Bioavailability Of Polycyclic Aromatic Hydrocarbons Research Articles

Differential Responses of Eubacterial, Mycobacterium, and Sphingomonas Communities in Polycyclic Aromatic Hydrocarbon (PAH)‐Contaminated Soil to Artificially Induced Changes in PAH Profile

Recent reports suggest that Mycobacterium is better adapted to soils containing poorly bioavailable polycyclic aromatic hydrocarbons (PAHs) compared to Sphingomonas. To study this hypothesis, artificial conditions regarding PAH profile and PAH bioavailability were induced in two PAH-contaminated soils and the response of the eubacterial, Mycobacterium, and Sphingomonas communities to these changed conditions was monitored during laboratory incubation. Soil K3663 with a relatively high proportion of high molecular weight PAHs was amended with phenanthrene or pyrene to artificially change the soil into a soil with a relatively increased bioavailable PAH contamination. Soil AndE with a relatively high proportion of bioavailable low molecular weight PAHs was treated by a single-step Tenax extraction to remove the largest part of the easily bioavailable PAH contamination. In soil K3663, the added phenanthrene or pyrene compounds were rapidly degraded, concomitant with a significant increase in the number of phenanthrene and pyrene degraders, and minor and no changes in the Mycobacterium community and Sphingomonas community, respectively. However, a transient change in the eubacterial community related to the proliferation of several gamma-proteobacteria was noted in the phenanthrene-amended soil. In the extracted AndE soil, the Sphingomonas community initially developed into a more diverse community but finally decreased in size below the detection limit. Mycobacterium in that soil never increased to a detectable size, while the eubacterial community became dominated by a gamma-proteobacterial population. The results suggest that the relative bioavailability of PAH contamination in soil affects bacterial community structure but that the behavior of Mycobacterium and Sphingomonas in soil is more complex than prospected from studies on their ecology and physiology.

Biomimetic accumulation of PAHs from soils by triolein-embedded cellulose acetate membranes (TECAMs) to estimate their bioavailability

A new passive sampling device (PSD), a triolein-embedded cellulose acetate membrane (TECAM), was used to biomimetically accumulate naphthalene, phenanthrene, pyrene and benzo[ a]pyrene from ten spiked soils and a soil spiked with different concentrations of these polycyclic aromatic hydrocarbons (PAHs). TECAM exposure conditions were optimized. The quantities of PAHs accumulated by TECAMs were positively and linearly related to their concentrations in the soil. PAHs accumulated by TECAMs were negatively related to soil organic matter (SOM) and positively related to the dissolved organic carbon (DOC) according to the results obtained from ten spiked soils. Aging time (1–150 days) had a significant effect on accumulation of PAHs by TECAMs. A good linear relationship ( R 2=0.970–0.993) was observed between TECAM-accumulated PAHs and PAHs accumulated by earthworms ( Eisenia andrei). The data indicate that TECAM represents a useful surrogate to estimate the bioavailability of PAHs and perhaps other hydrophobic organic contaminants (HOCs) in soils.

Theory and Application of Landfarming to Remediate Polycyclic Aromatic Hydrocarbons and Mineral Oil‐Contaminated Sediments; Beneficial Reuse

When applying landfarming for the remediation of contaminated soil and sediment, a fraction of the soil-bound contaminant is rapidly degraded; however, a residual concentration may remain, which slowly degrades. Degradation of polycyclic aromatic hydrocarbons (PAHs) and mineral oil can be described using a multi-compartment model and first-order kinetics, in which three degradable fractions are distinguished; (1) rapid, (2) slowly, and (3) very slowly degradable. Using this model populated with data from long-term experiments (initiated in 1990), it is shown that time frames from years to decades can be necessary to clean the soil or sediment to obtain a target below regulatory guidelines. In passive landfarms without active management, three principal potentially limiting factors can be identified: (1) availability of appropriate microorganisms, (2) supply of oxygen for the biodegradation process, and (3) bioavailability of the pollutants to the microorganisms. Bioavailable PAHs and mineral oil are readily biodegradable contaminants under aerobic conditions, and presence and activity of microorganisms are not problems. The other two factors can be limiting and are theoretically described. Using these descriptions, which are in agreement with field experiments of 10 to 15 yr, it is shown if and when optimization of the biodegradation process is an option. Because a long time period is necessary to degrade the slowly and very slowly degradable fractions, passive landfarming should be combined with beneficial use of the land area. Examples include the development of natural environments, use in constructions, growing of biomass for energy production, including biofuels, and use as cover for landfills.

