Validating the use of performance reference compounds in passive samplers to assess porewater concentrations in sediment beds

Direct visualization of pyrene diffusion in polyethylene and polyoxymethylene passive samplers

While passive sampling of ultra-low aqueous concentrations of hydrophobic organic compounds in environmental aqueous media has emerged as a promising analytical technique, there is a lack of good understanding of the fundamental diffusive processes. In this research, we used a fluorophore, pyrene, as a model compound to track diffusion in polymers through absorption and environmental media exchange processes. We directly tracked the penetration of pyrene into polyethylene (PE) and polyoxymethylene (POM) rods during absorption from water by sectioning the rod after different stages of absorption and observing the fluorescence signal through a microscope. Diffusion profiles of pyrene in polymers were simulated by numerical integration of Fickian diffusion. The results indicated that the uptake process in PE is governed by Fick's law and the absorption and desorption kinetics are similar in this polymer. However, the observed uptake profiles of pyrene in POM were non-Fickian and the release kinetics out of POM was slower compared to uptake into the polymer. We show that slower desorption from POM makes corrections for nonequilibrium using performance reference compounds (PRCs) problematic for deployments in water or sediment where there is significant advection. However, for static sediment deployments, the overall kinetics of exchange is controlled by slow transport through sediment and the hysteretic behavior of POM may not preclude the use of PRCs to interpret equilibrium status.

Development of an in situ equilibrium polydimethylsiloxane passive sampler for measuring volatile organic compounds in soil vapor

An equilibrium passive sampler made of polydimethylsiloxane (PDMS) fiber was developed to measure volatile organic compounds (VOCs) in soil vapor. Expanded polytetrafluoroethylene (ePTFE) was used to protect PDMS from pollution and direct contact with soil components. For all tested VOCs, equilibrium was reached after 7 days at 5 °C. The equilibrium partition coefficients of VOCs between PDMS, gas, and water were measured at three different temperatures. The analyte concentrations in PDMS exposed to gas and water separately were almost the same, which suggests that C_gas and C_water in soil pores can be accurately deduced from C_PDMS after equilibrium at various temperatures. To evaluate the passive sampler, active sampling measurements were performed simultaneously. Concentrations of VOCs deduced from the passive sampler were consistent with the concentrations measured by active sampling near the 1:1 line. Tests with artificial soils were conducted to observe the effects of soil components on passive sampling. The results suggest that the effect of water saturation can be ignored; in other words, the developed passive sampler can be applied in the vadose zone, which has fluctuating water saturation. With a holder for the sampler made of stainless steel, the developed in situ passive sampler can measure VOCs in contaminated soil vapor. The developed passive sampler was proven to be an alternative for measuring VOCs in soil vapor, which can be helpful for soil risk assessment and for observing the diffusion of VOCs in contaminated sites.

Techniques for monitoring bioavailable organic pollutants in sediment: Application of poly(methyl methacrylate) as a passive sampler

A poly(methyl methacrylate) (PMMA) passive sampler was applied to harbor sediment to examine whether the substrate could be used as a tool to measure freely dissolved concentrations of contaminants. An ex situ method required at least 1 g of PMMA to detect freely dissolved polycyclic aromatic hydrocarbons (PAHs) in sediment with <100 ng/g dry weight. Two weeks were sufficient to reach equilibrium under 180 rpm for PAHs with a molar volume of <250 cm³/mol. For the in situ method, a deployment time of four months was sufficient to measure PAHs with a molar volume up to 250 cm³/mol in the sediment bed. The PMMA passive sampler could be used to measure the bioavailable fraction of PAHs in porewater, reflecting the complex properties of sediment with strong sorption such as black carbons.

Interlaboratory Study of Polyethylene and Polydimethylsiloxane Polymeric Samplers for Ex Situ Measurement of Freely Dissolved Hydrophobic Organic Compounds in Sediment Porewater

We evaluated the precision and accuracy of multilaboratory measurements for determining freely dissolved concentrations (C_free ) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediment porewater using polydimethylsiloxane (PDMS) and low-density polyethylene (LDPE) polymeric samplers. Four laboratories exposed performance reference compound (PRC) preloaded polymers to actively mixed and static ex situ sediment for approximately 1 month; two laboratories had longer exposures (2 and 3 months). For C_free results, intralaboratory precision was high for single compounds (coefficient of variation 50% or less), and for most PAHs and PCBs interlaboratory variability was low (magnitude of difference was a factor of 2 or less) across polymers and exposure methods. Variability was higher for the most hydrophobic PAHs and PCBs, which were present at low concentrations and required larger PRC-based corrections, and also for naphthalene, likely due to differential volatilization losses between laboratories. Overall, intra- and interlaboratory variability between methods (PDMS vs. LDPE, actively mixed vs. static exposures) was low. The results that showed C_free polymer equilibrium was achieved in approximately 1 month during active exposures, suggesting that the use of PRCs may be avoided for ex situ analysis using comparable active exposure; however, such ex situ testing may not reflect field conditions. Polymer-derived C_free concentrations for most PCBs and PAHs were on average within a factor of 2 compared with concentrations in isolated porewater, which were directly measured by one laboratory; difference factors of up to 6 were observed for naphthalene and the most hydrophobic PAHs and PCBs. The C_free results were similar for academic and private sector laboratories. The accuracy and precision that we demonstrate for determination of C_free using polymer sampling are anticipated to increase regulatory acceptance and confidence in use of the method. Environ Toxicol Chem 2022;41:1885-1902. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Evaluating sedimentary PAH bioavailability based on equilibrium partitioning and passive sampling at the Dover Gas Light Superfund Site (Dover, Delaware, USA)

