Detecting air-water and surface-deep water gradients of PCBs using polyethylene passive samplers

Polyethylene passive samplers (PEs) were deployed in a vertical array (bottom water, surface water, near-surface air) to study the cycling of active polychlorinated biphenyls (PCBs) between reservoirs in an urban estuary (Narragansett Bay, RI), from May to November 2006. Performance reference compounds were used to account for nonequilibrium of PCBs in PEs. Activity gradients were established from direct comparisons of temperature, salt, and nonequilibrium corrected PE concentrations. The uncertainty of determining air-water gradients was < 70%, and < 50% within the water column. Except during the height of summer, PCB activities were up to 30 times higher in the air than in the surface water, but closer to equilibrium in the water column. Surface waters became depleted in PCBs during periods of highest temperature and stratification, leading to the uptake of gaseous PCBs. Our results demonstrate that passive samplers are powerful tools to determine the flux directions of organic contaminants in the environment.     

Field deployment of polyethylene devices to measure PCB concentrations in pore water of contaminated sediment

Sediment pore water concentrations of polychlorinated biphenyls (PCBs) in a contaminated mudflat in San Francisco Bay, CA were determined by field-deployed polyethylene devices (PEDs). Sequential sampling of PEDs deployed in the field showed large differences in uptake rates and time to equilibrium compared to PEDs mixed with field-collected sediment in the laboratory. We demonstrate a modeling approach that involves the use of impregnated performance reference compounds (PRCs) and interpretation of the data either by PCB molar volume adjustment or environmental adjustment factors to measure pore water concentrations of 118 PCB congeners. Both adjustment methods predicted comparable sampling rates, and PCB pore water concentrations estimated by use of the molar volume adjustment method were similar to values analytically measured in pore waters from the laboratory and field. The utility of PEDs for sampling pore water in the field was evaluated at a tidal mudflat amended with activated carbon to sequester PCBs. Pore water concentrations decreased up to 60% within 18 months after activated carbon amendment, as compared to a mechanical-mixed control plot Results of this study illustrate PEDs provide an inexpensive, in situ method to measure total PCB contamination in sediment pore water using a small set of PRCs.     

Time-weighted average water sampling in Lake Ontario with solid-phase microextraction passive samplers

In this study, three types of solid-phase microextraction (SPME) passive samplers, including a fiber-retracted device, a polydimethylsiloxane (PDMS)-rod and a PDMS-membrane, were evaluated to determine the time weighted average (TWA) concentrations of polycyclic aromatic hydrocarbons (PAHs) in Hamilton Harbor (the western tip of Lake Ontario, ON, Canada). Field trials demonstrated that these types of SPME samplers are suitable for the long-term monitoring of organic pollutants in water. These samplers possess all of the advantages of SPME: they are solvent-free, sampling, extraction and concentration are combined into one step, and they can be directly injected into a gas chromatograph (GC) for analysis without further treatment. These samplers also address the additional needs of a passive sampling technique: they are economical, easy to deploy, and the TWA concentrations of target analytes can be obtained with one sampler. Moreover, the mass uptake of these samplers is independent of the face velocity, or the effect can be calibrated, which is desirable for long-term field sampling, especially when the convection conditions of the sampling environment are difficult to measure and calibrate. Among the three types of SPME samplers that were tested, the PDMS-membrane possesses the highest surface-to-volume ratio, which results in the highest sensitivity and mass uptake and the lowest detection level.     