Dynamics of the hydrocarbon‐degrading Cycloclasticus bacteria during mesocosm‐simulated oil spills

We used catalysed reported deposition - fluorescence in situ hybridization (CARD-FISH) to analyse changes in the abundance of the bacterial groups Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes, and of hydrocarbon-degrading Cycloclasticus bacteria in mesocosms that had received polycyclic aromatic hydrocarbons (PAHs) additions. The effects of PAHs were assessed under four contrasting hydrographic conditions in the coastal upwelling system of the Rías Baixas: winter mixing, spring bloom, summer stratification and autumn upwelling. We used realistic additions of water soluble PAHs (approximately 20-30 microg l(-1) equivalent of chrysene), but during the winter period we also investigated the effect of higher PAHs concentrations (10-80 microg l(-1) chrysene) on the bacterial community using microcosms. The most significant change observed was a significant reduction (68 +/- 5%) in the relative abundance of Alphaproteobacteria. The magnitude of the response of Cycloclasticus bacteria (positive with probe CYPU829) to PAHs additions varied depending on the initial environmental conditions, and on the initial concentration of added PAHs. Our results clearly show that bacteria of the Cycloclasticus group play a major role in low molecular weight PAHs biodegradation in this planktonic ecosystem. Their response was stronger in colder waters, when their background abundance was also higher. During the warm periods, the response of Cycloclasticus was limited, possibly due to both, a lower bioavailability of PAHs caused by abiotic factors (solar radiation, temperature), and by inorganic nutrient limitation of bacterial growth.

Anthracene biodegradation and surface activity by an iron-stimulated Pseudomonas sp.

Iron may enhance polycyclic aromatic hydrocarbons (PAHs) degradation directly by increasing the activity of the enzymes involved in the aerobic biodegradation pathways for hydrocarbons, and indirectly by increasing the PAHs bioavailability due to the stimulation of biosurfactant production. In the present work, the PAH anthracene was used in order to study the effect of different forms and concentrations of iron on its biodegradation and surfactant production by Pseudomonas spp. isolates from a 14-years old petrochemical sludge landfarm site. Among the iron forms, iron nitrate was chosen based on its high solubility and effect on the increase in the growth of the isolate. Iron concentration of 0.1 mM was selected as the limit between deficiency and toxicity for isolates growth and anthracene degradation. After 48 days Pseudomonas citronellolis isolate 222A degraded 72% of anthracene related to iron stimulation and surface tension decrease, indicating surfactant production. Pseudomonas aeruginosa isolate 332C was iron-stimulated but did not reduce surface tension while P. aeruginosa isolate 312A exhibited a noniron and surfactant dependence to degrade 72% of anthracene. Isolate 222A showed a direct dependence on iron to stimulate surfactant activity, which probably increased anthracene bioavailability. To our knowledge, this is the first report about the iron effect on anthracene degradation and surfactant production by a Pseudomonas sp. Based on the iron requirement and surfactant activity, the Pseudomonas isolates may be useful for bioremediation of PAHs.

Adsorption of phenanthrene on activated carbon increases mineralization rate by specific bacteria

Bioavailability of polycyclic aromatic hydrocarbons (PAH) in soil is affected by PAH sorption to solid phase. We studied the influence of activated carbon (AC) on phenanthrene (PHE) mineralization by five degrading bacterial strains isolated from contaminated soil. PHE adsorption on AC was important and reduced PHE aqueous concentration up to 90%. PHE degradation was improved in the presence of activated carbon with three of the bacterial strains, named NAH1, MATE3 and MATE7, which produced biofilms, whereas it was not improved with the two other ones, which did not produce biofilms, MATE10 and MATE12. Monitoring PHE distribution during incubation showed that aqueous PHE concentration was significantly higher with the biofilm-producing NAH1 than with MATE10. Bacterial adhesion on AC was also investigated. The precoating of AC with PHE increased NAH1 and MATE3 adhesion to the solid surface (>16 and >13%, respectively). Bacterial properties, such as biofilm production and adhesion to AC capacity seemed to be related to their ability to optimize PHE degradation by improving PHE diffusion and reducing diffusion path length.

