took place in the laboratory, being SPME, polyoxymethylene solid-phase extraction (POM-SPE), hydroxypropyl-beta-yclodextrin-(HPCD), and 6 h-Tenax extraction were applied to sediments collected at the locations. Using equilibrium partitioning-based calculations, biotic PAH levels were calculated from the concentrations or fractions extracted by the used methods. In general, method-predicted concentrations were within a factor of 10 of those measured in field-exposed oligochaetes, with in situ SPME and laboratory-based POM-SPE yielding the best results. As a reference, the currently used generic risk assessment approach overpredicted biotic concentrations by a factor of 10-100, which corresponded to in situ SPME-derived sediment-water distribution coefficients and biota-to-sediment accumulation factors being up to 2 orders of magnitude higher and lower, respectively, than generic values. These observations advocate site-specific risk assessment for PAHs, for which potential tools were evaluated in this study.

Strong sorption to black carbon may limit the environmental risks of organic pollutants, but interactions with cosorbing humic acid (HA) may interfere. We studied the attenuative effect of HA additions on the sorption of polychlorinated biphenyls (PCBs) to a charcoal. "Intrinsic" sorption to HA-amended charcoal was calculated by subtracting the sorption contribution of HA from the total sorption to charcoal and HA. Association of PCBs with HA was proportional to hydrophobicity. However, the planar PCBs 77 and 126 had an additional 2-4 times stronger association than expected from hydrophobicity alone. Sorption isotherms for the raw charcoal fitted slightly better to a three-parameter Polanyi-Dubinin-Manes model than to a two-parameter Langmuir model. Preloading the charcoal with 1-75 mg of HA/g of charcoal increasingly attenuated sorption to charcoal with up to a factor of 10. The resultant isotherms could be described adequately with the Freundlich model. Isotherm nonlinearity increased with HA loading, suggesting increased sorption competition between HA and PCBs. Attenuation was negligible in the PCB picogram per liter to nanogram per liter range and increased at higher PCB concentrations, which points to saturation of binding sites on the charcoal. Attenuation was highest for planar congeners, which suggests an additional site blockage mechanism. These variations due to HA loading and PCB concentration can explain the variability in attenuation reported in earlier work and imply that the use of constant "attenuation factors" to adjust sorption coefficients determined for pure carbonaceous materials in order to apply them to field situations may not be warranted.

The debate on whether highly hydrophobic organic chemicals (with log Kow > 5-6) bioconcentrate less than may be expected from their hydrophobicity is still not settled. The often-observed hydrophobicity "cutoff" might either be explained by artifacts occurring during bioconcentration factor (BCF) measurements or by a true mechanism, i.e., reduced uptake of larger molecules due to decreased membrane permeation. In this paper, we advocate there is no hydrophobicity cutoff, at least not for compounds with log Kow of up to 7.5. Data are presented on the uptake of polycyclic aromatic hydrocarbons (PAHs) in the aquatic worm Lumbriculus variegatus. For this combination of chemicals/organism, BCFs were measured using several approaches, including traditional batch uptake kinetics measurements and alternative ones, involving solid-phase microextraction (SPME), polyoxymethylene solid-phase extraction (POM-SPE), field exposures, and the substitution of living worms by dead worm material or liposomes. A hydrophobicity cutoff was observed at two levels during the traditional approach only, whereas for the other approaches it was absent. The data were used to demonstrate the presence and impact of artifacts due to so-called "third phase effects" and nonequilibrium conditions that can obscure "true uptake". The experiments suggest that previously observed cutoff effects can be ascribed to artifacts, and that current risk assessment (often incorporating a BCF cutoff) as well as BCF measurement techniques of very hydrophobic chemicals should be revised.

