Carol B. Grabanski

Measured partitioning coefficients for parent and alkyl polycyclic aromatic hydrocarbons in 114 historically contaminated sediments: Part 1. KOC values

Polycyclic aromatic hydrocarbon (PAH) partitioning coefficients between sediment organic carbon and water (K(OC)) values were determined using 114 historically contaminated and background sediments collected from eight different rural and urban waterways in the northeastern United States. More than 2100 individual K(OC) values were measured in quadruplicate for PAHs ranging from two to six rings, along with the first reported K(OC) values for alkyl PAHs included in the U.S. Environmental Protection Agencys (U.S. EPA) sediment narcosis model for the prediction of PAH toxicity to benthic organisms. Sediment PAH concentrations ranged from 0.2 to 8600 microg/g (U.S. EPA 16 parent PAHs), but no observable trends in K(OC) values with concentration were observed for any of the individual PAHs. Literature K(OC) values that are commonly used for environmental modeling are similar to the lowest measured values for a particular PAH, with actual measured values typically ranging up to two orders of magnitude higher for both background and contaminated sediments. For example, the median log K(OC) values we determined for naphthalene, pyrene, and benzo[a]pyrene were 4.3, 5.8, and 6.7, respectively, compared to typical literature K(OC) values for the same PAHs of 2.9, 4.8, and 5.8, respectively. Our results clearly demonstrate that the common practice of using PAH K(OC) values derived from spiked sediments and modeled values based on n-octanol-water coefficients can greatly overestimate the actual partitioning of PAHs into water from field sediments.

Simple method for estimating polychlorinated biphenyl concentrations on soils and sediments using subcritical water extraction coupled with solid-phase microextraction

Abstract A rapid method for estimating polychlorinated biphenyl (PCB) concentrations in contaminated soils and sediments has been developed by coupling static subcritical water extraction with solid-phase microextraction (SPME). Soil, water, and internal standards are placed in a sealed extraction cell, heated at 250°C for 15 to 60 min, cooled, and the PCB concentrations in the extractant water determined by SPME and GC–electron-capture detection. When PCB 103 and 169 (not found in contaminated samples) are used as internal standards to calibrate for the soil/water and water/SPME equilibria, quantitative results for individual PCB congeners typically agree within 80 to 130% of the concentrations based on Soxhlet extraction and conventional GC analysis. The reproducibility of replicate subcritical water extraction/SPME determinations is typically 10 to 15% relative standard deviation. Analysis of water extracts stored for 24 h agrees with fresh extracts, demonstrating that extracts can be stored for later SPME analysis without significant loss of the PCBs from the extractant water. The method is simple to perform, uses field-rugged and inexpensive apparatus, and generates no organic solvent waste.

Static subcritical water extraction with simultaneous solid-phase extraction for determining polycyclic aromatic hydrocarbons on environmental solids.

A rapid and very simple method for extracting polycyclic aromatic hydrocarbons (PAHs) from soils, sediments, and air particulate matter has been developed by coupling static subcritical water extraction with styrene-divinylbenzene (SDB-XC) extraction discs. Soil, water, and the SDB-XC disc are placed in a sealed extraction cell, heated to 250 degrees C for 15 to 60 min, cooled, and the PAHs recovered from the disc with acetone/methylene chloride. If the cells are mixed during heating, all PAHs with molecular weights from 128 to 276 are quantitatively (>90%) extracted and collected on the sorbent disc and are then recovered by shaking with acetone/methylene chloride. After water extraction, the sorbent discs can be stored in autosampler vials without loss of the PAHs, thus providing a convenient method of shipping PAH extracts from field sites to the analytical laboratory. The method gives good quantitative agreement with standard Soxhlet extraction, and with certified reference materials for PAH concentrations on soil, sediment (SRM 1944), and air particulate matter (SRM 1649a).