Greatly reduced bioavailability and toxicity of polycyclic aromatic hydrocarbons to Hyalella azteca in sediments from manufactured‐gas plant sites

The toxicity of polycyclic aromatic hydrocarbons (PAHs) to Hyalella azteca, was measured in 34 sediment samples collected from four manufactured-gas plant (MGP) sites ranging in total PAH16 (sum of 16 U.S. Environmental Protection Agency priority pollutant PAHs) concentrations from 4 to 5700 mg/kg, total organic carbon content from 0.6 to 11%, and soot carbon from 0.2 to 5.1%. The survival and growth of H. azteca in 28-d bioassays were unrelated to total PAH concentration, with 100% survival in one sediment having 1,730 mg/kg total PAH16, whereas no survival was observed in sediment samples with concentrations as low as 54 mg/kg total PAH16. Twenty-five of the 34 sediment samples exceeded the probable effects concentration screening value of 22.8 mg/kg total PAH13 (sum of 13 PAHs) and equilibrium partitioning sediment benchmarks for PAH mixtures (on the basis of the measurement of 18 parent PAHs and 16 groups of alkylated PAHs, [PAH34]); yet, 19 (76%) of the 25 samples predicted to be toxic were not toxic to H. azteca. However, the toxicity of PAHs to H. azteca was accurately predicted when either the rapidly released concentrations as determined by mild supercritical fluid extraction (SFE) or the pore-water concentrations were used to establish the bioavailability of PAHs. These results demonstrate that the PAHs present in many sediments collected from MGP sites have low bioavailability and that both the measurement of the rapidly released PAH concentrations with mild SFE and the dissolved pore-water concentrations of PAHs are useful tools for estimating chronic toxicity to H. azteca.

Bioavailability of polycyclic aromatic hydrocarbons sequestered in sediment: Microbial study and model prediction

In field studies and remediation projects, contaminants persist in soil and sediment much longer than would be estimated based on contaminant physical and chemical properties; such observations indicate that a fraction of contaminants in soil/sediment is much less available to the degrading microorganisms or chemical reagents. Many researchers attribute this reduced availability/ bioavailability to the sequestration (also referred to as resistant desorption or desorption hysteresis) of contaminants in soil/sediment. In the present research, desorption and bioavailability of naphthalene, phenanthrene, and fluoranthene were studied to evaluate the impact of sequestration on the biodegradability of these three polycyclic aromatic hydrocarbons (PAHs). Experimental results indicate that only desorbed PAHs are bioavailable and that the bioavailability of sequestered PAHs could be well predicted with a modified bioavailability model, which uses a biphasic desorption model to replace the conventional adsorption/desorption model. Findings in the present study might have important implications for site remediation: After the initial stage of remediation (i.e., after the readily desorbable fraction of contaminants is removed from soil/sediment), desorption of sequestered contaminants becomes the rate-limiting step of remediation. In this stage, the availability of contaminants is so low that even aggressive remediation would have little effect on overall mass reduction. Thus, a more cost-effective approach for site remediation might consist of an initial aggressive treatment followed by plume control, such as monitored natural attenuation.

Levels of polycyclic aromatic hydrocarbons and dibenzothiophenes in wetland sediments and aquatic insects in the oil sands area of Northeastern Alberta, Canada

An immense volume of tailings and tailings water is accumulating in tailings ponds located on mine leases in the oil sands area of Alberta, Canada. Oil sands mining companies have proposed to use tailings- and tailings water-amended lakes and wetlands as part of their mine remediation plans. Polycyclic aromatic hydrocarbons (PAHs) are substances of concern in oil sands tailings and tailings water. In this study, we determined concentrations of PAHs in sediments, insect larvae and adult insects collected in or adjacent to three groups of wetlands: experimental wetlands to which tailings or tailings water had been purposely added, oil sands wetlands that were located on the mine leases but which had not been experimentally manipulated and reference wetlands located near the mine leases. Alkylated PAHs dominated the PAH profile in all types of samples in the three categories of wetlands. Median and maximum PAH concentrations, especially alkylated PAH concentrations, tended to be higher in sediments and insect larvae in experimental wetlands than in the other types of wetlands. Such was not the case for adult insects, which contained higher than expected levels of PAHs in the three types of ponds. Overlap in PAH concentrations in larvae among pond types suggests that any increase in PAH levels resulting from the addition of tailings and tailings water to wetlands would be modest. Biota-sediment accumulation factors were higher for alkylated PAHs than for their parent counterparts and were lower in experimental wetlands than in oil sands and reference wetlands. Research is needed to examine factors that affect the bioavailability of PAHs in oil sands tailings- or tailings water-amended wetlands.