From 1859 to 1948, the Dover Gas Light plant produced combustible gas for industrial, commercial, and residential applications using pine resin, coking coal, oil, and wood, and finally, a coal-gas process. Waste coal tar was discharged into the St. Jones River in Dover, Delaware (USA), via a ditch and culvert and, following plant closure in the 1940s, through groundwater flow from structures buried on the site. By the end of the 20th century, polycyclic aromatic hydrocarbon (PAH) contamination of the sediments in the St. Jones River was suspected to have occurred, and state and federal agencies initiated environmental assessments of the newly designated Superfund site. The current study investigated the spatial distributions of total PAHs in St. Jones River sediments adjacent to the site and evaluated their bioavailability. In 2017, 34 sediment cores were collected, sectioned, and analyzed using an on-site fluorometric screening technology indicating total PAH sediment concentrations ranging from 0.1 to 15 000 mg/kg (wet). A subset of cores involving 20 samples of various depths was selected and further analyzed by conventional GC/MS analysis for 16 parent PAHs. In addition, a 34-day in situ deployment of polyethylene passive samplers was performed to measure vertical bioavailability profiles of parent PAHs in sediments at three locations and overlying waters at four stations. Freely dissolved concentrations (C _free ) of total PAHs were estimated based on equilibrium partitioning (EqP) of the GC/MS results and the passive sampling findings. C _free values were used to calculate acute and chronic toxic units ranging from 1.4 to 56, based on EqP and 1.3 to 15 based on passive sampling. For six samples where comparative data were available, EqP calculations overestimated bioavailability by < 2- to 54-fold. Combining rapid field measurements with more accurate analyses of sediment concentrations and bioavailability in a tiered framework supported a time-efficient and cost-effective site investigation. Integr Environ Assess Manag 2021;17:1215-1228. © Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Possibilities of poly(methyl methacrylate) as a passive sampler for determination of bioavailable concentrations in seawater

Solvent-treated poly(methyl methacrylate) (PMMA) was recently introduced as a passive sampler for determining bioavailable concentrations, i.e., freely dissolved concentrations. However, the much knowledge required to obtain accurate bioavailable concentrations using the thus treated PMMA, applied in a marine environment, is still lacking. In this study, uptake experiments with PMMA after solvent treatment were conducted to investigate its uptake capacity and the effects of water temperature and salinity on the PMMA-water partition coefficient (K_PMMA-W) for polycyclic aromatic hydrocarbons (PAHs). Thus, PMMA passive samplers preloaded with performance reference compounds were exposed to seawater to first estimate the deployment time and then to confirm if the PMMA could give the residual concentrations of PAH in mussel. The less hydrophobic PAHs (log octanol-water partition coefficient < 5.5) had higher uptake capacity of PMMA-uptake was increased by a factor of up to 10. Whereas for these PAHs the K_PMMA-W values and seawater temperature showed a parabolic relationship, the effect of salinity on K_PMMA-W was not observed. The less hydrophobic PAH concentrations in seawater can be measured using the PMMA passive sampler over a period of about three weeks. For the PAHs detected in both PMMA and mussel, the PAH concentrations in mussel predicted from PMMA were found to be within one order of magnitude of the measured concentrations. This, therefore, suggests that solvent-treated PMMA could be used as a passive sampler to provide information on bioavailable concentrations for less hydrophobic PAHs.

In-situ and ex-situ measurement of hydrophobic organic contaminants in soil air based on passive sampling: PAH exchange kinetics, non-equilibrium correction and comparison with traditional estimations

It is a great challenge to accurately estimate chemical activity of hydrophobic organic contaminants in field soils. Ex-situ and in-situ determinations were developed for this purpose based on low-density polyethylene (LDPE) passive sampling and non-equilibrium correction by release of performance reference compounds (PRCs) previously spiked to the samplers. This work investigated kinetic processes of target contaminants' uptake into and PRCs' release from the sampler in an ex-situ soil suspension incubated for 100 days. A close agreement of kinetic parameters for pyrene's (target) uptake into and deuterated pyrene's (PRC) release from LDPE indicated their similar exchange kinetics. Three kinetic models were developed to correct uptake of target compounds in non-equilibrium conditions via release processes of PRCs. The second-order kinetic model was recommended for ex-situ measurements. The PRC-based non-equilibrium corrections were further applied to in-situ static passive sampling from several weeks to months in a PAH-contaminated field site. Two-weeks' deployments were sufficient for quantifying lighter PAHs (logK_OA < 8.0), but not recommended to accurately estimate heavier PAHs (logK_OA > 9.0), even if over four months. Concentration estimates from the in-situ and ex-situ passive samplings were comparable in order of magnitude with traditional estimation from equilibrium partitioning models considering both organic and black carbon fractions.

Kinetic Passive Sampling: In Situ Calibration Using the Contaminant Mass Measured in Parallel Samplers with Different Thicknesses

The use of single-phase passive samplers is a common method for sampling bioavailable concentrations of hydrophobic aquatic pollutants. Often such samplers are used in the kinetic stage, and in situ calibration is necessary. Most commonly, exchange kinetics are derived from the release rates of performance reference compounds (PRCs). In this study, a complementary calibration approach was developed, in which measuring the contaminant mass ratio (CMR) from two samplers with different thicknesses allows the dissolved concentrations to be determined. This new CMR calibration was tested (1) in a laboratory experiment with defined and constant concentrations and (2) in the field, at a storm water retention site. Silicone passive samplers with different thicknesses were used to sample a range of dissolved polycyclic aromatic hydrocarbons. In the laboratory study, the concentrations derived from the CMR calibration were compared with those from water extraction and passive dosing and differences below a factor 2 were found. In the field study, CMR-derived concentrations were compared to those from PRC calibration. Here, differences ranged by only a factor 1 to 3 between both methods. These findings indicate that the CMR calibration can be applied as a stand-alone or complementary calibration method for kinetic passive sampling.