Methylantimony and -arsenic species in sediment pore water tested with the sediment or fauna incubation experiment

In this study, the speciation of arsenic (As) and antimony (Sb) across a water-sediment interface and the formation of mono-, di-, and trimethylated species overtime in a microfiltered pore water solution were examined. We used an experimental technique, known as the sediment or fauna incubation experiment (SOFIE), which enables the determination of chemical speciation across redox zones in undisturbed systems. Five different incubation experiments were run: Over a 76 day incubation period, pore water was sampled and speciated 5 times. These experiments revealed the complete methylated species pattern for arsenic and antimony in the microfiltered sediment pore water. This constitutes the first report of methylated As and Sb species in a true pore water solution of sediments. Predominant organic species were dimethylantimony (DMSb up to 2.7 microg/L) and dimethylarsenic (DMAs up to 4.3 microg/L) followed by monomethylated species (MMAs and MMSb). These data (i) indicate that methylation significantly influences the translocation of As and Sb in sediments, (ii) demonstrate good agreement between the occurrence of methylantimony and the occurrence of methylarsenic in the pore water, (iii) reveal that As transformation in sediments is faster than Sb transformation but is more susceptible to disturbances from acidification, and (iv) regarding the translocation of these elements and antimony in particular, methylation is clearly a relevant, and perhaps as yet underestimated, factor.     

Spatial and temporal trends of chiral organochlorine signatures in Great Lakes air using passive air samplers

Passive air samples (PAS) were collected and analyzed to assess the spatial and temporal trends of chiral organochlorine signatures in the Laurentian Great Lakes. Samples were collected from 15 sites and analyzed for the concentrations and enantiomer signature of chlordanes and alpha-hexachlorocyclohexane (alpha-HCH). Levels of the chlordanes were typically 4 times higher in urban areas than what were observed at rural and remote locations, exhibiting strong urban-rural gradients. Near racemic residues were seen for the chlordane enantiomers in samples collected from sites located in Toronto and Chicago, which can be attributed to continued emissions of historical use of the technical chlordane mixture, while the chiral signature observed at sites located in rural and remote locations was indicative of an aged source. Knowledge of the spatial and temporal distribution of the enantiomer signatures of chlordane and alpha-HCH in air is useful for distinguishing sources of these compounds to ambient air. Results suggest that potential sources, such as those associated with Toronto and Chicago, have limited influence over the levels at rural and remote sites within the Great Lakes. Sources that are relatively close to sample sites, however, have a strong influence on levels observed at those sites. For instance, results indicate that Lake Superior continues to act as a source of alpha-HCH to sites located on its shores. Generally, it appears that during the warmer months, local enhanced surface-air exchange influences air concentrations and that during the cooler periods of the year, levels in the atmosphere are more strongly influenced by advective transport from source regions.     

In situ two-dimensional high-resolution profiling of sulfide in sediment interstitial waters

A recently developed technique of diffusive gradients in thin films (D6T)-computer-imaging densitometry (CID) was improved to study in situ two-dimensional distributions of sulfide in sediment interstitial waters adjacent to the DGT device. The in situ profiler accumulates sulfide from the sediment interstitial water through a diffusive gel onto a AgI binding gel to form black Ag2S. The amount of sulfide bound in the binding gel is then determined from the gray scale density of the dried binding gel. New gel-making procedures were employed to produce stable, evenly dispersed AgI binding gels and to minimize the darkening of the AgI gel upon exposure to light The improved DGT-CID technique was used to profile the distribution of sulfide in sediment interstitial waters at Delta Marsh, a highly productive Prairie wetland on the south shore of Lake Manitoba, at a vertical and lateral resolution of < or = 0.4 mm. The in situ high-resolution microprofiles revealed unprecedented two-dimensional heterogeneity in sulfide concentrations in the sediment interstitial waters adjacent to the DGT device. The mosaic distribution of oxic and sulfidic microenvironments suggested not only the complexity and heterogeneity of the biogeochemistry of sulfur species and sulfide-binding metals (e.g., Cd, Cu, Pb, Hg, Zn) in sediments but also the capability of aquatic organisms for coping with the sulfidic environment     

Solid-phase microextraction measurement of parent and alkyl polycyclic aromatic hydrocarbons in milliliter sediment pore water samples and determination of K(DOC) values