Development of Engineered Natural Organic Sorbents for Environmental Applications: 3. Reducing PAH Mobility and Bioavailability in Contaminated Soil and Sediment Systems

The effects of engineered natural organic amendments on two measures of the environmental "availability" of polycyclic aromatic hydrocarbons (PAHs) associated with soil and sediment samples are assessed. Two soils spiked with pyrene alone and a sediment spiked with a mixture of 4 PAH compounds were amended with raw or superheated-water processed peat or soybean stalks, then aged for periods of either 62 or 105 days. The aged soils were then examined with respect to bioaccumulation of spiked pyrene by earthworms (Eisenia foetida), and to its human bioaccessibility as measured by extraction with simulated gastrointestinal fluid. Additions of processed amendments reduced both measures of availability by factors ranging from 7.6 to 27.0 for earthworm bioaccumulation and from 2.3 to 8.8 for gastrointestinal extractability. All PAH compounds spiked to the sediment were reduced to varying extents in their availabilities to E. foetida and leachabilities by water by both processed and raw organic amendments.

Polyaromatic Hydrocarbons in Rhizosphere Soil of Different Plants: Effect of Soil Properties, Plant Species, and Intensity of Anthropogenic Pressure

The objective of the present study was to determine the content of polycyclic aromatic hydrocarbons (PAH) in the rhizospheres of some selected plant species (Cucumis dativus, Daucus carota, Allium cepa, Cueurbita, Petroselinum sativum, Cucurbitaceae, Phaseolus vulgaris, Beta vulgaris, Apium graveolens, Allium porrum, Vicia faba). Various anthropogenic influences on the PAH content in the rhizospheres of the three species selected were also studied. The PAH content was determined using the high performance liquid chromatography (HPLC) method with ultraviolet (UV) detection after a preliminary sample treatment with ultrasonic techniques. On the basis of the PAH content, the organic carbon content and the value of log Koc, a potentially bioavailable PAH fraction present in the rhizospheres of the plants studied, were calculated. The lowest content of the PAH sum (<1100 µg/kg) was found in the Petroselinum sativum, Cucurbitaceae, and Allium porrum rhizospheres. The content of the compounds studied was more than 67% lower than in the control soil (3307 µg/kg). Moreover, in the rhizosphere of the Allium porrum, the lowest content of all the five‐ and six‐ring PAH samples studied was found. The contribution of the 16 PAHs' sum, determined on the basis of an equilibrium partition in all rhizospheres studied, was higher than in the control soil. The evaluation of the PAH content in the rhizospheres of the three plants as related to the influence of anthropogenic sources showed a higher PAH content in them than in the control soil. The evaluation of the relation between the PAH content and the soil properties studied showed only sporadically statistically significant correlations.

Comparing bulk extraction methods for chemically available polycyclic aromatic hydrocarbons with bioaccumulation in worms

Environmental context. Determining the bioavailability of organic contaminants in sediments is a critical step in assessing the ecological risks of contamination in aquatic ecosystems. Standardised sediment bioaccumulation tests using benthic organisms are often performed to determine the relative bioavailability of sediment contamination. Unfortunately biological methods are time consuming, expensive and organisms are often difficult to maintain in good health in a laboratory exposure system. Contradictory results have been reported in the last decade and factors that affect the behaviour of extractants need to be examined for a large range of sediments. A study was conducted to determine the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in sediment using worms and to compare the uptake by the biological samplers with mild solid/liquid extractions when exposed to unspiked low and highly contaminated marine and freshwater sediments. Abstract. The purpose of this study is to evaluate different techniques for assessing the availability of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediments. This goal was achieved by comparing results from 28-day uptake experiments by Nereis virens and Lumbriculus variegatus with PAHs extracted by three non-exhaustive extraction methods using: n-Butanol (BuOH, 100%), an aqueous solution of hydroxypropyl-β-cyclodextrin (HPCD) and a surfactant solution of Brij700 (B700). Our results highlight the importance of considering both the PAH level in sediments and the molecular size of PAHs when attempting to predict their bioaccumulation in a biological sampler like worms using a solid/liquid extraction method. The surfactant B700 solution was quite successful to predict PAH bioaccumulation when exposed to unspiked highly contaminated sediments (25–5700 μg g–1). When low contaminated sediments (0.06–11 μg g–1) were used, HPCD and BuOH were better extractants for estimating bioaccumulation whereas B700 appeared to be too mild an extractant for most samples. Our results illustrate the interest and difficulties in finding an adequate chemical predictor for PAH bioavailabilty, particularly because PAH concentrations and sequestration processes play a determining role in the quality of results. Because B700 is not expansive and extraction solutions are easy to prepare, an extraction procedure involving this surfactant is proposed as a reliable predictor for aged highly contaminated sediments.

