Article

Investigating Desorption of Native Pyrene from Sediment on Minute- to Month-Timescales by Time-Gated Fluorescence Spectroscopy

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Abstract

We investigated desorption of native pyrene from field-aged sediments using time-gated, laser-induced fluorescence (LIF) spectroscopy. LIF is superior to conventional analytical methods for the measurement of quickly changing dissolved pyrene because it allows observations at minute-scale resolution, has a low detection limit (approximately 1 ng/L), and minimizes sample loss and disturbance since it requires no system subsampling and chemical analysis. The efficacy of LIF was demonstrated in studies of pyrene desorption from Boston Harbor sediment segregated into different size-fractions (38-75, 75-106, and 180-250 microm diameter) and used in varying solid-to-water ratios (20, 70, and 280 mg(solid)/L). The effects of particle size and solid loading on desorption were consistent with diffusion physics. For suspension conditions between 20 and 280 mg(solids)/L, we observed desorption continuing toward an apparent plateau level over the course of weeks to months. This implies that the characteristic desorption time of pyrene from fine sediments and, by inference, other sediment-bound hydrophobic organic compounds (HOCs) of similar hydrophobicity, exceeds the typical characteristic times for pore water flushing and resuspension events. Consequently, the assumption of local sorption equilibrium in modeling efforts would be inappropriate.

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... The absorbance of these solutions at excitation (Xexc: 337 nm) and emission (Xem: 387 nm) wavelengths was determined using a Beckman DU600 spectrophotometer. Due to the presence of other flourophores in these aqueous solutions, pyrene fluorescence measurements in aqueous solutions containing melanoidin and DOM were made using time-gated, laser-induced fluorescence (TGLIF) spectroscopy (Kuo et al., 2007;Rudnick, 1998;Rudnick and Chen, 1998). To correct for the absorbance of melanoidin and DOM considering the illumination geometry of the TGLIF system, we corrected our inner filter effects according to Kuo et al. (2007): We used a numerical integration approach to correct for inner filter effect and followed the same approximation that Kuo et al. (2007) used to estimate G(x): ...
... Due to the presence of other flourophores in these aqueous solutions, pyrene fluorescence measurements in aqueous solutions containing melanoidin and DOM were made using time-gated, laser-induced fluorescence (TGLIF) spectroscopy (Kuo et al., 2007;Rudnick, 1998;Rudnick and Chen, 1998). To correct for the absorbance of melanoidin and DOM considering the illumination geometry of the TGLIF system, we corrected our inner filter effects according to Kuo et al. (2007): We used a numerical integration approach to correct for inner filter effect and followed the same approximation that Kuo et al. (2007) used to estimate G(x): ...
... Due to the presence of other flourophores in these aqueous solutions, pyrene fluorescence measurements in aqueous solutions containing melanoidin and DOM were made using time-gated, laser-induced fluorescence (TGLIF) spectroscopy (Kuo et al., 2007;Rudnick, 1998;Rudnick and Chen, 1998). To correct for the absorbance of melanoidin and DOM considering the illumination geometry of the TGLIF system, we corrected our inner filter effects according to Kuo et al. (2007): We used a numerical integration approach to correct for inner filter effect and followed the same approximation that Kuo et al. (2007) used to estimate G(x): ...
Article
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008. Includes bibliographical references. Emissions of black carbon (BC), the soot and char formed during incomplete combustion of fossil and biomass fuels, have increased over the last century and are estimated to be between 8 and 270 Tg BC/yr. BC may affect problems as diverse as global warming, human health, carbon cycling in ecosystems, and pollutant dynamics. However, currently there is substantial uncertainty with respect to the fate of BC released to the environment. To increase our understanding of BC's fate and effects, modifications to the Chemo-Thermal Oxidation method at 375 'C (CTO 375), a current method used to quantify BC in marine sediments, were made to measure BC concentrations in, and fluxes out of, the water column in the Gulf of Maine (GoM), a representative coastal area downwind of important BC sources of the Northeastern United States. In addition, an alternative method to infer BC concentrations in seawater by observing pyrene fluorescence losses (PFL) in spiked samples was developed. Average concentrations measured in the GoM were 5 and 4 [tg/L using the modified CTO 375 and PFL methods, respectively. Although these two methodologies involve independent observations, correspondence between the modified CTO 375 and PFL methods suggested that the isolated material was both highly sorptive and refractory. These concentrations also suggested that (a) up to 50% of the "molecularly uncharacterized" particulate organic carbon (POC) in surface seawater is BC; (b) the presence of this recalcitrant organic carbon may explain why some POC is not recycled to CO2 during its transport to depth and even within the sediment beds below; and (c) hydrophobic pollutants like polycyclic aromatic hydrocarbons (PAHs) and dioxins would have their "bioavailabilities" controlled by sorption to BC. (cont.) The observed BC spatial distributions and average water-column export fluxes near 10 gBC/m2 year imply that most of the BC is carried offshore by wind and is accumulated in the coastal zone. Finally, sediment records of CTO-375-derived BC inputs into the GoM for the past 100 years were consistent with historical changes in fossil and biomass fuel emissions to this area. by Déborah Xanat Flores-Cervantes. Ph.D.
... The choice of pyrene as the chemical probe for our analysis was based on observations by Rudnick and Chen (17), previous work in our research group (14,15,18), and experience in our lab. First, pyrene has a substantial affinity for BC (14,15). ...
... Next, Rudnick and Chen (17) found this PAH only occurred at ng/L levels in Boston Harbor seawater, implying we could control total pyrene levels in our samples with µg/L spikes. Finally, truly dissolved pyrene concentrations can be assessed via static fluorescence measures down to subµg/L levels (14,19), and the uniquely long fluorescence lifetime of this PAH allows dissolved pyrene to be detected among many other natural and pollutant fluorophores using time-gated approaches, if necessary (17,18). ...
... To test the accuracy of our fluorescence observations below 0.5 µg pyrene/L, we compared our measured concentrations with those found on the same samples using time-gated laser-induced fluorescence spectroscopy (TG-LIF) (17,18) with inner filter effect corrections made as described by Kuo et al. (18) (Supporting Information). TGLIF triggers a time-gated mechanism that allows the system to filter out short-lived fluorescence signals from fluorophores such as humic substances or PAHs other than pyrene (17) by imposing a time delay for the detection of the emitted photons. ...
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Black carbon (BC), the soot and char formed during incomplete combustion of fossil and biomass fuels, is ubiquitous, participates in diverse environmental processes, and has adverse effects on human health. However, uncertainty persists regarding how accurately the present measurement methods quantify total BC or even defined subportions of the BC continuum. Hence, we sought to improve this situation by developing a new, low-sample manipulation methodology that does not require any oxidative or pyrolytic treatments but rather differentiates BC from other non-BC organic carbon (OC) using its sorbent properties. The procedure, referred to as the pyrene fluorescence loss (PFL) method, infers BC concentrations in particulate organic matter (POM) by observing the decrease in fluorescence from pyrene spiked into aqueous POM suspensions. The method was first tested using diverse materials previously utilized in an international BC method intercomparison study, and then its effectiveness (e.g., sensitivity and geochemical reasonableness) was tested by applying itto sediment and seawater POM samples collected from a coastal area downwind of important BC sources. Parallel evaluation of BC, using the PFL method and CTO-375 procedure, suggested we can characterize the predominant BC in a given sample as (i) thermally recalcitrant and highly sorptive per mass (e.g., soot), (ii) thermally labile and highly sorptive per mass (e.g., char), or (iii) thermally recalcitrant but not highly sorptive (e.g., lignite coal).