Measuring Low Picogram Per Liter Concentrations of Freely Dissolved Polychlorinated Biphenyls in Sediment Pore Water Using Passive Sampling with Polyoxymethylene

Studies into bioaccumulation of polychlorinated biphenyls (PCBs) have increasingly focused on congeners that are freely dissolved in sediment interstitial pore water. Because of their low water solubilities and their tendency to persist and concentrate as they progress in the food chain, interest has grown in methods capable of measuring individual PCB congeners at low part-per-quadrillion (picogram per liter) concentrations. Obtaining large volumes of pore water is difficult (or impossible), which makes conventional analytical approaches incapable of attaining suitable detection limits. In the present study, nondepletive sampling is used to achieve very low detection limits of freely dissolved PCBs, while requiring no separation of the sediment and water slurry. Commercially available 76 microm thick polyoxymethylene (POM) coupons were placed directly into wet sediments and left to reach equilibrium with the pore water and sediment PCBs for up to 84 days, with 28 days found to be sufficient. Freely dissolved concentrations were then calculated by dividing the PCB concentration found in the POM by its POM/water partitioning coefficient (K(POM)). The K(POM) values required for determining water concentrations were measured using two spiked sediments and two historically contaminated sediments for all 62 PCB congeners that are present at greater than trace concentrations in commercial Aroclors. Log K(POM) values ranged from ca. 4.6 for dichloro-congeners to ca. 7.0 for octachloro-congeners and correlate well with octanol/water coefficients (K(OW)) (r(2) = 0.947) so that a simple linear equation can be used to calculate dissolved concentrations within a factor of 2 or better for congeners having no measured K(POM) value. Detection limits for freely dissolved PCBs ranged from ca. 20 pg/L (part-per-quadrillion) for dichloro-congeners down to ca. 0.2 pg/L for higher-molecular-weight congeners. Sorption isotherms were found to be linear (r(2) > 0.995) over at least 3 orders of magnitude for all congeners, demonstrating good quantitative linearity of the method for determining freely dissolved PCB concentrations at environmentally relevant levels.

Solid-phase microextraction with pH adjustment for the determination of aromatic acids and bases in water

Adjusting the pH of water samples before performing solid-phase microextraction (SPME) analysis can be used to selectively extract organic acids (at pH 2) and bases (at pH 12). Sorption behavior of test organics is predictable based on the acid dissociation constant in water. In general, polyacrylate (PA) and Carbowax-divinylbenzene (CW-DVB) show substantially higher fiber/water sorption coefficients (Kd values) than a polydimethylsiloxane (PDMS) coated fiber. Gas chromatography-flame ionization detection (GC-FID) detection limits with the CW-DVB sorbent are approximately 0.5 to 10 ng/ml in a 2-ml water sample for a variety of aromatic amines, phenols, and chlorinated phenols, and are approximately 1 to 50 ng/ml for the same solutes using the PA sorbent. However, the PA fiber is more selective (depending on the water pH) for the acid or base components than the CW-DVB fiber. With proper pH adjustment, the recovery of spiked aromatic amines and phenols from a surface wetlands water ranged from 73 to 118% of the known values, with a precision (R.S.D.) of approximately 5 to 20%. SPME quantitation of phenols in a coal gasification wastewater using a PA fiber also gave excellent agreement with conventional methylene chloride extraction, although continued use of a single fiber with this wastewater led to poorer precision.

Measured partition coefficients for parent and alkyl polycyclic aromatic hydrocarbons in 114 historically contaminated sediments: Part 2. Testing the KOCKBC two carbon–type model