Bioavailability modification and fungal biodegradation of PAHs in aged industrial soils

Abstract Bioavailability of pollutants in contaminated soils represents an important factor influencing the bioremediation process. We investigated the impact of the bioavailability of polycyclic aromatic hydrocarbons (PAHs) on the efficacy of mycoremediation of aged matrices. Two historically contaminated soils, differing in both overall PAH concentrations (2320 vs. 612 mg PAHs kg - 1 ) and in the relative amount of the non-bioavailable fraction (4.0 vs. 32%, respectively), were incubated with two white rot fungi – Irpex lacteus and Pleurotus ostreatus. When relating biodegradation results with the amount of PAH bioavailable fractions estimated by sequential supercritical fluid extractions, the correlation coefficients ranged from 0.60 to 0.83. In order to assess a possible increase of the mycoremediation efficiency, four different mobilizing agents (MAs), i.e. soybean oil, Tween 20, Tween 80 and olive-mill wastewater, were added to soil prior to fungal incubations. The addition of MAs to the soil with a negligible amount of the non-bioavailable fraction had either a limited or even a negative impact on PAH degradation. The same was true also in the case of the other soil, characterized by a larger non-bioavailable fraction. Both white rot fungi under study markedly degraded PAHs in historically contaminated soils differing significantly in PAH content and the bioavailability. However, both the fungi performed better in the soil with higher pollutant bioavailability. Consequently, a preliminary determination of non-bioavailable fraction might provide a useful indication of the performance of bioremediation treatment.

Comparison of techniques for estimating PAH bioavailability: Uptake in Eisenia fetida, passive samplers and leaching using various solvents and additives

The aim of this study was to evaluate different techniques for assessing the availability of polycyclic aromatic hydrocarbons (PAHs) in soil. This was done by comparing the amounts (total and relative) taken up by the earthworm Eisenia fetida with the amounts extracted by solid-phase microextraction (SPME), semi-permeable membrane devices (SPMDs), leaching with various solvent mixtures, leaching using additives, and sequential leaching. Bioconcentration factors of PAHs in the earthworms based on equilibrium partitioning theory resulted in poor correlations to observed values. This was most notable for PAHs with high concentrations in the studied soil. Evaluation by principal component analysis (PCA) showed distinct differences between the evaluated techniques and, generally, there were larger proportions of carcinogenic PAHs (4–6 fused rings) in the earthworms. These results suggest that it may be difficult to develop a chemical method that is capable of mimicking biological uptake, and thus estimating the bioavailability of PAHs.

Hepatic and immune biological effect assays in C57BL/6 mice to measure polycyclic aromatic hydrocarbon bioavailability under laboratory exposures with increasing environmental relevance