Impact of passive sampler protection apparatus on sediment porewater profiles of hydrophobic organic compounds

Passive sampling techniques have been widely used to determine the dissolved concentration profiles of hydrophobic organic compounds (HOCs) in sediment porewater. However, the effects of having a protection for the passive sampler on profiling HOCs concentrations in sediment porewater, especially in deep sediment, have remained unclear. To address this issue, low density polyethylene passive samplers with and without protectors, which consisted of glass fiber filter and porous stainless steel shield, were simultaneously deployed in sediment of the Dongjiang River, South China. The results showed that the protectors retarded the dissipation of performance reference compounds (PRCs) from the sampler by a factor of 2-9. The protectors seemed to exert a negligible effect on the measured concentrations of PAHs, BDE-47, and BDE-99 in surficial sediment porewater (0-14 cm depth) from both samplers. However, the sediment porewater concentration profiles of PAHs and BDE-47 from the sampler with protectors were in agreement with those normalized by dry weight in deep sediment (16-34 cm depth), indicating that a diffusion layer established by the protectors may minimize the probability of local depletion of the target analytes in deep sediment. In addition, the log K_oc values of PAHs, BDE-47, and BDE-99 exhibited a slight increasing trend with sediment depth. This finding suggested that in situ passive sampling techniques could be a feasible tool in determining the site-specific log K_oc values of HOCs at different sediment depths.

Assessing Benthic Bioaccumulation of Polychlorinated Dioxins/Furans and Polychlorinated Biphenyls in the Lower Passaic River (NJ, USA) Based on In Situ Passive Sampling

Passive sampling has emerged as a promising tool to assess the presence of hydrophobic organic contaminants (HOC) in water, sediment, and biota, such as polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) or polychlorinated biphenyls (PCBs). Previous work evaluated the ability of passive samplers to predict the bioavailability of sedimentary HOCs mostly in the laboratory, often for marine organisms. The present study assessed the use of low-density polyethylene (LDPE) to derive freely dissolved concentrations of PCDD/Fs and PCBs in porewater in situ versus ex situ and in river water. An LDPE-based multisampler system was deployed at 4 locations along the lower Passaic River (NJ, USA) in sediment and the water column, where sediment and benthic species samples were also collected. Good agreement was generally observed for PCDD/F and PCB concentrations comparing in situ and ex situ approaches (within 0.30-39%). Significant linear relationships were derived between log LDPE-based and log lipid-based concentrations of PCDD/Fs and PCBs. The in situ multisampler system showed promise to derive HOC concentrations in porewater and river water and to predict the bioaccumulation potential of HOCs in benthic biota. Environ Toxicol Chem 2020;39:1174-1185. © 2020 SETAC.

Ex situ determination of freely dissolved concentrations of hydrophobic organic chemicals in sediments and soils: basis for interpreting toxicity and assessing bioavailability, risks and remediation necessity

The freely dissolved concentration (C_free) of hydrophobic organic chemicals in sediments and soils is considered the driver behind chemical bioavailability and, ultimately, toxic effects in benthic organisms. Therefore, quantifying C_free, although challenging, is critical when assessing risks of contamination in field and spiked sediments and soils (e.g., when judging remediation necessity or interpreting results of toxicity assays performed for chemical safety assessments). Here, we provide a state-of-the-art passive sampling protocol for determining C_free in sediment and soil samples. It represents an international consensus procedure, developed during a recent interlaboratory comparison study. The protocol describes the selection and preconditioning of the passive sampling polymer, critical incubation system component dimensions, equilibration and equilibrium condition confirmation, quantitative sampler extraction, quality assurance/control issues and final calculations of C_free. The full procedure requires several weeks (depending on the sampler used) because of prolonged equilibration times. However, hands-on time, excluding chemical analysis, is approximately 3 d for a set of about 15 replicated samples.

An analytical model for the fate and transport of performance reference compounds and target compounds around cylindrical passive samplers

Passive sampling by deploying organic polymers for 20-30 days in soils or sediments has been used for the assessment of bioavailability and mobility of hydrophobic organic contaminants. An important step in their interpretation is the estimation of the degree of equilibration, typically through the release of performance reference compounds (PRCs). This paper develops an improved modeling tool for predicting the behaviors of PRCs and contaminant compounds in devices in cylindrical geometry, such as polydimethylsiloxane (PDMS) fibers or dialysis samplers of cylindrical cross-section. The model is solved by both a numerically inverted Laplace domain solution and an asymptotic analytical solution. The solutions are verified with the numerically simulated results. A comparison of the developed model to existing models for the calibration of uptake/release rates and the estimation of soil or sediment transport properties is performed. The result suggests that the cylindrical model provides a more accurate prediction for the transient behavior of PRC and target compounds as well as a better estimate of transport properties in the media.

Comparison of freely dissolved concentrations of PAHs in contaminated pot soils under saturated and unsaturated water conditions

Passive sampling (PS, equally used for passive sampler) methods have successfully been applied in situ to quantify the bioavailability of hydrophobic organic compounds in air, water and sediments. However, very little is known on the applicability of PS in unsaturated soils. Here, we present the results of a greenhouse experiment in which we applied in situ PS methods in pots. Low density polyethylene (LDPE) and polydimethylsiloxane (PDMS) fibres with a newly developed PS holder were used to analyse freely dissolved polycyclic aromatic hydrocarbon (PAH) concentrations (C_free) in a skeet shooting range soil and an uncontaminated control soil under water saturated and unsaturated conditions for up to nine months. A short exposure time of three months was not sufficient for the PDMS samplers to reach distribution equilibrium with the surrounding soil. Under saturated water conditions, the in situ results agreed well with measurements obtained from the conventional ex situ soil suspension method. They were in accordance with similar comparisons made in previous studies on sediments, as well as with model predictions. However, for unsaturated water conditions, the results differed considerably from the ex situ C_free values, in particular for the light molecular weight (LMW) PAHs such as phenanthrene, fluoranthene, and pyrene. The results of the two in situ PS methods were in good agreement with each other under both soil water conditions, indicating that dissipation mechanisms, such as degradation or volatilization, led to a substantial decrease in C_free under unsaturated conditions, especially for the LMW PAHs (log₁₀K_OW < 5.85) over a period of six months or more. Thus, in their current state of development, in situ PS methods can be used in soils under water-saturated conditions. However, an adequate method to correct for non-equilibrium conditions needs to be developed before they can be applied to unsaturated conditions, mainly for LMW PAHs.