... ESEM has greater magnification (100,000Â) than optical microscopy, it can study samples with the temperature range from À200 to 1000°C (McDonald, 2010), and provide detailed three-dimensional and topographical images of the OSAs surface, which makes it a great tool to investigate the morphological properties of OSAs (Stoffyn-Egli and Lee, 2002). Compared with the conventional scanning electron microscopy which only observe dry and electrically insulating materials (Stokes, 2003), ESEM employs differential pumping systems which can transfer electron beam from the gun area with high vacuums to the specimen chamber with high pressures, enabling it to image specimens in the natural state (e.g., wet samples) much faster and easier (Kuo et al., 2007). Stoffyn-Egli and Lee (2002) applied ESEM to imaging dry and wet OSAs, and observed the minerals were coated on the oil droplets, and the relationship between minerals and oil droplets is more visible for dry samples. ...
... Kepkay et al. (2002) described a UV fluorescence spectroscopy method to directly (without extraction) analyze OSAs in seawater, and confirmed this method could be used to analyze the dispersed/dissolved oil and OSAs in seawater and predict the extent of OSAs formation. Kuo et al. (2007) used time-gated laser-induced fluorescence (LIF) spectroscopy to investigate desorption of pyrene from aged sediment. The results showed this method is superior to conventional methods (e.g., GC-MS) as it can measure the changes in concentration of dissolved pyrene at minute-scale resolutions and at a detection limit of approximately 1 ng/L. ...
... Sediment samples (20 to 80 mg) were introduced into 60-ml BOD glass bottles (Wheaton), together with 50 ml of distilled water containing 8.4 ng/ml dissolved 14 C-pyrene (5,000 dpm/ml). The resulting range of concentrations of suspended solids (400 to 1,600 mg solids/liter) can be considered realistic for natural estuary, harbor, or tributary water columns, which typically contain 20 to 500 mg of solids/liter (20), and for waters receiving inputs of solids (130 to 2,300 mg solids/liter) during resuspensions of PAH-polluted sediments (37). The radiolabeled compound had been added to the aqueous solution dissolved in acetone (0.1 ml acetone per liter of water). ...
... The log K d values estimated for NQB and NQB-BC sediments were 3.38 Ϯ 0.04 and 4.09 Ϯ 0.04, respectively. The former was close to, but lower than, the value previously reported with this sediment, 3.72 Ϯ 0.17 (1), presumably because the sorptive equilibrium for this system was not fully reached even at 200 h (20). ...
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Sorption to sediment black carbon (BC) may limit the aerobic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in resuspension events and intact sediment beds. We examined this hypothesis experimentally under conditions that were realistic in terms of oxygen concentrations and BC content. A new method, based on synchronous fluorescence observations of 14C-pyrene, was developed for continuously measuring the uptake of dissolved pyrene by Mycobacterium gilvum VM552, a representative degrader of PAHs. The effect of oxygen and pyrene concentrations on pyrene uptake followed Michaelis-Menten kinetics, resulting in a dissolved oxygen half-saturation constant (Kom) of 14.1 μM and a dissolved pyrene half-saturation constant (Kpm) of 6 nM. The fluorescence of 14C-pyrene in air-saturated suspensions of sediments and induced cells followed time courses that reflected simultaneous desorption and biodegradation of pyrene, ultimately causing a quasi-steady-state concentration of dissolved pyrene balancing desorptive inputs and biodegradation removals. The increasing concentrations of 14CO2 in these suspensions, as determined with liquid scintillation, evidenced the strong impact of sorption to BC-rich sediments on the biodegradation rate. Using the best-fit parameter values, we integrated oxygen and sorption effects and showed that oxygen tensions far below saturation levels in water are sufficient to enable significant decreases in the steady-state concentrations of aqueous-phase pyrene. These findings may be relevant for bioaccumulation scenarios that consider the effect of sediment resuspension events on exposure to water column and sediment pore water, as well as the direct uptake of PAHs from sediments.
... It has been reported that time-gated luminescence methods have the ability to reduce or avoid the interference of background luminescence with a short lifetime. Kuo et al. (Kuo et al., 2007) filtered out the short-lived fluorescence signals from other chromophores to investigate the desorption process of native pyrene from sediment. This method has a low detection limit (~1 ng/L), and it allows observations at minute-scale resolutions. ...
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... petrogenic materials) are equilibrating more quickly with the samplers than PAHs from source material with slower desorption kinetics (e.g. pyrogenic materials) (Kuo et al. 2007). ...
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... It has been reported that time-gated luminescence methods have the ability to reduce or avoid the interference of background luminescence with a short lifetime. Kuo et al. (Kuo et al., 2007) filtered out the short-lived fluorescence signals from other chromophores to investigate the desorption process of native pyrene from sediment. This method has a low detection limit (~1 ng/L), and it allows observations at minute-scale resolutions. ...
... The new method is based on characteristic fluorescence properties of PBDEs under room temperature. Although fluorescence-based methods have been widely used in analyzing hydrophobic organic compounds in aqueous phase [20][21][22][23], sediments [24,25], and engineered nanoporous materials [26], its application to analyze PBDEs has not been reported to our knowledge. The major objectives of this study are therefore to (1) characterize fluorescent properties of six major PBDEs congeners that are commonly found in environment and (2) demonstrate the efficacy of the fluorescence spectroscopy method for measuring the concentrations of PBDEs in aqueous samples. ...
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Long-term temporal phase distribution relationships (PDRs) were measured for sorption of a hydrophobic organic contaminant probe by seven EPA reference soils and sediments and six shale and kerogen samples. The times required for attainment of apparent sorption equilibrium by the phenanthrene probe were found to be highly dependent upon the aqueous phase-solute concentration, C(t), for a given sorbent, and the type of soil organic matter (SOM) associated with a particular sorbent. Organic-carbon-normalized single-point temporal distribution ratios corresponding to low residual solution phase concentrations were found to approach their respective apparent equilibrium values after times ranging from several days to 90 days for the EPA soils and sediments and from 90 days to ≥ 368 days for the shales and kerogens. Conversely, at residual solution phase concentrations 2 orders of magnitude larger, apparent equilibrium conditions were attained within a few hours for the EPA soils and sediments and within a year for the shale and kerogen samples. The observed dependencies of sorption rate on C(t) and on the type of SOM appear to result from differences in solute diffusion behavior within chemically reduced and structurally condensed SOM domains and that in highly amorphous SOM domains. In the former case the very slow and concentration-dependent non-Fickian behavior observed is likely attributable to the slow and energetically driven reconfiguration of local condensed SOM structures to accommodate solute migration into the matrixes. The results of the study extend the applicability of the Dual Reactive Domain Model introduced earlier in this series of papers to the interpretation and description of sorption rate behavior.
Article
In the present study, the desorption kinetics of 15 PAHs (two to six rings) from sediments were determined before and after bioremediation in a bioreactor or landfarm. Desorption kinetics were measured with a method in which the water phase was kept PAH-free by Tenax TA beads. For almost all degraded PAHs, rapidly desorbing fractions (desorption rate constants > 0.1 h-1) were much smaller after bioremediation than before treatment whereas the slowly desorbing amounts remained unchanged. Thus, mainly the rapidly desorbing PAHs are degraded during bioremediation. The extent of possible PAH degradation could be roughly predicted from the initial rapidly desorbing fraction. For nondegraded PAHs, the rapidly desorbing fractions were substantial (up to 55%) and remained unchanged by remediation. The magnitude of the rapidly desorbing fractions of the nondegraded PAHs suggests that their persistence is due to microbial factors, not bioavailability.