Monitoring biological responses that are mediated via the aryl-hydrocarbon receptor (AhR) in animals exposed to environmental contaminants can indicate both the presence of chemicals that act through this biochemical pathway and whether these chemicals are bioavailable. The use of an ex-situ method that incorporated biological responsiveness monitoring in mice for determining the presence of 'biologically active' hydrocarbons in contaminated soils was investigated. The use of C57BL/6 as a test organism was validated by determining hepatic and immune responsiveness to two polyaromatic hydrocarbons (PAHs): 3,4 benz[a]pyrene (B[a]P) and 1,2 benz (a)anthracene (BA) administered via intraperitoneal (i.p.) injection. The responsiveness of mice exposed to soils spiked with hydrocarbons or ex situ exposures to soil removed from two contaminated sites was also investigated. Mice that were exposed to B[a]P via i.p. injections showed a 14-fold increase in liver microsomal ethoxyresorufin O-deethylase (EROD) activity compared to the control group. In contrast EROD activity following BA exposure at the same level was not significantly enhanced. Mouse immune response was significantly inhibited in a dose-dependent manner by i.p. injections of B[a]P. No significant inhibition occurred with the same doses of BA. Following i.p. exposure, the retention of B[a]P in mouse carcasses was greater than BA. Mice exposed to clean soils spiked with environmentally relevant concentrations of B[a]P and BA failed to show any significantly different hepatic or immune responses. Carcass residue data indicated a limited uptake of PAH from the soil. In contrast, EROD activity in mice exposed (ex situ) to hydrocarbon-contaminated soils removed from a fuel-loading depot and decommissioned gas works was significantly enhanced (4- and 2-fold respectively). However, this increase in EROD activity did not appear to correlate with either soil or carcass PAH concentrations. These results support the assumption that B[a]P has a higher affinity for the aryl hydrocarbon receptor (AhR) compared to BA. Soil parameters such as organic carbon content, structure and particle size distribution can modulate the bioavailability of contaminants to biological receptors. These factors are implicated in the lack of responsiveness demonstrated in the spiked soil experiments. However the responsiveness of EROD activity in mice exposed (ex situ) to soil contaminated with complex mixtures of hydrocarbon compounds confirms the potential usefulness of this model to determine the presence of 'biologically active' compounds in aged soils removed from contaminated sites.

Bioavailability of polycyclic aromatic hydrocarbons from buried shoreline oil residues thirteen years after the Exxon Valdez oil spill: A multispecies assessment

Seven taxa of intertidal plants and animals were sampled at 17 shoreline sites in Prince William Sound ([PWS]; AK, USA), that were heavily oiled in 1989 by the Exxon Valdez oil spill (EVOS) to determine if polycyclic aromatic hydrocarbons (PAH) from buried oil in intertidal sediments are sufficiently bioavailable to intertidal prey organisms that they might pose a health risk to populations of birds and wildlife that forage on the shore. Buried residues of EVOS oil are present in upper and middle intertidal sediments at 16 sites. Lower intertidal (0 m) sediments contain little oil. Much of the PAH in lower intertidal sediments are from combustion sources. Mean tissue total PAH (TPAH) concentrations in intertidal clams, mussels, and worms from oiled sites range from 24 to 36 ng/g (parts per billion) dry weight; sea lettuce, whelks, hermit crabs, and intertidal fish contain lower concentrations. Concentrations of TPAH are similar or slightly lower in biota from unoiled reference sites. The low EVOS PAH concentrations detected in intertidal biota at oiled shoreline sites indicate that the PAH from EVOS oil buried in intertidal sediments at these sites have a low bioavailability to intertidal plants and animals. Individual sea otters or shorebirds that consumed a diet of intertidal clams and mussels exclusively from the 17 oiled shores in 2002 were at low risk of significant health problems. The low concentrations of EVOS PAH found in some intertidal organisms at some oiled shoreline sites in PWS do not represent a health risk to populations of marine birds and mammals that forage in the intertidal zone.

A Chemical Extraction Method for Mimicking Bioavailability of Polycyclic Aromatic Hydrocarbons to Wheat Grown in Soils Containing Various Amounts of Organic Matter

In this study, we have evaluated the extent to which organic matter contents in soils influence the accumulation of PAHs by the roots of wheat plants and have developed a rapid chemical method for determining the bioavailability of PAH. Four polycyclic aromatic hydrocarbons (PAHs), naphthalene, acenaphthylene, fluorene, and phenanthrene, were added to natural soil samples with different amounts of organic matterfor pot experiments to evaluate apparent bioavailability of PAHs to wheat roots (Triticum aestivum L.). The extractabilities of PAHs in the soil were tested by a sequential extraction scheme using accelerated solvent extraction with water, n-hexane, and a mixture of dichloromethane and acetone as solvents. The water or n-hexane-extractable PAHs were positively correlated to dissolved organic matter (DOM) and negatively correlated to total organic matter (TOM), indicating mobilization and immobilization effects of DOM and TOM on soil PAHs, respectively. The apparent accumulation of PAHs by wheat roots was also positively and negatively correlated to DOM and TOM, respectively. As a result, there are positive correlations between the amounts of PAHs extracted by water or n-hexane and the quantities accumulated in plant roots, suggesting the feasibility of using water- or n-hexanes-extractable fractions as indicators of PAH availability to plants.