The U.S. Environmental Protection Agency (EPA) narcosis model for benthic organisms in polycyclic aromatic hydrocarbon (PAH) contaminated sediments requires the measurement of 18 parent PAHs and 16 groups of alkyl PAHs ("34" PAHs) in pore water with desired detection limits as low as nanograms per liter. Solid-phase microextraction (SPME) with gas chromatographic/mass spectrometric (GC/ MS) analysis can achieve such detection limits in small water samples, which greatly reduces the quantity of sediment pore water that has to be collected, shipped, stored, and prepared for analysis. Four sediments that ranged from urban background levels (50 mg/kg total "34" PAHs) to highly contaminated (10 000 mg/kg total PAHs) were used to develop SPME methodology for the "34" PAH determinations with only 1.5 mL of pore water per analysis. Pore water was obtained by centrifuging the wet sediment, and alum flocculation was used to remove colloids. Quantitative calibration was simplified by adding 15 two- to six-ring perdeuterated PAHs as internal standards to the water calibration standards and the pore water samples. Response factors for SPME followed by GC/MS were measured for 22 alkyl PAHs compared to their parent PAHs and used to calibrate for the 18 groups of alkyl PAHs. Dissolved organic carbon (DOC) ranging from 4 to 27 mg/L had no measurable effect on the freely dissolved concentrations of two- and three-ring PAHs. In contrast, 5-80% of the total dissolved four- to six-ring PAHs were associated with the DOC rather than being freely dissolved, corresponding to DOC/water partitioning coefficients (K(DOC)) with log K(DOC) values ranging from 4.1 (for fluoranthene) to 5.6 (for benzo[ghi]perylene). However, DOC-associated versus freely dissolved PAHs had no significant effect on the total "34" PAH concentrations or the sum of the "toxic units" (calculated bythe EPA protocol), since virtually all (86-99%) of the dissolved PAH concentrations and toxic units were contributed by two- and three-ring PAHs.     

Biodynamic modeling of PCB uptake by Macoma balthica and Corbicula fluminea from sediment amended with activated carbon

Activated carbon amendment was assessed in the laboratory as a remediation strategy for freshwater sediment contaminated with polychlorinated biphenyls (PCBs) from the Grasse River (near Massena, NY). Three end points were evaluated: aqueous equilibrium PCB concentration, uptake into semipermeable membrane devices (SPMDs), and 28-day bioaccumulation in the clam Corbicula fluminea. PCB uptake by water, SPMDs, and clams followed similar trends, with reductions increasing as a function of carbon dose. Average percent reductions in clam tissue PCBs were 67, 86, and 95% for activated carbon doses of 0.7, 1.3, and 2.5% dry wt, respectively. A biodynamic model that incorporates sediment geochemistry and dietary and aqueous uptake routes was found to agree well with observed uptake by C. fluminea in our laboratory test systems. Results from this study were compared to 28-day bioaccumulation experiments involving PCB-contaminated sediment from Hunters Point Naval Shipyard (San Francisco Bay, CA) and the clam Macoma balthica. Due to differences in feeding strategy, M. balthica deposit-feeds whereas C. fluminea filter-feeds, the relative importance of the aqueous uptake route is predicted to be much higher for C. fluminea than for M. balthica. Whereas M. balthica takes up approximately 90% of its body burden through sediment ingestion, C. fluminea only accumulates approximately 45% via this route. In both cases, results strongly suggest that it is the mass transfer of PCBs from native sediment to added carbon particles, not merely reductions in aqueous PCB concentrations, that effectively reduces PCB bioavailability and uptake by sediment-dwelling organisms.     

In situ measurement of white wine absorbance in clear and in coloured bottles using a modified laboratory spectrophotometer