Article
Isothermal desorption rates were measured at 15, 30, and 60 °C for trichloroethylene (TCE) on a silica gel, an aquifer sediment, a soil, a sand fraction, and a clay and silt fraction, all at 100% relative humidity. Temperature-stepped desorption (TSD) rates were measured for these solids in columns prepared and equilibrated at 30 °C, but heated instantaneously to 60 °C after 1000 min of slow desorption. Fast and slow elution rates are observed for all solids. Modeling results for the fast eluting fraction of TCE show that fast desorption is controlled by diffusion through aqueous filled mesopores. Rates predicted from diffusion and surface-barrier models are compared to slow isothermal and TSD rates. Diffusion model fits are superior to surface-barrier model fits in all cases. Slow diffusion coef ficients and a high activation energy calculated from silica gel data (34 kJ/mol) indicate that slow desorption is controlled by activated diffusion in micropores. Initial amounts of slow desorbing TCE do not affect these rates and are found to obey Polanyi's equation. The mass adsorbed in non-Freundlich isotherm regions, where micropores are hypothesized to control adsorption, is 10 times greater than the mass adsorbed at the onset of slow desorption, sug gesting that these pores are undulating in nature. TSD column results are consistent with a mechanism where slow diffusion rates are controlled by sorptive forces at hydrophobic micropore constrictions.
Article
The use of equilibrium expressions for sorption to natural particles in fate and transport models is often invalid due to slow kinetics. This paper reviews recent research into the causes of slow sorption and desorption rates at the intraparticle level and how this phenomenon relates to contaminant transport, bioavailability, and remediation. Sorption kinetics are complex and poorly predictable at present. Diffusion limitations appear to play a major role. Contending mechanisms include diffusion through natural organic matter matrices and diffusion through intraparticle nanopores. These mechanisms probably operate simultaneously, but the relative importance of each in a given system is indeterminate. Sorption shows anomalous behaviors that are presently not well explained by the simple diffusion models, including concentration dependence of the slow fraction, distributed rate constants, and kinetic hysteresis. Research is needed to determine whether adsorption/desorption bond energies may play a role along with molecular diffusion in slow kinetics. The possible existence of high-energy adsorption sites both within the internal matrix of organic matter and in nanopores is discussed. Sorption can be rate-limiting to biodegradation, bioavailablity, and subsurface transport of contaminants. Characterization of mechanism is thus critical for fate and risk assessment. Studies are needed to measure desorption kinetics under digestive and respiratory conditions in receptor organisms. Conditions under which the constraint of slow desorption may be overcome are discussed, including the addition of biological or chemical agents, the application of heat, and the physical alteration of the soil.
Article
As they persist, or age, in soil, organic compounds become progressively less available for uptake by organisms, for exerting toxic effects, and for biodegradation and bioremediation by microorganisms. This declining bioavailability is not reflected by currently used methods for the chemical analysis of soils for determining concentrations of organic pollutants. As a result, such methods overestimate exposure, and thus risk, from toxic chemicals in contaminated sites.
Article
A fluorescence-quenching method was developed to assess the hydrophobic organic pollutant binding potential of organic colloids (OC) in unaltered natural waters. This method allows (1) direct assessment of the importance of OC-enhanced pollutant transport for environmental samples under in situ water chemistry conditions, without requiring the isolation of OC or separation of equilibrated phases; (2) testing of chemical that suffer substantial wall losses from aqueous solutions; and (3) examination of unstable water samples such as anoxic samples. Their experiments show that some OC (Aldrich humic acids) fully quench OC-associated perylene fluorescence, but others (bovine serum albumin) do not. This implies that fluorescence-quenching results collected for a single (OC) or over a limited (OC) range provide only a lower limit estimate of the potential for OC association. Tests with groundwater, recharged with secondarily treated sewage and containing OC at â¼ 1 mg of C/L, showed temporal variation in the ability of OC present to quench or bind perylene.
Article
The rate of sorptive uptake of tetrachloroethene (PCE) and 1,2,4,5-tetrachlorobenzene (TeCB) was studied on sandy aquifer material from Borden, ON, by use of a batch methodology designed to accurately measure sorption over long equilibration periods. Measured rates of uptake were interpreted with an intraparticle diffusion model and diffusive rate constants were determined for different size fractions of the Borden solids as well as with pulverized material. In general, measured rates were quite slow in comparison with previously reported results in other systems. The rate constants for TeCB were consistently lower than for PCE, with inverse correlation between observed rate constants and equilibrium distribution coefficients, consistent with a concept of retarded intraparticle diffusion. Good model fits with the coarsest size fractions and dramatic increases in rate with particle pulverization suggest that sorption occurs throughout the grain volume and that particle radius may be the appropriate length scale for diffusion. Based on measured particle size and independent estimates of porosity and internal retardation, effective pore diffusion coefficients are estimated to be roughly 2-3 orders of magnitude lower than bulk aqueous diffusivities, consistent with the low porosity of the calcareous rock fragments studied and an additional 3- to 20-fold rate reduction due to constrictive effects of pore size. Interpretations of results assuming intraorganic matter diffusion are also presented and discussed. 57 refs.
Article
There is an increasing recognition of the necessity to consider the heterogeneity of geosorbents, and in particular the condensed carbon facies fraction, to improve prediction of hydrophobic pollutant phase speciation. Field observations of much elevated organic-carbon normalized distribution coefficients (Koc) of PAHsrelative to predictions from bulk organic-matter partitioning modelshave been suggested to be explainable by soot sorption. To afford testing of this hypothesis, we here report on the soot-water distribution coefficients (Ksc) for a series of PAHs (naphthalene (NP), fluorene (FL), phenanthrene (PH), and pyrene (PY)) using diesel particulate matter (NIST standard reference material SRM-1650) as model soot sorbent. Specifically adapted batch and column experiments yielded average log Ksc values of 5.23, 5.40, 5.82, and 6.59 (batch) and 4.63, 6.03, 6.62, and 7.03 (column) for NP, FL, PH, and PY, respectively (all data in [Lw/kgsc]). The obtained values are 35−250 times higher than respective Koc predictions and are considerably closer to theoretically estimated soot-water distribution coefficients. Our data are among the highest solid-water distribution coefficients of an environmentally relevant sorbent ever reported and lend direct empirical support of active soot sorption as a viable explanation to the enhanced PAH partitioning. Sorption kinetics on the hours-days time scale and similarity of external geometric and BET surface areas suggest that interaction sites are largely restricted to the outer surface of the soot. The constrained Ksc values facilitate prediction of speciation and bioavailable exposures of PAHs in aquatic and sedimentary environments.
Article
Batch and column experiments were conducted to assist in elucidation of the mechanism and rates of slow diffusion of 1,2,4-trichlorobenzene into Borden sand. Batch rate experiments were conducted at three concentration levels, and a full isotherm was developed over 550 d. The equilibrium isotherm showed significant nonlinearity (Freundlich exponent = 0.75). Three column experiments were conducted—two at low velocity (each at a different input concentration) and one at high velocity. The data were analyzed with four different models; the two most successful are described in detail here. These two models divided sorption between instantaneously equilibrating and diffusion-limited domains, with either a linear or nonlinear sorption isotherm assumed for the instantaneously equilibrating fraction of sorption sites. Either model could simulate any single data set by adjustment of two parameters; however, no single parameter set could simulate all data sets. The model with a linearly sorbing instantaneous fraction described the batch data better than the model with a nonlinearly sorbing instantaneous fraction; however, a nonlinearly sorbing instantaneous fraction described the slow column experiments much better than a linearly sorbing instantaneous fraction. The high-flow-rate column experiment indicated that the assumed instantaneous fraction is actually influenced by rate limitations, suggesting that more complex models are needed in order to simulate this shorter time scale behavior. Overall, our work illustrates how one needs to include a wide variety of experimental conditions in order to fully test the complex set of sorption equilibrium and rate mechanisms that are present in natural solids.