Polycyclic aromatic hydrocarbon (PAH) desorption partition coefficients between black carbon and water (K(BC)) were determined using 114 historically contaminated and background sediments from eight different rural and urban waterways. Black carbon was measured after oxidation at 375 degrees C for 24 h. Organic carbon-water partition coefficients (K(OC)) required for the calculation of K(BC) values were determined for two- to six-ring parent and C1- to C4-alkyl PAHs based on the lower range of measured K(OC) values from the same sediments and comparisons to literature K(OC) values. Approximately 2,050 log K(BC) values were determined on sediments having a range of total organic carbon from 0.3 to 42% by weight, black carbon from 0.1 to 40% by weight, and total PAH concentrations (U.S. Environmental Protection Agency 16 parent PAHs) from 0.2 to 8,600 microg/g. Contrary to expectations, PAH partitioning was not better explained using the combined K(OC) and K(BC) models rather than the simple K(OC) model (i.e., K(BC) values for each individual PAH ranged nearly three orders of magnitude). No effect of PAH concentration on measured K(BC) values was apparent. Values of K(BC) also showed no trends with total organic carbon, black carbon, or the presence or absence of a non- aqueous phase liquid. Multiple linear regression analysis with K(OC) and K(BC) as fitted values also failed to explain the variance of the experimental data (r(2) values typically less than 0.20, and standard errors greater than two orders of magnitude). These results demonstrate that models of PAH partitioning that account for different carbon types, although useful for understanding partitioning mechanisms, cannot yet be used to accurately predict PAH partitioning from historically contaminated sediments.

Improving predictability of sediment-porewater partitioning models using trends observed with PCB-contaminated field sediments.

More than 1900 sediment-water partitioning coefficients were measured for 58 polychlorinated biphenyl (PCB) congeners in 53 historically contaminated sediments collected from 10 urban and rural waterways in the United States and Canada. Freely dissolved porewater concentrations were determined using passive sampling with polyoxymethylene. Measured total organic carbon (TOC)/water partitioning coefficients, K(TOC), ranged from one to nearly three orders-of-magnitude higher than typical literature values based on spiking experiments and model predictions. Although total PCB concentrations ranged from 0.08 to 194 mg/kg, the more highly contaminated sediments showed only slightly lower K(TOC) values than less-contaminated sediments. No correlation was observed between log K(TOC) values and sediment TOC, black carbon (BC), or BC/TOC fractions (r(2) typically <0.1). Utilizing a two-carbon model incorporating anthropogenic BC did not improve predictions over a one-carbon TOC model. A comparison of models recently validated for field data showed that a coal-tar poly parameter linear-free energy relationship (PP-LFER) and a Raoults Law model were successful at predicting average log K(TOC) values, without the need for any calibration or fitting (within a factor of 10 more than 90% of the time, and within a factor of 30 more than 99% of the time). Predictions were further improved by the introduction of a Weathering Factor (WF) that accounts for the relative depletion of lower molecular weight congeners due to weathering. Highly weathered sediments (with a WF near 1) tended to follow the coal-tar PP-LFER and Raoults Law model the closest. Less-weathered sediments (with WF ≪ 1) sorbed less than predicted by these models. Noncalibrated WF inclusive coal-tar PP-LFER and Raoults Law models performed as well or better than a quantitative-structure activity relationship (QSAR) model calibrated specifically to the data. These recommended partitioning models here can readily be used for all 209-PCB congeners.

Review of polyoxymethylene passive sampling methods for quantifying freely dissolved porewater concentrations of hydrophobic organic contaminants

Meth ods involving polyoxymethylene (POM) as a passive sampler are increasing in popularity to assess contaminant freely dissolved porewater concentrations in soils and sediments. These methods require contaminant-specific POM-water partition coefficients, KPOM . Certain methods for determining KPOM perform reproducibly (within 0.2 log units). However, other methods can give highly varying KPOM values (up to 2 log units), especially for polycyclic aromatic hydrocarbons (PAHs). To account for this variation, the authors tested the influence of key methodological components in KPOM determinations, including POM thickness, extraction procedures, and environmental temperature and salinity, as well as uptake kinetics in mixed and static systems. All inconsistencies in the peer-reviewed literature can be accounted for by the likelihood that thick POM materials (500 μm or thicker) do not achieve equilibrium (causing negative biases up to 1 log unit), or that certain POM extraction procedures do not ensure quantitative extraction (causing negative biases up to 2 log units). Temperature can also influence KPOM , although all previous literature studies were carried out at room temperature. The present study found that KPOM values at room temperature are independent (within 0.2 log units) of POM manufacture method, of thickness between 17 μm and 80 μm, and of salinity between 0% and 10%. Regarding kinetics, monochloro- to hexachloro-polychlorinated biphenyls (PCBs) were within 0.2 log units of equilibrium after 28 d in the mixed system, but only dichloro-PCBs achieved near equilibrium after 126 d in the static system. Based on these insights, recommended methods and KPOM values to facilitate interlaboratory reproducibility are presented.