Development of film-based passive samplers for in situ monitoring of trace levels of pyrethroids in sediment

Residues of pyrethroid insecticides tend to accumulate in bed sediments due to their strong hydrophobicity. Rather than the total or bulk sediment concentration, it is the freely dissolved concentration (C_free) that drives toxicity to benthic invertebrates. In this study we developed thin film-based samplers for in situ ambient monitoring of pyrethroids at trace levels in sediment. Out of five common polymer materials, polyethylene (PE) and silicone rubber (SR), were identified to offer superior enrichment for pyrethroids from sediment. To circumvent the slow equilibrium process, ¹³C-permethrin and bifenthrin-d₅ were preloaded onto the films as performance reference compounds (PRCs). The PRC-preloaded film samplers were deployed at five sites in Southern California under field conditions for 7 d and retrieved for analysis. The sediment porewater C_free of eight pyrethroids derived from PRC-PE films ranged from 173 to 903 ng/L, accounting for 18.2-36.1% of the corresponding total porewater concentrations. The PRC-SR film samplers yielded C_free values closely mimicking those from the PRC-PE samplers, cross-validating the two sampling devices. Additionally, a significant positive association was found between the observed mortality from toxicity tests using Hyalella azteca and the C_free of bifenthrin (r = 0.628, p = 0.02). A significant linear correlation (R² = 0.99) between C_free derived from in situ monitoring and that of ex situ measurement under equilibrium conditions was also observed. Results from this study demonstrated that the film-based samplers may be used for in situ ambient monitoring to detect biologically relevant contamination of pyrethroids in bed sediments, which may contribute to improved risk assessment for this class of widely used insecticides.

Expanded Application of the Passive Flux Meter: In-Situ Measurements of 1,4-Dioxane, Sulfate, Cr(VI) and RDX

Passive flux meters (PFMs) have become invaluable tools for site characterization and evaluation of remediation performance at groundwater contaminated sites. To date, PFMs technology has been demonstrated in the field to measure midrange hydrophobic contaminants (e.g., chlorinated ethenes, fuel hydrocarbons, perchlorate) and inorganic ions (e.g., uranium and nitrate). However, flux measurements of low partitioning contaminants (e.g., 1,4-dioxane, hexahydro-1,3,5-trinitro-s-triazine (RDX)) and reactive ions-species (e.g., sulfate (SO42−), Chromium(VI) (Cr(VI)) are still challenging because of their low retardation during transport and quick transformation under highly reducing conditions, respectively. This study is the first application of PFMs for in-situ mass flux measurements of 1,4-dioxane, RDX, Cr(VI) and SO42− reduction rates. Laboratory experiments were performed to model kinetic uptake rates and extraction efficiency for sorbent selections. Silver impregnated granular activated carbon (GAC) was selected for the capture of 1,4-dioxane and RDX, whereas Purolite 300A (Bala Cynwyd, PA, USA) was selected for Cr(VI) and SO42−. PFM field demonstrations measured 1,4-dioxane fluxes ranging from 13.3 to 55.9 mg/m2/day, an RDX flux of 4.9 mg/m2/day, Cr(VI) fluxes ranging from 2.3 to 2.8 mg/m2/day and SO42− consumption rates ranging from 20 to 100 mg/L/day. This data suggests other low-partitioning contaminates and reactive ion-species could be monitored using the PFM.

Using performance reference compounds to compare mass transfer calibration methodologies in passive samplers deployed in the water column

Performance reference compounds (PRCs) are often added to passive samplers prior to field deployments to provide information about mass transfer kinetics between the sampled environment and the passive sampler. Their popularity has resulted in different methods of varying complexity to estimate mass transfer and better estimate freely dissolved concentrations (Cfree ) of targeted compounds. Three methods for describing a mass transfer model are commonly used: a first-order kinetic method, a nonlinear least squares fitting of sampling rate, and a diffusion method. Low-density polyethylene strips loaded with PRCs and of 4 different thicknesses were used as passive samplers to create an array of PRC results to assess the comparability and reproducibility of each of the methods. Samplers were deployed in the water column at 3 stations in New Bedford Harbor (MA, USA). Collected data allowed Cfree comparisons to be performed in 2 ways: 1) comparison of Cfree derived from one thickness using different methods, and 2) comparison of Cfree derived by the same method using different thicknesses of polyethylene. Overall, the nonlinear least squares and diffusion methods demonstrated the most precise results for all the PCBs measured and generated Cfree values that were often statistically indistinguishable. Relative standard deviations (RSDs) for total PCB measurements using the same thickness and varying model types ranged from 0.04 to 12% and increased with sampler thickness, and RSDs for estimates using the same method and varying thickness ranged from 8 to 18%. Environmental scientists and managers are encouraged to use these methods when estimating Cfree from passive sampling and PRC data. Environ Toxicol Chem 2018;37:2089-2097. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Performance of passive sampling with low-density polyethylene membranes for the estimation of freely dissolved DDx concentrations in lake environments

Laboratory and field studies were used to evaluate the performance of low-density polyethylene (PE) passive samplers for assessing the freely dissolved concentrations of DDT and its degradates (DDD and DDE, together referred to as DDx) in an Italian lake environment. We tested commercially available 25 μm thick PE sheets as well as specially synthesized, 10 μm thick PE films which equilibrated with their surroundings more quickly. We measured PE-water partitioning coefficients (K_pew) of the 10 μm thick PE films, finding good correspondence with previously reported values for thicker PE. Use of the 10 μm PE for ex situ sampling of a lake sediment containing DDx in laboratory tumbling experiments showed repeatability of ±15% (= standard deviation/mean). Next, we deployed replicate 10 μm and 25 μm PE samplers (N = 4 for 10 d and for 30 d) in the water and sediment of a lake located in northern Italy; the results showed dissolved DDx concentrations in the picogram/L range in porewater and the bottom water. Values deduced from 10 μm thick PE films compared well (95% of all comparison pairs matched within a factor of 5) with those obtained using PE films of 25 μm thickness when dissolved DDx concentrations were estimated using performance reference compound (PRC) corrections, whether left at the bed-water interface for 10 or 30 days. These results demonstrated the potential of this sampling method to provide estimation of the truly dissolved DDx concentrations, and thereby the mobile and bio-available fractions in both surface waters and sediment beds.