Article
The ability to predict accumulation levels of sediment-sorbed hydrophobic organic contaminants (HOCs) by depositfeeding organisms based on sediment concentrations is limited in part by an incomplete understanding of the chemistry that controls assimilation efficiency. This study was designed to test the hypothesis that desorption is an important process that controls the bioavailability of HOCs to deposit-feeding organisms; we planned to do so by conducting desorption and bioavailability experiments with field-contaminated sediments collected from New York Harbor, New York, USA. Three classes of organic contaminants, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and linear alkylbenzenes (LABs) were studied. In order to address the effects of contaminant aging, we compared the contaminant desorption rates from sediments collected from surface and at depth in an area of known high-sediment accumulation to retarded intraparticle model predictions. Measured desorption rates of the LABs and the most hydrophobic PCBs compare well with model predictions. However, the PAH and less hydrophobic PCB desorption rates range from one to four orders of magnitude slower than model predictions. We postulate that these compounds are present in a resistant sedimentary phase and may represent only a small fraction of what was originally sorbed. The fraction of PCBs, PAHs, and LABs desorbed after 48 h correlate well with measured biota-sediment factors (BSFs) in Yoldia limatula that were exposed to the same sediments, indicating that desorption rate-limited assimilation. Several studies have related field BSFs with log Kow and have observed a maximum at intermediate Kows (∼6.0-6.5). This maximum may be due to predictably slow desorption of high-Kow compounds and may be lower than predicted rates and extent of desorption of the low-Kow compounds because of association with resistant phases.
Article
A fiber-optical sensor system for the on-line and in situ detection of aquatic polycyclic aromatic hydrocarbons (PAH) has been described. Detection limits in the ng l−1 range have been obtained using time-resolved laser-induced fluorescence spectroscopy. The method has been applied to the detection of pyrene in real samples from a contaminated area. Interferences from humic material has been eliminated by the use of chemometric methods such as three dimensional least squares and partial least squares.
Article
Desorption of 2,5,2′,5′-tetrachlorobiphenyl (PCB-52) and 2,4,5,2′,4′,5′-hexachlorobiphenyl (PCB-153)from suspended sediment particles has been studied in a gas stripping reactor. Physical properties of the sediment particles such as particle size distribution, pore size distribution, surface area and organic carbon content were independently measured. Experimental results indicated that PCB desorption can be characterized by: (1) two-stage behavior (i.e., an initial rapid desorption followed by a prolonged slower desorption); (2) a dependence on Kow; (3) an independence of the first stage and a dependence of the second stage on particle size; and (4) a dependence on equilibration time (aging effect). The equilibration time tested ranged from one month to three years. The aging effect observed in this study suggests that release rates of PCBs in natural systems are likely much lower than those observed in short-term laboratory experiments, indicating not only that a kinetic model should be used in many aquatic system models, but also that kinetic constants obtained in short-term laboratory experiments may not be directly applicable to the desorption process in natural systems.
Article
For in situ and on-line detection of polynuclear aromatic hydrocarbons (PAHs) in water, a fibre-optic sensor system with a fibre length of 50 m is presented. Laser-induced, time-resolved fluorescence spectroscopy allows detection limits in the ng l−1 range. Analytical figures of merit are given for thirteen environmentally relevant PAHs in water. First results for a binary mixture of fluoranthene and pyrene are presented. A deconvolution algorithm is described that simplifies the analysis of time-resolved emission spectra of single- and multi-component PAH mixtures.
Article
Polycyclic aromatic hydrocarbons (PAH) in the marine environment are currently of great concern due to their potential carcinogenicity. The standard methods of detection and quantification of PAH in seawater and sediments are costly, time-consuming and do not account for the heterogeneous nature of their distribution and sources. Laser-induced, time-resolved fluorescence spectroscopy may help to overcome these limitations. Several PAH have relatively long-lived stimulated fluorescence emissions, which allow them to be detected among a background of more intense but shorter-lived chromophores. Using time-delayed techniques we have shown an ability to detect PAH, principally pyrene, at environmental levels (ng l−1) both in the laboratory and in situ in Boston Harbor and other study areas. Further development may lead to the rapid determination of several PAH in typical near-shore marine environments.
Article
The use of laser-induced fluorescence spectroscopy (LIFS) is fairly accepted as a fast and reliable method for the online detection of contaminations with polycyclic aromatic hydrocarbons (PAHs) and oil in groundwater and soils. Our work was focussed not only on the assessment of those contaminations, but on the use of LIFS as a generic tool to assess subsurface contaminations and aquifer properties. Pattern recognition techniques were successfully applied to map contaminant plumes surrounding waste disposal sites. Remediation activities at a former gas plant site were monitored using a sensor system based on time-resolved fluorescence spectroscopy. Tracer investigations in the saturated and unsaturated zone were enhanced due to the small time intervals between the single measurements. The determination of single analytes (e.g. pyrene, benzo(a)pyrene) out of a complex mixture of fluorescent compounds was possible by taking advantage of the fluorescence decay-times and by applying a site-specific calibration.
Article
A fiber-optic fluorometry system is used in conjunction with a benthic flux chamber in an attempt to estimate fluxes of dissolved organic carbon (DOC) and polycyclic aromatic hydrocarbons (PAH) in situ from coastal marine sediments. These initial deployments in San Diego Bay demonstrate the usefulness of laser-induced fluorescence measurements for continuous DOC determinations and reveal the possibility of using time-resolved fluorescence spectroscopy to estimate PAH concentrations. DOC fluxes from these contaminated sediments are high and may be a result of chamber contamination or may be associated with easily resuspended sediment particles. Sediment fluorescence profiles are also discussed.
Article
Polycyclic aromatic hydrocarbon (PAH) concentrations were measured in sediments and porewaters isolated from three cores from Boston Harbor, MA. Measured porewater PAH concentrations were significantly lower than the concentrations predicted by two- and three-phase equilibrium partitioning models. We hypothesize that only a fraction of the measured sediment PAH concentrations was available to partition rapidly into sediment porewaters.
Article
Polymer coated glass fibers were applied as disposable samplers to measure dissolved concentrations of persistent and bioaccumulative pollutants (PBPs) in sediment; porewater. The method is called matrix solid-phase microextraction (matrix-SPME), because it utilizes the entire sediment matrix as a reservoir for an equilibrium extraction: a glass fiber with a 15 mum coating of poly(dimethylsiloxane) (PDMS) was placed in a sediment sample until the PBPs reached their equilibrium distribution between the PDMS and the sediment matrix (1-30 days). PBP concentrations in the PDMS were determined by gas chromatography, and they were divided by PDMS water partition coefficients to derive at dissolved porewater concentrations. This approach was applied to measure porewater concentrations of spiked as well as field sediment, and several hydrophobic organic substances (log K-ow 5.2-7.5) were measured with high precision in the pg to ng/L range. Simple equilibrium partitioning is the basis for the substantial concentration factors that are built into matrix-SPME and for the low demands in materials and operation time. Matrix-SPME was in this study directed at the determination;of dissolved porewater concentrations in sediment, and it is further expected to be applicable to other environmental media, to field sampling, and to the sensing of fugacity.