The often-observed enhanced sorption of hydrophobic organic chemicals (HOCs) to sediments is frequently attributed to the presence of soot and soot-like materials. However, sediments may contain other hydrophobic phases, such as weathered oil residues. Previous experiments have shown that these residues can be efficient sorbents for certain PAHs. In this study we investigated sorption of PCBs to sediments contaminated with different concentrations and types of oils, and from that derived oil-water distribution coefficients (Koil). Sorption of PCBs to both fresh and weathered oils was proportional to sorbate hydrophobicity, and no effects of PCB planarity were observed. Furthermore, the experiments demonstrated that different oils sorbed PCBs similarly and extensively (Koil up to 108.3 for PCB 169), and that weathering caused an almost 2-fold increase in sorption of the lower chlorinated PCBs. Koil values indicated that at the PCB equilibrium concentrations tested (pg-ng/L range), for many congeners weathered oil is a stronger sorbent than pure soot and soot-like materials. Due to attenuation of adsorption to the latter materials in sediments (caused by competitive adsorption with organic matter), sedimentary weathered oil will therefore, if present as a separate phase, defeat sedimentary soot, coal, and charcoal as PCB sorbent in most cases. Consequently, weathered oil probably is the ultimate sedimentary sorbent for PCBs and should be included in HOC fate models.

Recent studies have shown that sorption of polycyclic aromatic hydrocarbons (PAHs) in soot-water systems is exceptionally strong. As a consequence, soot may fully control the actual fate of PAHs in the aquatic environment. However, sorption has only been characterized for a limited number of PAHs to diesel soot, and the mechanism is poorly understood. In this paper, we present an extensive data set of sorbent-water distribution coefficients (K(S), n = 236) for a series of PAHs (both native and added) and polychlorinated biphenyls (PCBs) to five different types of soot and five soot-like materials. Both Ks values and physicochemical properties of the sorbents show large variation. In general, sorption is very strong, with K(S) values up to 10(10), showing the highest distribution coefficients on a mass basis ever reported. Sorption of in particular PAHs is often over 1000 times as strong as sorption to amorphous sedimentary organic carbon. The variation in K(S) values cannot be explained by "soot carbon fractions" or specific surface areas of the sorbents. Instead, values for native PAHs are mostly determined by the sorbates' molar volume, and values for added PAHs and PCBs are determined by the sorbents' average pore diameter. From differences in K(S) values between native and added PAH analogues, it can be deduced that generally more than 50% (with values up to 97%) of the native PAH concentration in soot is not available for distribution to the aqueous phase. We conclude that this is caused by physical entrapment of the chemicals within the solid matrix. Furthermore, most sorbents appear to preferentially sorb PCBs with planar configurations, a phenomenon most likely driven by sorption in molecular-sized pores. Pore sorption is also concluded to be the most important sorption mechanism for added PAHs together with pi-pi interaction processes with flat aromatic sorbent surfaces. Frequently observed, slowly desorbing, resistant contaminant fractions in sediments may very well be explained on the basis of these results.

Soot contains high levels of toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Extraction of PAHs from soot for quantitative analysis is difficult because the compounds are extremely tightly bound to the sorbent matrix. This study was designed to investigate the effect of solvent type on PAH extraction yield, to identify the most optimal solvent for PAH extraction from soot, and to gain insight into the mechanism of PAH sorption to soot in aquatic environments. To that end, different types of soot as well as coal, charcoal, and sediments containing soot-like material were extracted with seven organic solvents. Large differences in extraction recoveries were observed among solvents, with relative values as low as 16% as compared to the best extracting solvent. These differences were much larger for soot than for sediments. Dichloromethane, which to date is the most widely used solvent for soot and sediment extractions, appeared to be the overall worst extractant, whereas toluene/methanol (1:6) gave the best results. Based on extraction yields and solvent properties, extraction of PAHs from soot was explained by a two-step mechanism involving swelling of the sorbent matrix and subsequent displacement of sorbates by solvent molecules. Due to the low displacement capacity of water, desorption of PAHs from soot in the aquatic environment will be strongly limited. Moreover, a certain fraction of the total PAH mass on soot is suggested to be physically entrapped, making it unavailable for partitioning to the aqueous phase.