In situ absorbance of visible light by white wine in bottles was determined with a modified spectrophotometer. A linear correlation was obtained between absorbance at 420 nm (A₄₂₀) measured in a cuvette (10 mm pathlength) and absorbance of that same wine measured in a 750 mL Flint bottle (colourless transparent glass). In addition, 5 types of coloured bottles, Emerald Green, Classic Green, French Green, Georgia Green and Cobalt Blue , also yielded strong correlations. A₄₂₀ of white wine in bottles of Antique Green or Amber glass could not be measured directly due to a strong absorbance of that wavelength by the glass. However, a strong correlation was established between measurement of A₄₂₀ (cuvette) and A₅₄₀ for white wine in Antique Green bottles and between A₄₂₀ (cuvette) and either A₅₄₀ or A₆₀₀ for white wine in Amber bottles. The method employed a standard UV-Visible spectrophotometer with an inexpensive modified sample port, and proved applicable to bottles with diameters ranging from 62 mm (375 mL capacity half bottles) up to 81 mm (750 mL capacity Burgundy bottles). In situ absorbance measurements plus subsequent chemical analysis and sensory assessment of a Chardonnay wine in Antique Green bottles showed that the method provided an estimate of oxidation in this white wine. Wine absorbance spectra over the full visible range were obtained in the Flint bottle. Measurements of the absorbance of visible light by the glass of empty bottles could also be obtained and used as a form of quality control for glass bottle manufacture.     

Characterizing uptake kinetics of PAHs from the air using polyethylene-based passive air samplers of multiple surface area-to-volume ratios

Polyethylene passive sampling devices (PSDs) were deployed to investigate how passive samplers of multiple surface area-to-volume ratios could be used to characterize uptake kinetics for polyaromatic hydrocarbons (PAHs). Theoretically, uptake profiles for different thickness PSDs of the same surface area should show the following: where uptake is linear, the amount of compound accumulated in the different PSDs will be the same and where equilibrium is approached, the amount accumulated by the different PSDs will be proportional to sampler thickness. Polyethylene sheets of the same surface area and approximately 100 and 200 microm thickness were collected after 30, 60, and 90 days of exposure along with samples from a codeployed high volume sampler. Twelve priority pollutant PAHs could be routinely quantified in replicate PSDs. Overall, reproducibility between replicate PSDs was satisfactory, with normalized differences rarely exceeding 25%. The smallest analytes quantified, fluorene, phenanthrene, and anthracene, were shown to approach equilibrium during the deployment period, whereas uptake for fluoranthene and pyrene moved into the curvilinear stage. For most of the larger molecular weight PAHs such as indeno[1,2,3-cd]pyrene, uptake could be described using a linear uptake model. Preliminary sampling rates for the compounds which remained in the linear stage of uptake ranged between 0.5 and 1.5 m3 d(-1) dm(-2). Sampler to air partition coefficients were estimated for PAHs which approached equilibrium and predicted for some of the other compounds. Results suggest that a single deployment of PSDs with multiple surface area-to-volume ratios can be sufficient to determine whether uptake was linear or approaching equilibrium for a range of PAHs.     

Polychlorinated naphthalenes in Great lakes air: assessing spatial trends and combustion inputs using PUF disk passive air samplers

Passive air samplers made from polyurethane foam (PUF) disks housed in stainless steel chambers were deployed over four seasons during 2002-2003, at 15 sites in the Laurentian Great lakes, to assess spatial and temporal trends of polychlorinated naphthalenes (PCNs). Sampling rates, determined using depuration compounds pre-spiked into the PUF disk prior to exposure, were, on average, 2.9 +/- 1.1 m3 d(-1), consistent with previous studies employing these samplers. PCN air concentrations exhibited strong urban-rural differences-typically a few pg m(-3) at rural sites and an order of magnitude higher at urban sites (Toronto, 12-31 pg m(-3) and Chicago,13-52 pg m(-3)). The high concentrations at urban sites were attributed to continued emissions of historically used technical PCN. Contributions from combustion-derived PCNs seemed to be more important at rural locations where congeners 24 and 50, associated with wood and coal burning, were elevated. Congener 66/67, associated with incineration and other industrial thermal processes, was elevated at two sites and explained by nearby and/or upwind sources. Probability density maps were constructed for each site and for every integration period were shown to be a useful complement to seasonally integrated passive sampling data to resolve source-receptor relationship for PCNs and other pollutants.     