Article
Adsorption and desorption of pollutants to soil and sediment materials are major fate mechanisms. The hypothesis that adsorption and desorption are reversible processes has been tested. The organic pollutants naphthalene, phenanthrene, and p-dichlorobenzene have been studied in the laboratory using batch reactors at room temperature from a few hours to over 2 months. The adsorption experiments were at equilibrium within 1-4 days and could be modeled using simple linear isotherms with K(p) values consistent with published K(oc) and K(ow) relationships. Desorption experiments were conducted with the contaminated sediments by successive dilutions. Desorption experiments varied from 1 day to 5 months, and observed desorption rates were from 1 to 3 orders of magnitude smaller than previously measured or predicted. If equilibrium were obtained during the desorption, typically over 82-99% of the adsorbed pollutant would have been desorbed, but generally only 30-50% of the adsorbed pollutant could be desorbed. These desorption results could not be explained by commonly invoked kinetic models or artifacts of the procedure. The possibility and consequences of such adsorption and desorption behavior being the result of either hysteresis or irreversible adsorption is discussed.
Article
Polycyclic aromatic hydrocarbons (PAHs) are a family of toxicants that are ubiquitous in the environment. These contaminants generate considerable interest, because some of them are highly carcinogenic in laboratory animals and have been implicated in breast, lung, and colon cancers in humans. These chemicals commonly enter the human body through inhalation of cigarette smoke or consumption of contaminated food. Of these two pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs have been published, factors affecting the accumulation of PAHs in the diet, their absorption following ingestion, and strategies to assess risk from exposure to these hydrocarbons following ingestion have received much less attention. This review, therefore, focuses on concentrations of PAHs in widely consumed dietary ingredients along with gastrointestinal absorption rates in humans. Metabolism and bioavailability of PAHs in animal models and the processes, which influence the disposition of these chemicals, are discussed. The utilitarian value of structure and metabolism in predicting PAH toxicity and carcinogenesis is also emphasized. Finally, based on intake, disposition, and tumorigenesis data, the exposure risk to PAHs from diet, and contaminated soil is presented. This information is expected to provide a framework for refinements in risk assessment of PAHs from a multimedia exposure perspective.
Article
Release rates of hydrophobic organic compounds (HOCs) from the soil matrix influence the availability of HOCs in soils or sediments for microbial degradation or removal by physical means (e.g., soil washing or soil venting). In this study it was shown that the initial contaminant concentration influences the desorption rate. This was attributed to the presence of a limited number of high affinity sites that cause nonlinear sorption behavior. The experimental results could be described with a kinetic model composed of two separate compartments. One compartment was described with a Freundlich isotherm and corresponding kinetics and was assumed to represent sorption to high affinity sites. The second compartment was described with a linear sorption isotherm and first-order kinetics. The model was used to simulate the influence of purging strategies on removal of QCB. The simulations showed that after removal of a fast-desorbing fraction, the slow-desorbing fraction could be efficiently removed at very low purging rates. Intermittent purging reduced the total purging time but the simulations showed large fluctuations in the aqueous pentachlorobenzene concentration. For each subsequent purging interval, the purging efficiency decreased due to the nonlinear desorption kinetics of the slow-desorbing fraction of pentachlorobenzene.
Article
Thesis (Ph. D .)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003. Includes bibliographical references (p. 149-154). In order to examine the importance of sediment resuspension on the sediment bed-to-water column transport of hydrophobic organic contaminants (HOCs) in the lower Hudson Estuary, the following areas of research were pursued: 1) a passive, in situ sampler, a polyethylene device (PED), for measuring HOCs in the aquatic environment was developed; 2) the desorption rate of pyrene, a polycyclic aromatic hydrocarbon (PAH), from native Hudson River sediments was measured, and 3) pyrene and 2,2',5,5'-tetrachlorobiphenyl (PCB #52), a polychlorinated biphenyl (PCB), concentrations were measured in the lower Hudson Estuary so that the input of these chemicals as a result of sediment resuspension could be compared to modeling expectations and the contribution of sediment resuspension to these chemicals' cycling could be quantified. The use of a new passive, in situ sampler, a polyethylene device (PED), for measuring hydrophobic organic contaminants (HOCs) in the aquatic environment was demonstrated. Like semipermeable membrane devices (SPMDs) and solid-phase microextraction (SPME), PEDs passively measure the concentration of chemical present in the dissolved phase. PEDs provide for in situ, time-averaged measurements with fast equilibration times (on the order of days) and simple laboratory extraction. Polyethylene-water equilibrium partitioning constants (KpEws) and polyethylene diffusivity coefficients (DPEs) were measured in the laboratory so that dissolved concentrations could be calculated subsequent to PED extraction. (cont.) KPEWs for eleven PAHs and PCBs were found to correlate closely with octanol-water equilibrium partitioning constants (Kows; log KPEW = 1.1 log Kow-0.45, R2 = 0.85). Temperature and salinity dependence of KPEW for the chemical of interest can be predicted with that chemical's excess enthalpy of solution and Setschenow constant, respectively. DpEs for several HOCs were measured in the laboratory so that the time for equilibrium uptake in the field could be predicted. PEDs allowed for quick, in situ, time-averaged measurements of phenanthrene and pyrene at pM concentrations and PCB #52 at fM concentrations in Boston Harbor seawater. Observations of disequilibrium between sorbed HOCs (e.g., PAHs & PCBs) and the surrounding environmental waters indicate that the times for desorption are important for understanding the fate of HOCs. Settling and resuspended particles can play a significant role in the cycling of HOCs. For PAHs, like pyrene, these chemicals' strong affinity for black carbon in the environment makes the rate of desorption less certain. The desorption rate for pyrene from native Hudson River sediment was measured in the laboratory and a diffusion rate constant (effective diffusivity/particle radius2) ranging from 1.OE-7 to 5.6E-7 s-1 was measured. The results were in good agreement with a physically- and chemically-based model for estimating effective diffusivity and the rate of desorption. by Rachel G. Adams. Ph.D .
Article
Rates and extents of phenanthrene desorption were studied for more than 250 days as functions of sorbent type, initial loading level, and aging. Apparent first-order desorption rate constants for the slowly desorbing fraction were found to (i) range from 0.00086 to 0.148 days-1 for geosorbents that contain geologically mature kerogen and less rigid humic-type soil organic matter, respectively, (ii) decrease by as much as an order of magnitude with decreasing initial sorbed solid-phase phenanthrene concentration, (iii) decrease by a factor of 2 with increasing aging time for a humic topsoil but remain unaffected by aging time beyond 3 months for a shale, and (iv) be 1-2 orders of magnitude lower than rate constants for the rapidly desorbing phenanthrene fractions for any given contaminated sample. Six models were used to fit the desorption rate data. Biphasic diffusion and biphasic first-order models with three fitting parameters possess broad utility and are potentially useful in a variety of environmental applications. Disadvantages of a five-parameter triphasic first-order desorption model, a two-parameter gamma-function model, and a one- or two-parameter pore diffusion model are also discussed.
Article
This study was carried out to assess the influence of physicochemical properties on PAH sequestration in sterile sewage sludge-amended arable soil. Radiolabeled phenanthrene (14C-9-Phe), pyrene (14C-4,5,9,10-Pyr), and benzo[a]pyrene (14C-7-B[a]P) were spiked and aged for up to 525 days in sterile soil microcosms. The degree of compound sequestration at various sampling times was determined by their extractability with organic solvents and release from soil residues by base saponification extraction. The amount of PAH extractable by butanol and dichloromethane decreased with compound aging in the soil. The decrease in PAH extractability with aging, and the formation of nonextractable bound residues, increased with compound molecular weight, KOW and KOC. The amount of total extractable PAH determined by sequential dichloromethane soxtec and methanolic saponification extraction decreased from 98%, 97%, and 94% at day 10 to 95%, 91%, and 77%, respectively for 14C-9-Phe, 14C-4,5,9,10-Pyr, and 14C-7-B[a]P after 525 days aging. During the same aging period there was an increase in the amount of PAH released from the soil by base saponification extraction, suggesting a progressive diffusion of PAHs into hydrolyzable and recalcitrant organic matter and mineral phases of soil. Calculated half-lives for the apparent loss of PAHs by sequestration in this experiment were dependent on the method used to extract them from soil. These half-lives ranged from 96 to 1,789 days depending on the compound, and are in agreement with values obtained from previous spiking experiments using nonsterile soils. These results suggest that a considerable fraction of PAHs assumed degraded in previous studies may have been sequestered within the organic carbon and, to a lesser extent, mineral phases of soil.