Polychlorinated biphenyl (PCB) contamination in Galveston Bay, Texas: Comparing concentrations and profiles in sediments, passive samplers, and fish

The industrialized portion of the Houston Ship Channel (HSC) is heavily contaminated with anthropogenic contaminants, most prominent of which are the polychlorinated biphenyls (PCBs). This contamination has driven adaptive evolution in a keystone species for Galveston Bay, the Gulf killifish (Fundulus grandis). We investigated the geographical extent of PCB impacts by sampling 12 sites, ranging from the heavily industrialized upper portion of the HSC to Galveston Island. At each site, PCB concentrations and profiles were determined in three environmental compartments: sediment, water (polyethylene passive samplers), and fish tissue (resident Gulf killifish). We observed a steep gradient of PCB contamination, ranging from 4.00 to 100,000 ng/g organic carbon in sediment, 290-110,000 ng/g lipid in fish, and 4.5-2300 ng/g polyethylene in passive samplers. The PCB congener profiles in Gulf killifish at the most heavily contaminated sites were shifted toward the higher chlorinated PCBs and were highly similar to the sediment contamination profiles. In addition, while magnitude of total PCB concentrations in sediment and total fish contamination levels were highly correlated between sites, the relative PCB congener profiles in fish and passive samplers were more alike. This strong correlation, along with a lack of dependency of biota-sediment accumulation factors with total contamination rates, confirm the likely non-migratory nature of Gulf killifish and suggest their contamination levels are a good site-specific indicator of contamination in the Galveston Bay area. The spatial gradient of PCB contamination in Galveston Bay was evident in all three matrices studied and was observed effectively using Gulf killifish contamination as an environmentally relevant bioindicator of localized contamination in this environment.

Investigating the Effect of Bioirrigation on In Situ Porewater Concentrations and Fluxes of Polychlorinated Biphenyls Using Passive Samplers

Polychlorinated biphenyl (PCB) fluxes from contaminated sediments can be caused by mechanisms including diffusion, bioirrigation, and resuspension, but it is often unclear which mechanisms are important. In the Lower Duwamish Waterway (Seattle, Washington), the presence of abundant benthic macrofauna suggests that porewater bioirrigation may be an important mechanism for PCB transport from the bed into the overlying water column. In this field study, the fluxes of PCBs due to bioirrigation were quantified by using (a) polyethylene (PE) samplers to quantify in situ and ex situ (i.e., equilibrium) PCB porewater concentration profiles and (b) measurements of the geochemical tracer ²²²Rn to quantify the rate of porewater exchange with overlying water. The results showed that bioirrigation caused sorptive disequilibrium with the surrounding sediment, which led to lower in situ porewater concentrations than expected from sediment concentrations. The combined fluxes of seven PCB congeners (Σ₇PCBs) were 1.6-26 ng/m²/day for the three field sites, similar in magnitude to the upper limit estimates of diffusive fluxes calculated assuming water-side boundary layer control (Σ₇PCBs = 1.3-47 ng/m²/day). Moreover, the depleted in situ porewater concentrations imply lower diffusive flux estimates than if the ex situ porewater concentrations had been used to estimate fluxes (Σ₇PCBs = 89-670 ng/m²/day). These results suggest that nondiffusive PCB fluxes from the sediment bed are occurring and that quantifying in situ porewater concentrations is crucial for accurately quantifying both diffusive and nondiffusive PCB fluxes.

Passive sampling of DDT, DDE and DDD in sediments: accounting for degradation processes with reaction-diffusion modeling

Passive sampling is becoming a widely used tool for assessing freely dissolved concentrations of hydrophobic organic contaminants in environmental media. For certain media and target analytes, the time to reach equilibrium exceeds the deployment time, and in such cases, the loss of performance reference compounds (PRCs), loaded in the sampler before deployment, is one of the common ways used to assess the fractional equilibration of target analytes. The key assumption behind the use of PRCs is that their release is solely diffusion driven. But in this work, we show that PRC transformations in the sediment can have a measurable impact on the PRC releases and even allow estimation of that compound's transformation rate in the environment of interest. We found that in both field and lab incubations, the loss of the ¹³C 2,4'-DDT PRC from a polyethylene (PE) passive sampler deployed at the sediment-water interface was accelerated compared to the loss of other PRCs (¹³C-labeled PCBs, ¹³C-labeled DDE and DDD). The DDT PRC loss was also accompanied by accumulation in the PE of its degradation product, ¹³C 2,4'-DDD. Using a 1D reaction-diffusion model, we deduced the in situ degradation rates of DDT from the measured PRC loss. The in situ degradation rates increased with depth into the sediment bed (0.14 d^-1 at 0-10 cm and 1.4 d^-1 at 30-40 cm) and although they could not be independently validated, these rates compared favorably with literature values. This work shows that passive sampling users should be cautious when choosing PRCs, as degradation processes can affect some PRC's releases from the passive sampler. More importantly, this work opens up the opportunity for novel applications of passive samplers, particularly with regard to investigating in situ degradation rates, pathways, and products for both legacy and emerging contaminants. However, further work is needed to confirm that the rates deduced from model fitting of PRC loss are a true reflection of DDT transformation rates in sediments.