Evaluation of PCB bioaccumulation by Lumbriculus variegatus in field‐collected sediments

Review of data from several contaminated sediment sites suggested that biota-sediment accumulation factors (BSAFs) declined with increasing contaminant concentrations in the sediment. To evaluate the consistency and possible causes of this behavior, polychlorinated biphenyl (PCB)-contaminated sediment samples from the Hudson, Grasse, and Fox River Superfund sites were used in sediment bioaccumulation tests with the freshwater oligochaete, Lumbriculus variegatus, with PCB concentrations in interstitial water (IW) quantified using polyoxymethylene passive samplers. Measured BSAFs tended to decrease with increasing PCB concentration in sediment, especially for the more highly chlorinated congeners. Measures of partitioning between sediment, IW, and oligochaetes showed that measured sediment-IW partition coefficients (KTOC ) tended to increase slightly with increasing sediment contamination, whereas the ratio of tissue PCB to IW PCB tended to decrease with increasing concentration in IW. Variation in accumulation among sediments was clearly influenced by bioavailability, as reflected by IW measurements, although the specific cause of varying KTOC was not clear. Calculated partitioning between IW and organism lipid (Klipid ) indicated that accumulation was generally 5 to 10-fold higher than would be predicted if Klipid was approximately equal to the n-octanol-water partition coefficient (KOW ). While affirming previous observations of decreasing BSAFs with increasing PCB contamination, the relatively shallow slope of the observed relationship in the current data may suggest that this concentration dependence is not a major uncertainty in sediment risk assessment, particularly if measurements of PCBs in IW are incorporated.

Assessment of supercritical fluid extraction use in whole sediment toxicity identification evaluations

Supercritical fluid extraction (SFE) with pure CO(2) was assessed as a confirmatory tool in phase III of whole sediment toxicity identification evaluations (TIEs). The SFE procedure was assessed on two reference sediments and three contaminated sediments by using a combination of toxicological and chemical measurements to quantify effectiveness. Sediment toxicity pre- and post-SFE treatment was quantified with a marine amphipod (Ampelisca abdita) and mysid (Americamysis bahia), and nonionic organic contaminants (NOCs) polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were measured in sediments, overlying waters, and interstitial waters. In general, use of SFE with the reference sediments was successful, with survival averaging 91% in post-SFE treatments. Substantial toxicity reductions and contaminant removal from sediments and water samples generated from extracted sediments of up to 99% in two of the contaminated sediments demonstrated SFE effectiveness. Furthermore, toxicological responses for these SFE-treated sediments showed comparable results to those from the same sediments treated with the powdered coconut charcoal addition manipulation. These data demonstrated the utility of SFE in phase III of a whole sediment TIE. Conversely, in one of the contaminated sediments, the SFE treatments had no effect on sediment toxicity, whereas sediment concentrations of PCBs and PAHs were reduced. We propose that, for some sediments, the SFE treatment may result in the release of otherwise nonbioavailable cationic metals that subsequently cause toxicity to test organisms. Overall, SFE treatment was found to be effective for reducing the toxicity and concentrations of NOCs in some contaminated sediments. However, these studies suggest that SFE treatment may enhance toxicity with some sediments, indicating that care must be taken when applying SFE and interpreting the results.