Article
We hypothesized that two mechanisms, absorption into natural organic matter and adsorption onto combustion-derived black carbon (BC), act in parallel to bind polycyclic aromatic hydrocarbons (PAHs) to Boston Harbor sediments. To focus on BC-adsorption, we removed the non-BC fraction by combusting near shore sediments at 375 degrees C for 24 h under air, leaving ca. 16% of the reduced carbon. The isotherm for pyrene sorption onto our combusted sediment was nonlinear with a Freundlich exponent of 0.62+/-0.12 and a BC-normalized distribution coefficient (microg/ kgBC)/(microg/L)n of 10(6.25)+/-0.14. Pyrene sorption to untreated sediment was reasonably estimated using Kd = f(oc) 10(4.7) + fBC 10(6.25) Cw(0.62-1) where f(oc) was the non-BC organic carbon content, 10(4.7) was the organic carbon-normalized absorption coefficient for pyrene (L/kg(oc)), fBC was the BC content, and Cw was the dissolved pyrene concentration (microg/ L). C/H/N ratios indicated that our environmental BC differed substantially from NIST diesel soot, possibly due to inclusion of larger BC particles from near source atmospheric fallout and urban runoff. The impact of BC on total PAH sorption may explain reports of nonlinear isotherms, Koc values for PAHs that exceed their respective Kow values, and discrepancies in bioavailability between planar and nonplanar sorbates.
Article
In contrast to equilibrium partitioning model (EqP) calculations, biota to sediment accumulation factors (BSAF) of hydrophobic organic compounds for deposit-feeders are highly variable. Recent literature suggests that this variability can be attributed to differences in sequestration or the presence of slowly desorbing fractions in the sediment. In the present study, we investigated whether the observed relationship between bioavailability and sequestration is causal. We determined BSAF values and sequestration status, measured as the distribution over rapidly and slowly desorbing fractions, of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in a manipulated sediment as well as in the original, unmanipulated sediment The manipulation, 48 h suspending with Tenax, resulted in reduction of the rapidly desorbing fraction, while other factors such as contact time and sediment properties remained constant. Contrary to expectations based on EqP, BSAF values did not remain constant but were reduced by a factor of 2-27, proportional to the reduction in rapidly desorbing fractions. The results provide direct evidence of a causal relationship between sequestration and bioavailability to deposit-feeders. Furthermore, the present study demonstrates the need to modify traditional use of the equilibrium partitioning model to account for variation in the sequestration status of HOC in sediments.
Article
Hysteresis, or isotherm nonsingularity, is a confounding issue in sorption research that undermines the commonplace assumption of reversibility in environmental fate and effects models for organic compounds in soil media. Until now, a molecular-level mechanism for true hysteresis when the sorbate is retrievable, structurally intact, has not been forthcoming. We show here that two organic soils exhibit the “conditioning effect”, which refers to the enhancement in sorption of a compound following brief exposure of the sorbent to high concentrations of the same or a similar compound. The conditioning effect has been used in support of a pore deformation mechanism for hysteresis in glassy polymers. By this mechanism, the sorbate causes irreversible changes in the structure of internal nanopores (holes) in the organic matrix upon its sorption. Trichloromethane was the test solute for dichloromethane-conditioned Pahokee soil (44.6% organic carbon), and chlorobenzene and 1,2,4-trichlorobenzene were the test solutes for benzene-conditioned Mount Pleasant silt loam (4.5% organic carbon). In each case, the isotherm of the test solute in the conditioned soil was shifted upward of, and was less linear than, the corresponding isotherm in the nonconditioned control. Application of the polymer-based Dual-Mode (partitioning-hole filling) Model shows an expansion of the hole domain as a result of conditioning. The memory of the conditioning effect persists for longer than 96 days at 21 °C but is lost upon heating the sample at 100 °C. A three-step (sorption−desorption−resorption) experiment demonstrated hysteresis followed by enhanced resorption, implying a mechanistic relationship between hysteresis and the conditioning effect. The results indicate that irreversible pore deformation is a mechanism for hysteresis in natural organic matter materials and suggest that slow matrix relaxation may contribute to the often-observed long-term resistance of some contaminants to desorption.
Article
We hypothesized that the sorption of polycyclic aromatic hydrocarbons (PAHs) to natural sediments and soils should consider both absorption into a biogenic/diagenetic organic carbon (OC) fraction and adsorption onto a combustion-derived, black carbon (BC) fraction. Here, two sets of literature data were reevaluated to illustrate that an OC absorbent and a BC adsorbenttogether can (1) account for sediment--pore-waterdistribution coefficients observed in the field that are greater than predicted by a simple f(OC)K(OC) partitioning model and (2) explain a group of nonlinear phenanthrene isotherms observed in the laboratory with a single value for the BC-normalized distribution coefficient (log K(BC) = 6.1 i 0.04) and a Freundlich exponent (n approximately 0.6 if log K(OC) = 4.0) that is strongly dependent on the K(OC) value selected.
Article
The bioavailability of polycyclic aromatic hydrocarbons (PAHs) for earthworms (Eisenia andrei) was experimentally determined in seven field-polluted soils and 15 soil-sediment mixtures. The pore-water concentration of most PAHs was higher than predicted. However, most of the compound was associated with dissolved organic carbon (DOC) and not directly available for uptake by earthworms. The apparent sorption could be reasonably predicted on the basis of interactions with DOC; however, the biota-soil accumulation factors (BSAFs) for earthworms were up to two orders of magnitude lower than predicted by equilibrium partitioning. The large variability between sites was not fully explained by differences in sorption. Experimental results indicate that the pool of freely dissolved PAHs in the pore water became partially depleted because of uptake by the earthworms and that bioaccumulation is thus also influenced by the kinetics of PAH desorption and mass transport. A pilot study with Lumbricus rubellus showed that steady-state body residues were well correlated to E. andrei. Current results show that depositing dredge spoil on land may lead to increased bioavailability of the lower-molecular-weight PAHs. However, risk assessment can conservatively rely on equilibrium partitioning, but accurate prediction requires quantification of the kinetics of bioavailability.
Article
We explored a novel technique to deploy solid-phase microextraction (SPME) fibers to nondestructively measure the explosive compound 2,4,6-trinitrotoluene (TNT) and its nitroaromatic (NA) degradation products in laboratory sediment toxicity tests and field sediments in situ. SPME fibers within steel mesh envelopes were exposed statically via direct burial within sediment. Six fiber types (polymer coatings) were tested. Polyacrylate (PA) SPME fiber was sufficiently durable for this application, yielded the lowest detection limits, and exhibited a linear uptake relationship across toxicologically relevant sediment NA concentrations (100-2000 nmol/g dw (20-500 microg/g dw)). Temperature greatly influenced SPME absorption kinetics. Via evaluation of absorption at different temperatures, recommended sampling times needed to achieve steady-state equilibrium were 48 h for room temperatures (23-25 degrees C) and up to 7 d for cold (5 degrees C) temperatures. Although a comparison of TNT residues by SPMEs and TNT bioavailability and toxicity in sediments has not been completed, differences in SPME availability of TNT and its degradation products were found between two different TNT-spiked sediments. Our disposable SPME technique was slightly less expensive and as precise as the conventional extraction for total NAs and may prove to be a powerful exposure evaluation tool for assessing the ecological risk of these compounds.