Organic carbon normalized sediment-water distribution coefficients (KOC) of a series of in situ and (mass-labeled) added chlorobenzenes, PCBs, and PAHs were determined in an aged and a more recently deposited sediment layer from Lake Ketelmeer, The Netherlands, using the cosolvent method. The resulting log KOC's for both in situ and added compounds are rather high compared to literature data (up to 9.3 for benzo[ghi]perylene), with the ones in the recently deposited layer being generally higher than those in the aged layer (up to 1.6 log units). The results do not show the well-established effects due to increased contact time of contaminants with sediments (i.e. "aging" or "slow sorption") and indicate that after only short equilibrium times (11 days) KOC's can even be higher than after several decades of contact time in the field. In addition, distribution coefficients show a remarkable dependence on sorbate planarity, manifested by significantly different log KOC-log KOW relationships for planar (chlorobenzenes, PAHs, and mono-ortho-substituted PCBs) and nonplanar (multiple-ortho-substituted PCBs) contaminants in both sediment layers. The confirmed presence of sootlike material for which planar aromatic compounds probably have strong affinity is brought up to explain these observations. Differences in KOC's between both layers are discussed in relation to contact time and analyzed soot fractions.

A comment by John C. Fetzer on modeling maximum adsorption capacities of soot and soot-like materials for PAH and PCB and the adsorption behavior of PAH on soots and on other adsorptive materials is presented. The authors (van Noort et al.) base their model on van der Waal's forces only. This may be a valid assumption for bioavailable PAH. These weak forces allow extraction by rain or surface water, and the equilibria are solubility limited. The PAH adsorb more strongly than just due to van der Waal's forces through the interactions of the ¿ electrons with those of the partially graphitic structures in soots and other solid combustion products. In the paper by Fetzer and Rechsteiner, they looked at soots, carbon blacks, and diesel particulate. Fetzer later work on fullerene-rich soots and other materials. There is no absolute definable level of total PAH. The solvent sequence used was dichloromethane, chlorobenzene, and 1,2,4-trichlorobenzene, with hexane as a starting solvent for some types of samples. The defined PAH in many materials, including standard reference materials, is defined by desorption conditions. A response to the comment by van Noort et al. is also presented. They doubt the theory of Fetzer that "PAH adsorb more strongly than just due to van der Waal's forces through the interactions of the ¿ electrons with those of the partially graphitic structures in soots and other solid combustion products". In fact this may not be the case as it has been shown that adsorption of aromatic compounds onto carbon surfaces can be quantitatively described on the basis of van der Waals interactions only. The comments illustrate that further work is needed on both the molecular characterization of adsorption on carbon surfaces and on the morphological characteristics of carbon sorbents influencing this sorption.

It is not clear whether sequestration or aging of organic chemicals like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) limits accumulation in higher levels of aquatic food chains. Therefore, the effect of aging on accumulation was studied in 1(-m3) model ecosystems that mimicked fish-dominated, macrophyte-dominated, and fish- and macrophyte-dominated shallow lakes. Also treatments without fish and macrophytes were included. General characteristics, biomasses, total (Soxhlet-extractable), and labile (6-h Tenax-extractable) PCB and PAH concentrations in sediment and biota were monitored over time. Accumulation data for PCB 28, PCB 149, and fluoranthene (native to the sediment taken from the field) were compared to those for spiked analogues PCB 29, PCB 155, and fluoranthene-d10. Labile fractions for spiked compounds were higher than for their native analogues and decreased over time, suggesting sequestration in the sediment. In the majority of cases, 6-h Tenax-extractable concentrations correlated better with concentrations in biota than Soxhlet-extractable concentrations. Ecosystem structure affected food web accumulation, but replicate variability was too high to detect clear treatment effects. Differences in accumulation between spiked compounds and their native analogues indicated an effect of aging for invertebrates, macrophytes, and benthivorous fish. Thus, aging may translate directly into reduced uptake at higher trophic levels.