Effects of soil water saturation on sampling equilibrium and kinetics of selected polycyclic aromatic hydrocarbons

Passive sampling can be applied for measuring the freely dissolved concentration of hydrophobic organic chemicals (HOCs) in soil pore water. When using passive samplers under field conditions, however, there are factors that might affect passive sampling equilibrium and kinetics, such as soil water saturation. To determine the effects of soil water saturation on passive sampling, the equilibrium and kinetics of passive sampling were evaluated by observing changes in the distribution coefficient between sampler and soil (K_sampler/soil) and the uptake rate constant (k_u) at various soil water saturations. Polydimethylsiloxane (PDMS) passive samplers were deployed into artificial soils spiked with seven selected polycyclic aromatic hydrocarbons (PAHs). In dry soil (0% water saturation), both K_sampler/soil and k_u values were much lower than those in wet soils likely due to the contribution of adsorption of PAHs onto soil mineral surfaces and the conformational changes in soil organic matter. For high molecular weight PAHs (chrysene, benzo[a]pyrene, and dibenzo[a,h]anthracene), both K_sampler/soil and k_u values increased with increasing soil water saturation, whereas they decreased with increasing soil water saturation for low molecular weight PAHs (phenanthrene, anthracene, fluoranthene, and pyrene). Changes in the sorption capacity of soil organic matter with soil water content would be the main cause of the changes in passive sampling equilibrium. Henry's law constant could explain the different behaviors in uptake kinetics of the selected PAHs. The results of this study would be helpful when passive samplers are deployed under various soil water saturations.

The atmosphere as a source/sink of polychlorinated biphenyls to/from the Lower Duwamish Waterway Superfund site

Waterbodies polluted with polychlorinated biphenyls (PCBs) may cause the air in the surrounding area to become PCB-contaminated. Conversely, when a waterbody is located in or near an urban area, the deposition of atmospheric PCBs may act as a low-level, ongoing source of PCB contamination to that water. Distinguishing these situations is necessary to be protective of human populations and to guide efforts seeking to cleanup such aquatic ecosystems. To assess the situation at the Lower Duwamish Waterway (LDW) Superfund site, low-density polyethylene passive samplers were deployed in the summer of 2015 to quantify freely dissolved water and gaseous air concentrations of PCBs thereby enabling estimates of the direction and magnitude of air-water exchange of PCB congeners. For the sum of the 27 PCB congeners, average concentrations were 220 pg/m³ (95% C.I.: 80-610) in the air and 320 pg/L (95% C.I.: 110-960) in the water. The sum of air-water exchange fluxes of these PCB congeners was estimated to be 68 ng/m²/day (95% C.I.: 30-148) into the lower atmosphere, contrasting with the reported wet and dry depositional flux of only 5.5 ng/m²/day (95% C.I.: 1-38) from the air into the water. Therefore, the atmosphere was ultimately a sink of PCBs from the LDW Superfund site, at least under 2015 summertime conditions. However, we conclude that air-water exchange of PCBs is likely only a minor sink of PCBs from the LDW and only a minor source of contamination to the region's local atmosphere.

Analysis of Measurement Errors in Passive Sampling of Porewater PCB Concentrations under Static and Periodically Vibrated Conditions

Although the field of passive sampling to measure freely dissolved concentrations in sediment porewater has been sufficiently advanced for organic compounds in the low- to midrange of hydrophobicity, in situ passive sampling of strongly hydrophobic polychlorinated biphenyls (PCBs) is still challenged by slow approach to equilibrium. Periodic vibration of polyethylene (PE) passive samplers during exposure has been previously shown to enhance the mass transfer of polycyclic aromatic hydrocarbons (PAHs) from sediment into PE. Herein, we used a new vibrating platform, developed based on our earlier platform design, to demonstrate the effectiveness of periodic vibration for strongly hydrophobic compounds such as hexa-, hepta-, and octachloro-PCBs. Uptake of PCBs in PE after 7, 14, 28, and 56 days under different vibration modes was compared to that under static and mixed laboratory deployments. All PCBs reached within 95-100% of equilibrium after 56 days of deployment in the system vibrated briefly every 2 min, while none of the congeners achieved more than 50% of equilibrium in static deployment for the same period. Periodic vibration also increased the dissipation rate of four performance reference compounds (PRCs) from passive samplers. Higher fractional loss of PRCs and closer approach to equilibrium in the vibrated deployment resulted in estimation of corrected porewater concentrations that were statistically indistinguishable from the true equilibrium values even after a short 7-day deployment. Porewater concentrations of the strongly hydrophobic PCB congeners were overestimated by up to an order of magnitude in the static passive sampler after the same deployment time.

Pyrogenic carbon in Australian soils

Pyrogenic carbon (PyC), the combustion residues of fossil fuel and biomass, is a versatile soil fraction active in biogeochemical processes. In this study, the chemo-thermal oxidation method (CTO-375) was applied to investigate the content and distribution of PyC in 30 Australian agricultural, pastoral, bushland and parkland soil with various soil types. Soils were sampled incrementally to 50cm in 6 locations and at another 7 locations at 0-10cm. Results showed that PyC in Australian soils typically ranged from 0.27-5.62mg/g, with three Dermosol soils ranging within 2.58-5.62mg/g. Soil PyC contributed 2.0-11% (N=29) to the total organic carbon (TOC), with one Ferrosol as high as 26%. PyC was concentrated either in the top (0-10cm) or bottom (30-50cm) soil layers, with the highest PyC:TOC ratio in the bottom (30-50cm) soil horizon in all soils. Principal component analysis - multiple linear regression (PCA-MLR) suggested the silt-associated organic C factor accounted for 38.5% of the variation in PyC. Our findings suggest that PyC is an important fraction of the TOC (2.0-11%, N=18) and chemically recalcitrant organic C (ROC) obtained by chemical C fractionation method accounts for a significant proportion of soil TOC (47.3-84.9%, N=18). This is the first study comparing these two methods, and it indicates both CTO-375 and C speciation methods can determine a fraction of recalcitrant organic C. However, estimated chemically recalcitrant organic carbon pool (ROC) was approximately an order of magnitude greater than that of thermally stable organic carbon (PyC).