Article
This research provides particle-scale understanding of PCB and PAH distribution in sediments obtained from three urban locations in the United States: Hunters Point, CA; Milwaukee Harbor, WI; and Harbor Point, NY. The sediments comprised mineral grains (primarily sand, silt, and clays) and carbonaceous particles (primarily coal, coke, charcoal, pitch, cenospheres, and wood). The carbonaceous sediment fractions were separated from the mineral fractions based on their lower density and were identified by petrographic analysis. In all three sediments, carbonaceous particles contributed 5-7% of the total mass and 60-90% of the PCBs and PAHs. The production of carbonaceous particles is not known to be associated with PCB contamination, and it is very unlikely that these particles can be the source of PCBs in the environment Thus, it appears that carbonaceous particles preferentially accumulate PCBs acting as sorbents in the aqueous environment if PCBs are released directly to the sediment or if deposited as airborne soot particles. Aerobic bioslurry treatment resulted in negligible PAH loss from the carbonaceous coal-derived material in Milwaukee Harbor sediment but resulted in 80% of the PAHs being removed from carbonaceous particles in Harbor Point sediment. Microscale PAH extraction and analysis revealed that PAHs in Harbor Point sediment were associated mainly with coal tar pitch residue. PAHs present in semisolid coal tar pitch are more bioavailable than PAHs sorbed on carbonaceous particles such as coal, coke, charcoal, and cenosphere. Results of this study illustrate the importance of understanding particle-scale association of hydrophobic organic contaminants for explaining bioavailability differences among sediments.
Article
Bioavailability refers to the extent to which humans and ecological receptors are exposed to contaminants in soil or sediment. Although long employed in toxicology and agricultural sciences, the concept of bioavailability has recently piqued the interest of the hazardous waste industry as an important consideration for deciding how much waste to clean up. The rationale is that if contaminants in soil and sediment are not bioavailable then more contaminant mass can be left in place without additional risk. To date, the concept has affected cleanup goals at a small number of sites (Table 1), and enthusiasm for the idea is growing. After two years of deliberation, a National Research Council (NRC) committee recently weighed in on using bioavailability in soil and sediment management. This article summarizes the resulting report, Bioavailability of Contaminants in Soils and Sediments Processes, Tools and Applicants (1).
Article
Measures of desorption are currently considered important as potential surrogates for bioaccumulation as measures of the bioavailability of sediment-sorbed contaminants. This study determined desorption rates of four laboratory spiked compounds, benzo[a]pyrene (BaP), 2,4,5,2',4',5'-hexachlorobiphenyl (HCBP), 3,4,3',4'-tetrachlorobiphenyl (TCBP), and pyrene (PY), to evaluate the effect of sediment characteristics. The compounds were sorbed onto seven sediments with a broad range of characteristics. Desorption was measured by Tenax-TA extraction from aqueous sediment suspensions. Desorption rates were modeled using an empirical three compartment model describing operationally defined rapid, slow, and very slow compartments. The sediments were characterized for plant pigments, organic carbon (OC), total nitrogen (TN), lipids, NaOH extractable residue, lignin, amino acids, soot carbon, and particle size fractions. Desorption from the rapid compartment for each of the planar compounds BaP, PY, and TCBP was significantly correlated to sediment characteristics that could be considered to represent younger (i.e., less diagenetically altered) organic matter, e.g., plant pigment, lipid, and lignin contents. However, for these compounds there were no significant correlations between desorption and OC, TN, soot carbon, or amino acid contents. HCBP desorption was different from the three planar molecules. For HCBP, the flux from the rapid compartment was negatively correlated (0.1 > p > 0.05) with the OC content of the sediment. Overall, HCBP desorption was dominated by the amount of OC and the particle size distribution of the sediments, while desorption of the planar compounds was dominated more by the compositional aspects of the organic matter.
Article
In an effort to determine whether bioavailability limitations are responsible for the slow or incomplete hydrocarbon biodegradation in aged soils, both the rate of desorption (rdes) and biodegradation (rbio) was measured for n-alkanes and polynuclear aromatic hydrocarbons (PAHs) at different times during the slurry biotreatment of six different soils. While all n-alkanes were biodegraded to various degrees depending on their respective carbon number and the soil organic matter content, none of them were desorbed to a significant extent, indicating that these saturated hydrocarbons do not need to be transferred from the soil particles into the aqueous phase in order to be metabolized by microorganisms. Most two- and three-ring PAHs biodegraded as fast as they were desorbed (rbio = rdes); that is, desorption rates controlled biodegradation rates. By contrast, the biodegradation kinetics of four-, five-, and six-ring PAHs was limited by microbial factors during the initial phase (rbio < rdes) while becoming mass-transfer rate limited during the final phase of bioremediation treatment (rbio = rdes). Whenever PAH biodegradation stalled or did not occur at all (rbio = 0), it was never due to bioavailability limitations (rdes > 0) but was more likely caused by microbial factors. such as the absence of specific PAH degraders or cometabolic substrates. Consequently, PAHs that are found to be microbially recalcitrant in aged soils may not be so because of limited bioavailability and thus could pose a greater risk to the environment than previously thought.
Article
Chemicals found in the environment as industrial byproducts or pollutants as well as those that are prescribed or part of our daily lives can have multiple effects on the human body. The manner in which we are exposed, and the levels we are exposed to are significant contributing factors. Adults have the bodily defense mechanisms in place to combat exposures to adverse toxicants and general pollution at a variety of levels. However, developing organisms may not have adequate defense mechanisms, and toxicants can have a significant effect on their health and development. In this review, we take particular note of the toxicities of chemicals on the developing female reproductive system as a result of in utero exposure. Environmental and prescribed chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), diethylstilbestrol, and genistein, as well as others, will be reviewed for their in utero toxicity in the neuroendocrine system, the ovary, oviduct, placenta, uterus, vagina, cervix, and mammary gland.
Article
Charcoal is found in water, soil, and sediment where it may act as a sorbent of organic pollutants. The sorption of organic compounds to natural solids often shows hysteresis. The purpose of this study was to determine the source of pronounced hysteresis that we found in the sorption of a hydrophobic compound (benzene) in water to a maplewood charcoal prepared by oxygen-limited pyrolysis at 673 K. Gas adsorption (N 2, Ar, CO 2), 13C NMR, and FTIR show the charcoal to be a microporous solid composed primarily of elemental (aromatic) C and secondarily of carboxyl and phenolic C. Nonlocal density functional theory (N 2, Ar) and Monte Carlo (CO 2) calculations reveal a porosity of 0.15 cm 3/g, specific surface area of 400 m 2/g, and appreciable porosity in ultramicropores < 10 Å. Benzene sorption-desorption conditions were chosen to eliminate artificial causes of hysteresis (rate-limiting diffusion, degradation, colloids effect). Charcoal sorbed up to its own weight of benzene at ∼69% of benzene water solubility. Sorption was highly irreversible over most of the range tested (10 -4-10 3 μg/mL). A dimensionless irreversibility index (I i) (0 ≤ I i ≤ 1) based on local slopes of adsorption and desorption branches was evaluated at numerous places along the isotherm. I i decreases as C increases, from 0.9-1 at low concentration to ∼0 (∼fully reversible) at the highest concentrations. Using sedimentation and volumetric displacement measurements, benzene is observed to cause pronounced swelling (up to > 2-fold) of the charcoal particles. It is proposed that hysteresis is due to pore deformation by the solute, which results in the pathway of sorption being different than the pathway of desorption and which leads to entrapment of some adsorbate as the polyaromatic scaffold collapses during desorption. It is suggested that intra-charcoal mass transport may be influenced by structural rearrangement of the solid, in addition to molecular diffusion.