Bioavailability Prediction of Polycyclic Aromatic Hydrocarbons in Field-Contaminated Sediment by Mild Extractions

Assessing the bioavailability of a group of polycyclic aromatic hydrocarbons (PAHs) coexisting in a field-aged contaminated sediment was examined using mild extractions by isopropanol- and ethanol-water solutions at concentrations of 5–100%, using extraction durations from 1 h to 7 days . At a given solvent concentration, an initial rapid phase of PAH desorption was generally observed during the first 12 h , followed by a subsequent slower phase of desorption. A similar biphasic desorption was evident with increases in solvent concentration. PAH removal by various mild extractions was compared with PAH biodegradation by indigenous microorganisms. The removal of individual PAHs using 1-day 70% ethanol extraction was closely correlated to corresponding PAH removal via biodegradation, suggesting the possibility of using alcohol-water solution to simultaneously predict the bioavailability of multiple PAHs in aged sediments to indigenous microorganisms.

Adsorption of Polycyclic Aromatic Hydrocarbons by Carbon Nanomaterials

Carbon nanomaterials are novel manufactured materials, having widespread potential applications. Adsorption of hydrophobic organic compounds (HOCs) by carbon nanomaterials may enhance their toxicity and affect the fate, transformation, and transport of HOCs in the environment. In this research, adsorption of naphthalene, phenanthrene, and pyrene onto six carbon nanomaterials, including fullerenes, single-walled carbon nanotubes, and multiwalled carbon nanotubes was investigated, which is the first systematic study on polycyclic aromatic hydrocarbons (PAHs) sorption by various carbon nanomaterials. All adsorption isotherms were nonlinear and were fitted well by the Polanyi-Manes model (PMM). Through both isotherm modeling and constructing "characteristic curve", Polanyi theory was useful to describe the adsorption process of PAHs by the carbon nanomaterials. The three fitted parameters (Q0, a, and b) of PMM depended on both PAH properties and the nature of carbon nanomaterials. For different PAHs, adsorption seems to relate with their molecular size, i.e., the larger the molecular size, the lower the adsorbed volume capacity (Q0), but higher a and b values. For different carbon nanomaterials, adsorption seems to relate with their surface area, micropore volume, and the volume ratios of mesopore to micropore. Quantitative relationships between these sorbent properties and the estimated parameters of PMM were obtained. These relationships may represent a first fundamental step toward establishing empirical equations for quantitative prediction of PAH adsorption by carbon nanomaterials and possibly other forms of carbonaceous (geo-) sorbents, and for evaluating their environmental impact. In addition, high adsorption capacity of PAHs by carbon nanotubes may add to their high environmental risks once released to the environment, and result in potential alteration of PAHs fate and bioavailability in the environment.

Predicting low biota to sediment accumulation factors of PAHs by using infinite-sink and equilibrium extraction methods as well as BC-inclusive modeling

Sequestration of polycyclic aromatic hydrocarbons (PAHs) results in the slow release of PAHs from sediment to the aqueous environment, thus limiting bioavailability. Three methods to account for the limited bioavailability of native PAHs to the gastropod Hinia reticulata were therefore investigated: (i) infinite-sink extractions that measure desorption; (ii) equilibrium extractions that measure freely dissolved pore water concentrations and (iii) black carbon-inclusive modeling. The rapidly desorbing fraction was estimated based on the amount desorbed by Tenax. Relatively small amounts of PAHs (<9%) were present in F rapid and the observed solid–water distribution ratios ( K d,obs) were approximately 1–2 orders of magnitude higher than literature K oc values. Biota to sediment accumulation factors (BSAFs) measured in the gastropod H. reticulata ranged from 0.02 to 0.07, 10–140 times lower than the theoretical value of approximately 1–2. The BSAFs calculated using the rapidly desorbing fraction or freely dissolved aqueous concentrations were also much lower than the theoretical value, and median values differed from the measured BSAFs by only a factor of 1.5–9. Furthermore, the result of using a BC-inclusive BSAF model could explain the deviation from the theoretical BSAF value and account for the low bioavailability of these native PAHs to H. reticulata. Risk assessment strategies of in situ contamination should therefore include a combination of chemical methods accounting for bioavailability, as well as bioaccumulation studies.