Development of passive samplers for in situ measurement of pyrethroid insecticides in surface water

Pyrethroid insecticides are widely used in urban environments, and their occurrence has been recently associated with aquatic toxicity in urban surface streams. Synthetic pyrethroids are strongly hydrophobic compounds, highlighting the importance of the freely dissolved concentration (C_free), rather than the total chemical concentration, for better prediction of potential effects in aquatic ecosystems. The goal of this study was to develop a simple, robust and field-applicable passive sampling methodology that may be used for in situ monitoring of trace levels of pyrethroids in surface water. Among a range of polymer films, polyethylene film (PE) was found to be the most efficient at absorbing pyrethroids from water. To circumvent the long equilibrium time, ¹³C-permethrin and bifenthrin-d₅ were preloaded on the PE sampler as performance reference compounds (PRC). Desorption of isotope-labeled PRCs was found to be isotropic to the absorption of target analytes. The optimized method was first tested in large circulating tanks simulating various environmental conditions. The derived C_free values were consistently smaller than the total aqueous concentration in salt water or water containing humic acids. The PE samplers were further deployed at multiple field sites for 7 d in Southern California and analysis demonstrated good monitoring reproducibility and sensitivity under ambient environmental conditions. The developed passive sampler approach is ideal for application for in situ sampling under field conditions, and the use of PRCs allows sampling with short and flexible time intervals.

A new application of passive samplers as indicators of in-situ biodegradation processes

In this paper, a method for evaluating the in-situ degradation of nitro polycyclic aromatic hydrocarbons (nitro-PAH) in sediments is presented. The methodology is adapted from the passive sampler technique, which commonly uses the dissipation rate of labeled compounds loaded in passive sampler devices to sense the environmental conditions of exposure. In the present study, polymeric passive samplers (made of polyethylene strips) loaded with a set of labeled polycyclic aromatic hydrocarbons (PAH) and nitro-PAH were immersed in sediments (in field and laboratory conditions) to track the degradation processes. This approach is theoretically based on the fact that a degradation process induces a steeper concentration gradient of the labeled compounds in the surrounding sediment, thereby increasing their compound dissipation rates compared with their dissipation in abiotic conditions. Postulating that the degradation magnitude is the same for the labeled compounds loaded in polyethylene strips and for their native homologs that are potentially present in the sediment, the field degradation of 3 nitro-PAH (2-nitro-fluorene, 1-nitro-pyrene, 6-nitro-chrysene) was semi-quantitatively analyzed using the developed method.

Non-equilibrium passive sampling of hydrophobic organic contaminants in sediment pore-water: PCB exchange kinetics

This study investigates the isotropic exchange kinetics of PCBs for polyethylene (PE) passive samplers in quiescent sediment and develops a novel non-equilibrium passive sampling method using PE with multiple thicknesses. The release and uptake kinetics of PCBs in quiescent sediment are reproduced by a 1-D diffusion model using sediment diffusion parameters fitted with the data from actual measurements. From the sediment diffusion parameters observed for uptake and release kinetics, it is seen that the uptake kinetics are distinctly slower than the release kinetics, most likely because of the sorption-desorption hysteresis of PCBs in the study sediment. Despite the presence of the anisotropic PCB exchange kinetics, a performance reference compound (PRC)-based method, which is grounded on the assumption of isotropic exchange kinetics, estimated the freely dissolved aqueous concentrations (Cfree) of PCBs in sediment pore-water with less than a factor of two error for the study sediment. The novel method developed in this study using PE with multiple thicknesses also gives reasonable estimates of Cfree, demonstrating its potential as another option for non-equilibrium passive sampling for hydrophobic organic contaminants in sediment pore-water.

In situ passive sampling of sediments in the Lower Duwamish Waterway Superfund site: Replicability, comparison with ex situ measurements, and use of data

Superfund sites with sediments contaminated by hydrophobic organic compounds (HOCs) can be difficult to characterize because of the complex nature of sorption to sediments. Porewater concentrations, which are often used to model transport of HOCs from the sediment bed into overlying water, benthic organisms, and the larger food web, are traditionally estimated using sediment concentrations and sorption coefficients estimated using equilibrium partitioning (EqP) theory. However, researchers have begun using polymeric samplers to determine porewater concentrations since this method does not require knowledge of the sediment's sorption properties. In this work, polyethylene passive samplers were deployed into sediments in the field (in situ passive sampling) and mixed with sediments in the laboratory (ex situ active sampling) that were contaminated with polychlorinated biphenyls (PCBs). The results show that porewater concentrations based on in situ and ex situ sampling generally agreed within a factor of two, but in situ concentrations were consistently lower than ex situ porewater concentrations. Imprecision arising from in situ passive sampling procedures does not explain this bias suggesting that field processes like bioirrigation may cause the differences observed between in situ and ex situ polymeric samplers.

The role of passive sampling in monitoring the environmental impacts of produced water discharges from the Norwegian oil and gas industry

Stringent and periodic iteration of regulations related to the monitoring of chemical releases from the offshore oil and gas industry requires the use of ever changing, rapidly developing and technologically advancing techniques. Passive samplers play an important role in water column monitoring of produced water (PW) discharge to seawater under Norwegian regulation, where they are used to; i) measure aqueous concentrations of pollutants, ii) quantify the exposure of caged organisms and investigate PW dispersal, and iii) validate dispersal models. This article summarises current Norwegian water column monitoring practice and identifies research and methodological gaps for the use of passive samplers in monitoring. The main gaps are; i) the range of passive samplers used should be extended, ii) differences observed in absolute concentrations accumulated by passive samplers and organisms should be understood, and iii) the link between PW discharge concentrations and observed acute and sub-lethal ecotoxicological end points in organisms should be investigated.