Determining air-water exchange, spatial and temporal trends of freely dissolved PAHs in an urban estuary using passive polyethylene samplers

Passive polyethylene (PE) samplers were deployed at six locations within Narragansett Bay (RI, USA) to determine sources and trends of freely dissolved and gas-phase polycyclic aromatic hydrocarbons (PAHs) from May to November 2006. Freely dissolved aqueous concentrations of PAHs were dominated by fluoranthene, pyrene, and phenanthrene, at concentrations ranging from tens to thousands of pg/L. These were also the dominant PAHs in the gas phase, at hundreds to thousands of pg/m3. All stations mostly followed the same temporal trends, with highest concentrations (up to 7300 pg/L for sum PAHs) during the second of 11 deployments, coinciding with a major rainstorm. Strong correlations of sum PAHs with river flows and wastewater treatment plant discharges highlighted the importance of rainfall in mobilizing PAHs from a combination of runoff and atmospheric washout. PAH concentrations declined through consecutive deployments III to V, which could be explained by an exponential decay due to flushing with cleaner ocean water during tides. The estimated residence time (tres) of the PAH pulse was 24 days, close to an earlier estimate of tres of 26 days for freshwater in the Bay. Air-water exchange gradients indicated net volatilization of most PAHs closest to Providence. Further south in the Bay, gradients had changed to mostly net uptake of the more volatile PAHs, but net volatilization for the less volatile PAHs. Based on characteristic PAH ratios, freely dissolved PAHs at most sites originated from the combustion of fossil fuels; only two sites were at times affected by fuel spill-derived PAHs.     

Predicting bioavailability of sediment polycyclic aromatic hydrocarbons to Hyalella azteca using equilibrium partitioning, supercritical fluid extraction, and pore water concentrations

Polycyclic aromatic hydrocarbon (PAH) bioavailability to Hyalella azteca was determined in 97 sediments from six former manufactured-gas plants and two aluminum smelter sites. Measurements of Soxhlet extractable, rapidly released based on mild supercritical fluid extraction, and pore water dissolved concentrations of 18 parent and 16 groups of alkyl PAHs (PAH34) were used to predict 28 daysurvival based on equilibrium partitioning and hydrocarbon narcosis models. Total PAH concentrations had little relationship to toxicity. Amphipods survived in sediments with PAH34 concentrations as high as 2990 microg/g, while sediments as low as 2.4 microg/g of PAH34 resulted in significant mortality. Equilibrium partitioning using either total extractable or rapidly released concentrations significantly improved predictions. However, pore water PAH34 concentrations were best for predicting amphipod survival and correctly classified toxic and nontoxic sediment samples with an overall model efficiency of 90%. Alkyl PAHs accounted for 80% of the toxicity, demonstrating that careful measurement of the 16 alkyl clusters in pore water is required. Regression analysis of the pore water PAH34 data from 97 field sediments against amphipod survival resulted in a mean 50% lethal residue value of 33 micromol/g of lipid, consistent with 32 micromol/g of lipid for fluoranthene determined by others in controlled laboratory conditions, thus demonstrating the applicability of EPA's hydrocarbon narcosis model when using pore water PAH34 concentrations.     

Sampling medium side resistance to uptake of semivolatile organic compounds in passive air samplers

Current theory of the uptake of semivolatile organic compounds in passive air samplers (PAS) assumes uniform chemical distribution and no kinetic resistance within the passive sampling media (PSM) such as polystyrene-divinylbenzene resin (XAD) and polyurethane foam (PUF). However, these assumptions have not been tested experimentally and are challenged by some recently reported observations. To test the assumptions, we performed kinetic uptake experiments indoors using cylindrical PSM that had been concentrically segmented into three layers. Both XAD and PUF were positioned in the same type of sampler housing to eliminate the variation caused by the different housing designs, which enabled us to quantify differences in uptake caused by the properties of the PSM. Duplicated XAD (PUF) samples were retrieved after being deployed for 0, 1 (0.5), 2 (1), 4 (2), 8 (4), 12 (8), and 24 (12) weeks. Upon retrieval, the PSM layers were separated and analyzed individually for PCBs. Passive sampling rates (R) were lower for heavier PCB homologues. Within a homologue group, R for XAD was higher than that for PUF, from which we infer that the design of the "cylindrical can" housing typically used for XAD PAS lowers the R compared to the "double bowl" shelter commonly used for PUF-disk PAS. Outer layers of the PSM sequestered much higher levels of PCBs than inner layers, indicative of a kinetic resistance to chemical transfer within the PSM. The effective diffusivities for chemical transfer within PSM were derived and were found negatively correlated with the partition coefficients between the PSM and air. Based on the results, we conclude that the PSM-side kinetic resistance should be considered when investigating factors influencing R and when deriving R based on the loss of depuration compounds.     