Article
The bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) by the filter-feeding soft-shell clam Mya arenaria was evaluated at three sites near Boston (MA, USA) by assessing the chemical activities of those hydrophobic organic compounds (HOCs) in the sediment bed, water column, and organisms. Polyethylene samplers were deployed to measure the activities of HOCs in the water column. Sediment activities were assessed by normalizing concentrations with sediment-water sorption coefficient values, including adsorption to black carbon in addition to absorption by organic carbon. Likewise, both lipids and proteins were considered in biota-water partition coefficients used to estimate chemical activities in the animals. Chemical activities of PAHs in M. arenaria were substantially less than those of the corresponding bed sediments in which they lived. In contrast, chemical activities of PCBs in M. arenaria often were greater than or equal to activities in the corresponding bed sediments. Activities of PAHs, such those of pyrene, in the water column were undersaturated relative to the sediment. However, some PCBs, such as congener 52, had higher activities in the water column than in the sediment. Tissue activities of pyrene generally were in between the sediment and water column activities, whereas activity of PCB congener 52 was nearest to water column activities. These results suggest that attempts to estimate bioaccumulation by benthic organisms should include interactions with both the bed sediment and the water column.
Article
The solid-water distribution ratios (Kd values) of "native" PAHs, PCBs, and PCDDs in Boston and New York Harbor sediments were determined using small passive polyethylene samplers incubated for extended times in sediment-water suspensions. Observed solid-water distribution coefficients exceeded the corresponding f(oc)Koc products by 1-2 orders of magnitude. It was hypothesized that black carbon (fBC), measured in the Boston harbor sediment at about 0.6% and in the New York harbor sediment at about 0.3%, was responsible for the additional sorption. The overall partitioning was then attributed to absorption into the organic carbon and to adsorption onto the black carbon via Kd = f(oc)Koc + f(BC)K(BC)C(w)n-1 with Cw in microg/L. Predictions based on published Koc, K(BC), and n values for phenanthrene and pyrene showed good agreement with observed Kd,obs values. Thus, assuming this dual sorption model applied to the other native PAHs, PCBs, and PCDDs, black carbon-normalized adsorption coefficients, K(BC)S, were deduced forthese contaminants. Log K(BC) values correlated with sorbate hydrophobicity for PAHs in Boston harbor (log K(BC) approximately 0.83 log gamma w(sat) - 1.6; R2 = 0.99, N= 8). The inferred sorption to the sedimentary BC phase dominated the solid-water partitioning of these compound classes, and its inclusion in these sediments is necessary to make accurate estimates of the mobility and bioavailability of PAHs, PCBs, and PCDDs.
Article
A new method for studying sorption with diesel and hexane sootwas developed, tested, and applied. A commercial silica-based chromatography medium was used as an inert inorganic carrier for immobilization (entrapment) of soot particles and their aggregates, thus creating a combined sorbent for sorption of hydrophobic organic chemicals (HOCs). After precombustion to remove potential organic carbon contaminants, the silica particles and soot samples were mixed under dry conditions that allowed the soot to be incorporated within the pore structure of the much larger (> 180 microm) carrier particles. Unincorporated soot was removed by multiple rinses with Milli-Q water. Sorption rate and equilibrium experiments were conducted, using phenanthrene as a probe HOC. Strong nonlinear sorption of phenanthrene was observed, in agreement with results previously obtained using air-bridge and flocculation-based methods. Batch kinetic studies suggested that 60 d of prewetting is required to obtain full water saturation, as perhaps needed for proper assessment of phenanthrene uptake rate by soot in aqueous systems. Forthe determination of equilibrium phenanthrene sorption, however, 1-d prewetting is sufficient so long as final equilibration is for at least 60 d. The new method is a practical approach to sorption measurement that may prove especially useful for study of strongly sorbing chemicals.
Article
Coke oven site soil was characterized to assess the particle association and availability of polycyclic aromatic hydrocarbons (PAHs). We identified various carbonaceous materials including coal, coke, pitch, and tar decanter sludge. Most of the PAHs were associated with the polymeric matrix of tar sludge or hard pitch as discrete particles, coatings on soil mineral particles, or complex aggregates. The PAH availability from these particles was very low due to hindered diffusive release from solid tar or pitch with apparent diffusivities of 6 x 10(-15) for phenanthrene, 3 x 10(-15) for pyrene, and 1 x 10(-15) cm2/s for benzo[a]pyrene. Significant concentrations of PAHs were observed in the interior of solid tar aggregates with up to 40,000 mg/kg total PAHs. The release of PAHs from the interior of such particles requires diffusion over a substantial distance, and semipermeable membrane device tests confirmed a very limited availability of PAHs. These findings explain the results from three years of phytoremediation of the site soil, for which no significant changes in the total PAH concentrations were observed in the test plot samples. The observed low bioavailability of PAHs probably inhibited PAH phytoremediation, as diffusion-limited mass transfer would limit the release of PAHs to the aqueous phase.
Article
The bioavailability to bacteria of 14C-labeled polycyclic aromatic hydrocarbons (PAHs) sorbed onto lake sediments was assessed using a mathematical model and three experimental series. The experiments were performed under similar conditions and included: (1) abiotic desorption of PAHs from sediments by Tenax extraction, (2) mineralization of dissolved PAHs with no sediment present, and (3) mineralization of PAHs sorbed onto sediments. Results obtained from the first two series were used to obtain the parameter values for the model, and the experimental results of the third series were compared to model results. We found that microorganisms were able to promote desorption of the more-labile fractions, but were unable to increase the desorption rate of the slow- and very slow-desorbing fractions. Also, our model predictions indicate that, after very long contact times, and in the concurrence of biodegradation, sorbed PAHs remain not under equilibrium conditions, but rather in a steady state. The net rates of PAH desorption from the three sediment domains considered (fast, slow, and very slow) become similar, and the ratio between the aqueous and the sediment concentration remains constant with time.
Article
The present paper describes a study on the bioaccumulation of native polycyclic aromatic hydrocarbons (PAHs) from three harbors in Norway using the polychaete Nereis diversicolor and the gastropod Hinia reticulata. First, biota-sediment accumulation factors (BSAFs) were measured in laboratory bioassays using the original sediments. Median BSAFs were 0.004 to 0.01 kg organic carbon/kg lipid (10 PAHs and 6 organism-sediment combinations), which was a factor of 89 to 240 below the theoretical BSAF based on total sediment contents (which is approximately one). However, if BSAFs were calculated on the basis of measured freely dissolved PAH concentrations in the pore water (measured with polyoxymethylene passive samplers), it appeared that these BSAFfree values agreed well with the measured BSAFs, within a factor of 1.7 to 4.3 (median values for 10 PAHs and six organism-sediment combinations). This means that for bioaccumulation, freely dissolved pore-water concentrations appear to be a much better measure than total sediment contents. Second, we tested the effect of 2% (of sediment dry wt) activated carbon (AC) amendments on BSAE The BSAFs were significantly reduced by a factor of six to seven for N. diversicolor in two sediments (i.e., two of six organism-sediment combinations), whereas no significant reduction was observed for H. reticulata. This implies that either site-specific evaluations of AC amendment are necessary, using several site-relevant benthic organisms, or that the physiology of H. reticulata caused artifactually high BSAF values in the presence of AC.