Utilizing the partitioning properties of silicone for the passive sampling of polychlorinated biphenyls (PCBs) in indoor air

The former use of polychlorinated biphenyls (PCBs) in construction materials can lead to elevated indoor air concentrations. We studied the partitioning of PCB congeners between indoor air and silicone with a view to establish passive sampling of PCBs. The release of PCB congeners from silicone followed first order kinetics and confirmed air-side rate-limited mass transfer. Logarithmic elimination rate constants decreased linearly with the logKOA values of the PCB congeners, but varied in a non-linear way with air velocity. Linear uptake of PCBs was found for silicone disks (0.5 mm thickness) in a petri dish, while PCBs reached equilibrium in silicone-coated paper sheets (0.001 mm silicone on each side) exposed to indoor air for 1-2 weeks. The ratios of equilibrium concentrations in silicone and conventionally measured air concentrations were roughly comparable with silicone-air partition coefficients, but further research is required for the determination of silicone-air partition coefficients. Avoiding performance reference compounds (PRCs) because of the indoor setting, the two formats were calibrated against conventional active measurements. Comparisons of air concentrations derived from active and kinetic passive sampling showed a divergence by factors of 2.4 and 2.0 (median values) for the petri dishes and the silicone-coated paper, respectively. With promising results for sensitivity and precision, the calibration of kinetic passive samplers remains the main challenge and will need suitable, non-hazardous PRCs. Equilibrium sampling indicated promising alternatives.

In Situ Passive Sampling of Sediment Porewater Enhanced by Periodic Vibration

Passive sampling for the measurement of freely dissolved concentrations of organic pollutants in sediment porewater has emerged as a promising approach, but in situ measurements are complicated by slow mass transfer of strongly hydrophobic compounds. The primary resistance to mass transfer arises in the sediment side where a concentration depletion layer develops in the vicinity of the polymeric passive sampling material. The slow mass transfer results in underequilibrated passive sampler measurements that need to be corrected for equilibrium, typically by extrapolation of the loss kinetics of performance reference compounds. Such corrections are prone to large errors, especially when deviation from equilibrium is large. In this research we address the challenge of slow mass transfer by disrupting the external depletion layer around an in situ passive sampler. We report an engineering innovation of adapting low-cost vibration motors for periodically disrupting the depletion layer in a passive sampler deployed in sediments. The uptake of 16 polycyclic aromatic hydrocarbons into polyethylene passive samplers was measured after 7, 14, 28, and 56 days of exposure to sediment under static, vibrating, and fully mixed modes. We demonstrate through laboratory experiments and numerical mass transfer modeling that short periodic shaking of a passive sampler deployed in static sediment enhances the rate of mass transfer and reduces the difference in the extent of equilibrium achieved compared to a well-mixed laboratory equilibrium. The improvement over static sediment deployment is especially evident for the high molecular weight compounds such as benzo(a)pyrene.

Understanding the rates of nonpolar organic chemical accumulation into passive samplers deployed in the environment: Guidance for passive sampler deployments

Polymeric passive samplers have become a common method for estimating freely dissolved concentrations in environmental media. However, this approach has not yet been adopted by investigators conducting remedial investigations of contaminated environmental sites. Successful adoption of this sampling methodology relies on an understanding of how passive samplers accumulate chemical mass as well as developing guidance for the design and deployment of passive samplers. Herein, we outline the development of a simple mathematical relationship of the environmental, polymer, and chemical properties that control the uptake rate. This relationship, called a timescale, is then used to illustrate how each property controls the rate of equilibration in samplers deployed in the water or in the sediment. Guidance is also given on how to use the timescales to select an appropriate polymer, deployment time, and suite of performance reference compounds. Integr Environ Assess Manag 2016;12:486-492. © 2015 SETAC.

Passive Sampling in Regulatory Chemical Monitoring of Nonpolar Organic Compounds in the Aquatic Environment

We reviewed compliance monitoring requirements in the European Union, the United States, and the Oslo-Paris Convention for the protection of the marine environment of the North-East Atlantic, and evaluated if these are met by passive sampling methods for nonpolar compounds. The strengths and shortcomings of passive sampling are assessed for water, sediments, and biota. Passive water sampling is a suitable technique for measuring concentrations of freely dissolved compounds. This method yields results that are incompatible with the EU's quality standard definition in terms of total concentrations in water, but this definition has little scientific basis. Insufficient quality control is a present weakness of passive sampling in water. Laboratory performance studies and the development of standardized methods are needed to improve data quality and to encourage the use of passive sampling by commercial laboratories and monitoring agencies. Successful prediction of bioaccumulation based on passive sampling is well documented for organisms at the lower trophic levels, but requires more research for higher levels. Despite the existence of several knowledge gaps, passive sampling presently is the best available technology for chemical monitoring of nonpolar organic compounds. Key issues to be addressed by scientists and environmental managers are outlined.

Modeling uptake of hydrophobic organic contaminants into polyethylene passive samplers

Single-phase passive samplers are gaining acceptance as a method to measure hydrophobic organic contaminant (HOC) concentration in water. Although the relationship between the HOC concentration in water and passive sampler is linear at equilibrium, mass transfer models are needed for nonequilibrium conditions. We report measurements of organochlorine pesticide diffusion and partition coefficients with respect to polyethylene (PE), and present a Fickian approach to modeling HOC uptake by PE in aqueous systems. The model is an analytic solution to Fick's second law applied through an aqueous diffusive boundary layer and a polyethylene layer. Comparisons of the model with existing methods indicate agreement at appropriate boundary conditions. Laboratory release experiments on the organochlorine pesticides DDT, DDE, DDD, and chlordane in well-mixed slurries support the model's applicability to aqueous systems. In general, the advantage of the model is its application in the cases of well-agitated systems, low values of polyethylene-water partioning coefficients, thick polyethylene relative to the boundary layer thickness, and/or short exposure times. Another significant advantage is the ability to estimate, or at least bound, the needed exposure time to reach a desired CPE without empirical model inputs. A further finding of this work is that polyethylene diffusivity does not vary by transport direction through the sampler thickness.