Measurement of dissolved H2, O2, and CO2 in groundwater using passive samplers for gas chromatographic analyses

A simple in-situ passive dissolved gas groundwater sampler, comprised of a short length of silicone tubing attached to a gastight or other syringe, was adapted and tested for in-situ collection of equilibrium gas samples. Sampler retrieval after several days of immersion in groundwater allowed the direct injection of the sample onto a gas chromatograph (GC), simplifying field collection and sample handling over the commonly used "bubble stripping" method for H2 analyses. A GC was modified by sequencing a thermal conductivity (TC) detector followed by a reductive gas (RG) detector so that linear calibration of H2 over the range 0.2-200,000 ppmv was attained using a 0.5-mL gas sample; inclusion of the TC detector allowed the simultaneous quantification of other fixed gases (O2, CO2, He, and Ne) to which the RG detector was not responsive. Uptake kinetics for H2 and He indicated that the passive sampler reached equilibrium within 12 h of immersion in water. Field testing of these passive samplers revealed unusually large equilibrium gas-phase H2 concentrations in groundwater, ranging from 0.1 to 13.9%, by volume, in 11 monitoring wells surrounding four former radiological wastewater disposal ponds at the Y-12 plant in Oak Ridge, Tennessee.     

In situ gelatinization of starch using hot stage microscopy

Starch gelatinization is important in food processing and industrial use. Granule swelling and gelatinization temperature of 11 starches from different plants were investigated in situ using hot stage microscopy during heating. The amylose content, swelling power, pasting temperature and thermal property of these starches were also measured. The results showed that hot stage microscopy was suitable for measuring granule swelling and the gelatinization temperature of starch during heating. The sectional area swelling percentage of starch granules measured using hot stage microscopy was significantly positively correlated with the swelling power. The gelatinization temperature measured using hot stage microscopy was significantly positively correlated with the pasting temperature and with the thermal property for all 11 starches. For rice starches with the same crystallinity and similar size, the gelatinization temperature was negatively correlated with the amylose content and positively correlated with the swelling power and the sectional area swelling percentage at 95°C.     

High-resolution measurement of pore saturation and colloid removal efficiency in quartz sand using fluorescence imaging

Colloid deposition in unsaturated, nonuniform porous media is poorly explained by current models and difficult to measure using breakthrough curves and retained mass profiles. We present new methods which enable time-lapse fluorescence imaging to quantify variations in pore saturation, theta, and colloid deposition in 2D, nonuniform unsaturated flow fields. Calibration experiments revealed direct proportionality between fluorescence F and theta in 20/30 mesh quartz sand. Analysis of breakthrough data in fluorescence images allows quantification of the mean mobile concentration, mean deposition rate, and hence the colloid removal efficiency eta directly from data at the pixel-scale throughoutthe flow field. We imaged carboxylate-modified latex microspheres from a point source in saturated flow and unsaturated flow across a capillary fringe at 10(-3), 10(-2), and 10(-1) M NaCl. Total numbers of colloids deposited and values of eta increased with ionic strength. We modeled the observed variations in eta with theta to estimate the partitioning of colloid deposition between air-water and solid-water interfaces. In the broad saturation range 0.2 < theta < 1, our results suggest that only at the lowest ionic strength, where deposition at solid-water interfaces was strongly unfavorable, did colloid deposition associated with air-water interfaces significantly influence the total colloid removal.